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  • Column liquid chromatography  (189)
  • Springer  (189)
  • American Association for the Advancement of Science (AAAS)
  • Cell Press
  • Periodicals Archive Online (PAO)
  • Springer Nature
  • 1995-1999  (189)
  • 1980-1984
  • 1925-1929
  • 1998  (107)
  • 1995  (82)
  • 1982
  • 1928
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  • Springer  (189)
  • American Association for the Advancement of Science (AAAS)
  • Cell Press
  • Periodicals Archive Online (PAO)
  • Springer Nature
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  • 1995-1999  (189)
  • 1980-1984
  • 1925-1929
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  • 1
    Electronic Resource
    Electronic Resource
    Oxidation of acetophenone in a high temperature open-tubular capillary column liquid chromatographic system (1995)
    Springer
    Chromatographia 40 (1995), S. 99-101 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; High temperature open-tubular columns ; Solvent make-up ; Acetophenone oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Acetophnone, a substance stable at room temperature, is readily oxidizes in a high temperature open tubular liquid chromatographic system by the residual oxygen in the mobile phase. The oxidation product is less UV absorptive and detection sensitivity decreases greatly. To prevent the oxidation, through degassing of the mobile phase is necessary.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274615
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  • 2
    Electronic Resource
    Electronic Resource
    The removal of endotoxins from protein solutions using column packings with aminated poly (γ-methyl L-glutamate) spheres (1995)
    Springer
    Chromatographia 40 (1995), S. 33-38 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Endotoxins ; Lipopolysaccharide ; Aminated poly(γ-methyl L-glutamate) ; Bovine serum albumin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method is described for the selective removal of endotoxins from various protein solutions using columns packed with aminated poly (γ-methyl L-glutamate) (PMLG-NH2) spheres. The PMLG-NH2 adsorbents showed a high adsorbing activity for endotoxins which had an ionic strength of μ=0.05–1.0 and pH 5.0–9.0. The endotoxin-adsorbing capacity per millitre of the wet adsorbent increased from 0.40 to 1.35 mg (E. coli O111: B4 LPS) at μ=0.2 and pH 7.0 while the aminogroup content of the adsorbent increased from 0.8 to 3.5 meq g−1. The PMLG-NH2-3.5 has an amino-group content of 3.5 meq g−1. This column packing selectively adsorbed endotoxins, without loss of the protein, from a γ-globulin or cytochromec solution which contained endotoxins at μ=0.05 and pH 7.0. On the other hand, when bovine serum albumin (BSA) was present in solution with endotoxins, both the endotoxins and the BSA were adsorbed by the column. The BSA-adsorbing activity increased with increasing amino-group content of the adsorbent. However, this undesirable adsorption was suppressed with increasing ionic strength of the buffer. As a result, when the packing which had an amino-group content of 1.5 meg g−1 was used in conditions of μ=0.2 and pH 7.0, the endotoxins were removed from a BSA-containing solution without affecting the recovery of the BSA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274604
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  • 3
    Electronic Resource
    Electronic Resource
    Analysis of lignin degradation products by capillary electrophoresis (1995)
    Springer
    Chromatographia 40 (1995), S. 51-57 
    Details
    ISSN: 1612-1112
    Keywords: Column electrophoresis ; Column liquid chromatography ; Phenolic lignin degradation compounds ; Sugar degradation products ; Quantitative analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method for the quantitative analysis of phenolic lignin degradation products by capillary electrophoresis (CE) with on-column UV detection has been developed. The liquid biomass solutions contain low molecular hemicellulosic sugars and phenolic lignin degradation products with various degrees of polymerization. Special attention has been paid to the monomeric phenolic components of lignin degradation fragments, e.g. derivatives of phenolic acids, aldehydes, and alcohols. Uncoated fused silica capillaries and borate-phosphate buffer systems at moderate pH conditions were used in order to separate the compounds of interest. To provide validation of the method, the same samples were analyzed independently by HPLC using gradient elution on a RP-C18 column. As sugar degradation fragment, furan-2-carboxylic acid was detected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274608
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  • 4
    Electronic Resource
    Electronic Resource
    Liquid chromatography of phenolic compounds in natural water using on-line trace enrichment (1995)
    Springer
    Chromatographia 40 (1995), S. 85-90 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Phenolic compounds ; Ion-pair solid phase extraction ; On-line trace enrichment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Two packing materials, C18 and PLRP-S, are studied for on-line trace enrichment of phenolic compounds in water. Various precolumns of different internal diameter are also tested and the addition of an ion-pair reagent to increase retention and thus, breakthrough volumes of phenolic compounds, is studied. Best results are obtained when a PLRP-S precolumn is coupled on-line with a C18 analytical column and DAD detector. Addition of TBA considerably increases breakthrough volumes. In contrast, when a C18 precolumn is used, breakthrough volumes are lower and it is impossible to determine TCP and PCP, under the experimental conditions used, because of interference of other nonpolar compounds in the samples. The performance of the system is evaluated with river and tap water and the preconcentration of 10 ml of sample in a PLRP-S precolumn involves a linear range between 1 μg 1−1 and 20 μl−1 and limits of determination between 0.5 μg l−1 and 1 μg l−1 are obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274612
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  • 5
    Electronic Resource
    Electronic Resource
    Screening of water samples for polar organic micropollutants using on-column sample enrichment (1995)
    Springer
    Chromatographia 40 (1995), S. 631-637 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Trace analysis ; Pesticides in tap water ; Aromatic sulphonates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Methodology and instrumentation are described which allow chromatographic screening of water samples under substantially simplified conditions and at reduced cost. A single column is used to accomplish sample extraction, trace enrichment, and separation. The performance of such a system is demonstrated, and the results compared with conventionally used concepts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02315129
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  • 6
    Electronic Resource
    Electronic Resource
    Analysis of pyrithiones by reversed-phase high-performance liquid chromatography (1995)
    Springer
    Chromatographia 40 (1995), S. 669-673 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Transchelation ; Zinc pyrithione and related compounds ; Antidandruff formulations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An analytical procedure has been developed for the determination of zinc pyrithione in antidandruff formulations. Zinc pyrithione was converted into a stable copper complex and then analysed by reversed-phase HPLC. The proposed method allows the separation of the analyte from related pyrithiones and therefore is able to verify the compliance of cosmetic preparations with current legislation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02315135
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  • 7
    Electronic Resource
    Electronic Resource
    Marked differences between acetonitrile/water and methanol/water mobile phase systems on the thermodynamic behavior of benzodiazepines in reversed phase liquid chromatography (1995)
    Springer
    Chromatographia 41 (1995), S. 84-87 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Benzodiazepines ; Solvent effects ; ACN clusters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Two different methods were used to determine the separation factor α at different temperatures and the Gibbs-Helmholtz parameters (Δ(ΔH), Δ(ΔS)) of two adjacent benzodiazepines on a chromatogram were obtained from plots of lnα versus 1/T. We first studied each factor (fraction of water ϕ in the ACN/water mixture and column temperatureT), which controls the retention mechanism, and then we examined the simultaneous variation of all these factors. The changes in Δ(ΔH) and Δ(ΔS) in relation to a volume fraction of water ϕ in an ACN/water mixture were examined. In the ACN/water system, Δ(ΔH) was fairly constant in the acetonitrile region of ϕ≤0.52 and appears to be a roughly linear function of ϕ for ϕ≥0.52. In this system Δ(ΔS) is approximately a parabolic function of ϕ with an optimum at ϕ≅0.52. The retention mechanism of ten benzodiazepines was found to be significantly different in the methanol/water and ACN/water mixtures. The separation optimization of these ten benzodiazepines was then considered. A fraction of water of 0.43 in the ACN/water mixture and a column temperature of 44°C gave the most efficient separation conditions in the ACN/water mixture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274199
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  • 8
    Electronic Resource
    Electronic Resource
    HPLC determination of urinary 2,4- and 2,6-toluendiamines as potential degradation products of polyurethane breast implants (1995)
    Springer
    Chromatographia 41 (1995), S. 661-664 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Polyurethane degradation products ; 2,4- and 2,6-toluendiamine ; Urine analysis ; Breast implants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A reversed-phase HPLC method has been developed for the urinary determination of mutagenic 2,4- and 2,6-toluendiamines. These amines are degradation products of polyurethane, a material used to cover textured silicone breast implants. FMOC-Cl was used as fluorescent derivatising agent in order to obtain a limit of detection of 15 ng/ml in urine. Pre-treatment of urine samples was by liquid/liquid extraction and urine specimens of patients after surgury were analysed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02267801
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  • 9
    Electronic Resource
    Electronic Resource
    HPLC analysis of flavonoids and phenolic acids and aldehydes inEucalyptus spp. (1995)
    Springer
    Chromatographia 41 (1995), S. 657-660 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Polyphenols ; Flavonoids ; Phenolic acids and aldehydes ; Eucalyptus spp.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Standards of the polyphenols occurring in wood, bark and leaf extracts ofEucalyptus spp. (i.e. flavonoids and phenolic acids and aldehydes) have been analyzed by HPLC using reversed phase columns, gradient elution and diode-array detection. The conditions used are reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02267800
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  • 10
    Electronic Resource
    Electronic Resource
    Polymer encapsulated stationary phases with improved efficiency (1995)
    Springer
    Chromatographia 40 (1995), S. 657-661 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Reversed phases ; Polyencapsulated silica ; Polyacrylates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary By copolymerization of silica modified with vinyl groups and acrylic acid esters in suspension highly efficient, polymeric-encapsulated stationary-phases can be prepared. The suspending liquid has to be selected such that the monomers are at least partially adsorbed on the surface and the polymer formed does not precipitate. Under these conditions stationary phases capable of speedy mass transfer can be prepared, where the reduced plate heights are between 2 and 3. The silica surface shielding is optimized so that basic and acidic solutes elute with symmetrical peak.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02315133
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  • 11
    Electronic Resource
    Electronic Resource
    Determination of D- and L-amino acid residues in peptides with fluorescent chiral tagging reagents by high-performance liquid chromatography (1995)
    Springer
    Chromatographia 40 (1995), S. 645-651 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chiral resolution of amino acids ; Pre-column derivatization ; Fluorescent chiral tagging reagents ; Stereochemical purity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Derivatization of amino acid enantiomers with fluorescent chiral Edman-type reagents, 4-(3-isothiocyanatopyrrolidin-1-yl)-7-nitro-2,1,3-benzoxadiazole [R(−)- and S(+)-NBD-PyNCS] and 4-(3-isothiocyanatopyrrolidin-1-yl)-7-(N,N-dimethylaminosulfonyl)-2,1,3-benzoxadiazole [R(−)-and S(+)-DBD-PyNCS], yields corresponding diastereomers separable by reversed-phase HPLC on normal achiral columns. The resolved diastereomers were detected fluorometrically at 530 nm with excitation at 490 nm for the NBD-PyNCS derivatives and at 560 nm with excitation at 450 nm for those derived from DBD-PyNCS reagents. This HPLC-derivatization method was used for evaluation of stereochemical purity for some synthetic commercial peptides. The enantioanalysis was reliable down to 0.05% racemization of the amino acid residues and a quantity of 100 μg peptide sample was usually enough for the analysis. Two acid hydrolysis methods, i.e. the standard procedure with constant-boiling hydrochloric acid (HCl) and a rapid vapor-phase procedure with HCl-trifluoroacetic acid (TFA) mixture, were compared. The later was found to be unsuitable owing to increased racemization of the amino acid residues during the hydrolysis. Judging from the results obtained for proline and leucine residues, most of the tested peptides including biologically active peptides, such as neurotensin, [d-Ala2,d-Leu5]-enkepharin and morphine tolerance peptide, possessed stereochemical purities higher than 98%. Influence of structural features of the peptides on the racemization of the amino acid residues was found to be significant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02315131
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  • 12
    Electronic Resource
    Electronic Resource
    HPLC-continuous-flow fast atom bombardment mass spectrometry (HPLC-CFFAB) — a convenient method for the analysis of bile acids in bile and serum (1995)
    Springer
    Chromatographia 40 (1995), S. 674-679 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Mass spectrometric detection ; Fast atom bombardment ionization ; Serum bile acid ; Rat bile
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary In order to analyse bile acids in biological matrices, e.g. rat bile and human serum, high performance liquid chromatography (HPLC) was coupled to continuous-flow fast atom bombardment mass spectrometry (CFFAB-MS). A gradient elution system which had already proved to be well suited for the quantitative determination of conjugated bile acids in bile was modified to allow HPLC-CFFAB-MS-coupling. Due to the sensitivity of this coupling method it is possible to obtain more information about the biliary bile acid pattern and species-specific secondary bile acids. Furthermore, we were able to identify obviously unknown bile acid species in rat bile which most likely classify as mono-oxo and di-oxo-taurocholates (MW 513 Da, 511 Da) and mono-oxo-glycocholates (MW 463 Da). In the present study we show that using this system it is possible to determine both conjugated and unconjugated as well as sulfated bile acids, without time consuming group separation and derivatization, from rat bile and human serum. In addition, it is suggested that the method presented here should be considered for use in routine analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02315136
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  • 13
    Electronic Resource
    Electronic Resource
    Fluorescence enhancement of dansylamino acids by bovine serum albumin as mobile phase additive in microcolumn liquid chromatography (1995)
    Springer
    Chromatographia 40 (1995), S. 159-162 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Fluorescence enhancement ; Bovine serum albumin ; Dansylamino acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The effects of acetonitrile and bovine serum albumin (BSA) concentrations on the signal intensity and retention behavior of dansylamino acids have been examined by using γ-cyclodextrin-bonded silica gel as the stationary phase in microcolumn liquid chromatography. Fluorescence intensities of dansylamino acids were enhanced by BSA as a mobile phase additive, e.g., detection limits of dansyl derivatives of L-Ala and L-Phe were improved by a factor of 12–18.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02272165
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  • 14
    Electronic Resource
    Electronic Resource
    A statistical study of the correlation between k′ or log k′ and log Pow for a group of benzene and naphthalene derivatives in micellar liquid chromatography using a C-18 column (1995)
    Springer
    Chromatographia 40 (1995), S. 185-192 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Micellar liquid phases ; Octanol-water partition coefficient ; Benzene and naphthalene derivatives
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary It is shown that the logarithm of the capacity factor (log k′) for fifteen benzene and naphthalene derivatives in micellar liquid chromatography with forty nine different mobile phases generally correlates better with the logarithm of the octanol-water partition coefficient (log Pow) than the capacity factor (k′). Optimum conditions are established to obtain the best linear correlations of log k′-log Pow.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02272169
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  • 15
    Electronic Resource
    Electronic Resource
    Improvement of selectivity of electrochemical detection for the determination of compounds with chloro aromatic rings (1995)
    Springer
    Chromatographia 40 (1995), S. 247-252 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Photolysis ; Electrochemical detection ; Drugs with chlorinated aromatic rings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Pharmaceuticals containing a thiazide ring or chlorinated aromatic ring were investigated with respect to enhanced selectivity in determination. Oxidative electrochemical detection coupled with HPLC was used to study the influence of the pH of the mobile phase under conditions of photolysis. To cover a pH range 3.9–12, the employment of a polymer column stable in alkaline media was necessary. The method offers the great advantage of derivatization without chemicals at low operating potentials, thereby providing high selectivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290353
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  • 16
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    Electronic Resource
    Separation of structural isomers using cyclodextrin-polymers coated on silica beads (1995)
    Springer
    Chromatographia 40 (1995), S. 296-302 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Structural isomer separation ; Cyclodextrin ; Polymers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Several β-cyclodextrin (CD)-bonded stationary phases for high performance liquid chromatography (HPLC) were prepared, based on silica beads coated with a poly(alkylamine), [poly(ethyleneimine)(PEI)]. In order to obtain stationary phases with a high content of CD and maximum accessibility of the CD cavity, the functionalization was carried out after the coating, using the mono-tosyl derivative of CD as the intermediate. The ability of these supports to separate ortho, meta and para isomers of some disubstituted benzene derivatives was examined. The contribution of the amino groups of the polymer and of the CD cavity to the separation process is discussed. The resolution is mainly based on the difference in the stability of the complexes of the various isomers with CD. The influence of the amount of CD on the height of the theoretical plate is also studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290360
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  • 17
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    Electronic Resource
    A potential application for large diameter pellicular supports in the reversed phase study of ultra high molecular mass polystyrenes (1995)
    Springer
    Chromatographia 40 (1995), S. 307-312 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Reversed phase ; Polystyrene ; Pellicular ; Ultra high molecular mass
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Ultra high molecular mass (〉 7 million dalton) polystyrenes are prone to degradation in size exclusion chromatography. In gradient elution reversed phase HPLC they do not elute visibly on small particle size porous supports. However, large diameter C18 pellicular particles were successfully employed for reversed phase study of ultra high molecular mass (15 million dalton) polystyrenes without polymer degradation during elution. Although retention for the lower molecular mass polystyrenes was lower than on small diameter porous particles, the medium high molecular mass polystyrenes (0.5–1 million dalton) showed similar retention. The addition of small diameter porous particles in small quantities, to the large diameter pellicular particles, increased the amount of retention of the low molecular mass polystyrenes without affecting the higher molecular mass polystyrenes.
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    URL: http://dx.doi.org/10.1007/BF02290362
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  • 18
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    Electronic Resource
    High performance liquid chromatographic determination of methyl ethyl ketone in urine as its 3-methyl-2-benzothiazolinone hydrazone derivative (1995)
    Springer
    Chromatographia 40 (1995), S. 336-340 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Methyl ethyl ketone in urine ; Derivatization ; 3-Methyl-2-benzothiazolinone hydrazone ; Comparison with GC-MS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A HPLC method for the determination of methyl ethyl ketone (MEK) in urine after derivatization with 3-methyl-2-benzothiazolinone hydrazone is proposed. The calibration curve for the ketone was linear, ranging between 0.23–10 mg/L, with a detection limit of 0.025 mg/L. The results were compared to those obtained by GC-MS, coupled to the headspace technique. MEK derivatization and the derivative purification processes were verified with respect to the main variables such as reaction temperature, reagent concentration, probable interferences and enrichment phase. The method is simple and reliable and shows a good sensitivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290366
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  • 19
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    Liquid chromatographic analysis of sulfornamides in foods (1995)
    Springer
    Chromatographia 40 (1995), S. 382-386 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Sulfonamides in foodstuffs ; Honey ; Milk ; Eggs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A procedure for the simultaneous determination of several sulfonamides in different foods, such as honey, milk and eggs is proposed. The analysis is carried out using reversed phase liquid chromatography with spectrophotometric detection. Optimization of the mobile phase led to good separation and a short analysis time when an initial isocratic step with a 3∶97 acetonitrile: water mixture was used for 5 minutes, followed by a linear gradient up to a 40∶60 mixture over 15 min. The proposed method is suitable for routine quality control analysis to ensure the absence of sulfonamides in foods. Recovery studies yielded good results for all food samples because there were no interferences from the matrices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269899
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  • 20
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    Determination of aflatoxins in peanut meal by LC/MS with a particle beam interface (1995)
    Springer
    Chromatographia 40 (1995), S. 411-416 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Particle beam LC/MS interface ; Capillary columns for LC ; Mycotoxins ; Peanut meal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new method for the analysis of aflatoxins in food extracts, based on liquid chromatography/mass spectrometry interfacing, is presented. The chromatographic separation was performed with a reversed phase packed capillary column coupled with a modified particle beam interface capable of handling microliter per minute flow rates. This system allows higher overall sensitivity and easier operation procedures. The method has proved to be particularly suitable for the analysis of the toxins in very complex matrices. The specificity of electron impact ionization allowed positive identification of the aflatoxins with an excellent response linearity for accurate quantitation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269904
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  • 21
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    Retention parameters of some isomeric 2-benzoylbenzoic acids in reversed-phase ion-pair high performance thin-layer and column chromatography (1995)
    Springer
    Chromatographia 40 (1995), S. 453-457 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Thin-layer chromatography ; Reversed phase ; 2-benzoylbenzoic acids ; Anionic and cationic counter ions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The 2-benzoylbenzoic acid series was investigated by reversed-phase, high-performance, thin-layer and column chromatography using various alkylammonium salts and di(2-ethylhexyl)orthophosphoric acid as polar associating reagents. The effects of the individual substituents on retention were quantified by Δlog k′ and ΔRM values. The compounds investigated differing in molecular structure (hydrophilic and hydrophobic substituents) commonly occurring groups in drugs and biologically active substances provide information on molecular interaction in these ion-pair systems. The combined effects on retention of organic modifier and ion-pair reagent concentration were investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269912
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  • 22
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    Determination of D- and L-amino acids in biological samples by two-dimensional column liquid chromatography (1995)
    Springer
    Chromatographia 41 (1995), S. 6-14 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Two-dimensional separation ; D- and L-amino acids ; Enantioseperation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A two-dimensional, column liquid chromatographic system is used for the determination of the D- and L-enantiomers of amino acids in biological samples. Separation of the amino acids is first on ion-exchange column by gradient elution with a sodium citratesodium chloride buffer. Enantioseparation is by subsequent injection of 3 μl heart-cuts of the individual amino acids onto a second column with a chiral crown ether stationary phase. Finally, fluorescence detection is after post-column labelling of the amino acids using ano-phthalaldehyde-2-mercaptoethanol reagent solution. The high separation power and selectivity of the system allow processing of complex samples with hardly any additional treatment and the determination of small quantities of D-amino acids in the presence of excess L-form. Applicability of the system is illustrated by the determination of D- and L-aspartate, serine, glutamate and alanine in various complex biological samples, such as protein hydrolysates, urine and biotechnological and food samples. Data are given on detectability, repeatability and linearity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274188
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    Simultaneous determination of preservatives, sweeteners and antioxidants in foods by paired-ion liquid chromatography (1995)
    Springer
    Chromatographia 41 (1995), S. 43-50 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion pair LC ; Sweeteners, preservatives and antioxidants ; Food additive analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A paired-ion, reversed-phase high-performance liquid chromatographic method was developed for the simultaneous determination of sweeteners (dulcin, saccharin-Na and acesulfame-K), preservatives (sodium dehydroacetate, sorbic acid, salicyclic acid, benzoic acid, succinic acid, methyl-para-hydroxybenzoic acid, ethylpara-hydroxybenzoic acid, n-propyl-para-hydroxybenzoic acid, isopropyl-para-hydroxybenzoic acid, n-butyl-para-hydroxybenzoic acid, and isobutyl-para-hydroxybenzoic acid), and antioxidants (3-tertiary-butyl-4-hydroxyanisole and tertiary-butyl-hydroquinone). A mobile phase of acetonitrile-50 mM aqueous α-hydroxy-isobutyric acid solution (pH 4.5) (2.2 ∶ 3.4 or 2.4 ∶ 3.6, v/v) containing 2.5 mM hexadecyltrimethylammonium bromide and a C18 column with a flow rate at 1.0 mL/min and detection at 233 nm were used. This method was found to be very reproducible with detection limits ranged from 0.15 to 3.00 μg. The retention factor (k) of each additive could be affected by concentrations of hexadecyltrimethylammonium bromide and α-hydroxyisobutyric acid, and pH and ratio of mobile phase. The presence of additives in some food samples was determined.
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    URL: http://dx.doi.org/10.1007/BF02274194
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    Prediction of precision from signal and noise measurement in liquid chromatography: Mathematical relationship between integration domain and precision (1995)
    Springer
    Chromatographia 41 (1995), S. 75-83 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Limit of detection ; Precision ; Uncertainty prediction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The precision of integration over noisy instrumental output for quantitative analysis is studied. A probability theory is developed to predict the relative standard deviation (RSD) of integration results over an integration domain from one-point integation (peak height measurement) to entire area integration in HPLC. Common integration modes of horizontal zero line and oblique zero line are taken into account, but no peak overlap is assumed. The question of the analytical superiority of peak height measurement or integration for quantitation is answered. In the HPLC apparatus used, the minimum RSD of measurements is found in the integration domain of ca. ±0.5 σ for analytes [peaks are approximated by the Gaussian signal of width, σ (standard deviation)]. The RSD of integration measurements is also shown to depend on the stochastic properties of back-ground noise (uncorrelated noise and correlated 1/f type noise). The theoretical conclusion is verified by Monte Carlo simulation and HPLC experiments for some aromatic compounds.
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    URL: http://dx.doi.org/10.1007/BF02274198
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    Ion-pair reversed-phase and low-molecular-weight aqueous gel permeation high-performance liquid chromatography methods for the determination of amoxicillin oligomersa (1995)
    Springer
    Chromatographia 41 (1995), S. 651-656 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-pair and GPC separations ; Amoxicillin oligomers ; β-Lactam ring polymers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Polymeric substances formed from concentrated sodium amoxicillin in an aqueous solution have been separated using two high-performance liquid chromatographic methods. We used a C18 reversed-phase column with tetrabutylammonium chloride as an ion-pairing agent with an acetonitrile gradient and a TSKgel G2500PWxl column with water as the solvent for gel permeation chromatography. The separated materials, ranging in size from the monomer to the tetramer, have been characterized by functional-group chemical analysis, while the identification of the piperazine-2,5-dione was done using a pure standard. A greater number of peaks which were also better defined were obtained using the ion-pair reversed-phase method, and open and closed beta-lactam ring polymer forms could be distinguished. Using the gel permeation method, only a few monomer, piperazine-2,5-dione, dimer, trimer and combined amoxicillin trimer and tetramer peaks were obtained with water, although those obtained were quite well defined. The data on the time-course of formation of the oligomers and the amoxicillin degradation product were virtually identical by both methods.
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    URL: http://dx.doi.org/10.1007/BF02267799
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    Signal enhancement by on-column fluorimetric detection in gradient elution of dansyl amino acids in liquid chromatography (1995)
    Springer
    Chromatographia 41 (1995), S. 148-152 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; On-column fluorimetric detection ; Gradient elution ; Dansyl amino acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Fluorimetric detection in the presence of a stationary phase has been applied to gradient elution of dansyl amino acids in liquid chromatography. A 1.5 mm ID quartz tube packed with the same materials as the separation column was employed for the flow cell. Conventional-size columns were employed. The peak height of analytes increased with increasing retention owing to focusing and environmental effects of the stationary phase, leading to improvements in sensitivity, which was pronounced for analytes eluting late. The lower the gradient, the larger the improvement in sensitivity achieved. Detection limits were improved by a factor of up to 5.1 by fluorimetric detection using the packed flow cell, compared with those achieved using a common empty flow cell.
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    URL: http://dx.doi.org/10.1007/BF02267946
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    A study of the behaviour of some new column materials in the chromatographic analysis of Cinchona alkaloids (1995)
    Springer
    Chromatographia 41 (1995), S. 153-160 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; LC-MS ; Cinchona alkaloids ; New column packing materials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A major problem in the HPLC analysis of alkaloids is the poor peak shape and consequently low resolution, due to the interactions of the basic alkaloids with the residual acidic silanol groups of most reversed phase materials. The performance of new packing materials specially designed for the separation of basic compounds has been studied using mobile phases without the special additives commonly applied in the analysis of alkaloids. Strongly basic Cinchona alkaloids were used as test compounds. Retention characteristics and selectivities of each material were studied, after mobile phase optimisation for the column. The influence of the major factors (nature and content of the organic modifier, pH value, salt concentration) affecting resolution was studied. The mobile phases were chosen so that they could be used in thermospray LC-MS. The addition of salts to the mobile phase improves separation but in general the modification of the mobile phase gave little change in selectivity. The performance of silicabased C18 material proved superior to the polymer materials tested.
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    URL: http://dx.doi.org/10.1007/BF02267947
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    Determination of vitamin A in pharmaceutical preparations by high-performance liquid chromatography with diode-array detection (1995)
    Springer
    Chromatographia 40 (1995), S. 143-146 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Diode-array detection ; Retinol acetate ; Pharmaceutical preparations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A very simple high-performance liquid chromatographic method for determination of Vitamin A in pharmaceutical preparations without the need for saponification was developed. A reversed-phase (Nova-Pack C18, 4 μm) column was used with a mobile phase of acetonitrile-tetrahydrofuran-water (55∶37∶8) and a flowrate of 1.5 ml/min. Sample treatment only consisted of the extraction of retinol acetate content from capsules or tablets with methanol. Total extraction was achieved by shaking vigorously with the aid of magnetic stirring for three hours at room temperature. No change of solvent is necessary to introduce the sample in the chromatographic system. This method is suitable for routine quantification of Vitamin A.
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    URL: http://dx.doi.org/10.1007/BF02272162
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    Thermodynamic behavior of mixed benzodiazepines by a new liquid chromatographic method (1995)
    Springer
    Chromatographia 40 (1995), S. 193-196 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chemometric methodology ; Elution order ; Simplex optimization ; Benzodiazepines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Using a rapid chemometric methodology to determine the separation factor, α, at different temperatures, Gibbs Helmholtz parameters (Δ (ΔH), Δ (ΔS), Δ (ΔG)) of two adjacent benodiazepines on a chromatogram were obtained from ln α versus T−1 plots. A temperature dependent reversal of the elution order was studied and the mobile phase composition and column temperature were optimized to obtain the best separation. A flow rate of 0.80 ml min−1 with 52.6% methanol in the methanol-water mixture and a column temperature of 48°C gave the most efficient separation of ten benzodiazepines.
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    URL: http://dx.doi.org/10.1007/BF02272170
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    Mixed-mode liquid chromatography of aliphatic anionic surfactants with a naphthalenetrisulfonate mobile phase (1995)
    Springer
    Chromatographia 40 (1995), S. 237-246 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Mixed mode stationary phases ; Indirect photometric and fluorometric detection ; Conductimetric detection ; Alkyl-sulphates, and sulphonat-phosphates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Separation of three classes of anionic surfactants (alkyl sulfates, alkanesulfonates, and alkyl phosphates) are achieved on a mixed-mode reversed phase (RP) phenyl/-anion exchange column using a naphthalenetrisulfonate (NTS)-acetonitrile (ACN) mobile phase via indirect photometric, indirect fluorometric, direct or indirect conductivity detection. Mixtures of C5−C18 sulfates, C6−C18 sulfonates, and C1−C4 phosphates (mono- and di-ester) can be separated in less than 20, 24, and 20 min respectively. Although hydrophobic effects are more pronounced in mixed-mode chromatography, equivalent-per-equivalent exchange of analysis and eluent ion is still required for sensitive indirect photometric, fluorometric, or conductivity detection. The detection limits of alkyl sulfates and alkanesulfonates are in the range of 3–15 pmoles which are at least an order of magnitude better than suppressed conductivity detection. The determination of surfactants in a variety of real samples is also presented.
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    URL: http://dx.doi.org/10.1007/BF02290352
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    Enantiomeric separation of D/L-carnitine using HPLC and CZE after derivatization (1995)
    Springer
    Chromatographia 40 (1995), S. 287-295 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Capillary zone electrophoresis ; Enantioseparation ; Carnitine ; Derivatization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Carnitine is an essential component in tissues of animals, higher plants and many microorganisms. Whereas the L-carnitine enantiomer plays an important role in the metabolism of long chain fatty acids, D-carnitine has a considerable toxic influence on biochemical processes. The analytical separation of D-and L-carnitine depends upon derivatization with UV-or fluorescently active substances, e.g. FMOC and (+)/(−)-FLEC. The separation of diastereomeric (+)- and (−)-FLEC carnitine esters was performed successfully with capillary zone electrophoresis (CZE) and HPLC, after optimization of the derivatization process and of the composition and pH of the buffer, using UV- and fluorescence detection. With HPLC separation a detection limit of the carnitine esters of 5 μmol/l when using fluorescence detection was achieved. With both separation systems baseline resolution and short analysis times could be obtained. The enantiomeric FMOC derivatives could be separated using the electrophoretic system and acidic buffers with high concentrations of an osmotic flow modifier together with γ-cyclodextrine as chiral selector. The applicability of the optimized separation conditions are demonstrated in the analysis of agar culture medium inoculated withPseudomonas putida and of pharmaceutical formulations. In all samples very low amounts of D- or L-carnitine could be determined in the presence of the other enantiomeric form. Problems caused by the impurity of the carnitine standards or the derivatization agent (+)/(−)-FLEC are discussed.
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    URL: http://dx.doi.org/10.1007/BF02290359
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    Retention of fullerenes by octadecyl silica. Correlation with NMR spectra at low temperatures (1995)
    Springer
    Chromatographia 40 (1995), S. 507-512 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Fullerenes ; Retention vs NMR spectra ; C18 phases ; Low temperature separations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The temperature effect on the retention of fullerenes in the range 80°C to −70°C in liquid chromatography (LC) has been examined using octadecylsilica stationary phases (ODS). It has been found that the maximum retention temperature lies around −10°C with a highly carbon loaded ODS phase. Solid state CPMAS NMR measurements on the stationary phases indicated that the relaxation time at the 30 ppm methylene signal changes with the temperature and has a minimum relaxation time at the temperature which closely matches the maximum retention temperature observed in chromatography. The interpretation of both NMR spectroscopic and LC chromatographic data are discussed.
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    URL: http://dx.doi.org/10.1007/BF02290260
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    Derivatisation of DL-amino acids by urethane — Protected α-amino acidN-carboxyanhydrides for separation by LC (1995)
    Springer
    Chromatographia 40 (1995), S. 601-606 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Amino acid analysis ; Chirality ; Diastereoisomers ; Dipeptides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Using a robotic autosampler, free DL-amino acids were derivatized with highly reactive, urethane-protected, L-α-amino acidN-carboxyanhydrides (NACs) with structures: Boc-Phe-NCA, Boc-Asn(Trt)-NCA, Fmoc-Lys(Boc)-NCA, Fmoc-Met-NCA, Fmoc-Ala-NCA, Z-Ala-NCA, Z-Val-NCA and Z-Leu-NCA (Boc=tert-butyloxycarbonyl, Trt=trityl, Fmoc=9-(fluor-enylmethyl)oxycarbonyl, Z=benzyloxycarbonyl). Using sodium borate buffer and acetonitrile solvent, derivatization was complete in 3.5 min at room temperature. By selection of an appropriate reagent, the resulting diastereomeric,N-protected dipeptides were separated on an octylsilica stationary phase using mixtures of sodium acetate buffer and acetonitrile as eluents.
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    High-performance liquid chromatography of dihydroxyacetone as its bis-2,4-dinitrophenylhydrazone derivative (1995)
    Springer
    Chromatographia 41 (1995), S. 61-65 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Dihydroxyacetone ; 2,4-dinitrophenylhydrazine ; Tanning creams
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A rapid and simple HPLC method for the identification and determination of dihydroxyacetone, a tanning agent widely used in a variety of preparations, is presented. The method consists of the analysis of the formulated products after a derivatization reaction which enhances the response and the detection limit of the chromatographic analysis. The characterization and the elucidation of the spacial geometry of the synthesized derivative are described.
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    High performance liquid chromatographic analysis of Patent Blue V in cheese (1995)
    Springer
    Chromatographia 41 (1995), S. 431-434 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Thin-layer chromatography ; Patent Blue V in cheese
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The HPLC method developed for the analysis of the dye Patent Blue V in extracts from cheese is sufficiently sensitive to detect and measure concentrations above 0.1 ppm with a standard deviation of 3%. The extraction procedure described gives a recovery from cheese of about 80%. The method has been applied to commercial samples of cheese and a concentration of the dye of about 0.12 ppm was measured in one case.
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    URL: http://dx.doi.org/10.1007/BF02318618
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    Modelling and prediction of retention in high-performance liquid chromatography by using neural networks (1995)
    Springer
    Chromatographia 41 (1995), S. 435-444 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Micellar liquid chromatography ; Neural networks ; Retention modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Multi-layer feed-forward neural networks trained with an error back-propagation algorithm have been used to model retention behaviour of liquid chromatography as a function of the composition of the mobile phases. Conventional hydro-organic and micellar mobile phases were considered. Accurate retention modelling and prediction have been achieved using mobile phases defined by two, three and four parameters. With micellar mobile phases, the parameters involved included the concentrations of surfactant and organic modifier, pH and temperature. It is shown that neural networks provide a competitive tool to model varied inherent nonlinear relationships of retention behaviour with respect to the mobile phase parameters. The soft models defined by the weights of the networks are capable of accommodating all types of linear and nonlinear relationships, neural networks being specially useful when the relationships between retention behaviour and the mobile phase parameters are unknown. However, to train neural networks more experimental points than with hard-modelling methods are required, hence the use of the networks is recommended only for those cases where adequate theoretical or empirical models do not exist.
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    URL: http://dx.doi.org/10.1007/BF02318619
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    Simultaneous assay of four stereoisomers of diltiazem hydrochloride. Application to in vitro chiral inversion studies (1995)
    Springer
    Chromatographia 41 (1995), S. 450-454 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Diltiazem hydrochloride stereoisomers ; Chiralcel OF ; Chiral inversion ; Epimerization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The simultaneous stereospecific assay of four stereoisomers of diltiazem hydrochloride in bulk drug and aqueous solution was developed using HPLC on a Chiralcel OF column. The four isomers were quantitated with good precision by the internal standard method. The chiral inversion of (+)-cis-diltiazem hydrochloride in vitro, stability of its (2S, 3S) configuration in the solid and aqueous states was examined by HPLC. Chiral inversion of (+)-cis-diltiazem hydrochloride was not observed in the solid state, and its (2S, 3S) configuration was stable to heat, humidity and light. Chiral inversion of (+)-cis-diltiazem hydrochloride (2S, 3S) was observed in aqueous solution under UV, but not in aqueous solution stored at 80°C for 5h nor under visible light for 10 h. The (+)-cis-diltiazem hydrochloride (2S, 3S) epimerized to (+)-trans-diltiazem hydrochloride (2R, 3S) with a half-life of 5h in aqueous solution under UV but the reverse chiral inversion of (+)-trans-diltiazem hydrochloride (2R, 3S) to (+)-cis-diltiazem hydrochloride (2S, 3S) was not observed.
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    Detoxification of acetonitrile-water wastes from liquid chromatography (1995)
    Springer
    Chromatographia 41 (1995), S. 488-491 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Acetonitrile disposal ; Acetonitrile hydrolysis ; Degradation kinetics ; Waste solvent management
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Acetonitrile is one of the most frequently used solvents in column liquid chromatography. Because of its toxicity, safe disposal of the waste solvent is essential. Combustion in a hazardous waste plant, if available, is recommended. Otherwise the waste can be degraded in the laboratory to acetic acid and ammonia by treatment with sodium hydroxide. The addition of hydrogen peroxide is not necessary. The waste needs to be diluted to 10% acetonitrile in water in order to prevent the formation of a two-phase system on addition of concentrated sodium hydroxide. This reagent must be added in excess; 2.5 mols of sodium hydroxide per mol of acetonitrile are recommended. It was found that the kinetics are of second order, with an activation energy of 89 kJ mol−1 and a frequency factor of 9×109. Therefore even at room temperature degradation is possible, although a hydrolysis time of approximately 15 days is needed under these conditions. At 80°C, where refluxing is not necessary, hydrolysis is complete after, e.g., 2 h, depending on the amount of sodium hydroxide added.
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    Retention behaviour of metal complexes with 5-sulphoquinoline-8-ol in reversed-phase ion-pair liquid chromatography (1995)
    Springer
    Chromatographia 41 (1995), S. 532-538 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-pair LC ; 5-Sulphoquinoline-8-ol ; Metal complexes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The reversed-phase ion-pair liquid chromatographic behaviour of several metal complexes with 5-sulphoquinoline-8-ol (HQS) on an octadecyl-modified silica column was investigated by using a fluorescence detector. The aluminum complex gave two peaks on the chromatograms when eluents containing phosphate buffer were used. The effects of the pH of the eluent, HQS concentration, the nature of anions in the eluent, and the column temperature on the retention behaviour of the aluminum complex are discussed on the basis of the equilibria and the kinetics of the complexation of the aluminum ion with HQS and anions in the eluent. The equilibrium constant for the interconversion reaction between the two Al(III)-HQS species which correspond to the two peaks observed and the second stepwise formation constant for the Zn(II)-HQS complex were evaluated from the HPLC data obtained.
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    Liquid chromatographic determination of aniline and derivatives in environmental waters at nanogram per litre levels using fluorescamine pre-column derivatization (1995)
    Springer
    Chromatographia 41 (1995), S. 568-572 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Fluorescamine derivatives ; Aniline and aniline derivatives ; Environmental waters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Fluorescamine (fluram) has been used as a fluorogenic compound for pre-column derivatization of aniline and some derivatives. Anilines were derivatized with fluram in citrate buffer media (pH 5.5) to form pyrrolinones. The highly fluorescence pyrrolinones were isolated and pre-concentrated by solid phase extraction. A reversed phase, Spherisorb RP-8 column and tetrahydrofuran: water:formic acid (42∶56∶2) mobile phase was used for separation. Detection method was by a sensitive fluorimetric method and quantitation was at 395 and 495 nm. The various parameters such as reaction conditions between anilines and fluram, solid phase extraction and chromatographic separation were optimized. Calibrations were linear over the range considered with excellent correlation coefficients (r〉0.999). Relative standard deviations are less than 2.5% and detection limits for aniline,p-toluidine, 4-chloroaniline and 4-bromoaniline were 6, 30, 6 and 8 ng L−1, respectively. This method has been used successfully for the determination of anilines in environmental waters.
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    Separation of saponins and determination of quinovic acid 3-O-α-L-rhamnopyranoside fromNauclea diderrichii (de Wild) Merr. Bark by high performance liquid chromatography (1995)
    Springer
    Chromatographia 41 (1995), S. 581-584 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Nauclea diderrichii (de Wild) Merr ; Saponins ; Alkaloid glycoside ; Chrysanthelline A
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A reversed-phase HPLC determination of 11 saponins and an alkaloid glycoside inNauclea diderrichii bark is described. Quantitative analysis of quinovic acid 3-O-α-L-rhamnopyranoside which is one of the main saponins was determined, using Chrysanthelline A as internal standard. The complete separation was achieved in 47 minutes. The method of quantification was validated.
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    URL: http://dx.doi.org/10.1007/BF02269723
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    Quantitative determination of toxic mono- and non-ortho polychlorinated biphenyls in cod liver oil after selective liquid chromatographic separation (1995)
    Springer
    Chromatographia 41 (1995), S. 585-593 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Column liquid chromatography ; Polychlorinated biphenyls ; Cod liver oil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary By application of a chromatographic column filled with Supelclean ENVI-Carb/Celite and elution with three solvents of different polarity three PCB fractions were obtained. Fraction A contained poly-ortho PCBs, Fraction B mono-ortho PCBs, and Fraction C non-ortho PCBs. The Supelclean ENVI-Carb/Celite column was used in combination with a sample preparation procedure for pre-cleaning of acid-stable chlorinated hydrocarbons such as DDT and its metabolites, HCH isomers, and regulation-relevant PCB congeners. The method was optimized using standard solutions of 55 PCB congeners, 8 chlorinated pesticides and contaminated cod liver oil samples. The influence of traces of remaining matrix on the elution profile of the organochlorine compounds on Supelclean ENVI-Carb/Celite was observed. Quantitation was carried out by GC-ECD with fused silica capillary columns of different polarity.
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    URL: http://dx.doi.org/10.1007/BF02269724
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    Application of SPE for the HPLC analysis of taxanes fromTaxus cell cultures (1998)
    Springer
    Chromatographia 47 (1998), S. 25-34 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Solid Phase Extraction ; RP-HPLC gradient analysis ; Taxus Cell Cultures ; Taxol and Taxanes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Solid phase extraction (SPE) methods are studied for the sample pretreatment for HPLC analysis ofTaxus cell suspension cultures. Various types of SPE materials were tested for the extraction of both the taxane standards and samples of various origin. Comparison between the different cartridges and the different elution solvents are made in terms of extraction recovery and sample clean-up. Selective elution of the taxanes is achieved by a gradient elution scheme.
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    URL: http://dx.doi.org/10.1007/BF02466782
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    Ionic strength dependence of heavy metal tartrate complex stabilities (1998)
    Springer
    Chromatographia 47 (1998), S. 77-80 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion chromatography ; Stability constants ; Ionic strength ; Heavy metals ; Tartaric acid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Ion chromatography and potentiometry were used for the determination of the stability constants Pb, Zn, Co, Ni, Mn tartrate complexes at different ionic strengths. An extrapolation function based on the Debye-Hückel equation was applied to obtain the thermodynamic stability constants.
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    URL: http://dx.doi.org/10.1007/BF02466789
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    Development of an Ion-pair HPLC method for the determination of 2,4- and 2,6-toluendiamine in human plasma (1998)
    Springer
    Chromatographia 47 (1998), S. 84-88 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-pair LC ; Plasma ; 2,4-Toluendiamine ; 2,6-Toluendiamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An ion-pair HPLC method is presented for the determination in plasma of 2,4- and 2,6-toluendiamine (TDA), known carcinogens. The chromatographic conditions consisted in isocratic elution on a reversed phase C18 column with 5 mM octanesulfonic acid in methanol-water, 45∶55, as mobile phase. UV detection was performed at 235 nm. Samples were analyzed after a simple single step liquid-liquid extraction and the method was validated by measurement of precision (interassay and intraassay), sensitivity, specificity, linearity, and recovery. The detection limit for both TDAs in plasma was 20 ng mL−1. The correlation coefficients based on the intrassay calibration curve were 0.998 and 0.997 for 2,6- and 2,4-TDA, respectively. The intraassay accuracy, expressed in terms of recovery, was found to be up to 89.91% and 97.05% for 2,6- and 2,4-TDA, respectively.
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    URL: http://dx.doi.org/10.1007/BF02466791
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    Direct resolution of a new antifungal agent, voriconazole (UK-109,496) and its potential impurities, by use of coupled achiral-chiral high-performance liquid chromatography (1998)
    Springer
    Chromatographia 47 (1998), S. 649-654 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Enantiomer separation ; Voriconazole (UK-109,496) ; Effect of organic mobile-phase modifier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Coupled achiral-chiral high-performance liquid chromatography (HPLC) with an achiral amino-based column coupled with a chiral amylose-based column has been used for qualitative and quantitative determination of the potential chiral and achiral impurities of Voriconazole (UK-109,496), a new antifungal agent with two stereogenic centres. The effect of the organic mobile-phase modifier, ethanol, was studied. The assay response was linearly dependent on concentration over the range 1.2–40.4 μg for Voriconazole and 2.5–104.0 ng for the impurities. The limit of detection was 2.5 ng for each analyte.
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    URL: http://dx.doi.org/10.1007/BF02467448
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    Separation of inorganic anions and cations on titania by use of acetic acid-sodium acetate and bicine-sodium hydroxide buffers (1998)
    Springer
    Chromatographia 47 (1998), S. 655-658 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion chromatography ; Titania packings ; Inorganic anions and cations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The ion-exchange retention behavior of titania synthesized in our laboratory was investigated by ion chromatography of inorganic anions and cations. Dilute acetic acid-sodium acetate and bicine-sodium hydroxide buffers were used as mobile phases with no use of suppresor. We observed that the titania, although poor at separating monovalent anions expcept nitrite ion in this experiment, was both an anion and a cation exchanger, and selectively retained fluoride and carbonate ions. We concluded that because of its specific retention properties there were possibilites of using this amphoteric exchanger for simultaneous analysis of anions and cations, and of using it as a selective packing material for ion chromatography.
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    URL: http://dx.doi.org/10.1007/BF02467449
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    Retention behavior of morphine and its metabolites on a porous graphitic carbon column (1998)
    Springer
    Chromatographia 47 (1998), S. 667-672 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Porous graphitic carbon ; Optimization ; Morphine and metabolites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The chromatographic behaviour of a series of morphine-based opiates has been investigated using a porous graphitic carbon packing material at acid and alkaline pH. The effects of mobile phase pH, mobile phase organic percentage, column temperature and ionpairing agents were studied. All six opiates were separated within a close retention window despite large differences in measured lipophilicities of the individual opiates. The retention order was not related to the log P values of the opiates and strong retention of the fully ionised compounds was observed, particularly those with acidic functional groups. The effect of pH on the retention of the compounds indicated that the degree of ionisation of the individual compounds was important in the separation mechanism, suggesting that hydrophobic interactions were present in addition to the polar retentive effects observed above. The strong retention of the ionised glucuronide and sulphate conjugates of morphine is a particularly useful feature of the porous graphitic carbon packing material which has general applicability to the analysis of polar or ionised drug metabolites.
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    URL: http://dx.doi.org/10.1007/BF02467451
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    Determination of clozapine in human plasma by solid-phase extraction and liquid chromatography with amperometric detection (1998)
    Springer
    Chromatographia 47 (1998), S. 8-12 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Amperometric detection ; Solid-phase extraction ; Plasma ; Clozapine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A sensitive and selective high-performance liquid chromatographic method has been developed for monitoring clozapine levels in human plasma. Chromatography was performed on a reversed-phase column (C8, 150 mm×4.6 mm i.d., 5 μm) with acetonitrile-aqueous sodium acetate solution, 88∶12 (v/v), as mobile phase; the flow rate was 1 mL min−1. Clozapine oxidation at +800 mV was detected amperometrically. Response was linearly dependent on concentration over the range 50–1500 ng mL−1 clozapine in plasma. Sample preparation by solid-phase extraction before HPLC analysis gave high extraction yield (94%). The accuracy and precision of the method were both very good (recovery: 97%;RSD〈3.3%).
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    URL: http://dx.doi.org/10.1007/BF02466779
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    Characterization of the precolumn bio trap 500 C18 for direct injection of plasma samples in a column-switching system (1998)
    Springer
    Chromatographia 47 (1998), S. 299-304 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Plasma samples ; Direct injection ; Restricted-access media ; Column-switching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new restricted access media (RAM) type of precolumn, Bio Trap 500 C18, for direct injection of plasma samples in column-switching systems was evaluated with respect to the elution of plasma proteins in different mobile phases, the loading capacity of plasma samples, the chromatographic behavior during plasma injections and protein contamination of the packing and sealings. More than 95% of plasma proteins could be excluded from the precolumn within three minutes for all selected mobile phases. Quantitative analyte recoveries could be obtained by injecting plasma samples ranging from 5 to 500 μL with the analyte mass〉150 ng onto a BioTrap 500 C18 column (20×4 mm I.D.). One precolumn tolerated about 15 mL of plasma injection without out noticeable change in retention and pressure. Clogging of the precolumn was encountered (≥45 mL of plasma) due mainly to the adsorption of proteins on the packing. The performance of the analytical column (Kromasil C18) was also examined. The column efficiency decreased by 60% after processing 45 mL plasma in total.
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    URL: http://dx.doi.org/10.1007/BF02466535
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    Characterisation of pitch by HPLC (1998)
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    Chromatographia 47 (1998), S. 373-382 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Polyaromatic hydrocarbons ; Pitch
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new high performance liquid chromatography method for the characterisation of toluene-soluble fractions of pitches has been developed. Although a chromatographic system typical of size exclusion chromatography was used, results indicate that, for these structurally complex samples, separation does not follow the usual discrimination by molecular size. A differentiation between several classes of polyaromatic hydrocarbons is achieved instead. Data are reported on the analysis of individual standard polyaromatic hydrocarbons, showing that four different elution ranges can be observed: three ofcata-condensed compounds (Cata1, Cata2 and Cata3) and one ofperi-condensed compounds (Peri). Results are reported proving the capacity of this high performance liquid chromatography method to distinguish between pitches of different origin and nature. It is also effective for the study of the chemical reactions occurring during heat treatment.
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    URL: http://dx.doi.org/10.1007/BF02466467
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    Determination of the five major opium alkaloids by reversed-phase high-performance liquid chromatography on a base-deactivated stationary phase (1998)
    Springer
    Chromatographia 47 (1998), S. 21-24 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Opium alkaloids ; Papaver somniferum L.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A reversed phase HPLC method for the separation of the five major alkaloids fromPapaver somniferum L., morphine, codeine, thebaine, papaverine and noscapine, has been developed and validated. By use of a basedeactivated silica-based stationary phase excellent peak shape was achieved for each substance. The five alkaloids were quantified by internal standardization within 20 min and with good precision. The method is applicable to opium and to poppy straw.
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    URL: http://dx.doi.org/10.1007/BF02466781
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    On-line extraction and determination of carbofuran in raw milk by direct HPLC injection on an ISRP column (1998)
    Springer
    Chromatographia 47 (1998), S. 81-83 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Carbofuran pesticides ; On-line analysis of milk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method has been developed for extraction and determination of carbofuran in milk. The method involved direct injection of raw milk on to a human serum albumin dimethyloctyl-silica gel (HSA-C8) column and the use of 80:20 (v/v) 0.01 M phosphate buffer pH 5.5-acetonitrile as mobile phase. UV spectrophotometric detection was performed at 220 nm. Identification was based on retention time. Quantification was performed by automatic peak-area determination and was calibrated by use of an external standard.
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    URL: http://dx.doi.org/10.1007/BF02466790
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    High-Performance liquid chromatographic determination of dibromomannitol in plasma (1998)
    Springer
    Chromatographia 48 (1998), S. 17-19 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Dibromomannitol in plasma ; Pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Myelobromol 1,6-dibromo-1,6-dideoxy-D-mannitol (dibromomannitol, DBM) is a bifunctional alkylating agent that has been in clinical use since 1963. It is currently included at high dose in preconditioning regimen for bone marrow transplantation (BMT) and is a main-stay of treatment for polycythaemia vera. A high-performance liquid chromatographic method was developed for the determination of DBM in the plasma. The basis of the assay is a derivatization with sodium-diethyldithiocarbamate at 42°C in the presence of 1-bromo-1-deoxy-3,6-anhydro-galactitol as internal standard (IS). The analysis was carried out on a 250×4mm Hypersil 5 CPS column equipped with a 20×4 mm Hypersil 10 CPS precolumn. The eluent consisted of heptane:isopropyl-alcohol: glacial acetic acid=600:76:80 w/w. The flow rate was 1.2 mL min−1. UV detection was performed at 254 nm. The calibration graph was linear in the concentration range of 2.5–260 μM of DBM in plasma. The limit of detection was 1.0 μM. The precision and accuracy of the method was between the good laboratory practice (GLP) required limits.
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    URL: http://dx.doi.org/10.1007/BF02467509
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    Monitoring of biologically active amines in cereals and cereal based food products by HPLC (1998)
    Springer
    Chromatographia 48 (1998), S. 37-42 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Biologically active amines ; Polyamines ; Cereal and Cereal products
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Biologically active amines (putreanine sulphate, N-acetyl putrescine, putrescine, cadaverine, histamine, agmatine, N-acetyl spermidine, spermidine, spermine) were separated and quantified in cereal flour and cereal products by a liquid chromatographic method. The method consists of the separation of ion pairs formed between biologically active amines and octanesulphonic acid on a reversed-phase column, postcolumn derivatization with o-phtalaldehyde-2-mercapthoethanol and spectrofluorometric detection. Results of the reliability study were satisfactory. The method was linear for each amine at 1–10 mg L−1. Putrescine and spermidine were the only amines always detected in cereal flour and cereal products, ranging from 2.45 to 47.83 mg kg−1 for putrescine and 3.27 to 37.14 mg kg−1 for spermidine. The most important differences among types of samples were found in polyamine derivatives.
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    Comparative study on determination of fumagillin in fish by normal and reversed phase chromatography (1998)
    Springer
    Chromatographia 48 (1998), S. 48-52 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Normal- and reversed-phase LC ; Fumagillin in fish samples
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Fumagillin is an antibiotic agent mostly used in the veterinary profession. A normal-phase liquid chromatographic method was developed for the determination of this drug in fish matrices. A hexane-dichloromethanedioxan-2-PrOH-acetic acid (43:43:9:5:0.1 v/v %) eluent was used on a Perkin Elmer silica gel column. For validation of the process a reversed-phase HPLC method was also developed (eluent: acetonitrile-water-bicyclohyxylamine 70:30:0.05 v/v %, with Spherisorb ODS, as stationary phase). Recovery is about 100% and the limit of detection is 5 ng g−1 for meat samples.
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    URL: http://dx.doi.org/10.1007/BF02467515
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    HPLC separation of hydrogenated derivatives of buckminsterfullerene (1998)
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    Chromatographia 48 (1998), S. 59-64 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Buckminsterfullerene ; Hydrogenation ; Separation technique
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The effect of composition and flow rate of the mobile phase on the HPLC separation of hydrogenated buckminsterfullerene (C60Hn n=2–38) was investigated on BuckySep column. Toluene was used as the basic solvent and hexane, heptane, cyclohexane, THF, acetonitrile, acetone, ethanol and 2-propanol as co-solvents. The fraction of co-solvents was varied 10–80%, and the flow rate 1–0.1 mL min−1. Toluene-acetonitrile 65∶35 and toluene-acetone 50∶50 provided the best separation. Under the best conditions complete separation of C60H2 and almost complete separation of the four most abundant isomers of C60H4 were achieved. Separation of derivatives with higher hydrogen content was very poor.
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    The preparative chromatographic enantioseparation of a racemic morphanthridine analog on a chiral stationary phase (1998)
    Springer
    Chromatographia 47 (1998), S. 440-442 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Preparative scale separations ; Chiral stationary phase ; Enantiomer separation ; Morphanthridine analog
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The preparative chromatographic enantioseparation of a chiral morphoanthridine analog has been performed on an analytical column using amylose-tris(3,5-dimethylphenylcarbamate) as chiral stationary phase. The racemate (100 mg) was resolved to baseline within 15 min. This paper describes the development of the method, estimation of the capacity of the chiral stationary phase and discussed the potential of the chromatography if performed under preparative conditions. From the results and calculations presented it seems likely that the resolution of 70 tons year−1 could easily be achieved on 30 kg of stationary phase with a mobile-phase consumption of only 720 L day−1.
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    URL: http://dx.doi.org/10.1007/BF02466476
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    An improved extraction of marrubiim fromMarrubium vulgare (1998)
    Springer
    Chromatographia 47 (1998), S. 449-450 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chitin stationary phase ; Marrubiin ; Analgesic activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Marrubiin is the main active compound isolated fromM. vulgare, a medicinal plant used in folk medicine to cure several diseases. The present study shows that chitin, an abundant natural polymer, may be successfully in chromatography column to separate marrubiin from complex mixtures. The experimental procedure described here represents an efficient and rapid method to obtain such compound in high yield.
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    Applications of molecularly imprinted materials as selective adsorbents: Emphasis on enzymatic equilibrium shifting and library screening (1998)
    Springer
    Chromatographia 47 (1998), S. 465-469 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Affinity chromatography ; Molecular imprinting ; Molecular recognition ; Combinatorial libraries
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Molecular imprinting is an attractive method for producing highly selective adsorbents, and several new and potentially useful applications based on molecularly imprinted polymers (MIPs) have been described in recent years. In this article, we highlight some of the areas where these materials have found application, and also describe some new fields of application where the selectivities of imprinted materials can be gainfully employed, for example as binding matrices in the screening of combinatorial libraries, and as auxiliary agents in enzymatic syntheses.
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    On-line monitoring of monosaccharides and ethanol during a fermentation by microdialysis sampling, liquid chromatography and two amperometric biosensors (1998)
    Springer
    Chromatographia 47 (1998), S. 501-508 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Fermentation ; Microdialysis sampling ; Monosaccharides and ethanol ; On-line monitoring ; Biosensors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Two amperometric biosensors were used as detection units in liquid chromatography for on-line monitoring of the production of fuel ethanol during a fermentation. Sampling was performed with a microdialysis probe, and the dialysate was introduced into a liquid chromatographic system providing separation of the substrates and the product: three monosaccharides and ethanol. The analytes were detected by two carbon paste electrodes based on pyranose oxidase and alcohol oxidase, respectively, co-immobilised with horseradish peroxidase, operating in parallel at −50 mVvs. Ag/AgCl. The measured linear ranges of the biosensors by direct injection into the LC system were for glucose 0.3–2.5 g L−1, xylose 0.5–6.7 g L−1, galactose 0.5–6.7 g L−1, and ethanol 1.6–11.7 g L−1, respectively. Injection of standard solutions were required to monitor the stability of the biosensors. Due to the strict selectivity of the biosensors, no interference from other compounds in the broth was encountered from other compounds in the broth was encountered in the quantification. The fermentation process was monitored for 16 h. The on-line results were compared with off-line measurements.
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    Determination of cisapride in human plasma by high-performance liquid chromatography (1998)
    Springer
    Chromatographia 47 (1998), S. 537-541 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Cisapride in plasma ; Pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An HPLC method has been developed for the quantification of cisapride in plasma for pharmacokinetic studies. Clebopride was used as internal standard. Plasma samples were extracted at alkaline pH withtert-butyl methyl ether. The organic phase was then extracted with sulphuric acid to eliminate endogenous interferences, and cisapride and the internal standard were then extracted at alkaline pH intotert-butyl methyl ether. After evaporation oftert-butyl methyl ether, the residue was analysed by HPLC. Chromatography was performed at 20°C on a 250mm×4mm i.d. reversed-phase column selective for basic compounds. The isocratic mobile phase was 48∶52 (v/v) acetonitrile-water containing 0.05 M potassium dihydrogen phosphate and 0.04 M triethylamine, adjusted to pH 5.5; the flow rate was 1 mL min−1. Cisapride and the internal standard were detected by ultraviolet monitoring at 276 nm. The calibration graph was linear for quantities of cisapride from 1 to 200 ng mL−1. Intra- and inter-day precision (CV) did not exceed 13.98%. The limit of quantitation (LOQ) was 0.68 ng mL−1 for human plasma. The applicability of the method has been demonstrated in a pharmacokinetic study of normal volunteers who received 10 mg cisapride orally.
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    Enantiomeric separation of four methylenedioxylated amphetamines on β-cyclodextrin chiral stationary phases (1998)
    Springer
    Chromatographia 47 (1998), S. 285-290 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Enantiomeric separation ; β-Cyclodextrins ; Methylenedioxylated amphetamines ; Ecstasy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Native and derivatized β-cyclodextrins such as chiral stationary phases (CSP) were used for the simultaneous enantiomeric separation of four methylenedioxylated amphetamines (MDA, MDMA, MDEA and MBDB) by liquid chromatography. Fluorimetric detection was used in order to enhance sensitivity and selectivity. The mobile phase was, optimised by studying the influence of pH, triethylamine concentration, organic solvent type, column temperature and flow rate of the mobile phase. This method was validated by determining linearity, precision, accuracy, limits of detection and quantification, and was applied to the stereoselective analysis of illicit tablets (23 samples) and of human whole blood samples (spiked samples and two post-mortem cases). Whereas no significant deviation from a racemic ratio was observed in the tablets contents, the analysis of blood samples showed an enantioselective metabolism of MDMA.
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    Aminopropyl-silica as an advantageous alternative to nonpolar sorbents for continuous cleanup/preconcentration of vitamin D3 metabolites (1998)
    Springer
    Chromatographia 47 (1998), S. 367-372 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Aminopropyl-silica sorbent ; Continuous cleanup/preconcentration ; Hydroxyvitamin D3 metabolites ; Flow injection analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new procedure for continuous cleanup and concentration of hydroxyvitamin D3 metabolites prior to their separation by HPLC and UV-detection is reported. The process is based on the use of aminopropyl-silica as solid-phase sorbent as an alternative to the use of nonpolar sorbents. The improvement thus achieved has been tested by comparing the results with those obtained using octadecyl-C18 as non-polar sorbent. The comparison has been based on the calibration graphs (linear range, detection and quantitation limits), precision and multiple standard addition method.
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    URL: http://dx.doi.org/10.1007/BF02466466
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    Simultaneous determination of 3,4-dihydroxymandelic acid, 4-hydroxy-3-methoxymandelic acid, 3,4-dihydroxyphenylglycol, 4-hydroxy-3-methoxyphenylglycol, and their precursors, in human urine by HPLC with electrochemical detection (1998)
    Springer
    Chromatographia 47 (1998), S. 396-400 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Coulometric detection ; Mandelic acids ; Phenylglycols ; Urine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method has been developed for the quantification of urinary 3,4-dihydroxymandelic acid (DOMA), 4-hydroxy-3-methoxymandelic acid (VMA), 3,4-dihydroxyphenylglycol (DHPG), and 4-hydroxy-3-methoxyphenyglycol (MHPG). Separation and determination of these compounds in biological samples was previously thought to be very difficult. In this work the separation has been achieved by reversed-phase high-performance liquid chromatography with step-wise gradient elution with three mobile phases. The conditions for coulometric detection have been optimized for effective determination of these compounds. In analysis of a sample of human urine, after a simple deproteinization proceudre, DOMA, VMA, DHPG, and MHPG were separated from interferences and quantified successfully; the average levels of these compounds in six different samples were 33.87±1.03, 1202±41.3, 31.3±1.92, and 80.6±2.15 μg (24 h)−1, respectively. Their precursors E, MN, DOPA, DA, NE, DOPAC, HVA, 3MT, and NMN, and the indolamine 5HT and its metabolite 5HIAA (a list of abbreviations is given at the end of the paper) can also be determined simultaneously in the same chromatographic run. The overlapping peak of DHPG was resolved by deconvolution.
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    Optimization of solvent selectivity for the chromatographic separation of fat-soluble vitamins using a mixture-design statistical technique (1998)
    Springer
    Chromatographia 47 (1998), S. 401-412 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Optimization ; Mixture design ; Special cubic polynomial model ; Pareto-optimality ; Overlapping resolution mapping (ORM)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A systematic approach, using a mixture-design statistical technique, has been developed for selecting the optimum mobile phase for the separation of fat-soluble vitamins in reversed-phase high-performance liquid chromatography. A quaternary mixture of methanol, acetonitrile, tetrahydrofuran and water was used as mobile phase. Retention time and peak width were recorded in ten runs augmented with five replicates and the data were subsequently fitted to special cubic polynomial models. The resulting mathematical equations enabled prediction of resolution over the entire parameter space. Contour plots of minimum effective resolution and maximum retention time as a function of mobile phase composition are presented and discussed. Visual inspection of these plots provides an overview of the quality of the separation and the analysis time required for each possible mobile-phase composition with n the parameter space. It is demonstrated that the methodology followed was an important tool which enabled the taking of informed decisions necessary for selection of the optimum mobile phase for a chromatographic separation. A combination ofR S minimum andt R maximum as optimization criteria in a multicriteria decision-making plot using pareto-optimality concept is discussed. This combination enabled visual demonstration of the compromise between separation quality and the economics of analysis time. Our methodology has been compared with the common used technique of ‘overlapping resolution mapping’.
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    Predicting the selectivity of imprinted polymers (1998)
    Springer
    Chromatographia 47 (1998), S. 457-464 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Imprinted polymer ; Non-covalent imprinting ; Selectivity and capacity ; Association constant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Imprinted polymers as stationary phases for HPLC separations have been the subject of extensive investigations in recent years. In order to aid the rational design of synthetic protocols for the preparation of imprinted polymers, a series of calculations were made to assess the equilibrium concentration of templatemonomer complexes as a function of association constant (K) for the functional groups involved in the interactions and initial concentrations of reactants. This data was then used to predict the selectivity of polymers prepared under different reaction conditions and the model was tested using an experimentally determined value ofK and separation factors taken from the literature.
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    Chiral discrimination ofN-(dansyl)-dl-amino acids on human serum albumin stationary phase: Effect of a mobile phase modifier (1998)
    Springer
    Chromatographia 48 (1998), S. 431-435 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; N-(dansyl)-dl-amino acids ; Human serum albumin ; Chiral discrimination ; Optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The effect of perchlorate anion as mobile phase modifier on the separation factor, α, forN-(dansyl)-dl-norvaline andN-(dansyl)-dl-tryptophan on a human serum albumin (HSA) column was studied by varying the concentration,c, of the chaotropic agent and the column temperatureT. Gibbs-Helmholtz parameters Δ(ΔH) and Δ(ΔS) between thed andl enantiomers were determined from linear van't Hoff plots of lnα against 1/T. Thermodynamic results indicated that the enhancement of the separation factor observed asc was increased was enthalpically controlled owing to stereoselective H-bonding interactions. Such behavior was used to optimize the chromatographic conditions for separation ofN-(dansyl)-amino acids on HSA.
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    Determination of two metabolites of albendazole, albendazole-sulfoxide and albendazole-sulfone in cow's milk using an HPLC method —A systematic approach to optimise extraction conditions (1998)
    Springer
    Chromatographia 48 (1998), S. 777-784 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Solid phase extraction ; Sample treatment optimisation ; Taguchi method ; Albendazole metabolites ; Milk samples
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Reversed phase HPLC methods for the determination of two metabolites of albendazole in cow's milk are described. Albendazole is an anthelmintic agent used both in veterinary and human practice. Its main metabolites are albendazole-sulfoxide and albendazole-sulfone. The separation of the two metabolites was performed on a μ-Bondapak C-18 column using an acetonitrile/methanol/phosphate buffer as mobile phase, with detection at 290 nm. For the sample preparation of the milk samples we used solid phase extraction. A new sample treatment optimisation procedure is also presented for the sample preparation method. Since sample preparation is a critical step in the analysis of residues in biological samples, the second part of our publication describes an optimisation using Taguchi's methodology that increased recovery, accuracy and reliability. After optimisation of the sample preparation, the limit of detection was 10 ng mL−1 milk and the recovery was 70–80% in the concentration range of 30–1000 ng mL−1 milk for both metabolities.
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    Development and validation of stability indicating high-performance liquid chromatographic assays for ketotifen in aqueous and silicon oil formulations (1998)
    Springer
    Chromatographia 48 (1998), S. 797-802 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ketotifen analysis ; Stability indicating analysis ; Aqueous and oil-based formulations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple and specific high-performance liquid chromatographic (HPLC) method for the analysis of ketotifen in aqueous solutions and silicon oil suspensions is described. The HPLC system is based on a reversed phase μBondapak C18 (30×0.39 cm) column with a mobile phase of phosphate buffer (0.001 M, pH 7.4):methanol: acetonitrile: trimethylamine (29.8:45:25:0.2, by volume) at a flow-rate of 1 mL min−1. The eluent was monitored by UV absorption at 299 nm. Silicon oil-based samples were extracted with HCl (0.05 M) using imipramine as internal standard. The recovery of ketotifen and imipramine was greater than 80%. The calibration curves for both assays were linear over the ranges examined, yielding correlation coefficients greater than 0.997. The assay was shown to be stability indicating by subjecting solutions of ketotifen in phosphate buffer to heat, oxidative stress and irradiation with ultraviolet light (254 and 369 nm)for up to 8 h. The methodology was also shown to be applicable for the analysis of ketotifen in simple aqueous based formulations, in suspension in silicon oil and for the analysis of samples derived fromin vitro skin transfer experiments.
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    An improved method for assay of vitamin C in fish feed and tissues (1998)
    Springer
    Chromatographia 48 (1998), S. 43-47 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Vitamin C analysis ; Ascorbate-2-phosphate and sulphate esters ; Enzyme shifting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method was devised to assay four forms of vitamin C: L-ascorbic acid (AA), dehydroascorbic acid (DHA), ascorbate-2-mono- and polyphosphate (AMP, APP), as well as ascorbate-2-monosulphate (AMS), in sample series of different fish tissues and feed. Direct and indirect detection were combined. Sample extractions were carried out with 0.2 mol L−1 sodium acetate buffer (pH 4.8) and extracts were deproteinized after different chemical or enzymatic reactions, with perchloric acid. The DHA was reduced to AA with dithioerythritol (DTE). Ascorbate oxidase enzyme was used for the detection of background and an acidic phosphatase enzyme for the hydrolysis of different phosphate esters. Ascorbate-2-sulphate was detected directly with help of coinjection of the compound. Chromatographic analysis was carried out with a single column isocratic reverse phase method. The mobile phase was an aqueous buffer of 0.04 M sodium-acetate, 0.05 mM EDTA, 0.5 mM tetrabutylammonium dihydrogen phosphate (TBA) adjusted to pH 3.76 with 85% H3PO4 and with 24 mL methanol added to 1000 mL. C-18 columns were used with 0.6 mL min−1 flow rate at 23°C. The vitamin C forms were detected by UV absorption at 250 nm. The determination limit was 1.0–5.0 μg g−1 in AA equivalent. The standard deviations were between 1–6% and depended on the concentrations of vitamin C forms and tissues. Recoveries were between 90–96% in samples.
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    Liquid chromatography of polymer mixtures by a combination of exclusion and full adsorption mechanisms. Three- and four-component polymer blends (1998)
    Springer
    Chromatographia 48 (1998), S. 65-70 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Multicomponent mixtures ; Separation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Coupling of full adsorption-desorption and size-exclusion chromatography (FAD-SEC) has been applied to the separation and molecular characterization of three- and four-component polymer blends. The method is based on the full adsorption of alln orn−1 components of the polymer blend in a specially designed FAD minicolumn. By appropriate eluent switching the adsorbed polymers are desorbed stepwise from the FAD minicolumn into an on-line SEC column for molecular characterization. It is shown that the desorption isotherms of particular blend components give valuable information about the appropriate displacer composition. The exact position of the desorption isotherms depends, however, both on the amount of polymer adsorbed and in the presence of other, chemically different, polymers within FAD column. The nature and composition of the displacer must, therfore, be adjusted if the intervals between the desorption of particular blend components are to be large enough to prevent displacement overlap.
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    The RP-HPLC analysis of anthocyanins (1998)
    Springer
    Chromatographia 48 (1998), S. 360-364 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Acylated anthocyanins ; Rudbeckia hirta L. ; In vitro cultures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Conditions were determined for the separation of a complex set of anthocyanins (free aglycones, mono- and multiglycosides and esterified forms) by HPLC. The optimised gradient elution method was then used to carry out qualitative and quantitative analysis of anthocyanin compounds present in the callus tissue ofRudbeckia hirta L. and the tubular flowers of the soil-based plant. The summary content of anthocyanin pigments and the content of the main pigment was identified in the analysed biomass. The method developed is useful for the purposes of monitoring the process of biosynthesis of anthocyanins in tissues obtained through in vitro cultures. The advantages of the method for anthocyanins and its application to other anthocyanin-rich materials are also discussed.
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    Effects of amine additives on the resolution of antipsychotic and antidepressant drugs on a cyanoalkyl HPLC column (1998)
    Springer
    Chromatographia 48 (1998), S. 770-776 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Basic drug compounds ; Amino additives ; Cyanoalkyl columns
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The separation of basic antidepressant and antipsychotic drugs on a cyanoalkyl-bonded silica column has been studied to determine the effects on peak retention, symmetry, efficiency, and resolution of six different amine mobile-phase additives. The amines—ammonia,n-butylamine, triethylamine,N,N-diisopropylethylamine,N,N-dimethylbutylamine andN,N-dimethyloctylamine—were, except forN,N-diisopropylethylamine, chosen because of their widespread use for improvement of peak symmetry in chromatographic methods;N,N-diisopropylethylamine was included as an example of a sterically hindered amine to see if the stereochemistry around the nitrogen atom is an important consideration in the selection of an additive. This study shows that a gain in symmetry and efficiency is accompanied by loss of resolution. The results obtained also indicate that one type of amine additive should be used when symmetry and efficiency are most important and another when resolution is paramount.
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    Extraction and liquid-chromatographic determination of amphotericin B in oil-water lecithin-based microemulsions (1998)
    Springer
    Chromatographia 48 (1998), S. 803-806 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Amphotericin B ; Oil-water lecithin-based microemulsions ; Extraction of drug from microemulsion ; Reversed-phase HPLC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method employing extraction then reproducible reversed-phase high-performance liquid chromatography (RPHPLC) with monitoring of the drug by absorbance at 405 nm has been developed and validated for the determination of amphotericin B in oil-water lecithin-based microemulsions. The precision and accuracy of the method are excellent (SD 2.4% and 4.2%, respectively). The established linearity range was 10–60 μg mL−1 (r 2=0.9967). The recovery of amphotericin B from spiked placebo was 〉90% over the linear range. The extraction procedure was simple and the HPLC conditions were able to separate the drug from its degradation products and excipients. The method has been used successfully for determining the amphotericin B content of microemulsions and for evaluating the chemical stability of amphotericin B-loaded microemulsions.
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    Studies on shape selectivity of RP C18-columns (1998)
    Springer
    Chromatographia 48 (1998), S. 183-189 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Polymeric phases ; Shape selectivity ; PAH selectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Stationary phases with octadecyl groups have been prepared with different carbon content without and in the presence of water and characterized for their selectivity for the shape of various polyaromatic hydrocarbons. It is shown that both a high hydrocarbon content and a good accessibility of the bonded groups within the pores is required to achieve shape recognition for PAH. High carbon content alone is not sufficient. The two tests for shape selectivity proposed by Sander and Wise as well as by Tanaka are compared. In most cases the results are similar: A low selectivity with the Sander and Wise test (α TBN/BaP〈1) corresponds to a high value with the Tanaka test (α TRI/o-TER〉3). However, not in all cases the tests give corresponding answers. Further studies on molecular recognition are required.
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    Chiral recognition by molecularly imprinted polymers in aqueous media (1998)
    Springer
    Chromatographia 48 (1998), S. 197-202 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Molecular imprinting ; Molecular recognition ; Chiral recognition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Molecularly imprinted polymers were prepared using 2-vinylpyridine and/or methacrylic acid as functional monomers in a self-assembly imprinting protocol. The resulting polymers were analyzed in aqueous media, and the effects from the pH of the mobile phase and the degree of added organic solvent were investigated. The results are indicative of the importance of ionic bonds in conjunction with hydrophobic interactions in the formation of the complexes between the analyte and the polymers.
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    Dye-coated stationary-phases: A retention model for anions in ion-interaction chromatography (1998)
    Springer
    Chromatographia 48 (1998), S. 190-196 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-interaction chromatography ; Dye-coated reversed phase ; Retention model ; Experimental design
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The separation of inorganic anions (NO3 −, NO2 −, Cl−, Br−, I−, SO4 2−, S2O3 2−) by ion-interaction chromatography mediated with a specific dye has been investigated. Chromatography was performed on a LiChrospher RP-18 colum dynamically coated with crystal violet, using acetonitrile-water buffered with phthalate as the mobile phase. The presence of the dye in the eluent enabled indirect spectrophotometric detection of the analytes, which have no significant UV absorption. Retention data were collected for the different anions by varying the composition of the mobile phase according to a full factorial experimental design. A theoretical model for the retention of singly- and doubly-charged analytes, on the basis of the two main processes of ion-exchange and ion-pair formation, has been proposed and validated with the experimental data.
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    Wheat β-amylase behaviour regarding salt promoted adsorption processes (1998)
    Springer
    Chromatographia 48 (1998), S. 209-214 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Covalent chromatography ; Thiophilic and hydrophobic ligands ; Wheat β-amylase ; Salt promoted adsorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The behaviour of wheat β-amylase from crude extracts in chromatography on agarose gels substituted with different ligand types was investigated. The enzyme displayed high salt promoted adsorption onto thiophilic gels provided with sulfone-thioether and 2-thiopyridine ligands. Quantitative recovery of the enzyme was easily accomplished by elution with buffer in the absence of Na2SO4. The 3-(2-pyridylthio)-2-hydroxypropylagarose (PyS-gel) also allowed elimination of pigments present in the wheat extract. These pigments showed no adsorption onto the gel, thus regeneration is easily achieved, allowing its re-use. The enzyme also displayed strong salt-dependent adsorption onto adsorbents provided with pyridyldisulfide moieties, but in this case enzyme binding was due to its thiol content since elution was achieved mainly through reduction with DTT. When the enzyme was chromatographed on a series of hydrophobic alkyl ligands in the presence of 0.5 M sodium sulphate, it was partially adsorbed on pentylagarose and quantitatively adsorbed on hexyl-agarose, elution being easily performed by sodium sulphate-free buffer. This behaviour was markedly different from that towards phenyl-Sepharose, to which the enzyme was strongly adsorbed and which required much more drastic elution conditions.
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    Retention and column efficiency in reversed phase liquid chromatography as a function of pH for optimization purposes (1998)
    Springer
    Chromatographia 48 (1998), S. 237-244 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chromatographic behavior ; pH optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The effects of pH on both the solute retention and the peak shape of ionogenic compounds are studied in order to propose accurate models for pH optimization purposes. Several mathematical models (theoretical and empirical) for describing the variation of the retention factor versus pH are compared within different pH ranges. Limits of such models used for optimizing the pH by requiring only 3 preliminary experimental runs, are discussed in terms of deviations (≤±5%) of predicted retention times from experimental retention times. An original procedure is developed for selecting the most convenient retention model, from a given set of three retention data. This set is also applied to modeling the variation of both peak width and peak asymmetry with mobile phase pH conditions. Such a procedure is demonstrated as helpful for the separation of ionogenic solutes by considering mobile phase pH as an additional variable that can be useful during optimization procedures.
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    The driving force for solute retention in electron donor-acceptor chromatography: Electrostatic versus charge-transfer interactions (1998)
    Springer
    Chromatographia 48 (1998), S. 523-528 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Retention mechanism ; Donor-acceptor complex ; Molecular interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Charge-transfer interactions are often assumed to be dominant among the noncovalent interactions that govern the solute retention in electron donor-acceptor chromatography. This popular view, however, has been called into question by recent studies that suggest an important role for electrostatic interactions in the formation of donor-acceptor complexes. We reported here an experimental investigation concerning the question as to whether charge-transfer or electrostatic interactions are the driving force for solute retention in donor-acceptor chromatography. Using three chromatographic systems composed of a dinitrobenzene derived stationary phase and a hexane based mobile phase, we determined retention factors for a range of aliphatic and aromatic hydrocarbons and correlated them with molecular properties that describe the solute's dispersion, charge-transfer, and electrostatic characteristics. It was found that the molecular polarizability and ionization potential give either very poor or no correlation with solute retention whereas the molecular quadrupole moment is a linear function of the logarithmic retention factor. These results were interpreted as showing that electrostatic, rather than charge-transfer or dispersion, interactions play a major role in determining solute retention. The dominance of the electrostatic interactions over the other noncovalent interactions was discussed in terms of distance dependency of the interaction energy.
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    Characterization of peak purity by fast multiscan circular dichroism detection (1998)
    Springer
    Chromatographia 48 (1998), S. 584-588 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Circular dichroism detection ; Multiscan detection ; Peak purity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method has been developed to detect inhomogeneity of apparently homogeneous peaks of very similar analytes. The method utilizes the rapid scan feature of state-of-the-art spectrometers/detectors that allow the recording of up to 30 spectra in a single chromatographic peak. Sensitivity and selectivity are enhanced by chiroptical/optical detection. Thus, identification of “front” and “rear” components of the peak can be carried out. The method is exemplified by mixtures of codeine, hydrocodone and oxycodone as analytes.
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    HPLC determination of berberine in plasma of patients with ischemic heart failure (1998)
    Springer
    Chromatographia 48 (1998), S. 589-590 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Berberine in plasma ; Ischemic heart failure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Berberine absorption by patients with ischemic heart failure (IHF) after oral administration and the relationship between clinical effect and plasma berberine concentration are studied. Plasma samples were pretreated by chloroform extraction. Berberine was determined on a μBondapak column with acetonitrile-phosphoric acid mobile phase and UV detection. The limit for berberine in plasma was 8 ng mL−1 for an injection volume of 50 μL. Average berberine recovery was 96.5%. Results showed that improvements in symptoms were more significant for patients with plasma berberine concentration〉0.1 mg L−1 than for those with〈0.1 mg L−1. Plasma berberine monitoring may be helpful in the treatment of patients with IHF.
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    Hexadecyltrimethylammonium bromide/ethanol/water systems as mobie phase in reverse phase high performance liquid chromatography. Study of metal-diethyldithiocarbamate complexes retention (1998)
    Springer
    Chromatographia 48 (1998), S. 517-522 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Micellar liquid chromatography ; Diethyldithiocarbamates ; Metal complexes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary This paper presents the, chromatographic retention of Co(II), Ni(II) and Cu(II) as diethyldithiocarbamate complexes in the presence of hexadecyltrimethylammonium bromide/ethanol/water systems, as mobile phase, by reversed phase high performance liquid chromatography. The presence of an organic modifier reduces the retention times and improves the efficiency. In order to evaluate the interaction between the metal complexes and the mixed micellar system the values of solute binding constants are calculated in, two ways: a) Arunyanart and Cline-Love's treatment and b) multiple regression analysis taking account of the ethanol percentages.
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    An improved high-performance liquid chromatography method for the determination of homocysteine in human plasma (1998)
    Springer
    Chromatographia 48 (1998), S. 506-510 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Homocysteine ; Human plasma ; Routine analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Elevated plasma homocysteine is, a known risk factor in arteriosclerotic vascular disease. To measure homocysteine in a large number of samples, we have developed a rapid, simple, robust and inexpensive reversed-phase HPLC method for routine analysis. Mercaptopro-pionylglycine was used as the internal standard and an external calibration in plasma was performed. Improvement was achieved by the use of gradient elution (using a sodium acetate buffer and methanol) resulting in a higher number of samples analyzed per day. Plasma samples were reduced with tributylphosphine and the proteins were precipitated with perchloric acid before addition of internal standard. The analytes were derivatized by use of 7-fluorobenzofurazone-4-sulfonic acid ammonium salt. For calibration human plasma was spiked with nine different concentrations of homocysteine (range 2–50 μmol L−1). The inter-assay precision of replicate (n=29) analysis of the concentration of homocysteine in a sample of pooled plasma was 3.0%. The limit of detection, defined as three times the signal-to-noise ratio, was 0.25 μmol L−1. The linearity of the assay was confirmed for a plasma concentration range of 2–2000 μmol L−1. The variation of duplicate analyses of 842 plasma samples was 2.6±1.7%.
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    URL: http://dx.doi.org/10.1007/BF02466641
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    High-performance liquid chromatographic assay for simultaneous determination of tramadol and its active metabolite in human plasma. Application to pharmacokinetic studies (1998)
    Springer
    Chromatographia 48 (1998), S. 555-560 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Tramadol andO-demethyl tramadol in plasma ; Pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A sensitive liquid chromatographic assay for the quantitative determination of the opioid analgesic tramadol and its active metabolite is described. Fluconazole was used as internal standard. The assay involved a singletert-butyl methyl ether extraction and LC analysis with fluorescence detection. Chromatography was at 30°C pumping an isocratic mobile phase of acetonitrile-water (19∶81, v/v) containing 0.06M NaH2PO4 and 0.05M triethylamine, adjusted to pH 7.90, at 1 mL min−1 through a reversed-phase, 250×4 mm base-stable column. The limit of quantitation of tramadol and its active metabolite was 1 ng mL−1, only 0.5 mL plasma sample was required for the determination. The calibration curve was linear from 1–1000 ng mL−1. Intra and inter-day precision (C.V.) did not exceed 10%. Mean recoveries of 96.38% for tramadol and 96.62% forO-demethyltramadol with CVs of 0.43% and 1.46% were obtained. Applicability of the method was demonstrated by a pharmacokinetic study on normal volunteers who received 100 mg tramadol intravenously.
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    URL: http://dx.doi.org/10.1007/BF02466649
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    A methodological and metabolite identification study of the metabolism of S-carboxymethyl-L-cysteine in man (1998)
    Springer
    Chromatographia 48 (1998), S. 561-568 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Planar chromatography ; S-Carboxymethyl-L-cysteine ; Metabolic studies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The analysis of 08:00–16:00 (0–8) hour urine collections following oral S-carboxymethyl-L-cysteine administration of 750 mg to 30 individuals identified S-carboxymethyl-L-cysteine, S-carboxymethyl-L-cysteine S-oxide, S-methyl-L-cysteine and S-methyl-L-cysteine S-oxide as the major urinary drug related compounds. No S-(carboxymethylthio)-L-cysteine mixed disulphide metabolite was found in the 08:00–16:00 hour urine collection but the metabolite was detected in the 16:00–00:00 (8–16) hour urune collection by paper chromatography, TLC and HPLC. The production of the S-oxide metabolites 08:00–16:00 hour urine collection) and the mixed disulphide metabolite (16:00–00:00 hour urine collection) were both shown to be biomodally distributed. A significant linear correlation of the S-oxides recovered following 08:00–16:00 hour urine collection as analysed by paper chromatography, TLC and HPLC is reported.
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    URL: http://dx.doi.org/10.1007/BF02466650
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  • 88
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    Normal phase gradient polymer elution chromatography of polyester resins (1998)
    Springer
    Chromatographia 48 (1998), S. 623-630 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Normal phase gradient elution ; Polyester resins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Polymers can be characterized by gradient elution techniques in order to obtain information on their chemical composition and molar mass. In this paper, features and applications of Normal Phase Gradient Polymer Elution Chromatography (NP-GPEC) for the characterization of (co)polyesters are investigated. Two polyesters were characterized, using various stationary and mobile phases. Separation was shown to be dominated by end groups in most cases, and to a lesser extent by molar mass. A distinct influence of both column type and mobile phase type was observed. A polymer based polyamine (PA) column povided the best results, although no complete separation between the mono- and di-acid fractions could be obtained. In all cases, separation was governed by sorption rather than by precipitation/redissolution. NP-GPEC was shown to be a potentially interesting technique for the characterization of copolyesters according to the chemical composition of the backbone, independent of end groups.
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    URL: http://dx.doi.org/10.1007/BF02467591
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  • 89
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    High performance liquid chromatographic analysis of theIn vitro N-dealkylated andN-oxide metabolites ofN-ethyl-N-methylaniline: Methodology for the determination of enzyme activity and stereoselectivity ofN-oxidation (1998)
    Springer
    Chromatographia 48 (1998), S. 664-670 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Enantiospecific analysis ; N-Ethyl-N-methylaniline ; N-Oxidation ; N-Dealkylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A robust, sensitive reverse-phase high-performance liquid chromatographic (HPLC) method for the quantification of the majorin vitro oxidative microsomal metabolites of the prochiral tertiary amineN-ethyl-N-methyllaniline (EMA) is described. The analytes were resolved on a Spherisorb 5 ODS1 HPLC column using an acetonitrile/phosphate buffer system under isocratic conditions. Use of solid-phase extraction (SPE) and ultraviolet (UV) detection at low wavelength (210 nm) enabled the detection of EMAN-oxide simultaneously with the majorN-dealkylated metabolites,N-ethyl andN-methylaniline. Previous chromatographic methods described for the quantification ofN,N-dialkylarylamineN-oxides have generally required sample pretreatment to reduce theN-oxide to its parent tertiary amine prior to analysis. The above method, in combination with a previously reported chromatographic resolution based on the Chiralcel OD chiral stationary phase (CSP), allows accurate and precise determination of both the quantity and stereochemical composition of metabolically derived EMAN-oxide.
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    URL: http://dx.doi.org/10.1007/BF02467596
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  • 90
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    High performance liquid chromatographic separation of chlorophyllc forms from marine phytoplankton on octylsilica bonded phases (1998)
    Springer
    Chromatographia 48 (1998), S. 677-680 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chlorophyllc ; Marine phytoplankton ; Octylsilica phases ; Photosynthetic pigments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The separation of mono- and divinyl chlorophyllc forms was estudied employing several octylsilica and octadecylsilica columns under isocratic conditions. In this paper we show that, using the adequate mobile phases, the monomeric C8 columns can separate the mentioned chlorophylls. A comparison between C8 and C18 columns reveals that monomeric OS phases provide always higher resolution of the MV- and DV chlorophyllc pairs. Such a result could be explained in terms of differences in column polarity. When adequate gradient profiles and injection conditions are used the separation is accomplished together with that of other chlorophylls and carotenoids.
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    URL: http://dx.doi.org/10.1007/BF02467598
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  • 91
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    Enantiomeric separation of trimetoquinol, denopamine and timepidium by capillary electrophoresis and HPLC and the application of capillary electrophoresis to the optical purity testing of the drugs (1995)
    Springer
    Chromatographia 40 (1995), S. 638-644 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Capillary electrophoresis ; Enantiomer separation ; Trimetoquinol ; Denopamine ; Timepidium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Two methods for the direct separation of the enantiomers of trimetoquinol hydrochloride, denopamine and timepidium bromide were investigated, namely capillary zone electrophoresis (CZE) using cyclodextrins (CDs) (CD-CZE) and high-performance liquid chromatography (HPLC) using chiral stationary phases (CSPs). By CZE, separation of the enantiomers of trimetoquinol was successfully achieved when using β-cyclodextrin (β-CD), heptakis(2,6-di-0-methyl)-β-cyclodextrin (DM-β-CD) and β-CD polymer, but direct HPLC separation of the enantiomers was not successful. The enantiomers of denopamine were successfully separated by both CZE, employing DM-β-CD under acidic conditions, and HPLC, with cyclodextrin immobilized CSPs (CD-CSPs). Timepidium bromide, which is a racemic drug, was successfully enantioseparated by both CD-CZE and HPLC with CD-CSPs. The CD-CZE mode was selected as the optical purity testing method for trimetoquinol and denopamine because of the superiority of capillary electrophoretic (CE) techniques. Method validation results obtained clearly show that the CE method would be useful as an quality control method for assessing the optical purity of the drugs.
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    URL: http://dx.doi.org/10.1007/BF02315130
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    Effects of kinematic viscosity of the slurry on the packing efficiency of PEEK microbore columns for liquid chromatography (1995)
    Springer
    Chromatographia 40 (1995), S. 662-668 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Microbore columns ; Column packing ; Slurry viscosity ; Surfactants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The kinematic viscosity of the slurry used for the packing of microbore columns for liquid chromatography has been correlated with the packing efficiency. The columns were packed into polyetheretherketone (PEEK) tubing with an internal diameter of 0.5 mm using unbonded and bonded spherical silica gels under constant pressure conditions. Higher efficiencies were obtained using slurries suspended in aqueous solutions of surfactants, such as polyoxyethylene sorbitane monolaurte (Tween-20) and sodium dodecyl sulphate, in comparison with organic solvents usually used for column packing. The concentration dependencies of the relative kinematic viscosities of six slurries were compared using capillary viscometry. The slurries with low relative viscosities possessed rheological properties which enabled high packing densities, typical of a stable dense random packing arrangement, to be obtained at moderate packing pressures. The unusually low relative viscosities are discussed in terms of a “porous hydrodynamic bearing” model. The techniques used should also be generally applicable to the slurry packing of conventional columns.
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    URL: http://dx.doi.org/10.1007/BF02315134
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    Effect of pH on the retention behaviour of some preservatives-antioxidants in reversed-phase high-performance liquid chromatography (1995)
    Springer
    Chromatographia 40 (1995), S. 652-656 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Preservatives-antioxidants ; Eluent pH ; Retention and separation factors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary In this paper the dependence of eluent pH on the efficiency of separation in RP-HPLC is described. Preservatives-antioxidants, esters ofp-hydroxybenzoic acid (methyl, ethyl, propyl and butyl parabens), sorbic acid, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate (PG) and L-ascorbic acid (Vitamine C) were investigated by reversed-phase high-performance liquid chromatography, utilising isocratic elution with UV detection. The mobile phase composition (methanol-water v/v containing 1% acetic acid), was varied in order to obtain the best separation. For all substances analysed the pH, pKa and the fitted pKa values were calculated in different mixtures of mobile phases using the graphical method of Charlot and Trémillon [1]. The retention factors (k) and the separation factors (α) were also calculated.
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    URL: http://dx.doi.org/10.1007/BF02315132
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    Evaluation of the loadability of an immobilised protein chiral stationary phase (1995)
    Springer
    Chromatographia 40 (1995), S. 680-683 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chiral stationary phase ; Preparative chromatography ; Benzodiazepines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary High performance liquid chromatography chiral stationary phases based on immobilized proteins are well known and commonly used. This work reports on an evaluation of a Human Serum Albumin stationary phase in the preparative separation of benzodiazepines.
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    URL: http://dx.doi.org/10.1007/BF02315137
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    An HPLC screening method for the detection of isonicotinic acid hydrazide in cattle milk (1995)
    Springer
    Chromatographia 40 (1995), S. 170-174 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Isoniazid in milk ; SPE preconcentration ; Diode array UV spectra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple, fast, accurate and highly sensitive (5 ng/ml) method for the detection of sionicotinic acid hydrazide (isoniazid) in cattle milk is described, based upon an RP-HPLC system, equipped with a C18 column and a UV detector. Milk was deproteinized with trichloroacetic acid and treated with cinnamaldehyde, before being injected into the HPLC system. Preconcentration of samples on an SPE phenyl cartridge allows the sensitivity of the method to be increased to 0.05 ng/ml using a UV detector. The presence of isoniazid can be confirmed at concentrations as low as 0.4 ng/ml, through a diode-array UV spectrum of isoniazid hydrazone. The analytical procedure here described is routinely applied to investigate the illegal administration of isoniazid to cattle, as it provides a means of screening that can be carried out in a very short time.
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    URL: http://dx.doi.org/10.1007/BF02272167
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    Description of the retention behaviour of solutes in micellar liquid chromatography with organic modifiers: Comparison of two methods (1995)
    Springer
    Chromatographia 40 (1995), S. 279-286 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Micellar liquid phases ; Hybrid mobile phases ; Retention behaviour
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Two methods for the description of the retention behaviour of solutes in micellar liquid chromatography are compared. One of them divides the parameter space into triangular subspaces, fitting a different equation in each subspace. The second method makes use of a unique equation, valid in the whole parameter space. In both cases, equations of the type log k=f (μ, ϕ), and 1/k=f (μ, ϕ), (μ and ϕ are the concentration of surfactant and alcohol, respectively), were used to describe the retention. The use of the hyperbolic function, 1/k=c0+c1μ+c3μϕ, to describe the whole parameter space yielded the best prediction. When a small portion of the parameter space was modelled, a simpler hyperbolic function, lacking the μϕ term often led to good results. The logarithmic equations usually gave the poorer predictions.
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    URL: http://dx.doi.org/10.1007/BF02290358
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    Use of high speed liquid chromatography (HSLC) in the pharmaceutical industry. Practical aspects and limitations (1995)
    Springer
    Chromatographia 40 (1995), S. 394-398 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; High speed LC ; Pharmaceutical drugs ; Routine analysis ; Fast HPLC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary High performance liquid chromatography (HPLC) is widely used in drug development and quality control. The main objective is to obtain dependable results in the shortest time in order to reduce the time taken to develop drugs and to ensure better quality of the final compound. High speed liquid chromatography (HSLC) helps us to reach this objective. In this paper pratical aspects of HSLC are discussed mainly in terms of instrument requirements and the practical needs of users. Comparison between HPLC and HSLC separations of pharmaceutical preparations are given and discussed. The contribution of HSLC to decrease solvent consumption and consequently analysis cost and its role in reducing environmental pollution, are also mentioned.
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    URL: http://dx.doi.org/10.1007/BF02269901
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    Indirect photometric detection of inorganic anions by microcolumn liquid chromatography using anthraquinone-disulfonate as visualization agent (1995)
    Springer
    Chromatographia 40 (1995), S. 379-381 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Indirect photometric detection ; Anthraquinone-disulfonate ion ; Inorganic anions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Disodium salts of several anthraquinone-disulfonic acids, which possess large molar absorptivity, were employed as the visualization agent for microcolumn ion chromatography with indirect photometric detection. Detection limits of inorganic anions were improved, e.g., concentration detection limits of chloride, nitrate and sulfate were 0.91–1.6 μmol L−1 at S/N=3, corresponding to mass detection limits of 18–32 fmol. The present system was applied to the determination of inorganic anions in tap water.
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    URL: http://dx.doi.org/10.1007/BF02269898
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    Determination of biogenic amines in wine after clean-up by solid-phase extraction (1995)
    Springer
    Chromatographia 40 (1995), S. 404-410 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Solid-phase extraction ; Wine ; Biogenic amines ; Phthalaldehyde
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A suitable method for the determination of 16 biogenic amines in wine has been developed. The method involves clean-up of wine samples using ion-exchange cartridges and a preconcentration step, under controlled vacuum, before derivatization of the amines by treatment with phthalaldehyde (PA) and reversedphase HPLC with gradient elution and fluorimetric detection. Linearity of response was obtained for all the biogenic amines from 100 μg L−1 to mg L−1. Limits of detection for the amines were similar for all PA-derivatives (25–50 μg L−1) and the quantitation limits were about 0.1 mg L−1. After clean-up and preconcentration, the concentration levels increased 10-fold for all amines except putrescine and cadaverine, which gave poor recovery by this method unlike the rest which gave recoveries of almost 90%. The overall process was successfully applied to identify and quantify biogenic amines in several red wines from the Tarragona region.
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    URL: http://dx.doi.org/10.1007/BF02269903
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  • 100
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    Elution behaviour of anions and cations on a mixed-bed stationary phase of anion and cation exchange resins (1995)
    Springer
    Chromatographia 40 (1995), S. 539-544 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Mixed-bed stationary phase ; Anion and cation exchange resins ; Retention mechanism of anions and cations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The retention mechanism of anions and cations on a mixed-bed column packed with a mixture of strong anion and cation exchange resins has been studied. Organic acids and inorganic anions have showed the same elution behaviour on the mixed-bed column as on a single anion exchange column. In contrast, different elution behaviours for cations have been observed between the mixed-bed column and a single cation exchange column. On the mixed-bed column, cations would be eluted by a mixed retention mechanism. The primary retention mechanism is ion exchange with eluent cation (H+) for all cations. The ion exchange mechanism on the sites occupied by anion exchange groups makes a greater contribution for monovalent cations. A partition mechanism between the stationary phase and mobile phase contributes to the separation of Mg2+ and Ca2+ by forming neutral compounds.
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    URL: http://dx.doi.org/10.1007/BF02290265
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