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  • Gas chromatography  (336)
  • General Chemistry
  • Humans
  • Inorganic Chemistry
  • Springer  (344)
  • 2015-2019
  • 1990-1994  (170)
  • 1985-1989  (174)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 38 (1994), S. 22-28 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Chiral separation ; Capillary column ; 2,6-Di-O-pentyl-3-O-propionyl-γ-cyclodextrin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary 2,6-Di-O-pentyl-3-O-propionyl-γ-cyclodextrin has been synthesized and used for enantiomer separation in capillary gas chromatography. Experimental results showed that the stationary phase has good enantiomer selectivity toward amino acids, amines, alcohols, diols, epoxides, and lactones,etc. 2,6-Di-O-pentyl-3-O-propionyl-γ-cyclodextrin has good thermal stability: the highest recommended temperature isca 170°C.
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  • 2
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Pentachlorophenol residues ; Off-flavours ; Wines and corks ; Electrolytic conductivity detector/mass spectrometry ; detectors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A gas chromatographic methodology with selective detection is presented for the analysis in wines and corks of pentachlorophenol residues, which are suspected to be the most likely precursors of some off-flavours described in several wine samples. After derivatisation, pentachlorophenol acetate residues were monitored by electrolytic conductivity detection and/or mass spectrometric detection in the selective ion mode at m/z 264 and 266. Recoveries varied from 80 to 96% for wine samples fortified with 5 to 100 μg l−1 and from 83 to 91% for corks (fortified at 25 to 100 μg kg−1). The proposed methodology allowed for a determination limit of μg l−1 for wine and 10 μg kg−1 for corks.
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  • 3
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    Chromatographia 38 (1994), S. 475-478 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Phenolic acids ; Olive and elm tree tissues ; Soil phenolics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method for the separation of phenolic acids along with shikimic and quinic acids by means of capillary gas chromatography is described and discussed. The method involves the previous derivatization of the acids to trimethylsilyl derivatives and it has been applied to the separation of acids extracted from olive leaves and roots, elm leaves and a soil A horizon. Quite good results were achieved both from qualitative and quantitative points of view. Qualitative differences have been pointed out in the phenolic acid composition of two olive cultivars and between leaves and roots of the same cultivar; also two elm species can be discriminated on the basis of the phenolic acid content.
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  • 4
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Porous polymer stationary phase ; Selectivity studies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The behaviour of GC columns packed with the copolymer of methacrylic ester of p,p'-dihydroxydiphenylpropane diglicydyl ether and divinylbenzene was studied. Selectivity studies were made for three polymer samples of different molar ratio of monomers. To determine the selectivities of these copolymers retention indices for seven test compounds in comparison to those obtained on Porapak Q are calculated. Additionally, the efficiency of porous polymer purification was studied by a SFE-GC-MS technique.
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  • 5
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    Chromatographia 38 (1994), S. 595-598 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Chiral / enantiomeric separation ; Amphetamine ; Methamphetamine ; Cyclodextrin-derivatized phases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Enantiomeric separation of amphetamine and methamphetamine as achiral derivatives on 2,6-di-O-pentyl-3-O-trifluoroacetyl-β-cyclodextrin, 2,6-di-O-pentyl-3-O-trifluoroacetyl-γ-cyclodextrin and 2,6-di-O-pentyl-3-O-propionyl-γ-cyclodextrin stationary phase in capillary gas chromatography is described. Trifluoroacetic anhydride and acetic anhydride were used as derivatizing reagents. Excellent precision was obtained for concentrations down to 0.1% / e.e. On 2,6-di-O-pentyl-3-O-propionyl-γ-cyclodextrin the elution order of R,S-amphetamine was reversed when the derivatizing reagent was changed but could not be reversed on any of the other phase types.
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  • 6
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Nitrogen phosphorus detection ; Atrazine and simazine ; Freeze-dried water analysis ; ELISA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The determination of atrazine in freeze-dried water samples containing simazine, 0.6% glycine as stabilizer and other pesticides has been compared using three different techniques: (i) direct rapid-magnetic particlebased ELISA, (ii) dichloromethane liquid-liquid extraction (LLE) and Florisil column clean-up prior to ELISA determination and (iii) LLE, Florisil column clean-up and gas chroamtography with nitrogen phosphorus detection (GC-NPD). The methodology developed in this paper has shown the advantages of the introduction of a clean-up step prior to ELISA determination and its correlation with GC-NPD determinations. Atrazine could be determined at levels between 0.1 to 5 μg l−1 in water smaples using the different methods described in this paper. The crossreactivity problems found in the ELISA test associated with the presence of simazine are also discussed.
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  • 7
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    Chromatographia 39 (1994), S. 71-73 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Spectinomycin ; Silylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A gas chromatographic assay for spectinomycin hydrochloride is described. The method is based on that prescribed by the United States Pharmacopeia (USP XXII). The method involves silylation of spectinomycin hydrochloride; phenazone is used as an internal standard. Spectinomycin and phenazone have adequate stability under the prescribed conditions. The stationary phase is 3% OV-17 on Gaschrom Q 100–120 mesh. The selectivity of the proposed method is better than that of the GLC method described in the USP XXII.
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  • 8
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Enantiomer separation ; Permethylated cyclodextrin stationary phases ; Side-chain fluorinated alkylbenzenes ; Thermodynamic data
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The separation of racemic side-chain fluorinated alkylbenzenes and bromofluorinated analogues by capillary gas chromatography using permethylated α, β and γ-cyclodextrins dissolved in polysiloxanes of different polarity as stationary phases is described. The influence of the achiral polysiloxane matrices on the separation of enantiomers is discussed in the light of the results obtained with the different phases. For a part of the tested compounds thermodynamic data are determined which describe the interaction of enantiomers with the stationary phase. The mechanism of separation is discussed on this basis and by comparison with data for structurally similar compounds.
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  • 9
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Method validation ; Reggedness test ; Residual solvents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Ruggedness testing is performed on a gas chromatographic method for the quantitative determination of residual solvents in steroids. Eight experimental variables or factors which were expected to influence the quantitative results were selected. These factors were divided into two independent groups, i.e. four factors related to the injection process and four factors related to separation and detection. In order to determine interaction between factors and quadratic effects, a central composite design was selected for the set-up of the experiments. Because in the method an internal standard is used, relative peak area was used as response. A deviation of up to 2.5% per factor for the quantitative results was regarded as acceptable. Other responses studied are related to the system suitability. Observed main, quadratic and interaction effects were translated into rugged intervals of the experimental variables by graphical presentation. It was found that besides main effects significant interaction effects were present, for example between the temperature of the injector and the split-flow. Interaction effects can easily result in the reduction of the rugged intervals by a factor of 2. The calculated rugged intervals were compared with the precision of the instrument or factor settings in order to estimate the ruggedness of the factors. Eventually, the maximum effect of the variation in the instrument settings on the quantitative results regarding the precision of the factor settings was found to be only 2.2%. Overall, the method proved to be rugged for most factors, except for the split-flow of the injector for which the method was only rugged to a limited extent.
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  • 10
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Retention/structure and retention/temperature ; relationships ; Experimental design ; Enthalpy-entropy compensation ; para-Hydroxy benzoic esters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An experimental design has been used to study the effect of column temperature on the gas chromatographic retention of eightpara-hydroxy benzoic esters. A rapid procedure has been developed to reduce the number of experiments compared with traditional methods. Capacity factors were determined and the enthalpy and entropy of transfer from the mobile phase to the stationary phase, ΔHo and ΔSo, respectively, were calculated using the linear Van't Hoff equation (dependence of ln k′ on 1/T). A retention prediction system (RPS) for these compounds in GC was investigated. The molecular connectivity index was used to describe the quantitative structure relationships. Enthalpy — entropy compensation revealed that the mechanism was similar for all the compounds studied.
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  • 11
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Priority pollutants ; EPA methods ; Unleaded gasoline ; Volatile organochlorine compounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The complete separation of the sixty volatile organochlorine (VOC) priority pollutants has been achieved by coupling two different liquid-modified adsorption chromatography columns. Two temperature programs were used to obtain the complete separation in a relatively short analysis time. Detection was by FID alone
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  • 12
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    Chromatographia 38 (1994), S. 93-97 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Retention index ; Adsorption effects ; Terpene alcohols ; Fused-silica capillary columns
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Retention indices of 6 selected hydroxy compounds (aliphatic and bicyclic alcohols, phenols) were determined on 2 HP-5 fused-silica, capillary columns with different film thicknesses (0.11 μm and 0.33 μm) at 8 different oven temperatures between 80 and 150°C. For some substances the I-T plot was found to show a minimum which cannot be explained by the common retention-index temperature-dependence in gas-liquid chromatography. This result is discussed in terms of adsorption at the liquid-solid interface of the capillary column.
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  • 13
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Stationary Phase and solute polarity ; Molecular structural coefficients ; Retention index ; Takács equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Molecular structural coefficients, Sc, for one hundred solutes have been calculated by means of the Takács equation using retention data obtained with over fifty stationary phases, SP. Employing data of seven SP's (characterized in our laboratories) it was found that the variation of Sc with column temperature was linear for most solutes. With data of n-decane and the ten McReynolds probes on up to fifty SP's of polarity less than RP=72, at 120°C, it was found that the Sc of n-decane and cis-hydrindane decreased slightly with increasing SP polarity, while the Sc of non-alkanes remained constant or increased very little as the SP polarity increased. The points for n-decane fit well to a second order polynomial. Again using a temperature of 120°C, the increments of Sc for solutes belonging to an homologous series were correlated with the polarity of SP's. Reasonably straight lines were obtained for all the chemical functions studied, Sc increasing with increasing SP polarity.
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  • 14
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Stationary phase characterization ; Principal component analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary In this study, several new stationary phases were characterized by principal component analysis. Fourteen new stationary phases, including substituted phenyl and oligoethyleneoxide functionalities on polysiloxane polymers, were tested and compared to three well known stationary phases. The main features of these phases were studied using a series of test solutes of varying chemical characteristics representing the data set for principal component analysis. Two principal compounds were found to account for 99.20% of the variance (the first accounted for 94.96% and the second for 4.24%). The data were represented as a two-dimensional map for visual representation of the characteristics of these stationary phases. The first principal component represented a selectivity based on polarity (r2=0.998), while the second showed Lewis acid-base characteristics of the phases. Polarizable and amphoteric characteristics of these phases also became evident using this evaluation method.
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  • 15
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Liquid-liquid extraction ; Supercritical fluid extraction ; Pesticides ; Freeze-dried water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The stability of freeze-dried water samples spiked with eight agrochemicals (atrazine, simazine, linuron, carbaryl, propanil, fenitrothion, parathion and fenamiphos) were examined to evaluate their suitability as candidate reference materials for their determination in water samples. In addition, two different extraction procedures, liquid-liquid and supercritical fluid extraction, were compared for the isolation and trace enrichment of target analytes from freeze-dried water samples. Final analytical determinations were by gas chromatography-nitrogen phosphorus detection and electronic impact mass spectrometry, and by liquid chromatography-diode array detection. The whole methodology developed in this paper permitted the determination of pesticides spiked in water at levels varying from 0.03 to 6.9 μg L−1.
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  • 16
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    Chromatographia 38 (1994), S. 624-628 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Ion-trap detection ; Nitriles ; Cerelas ; Perfluoroacylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Bromoxynil and ioxynil have been determined inplants and soil by gas chromatography. These herbicides are extracted from soil samples with methylene chloride at acidic pH. Plant samples are extracted with a basic acqueous solution and extracts purified by solvent partitioning. Herbicide residues are submitted to perfluoroacylation prior to GC separation. These compoiunds are determined by ion-trap detection with single ion monitoring; N-(3-chloro-4 methyl-phenyl_ perfluoropropyl amide is used as internal standard. The detection limit of the method is near 0.001 μg g−1 for the samples studied. The proposed methods are sensitive and reproducible enough to allow determination of these herbicides at residue levels in plants and soil.
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  • 17
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    Chromatographia 39 (1994), S. 11-14 
    ISSN: 1612-1112
    Keywords: Supercritical fluid extraction (SFE) ; Gas chromatography ; Pesticide residues ; Oxadixyl
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary This work describes the study of a degradation curve of Oxadixyl in field-treated potato and tomato samples. The residues were extracted using classical and supercritical fluid (SFE) extraction methods and analyzed by HRGC/ECD. The extraction techniques were compared and the results indicate the advantages of using SFE as an alternative method for pesticide analyses in these samples.
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  • 18
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    Chromatographia 39 (1994), S. 706-712 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Short chain fatty acids ; Intestinal fluids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The quantification of short chain fatty acids in their free form, by gas chromatography, is the method of choice provided that the underivatized acids elute with good peak shape and reproducibility. In biological samples not only the highly polar acids themselves but also deposits of nonvolatile sample components may interact with the column or the packing material. As a result, the peak symmetry of the fatty acids and their reproducibility can become increasingly poor. Reduction of the nonvolatile matrix components by filtration of the sample has been examined in order to achieve direct analysis of the short chain fatty acids in intestinal samples by packed column GC. Membrane filter units (0.8 μm) allow a quick and simple filtration of the samples. This pretreatment reduces the peak tailing and the broadening of the peaks. The method, when applied to different intestinal samples, allowed the quantification of short chain fatty acids in hundreds of samples without derivatization. Good results are obtained at sample concentrations higher than 0.2 mmol l−1 for each acid.
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  • 19
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    Chromatographia 39 (1994), S. 224-227 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; C1−C4 alkyl tert-butyl ethers ; Retention index
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The separation of C1−C4 alkyl tert-butyl ethers with the general formula (CH3)3C−O−R (R-alkyl substituent) on fused-silica capillary columns coated with dimethylsilicone and cyanopropylmethylsilicone stationary phases was investigated. Retention indices were determined at two temperatures in order to understand their chromatographic behaviour. The respective standard deviations were 0.3 and 0.5 i.u.
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  • 20
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Organonitrogen pesticides ; Organophosphorus pesticides ; Apples ; Solvent extraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A gas chromatographic method employing a capillary column and a selective nitrogen/phosphorus detector (NPD) has been developed for the determination of organophosphorus (OP) and organonitrogen (NP) pesticides in horticultural samples (apples). The separation of sixteen pesticides and the internal standard was performed in thirteen minutes. The analytical characteristics of the method, including linear response ranges, detection limits, and reproducibility, have been studied using a 1∶1 mixture of ethyl acetate and xylene as extraction solvent. The possibility of mutual interference between pesticides has also been studied. A procedure for the quantitative extraction of the sixteen pesticides from apple samples has also been developed; for fifteen of the pesticides recoveries 〉85% were obtained after 90 minutes extraction. The effect of different solvents both on recovery and on the sensitivity of the subsequent chromatography were also investigated. It was found that the sensitivity required must be considered when the solvent for sample treatment is selected.
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  • 21
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    Chromatographia 39 (1994), S. 419-426 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Gas chromatography ; Chirasil-Val ; Amino acid enantiomers ; N-Isobutyryl-cysteine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Free D-amino acids (D-AA) were detected as native constituents in juices of vegetables (cultivars of cabbage, tomato, carrot, garlic) and fruits (organes, clementine, grapefruit, lemon, apples, pear, grapes) using gas chromatography (GC) or high-performance liquid chromatography (LC). For investigation by GC, AA enantiomers were converted into theirN(O)-pentafluoropropionyl 2-propyl esters and resolved on a Chirasil-L-Val capillary column. For determination by LC, precolumn derivatization of AA enantiomers usingo-phthaldialdehyde together with the chiral thiolsN-isobutyryl-L-cysteine orN-isobutyryl-D-cysteine and fluorescence detection of the diastereomeric isoindole derivatives, resolvable on an octadecylsilyl stationary phase, were used. D-Ala (0.6–3.8%) was detected in all freshly pressed plant juices usually in the highest relative amounts. Other D-AA detected were D-Asx (0.1–1.9%), D-Glx (0–1.3%), D-Ser (0–1.7%), D-Arg (0.4–1.2%, in grapes, orange, grapefruit, and clementine) and D-Leu and D-Val (1% in cabbage). Absolute amounts of native D-AA were totally 28–57 μmol L−1 in fruit juices, 14.5 μmol L−1 in a tomato juice and 8.5 μmol L−1 in a carrot juice.
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  • 22
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Correlation chromatography ; Simulation model ; Adsorption effects ; Separation improvement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Experiments and simulations prove that correlation chromatography can greatly reduce the disadvantage of a non-linear response of the chromatographic column. A factor that has been accepted as being an important source of error in correlation or multiplex chromatography, has been shown not to be. Separations affected, improve dramatically when correlation chromatography is used, and a substantial amount of correlation noise only arises when there is a large difference in separation between a conventional chromatogram and a correlogram. A model has been developed for simulating these nonlinearities. It is shown that, especially for correlation chromatography, the simulation results match the practical measurements very well.
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  • 23
    ISSN: 1612-1112
    Keywords: Gas chromatography ; PTV injection system ; Aqueous samples ; Pesticides ; Breakthrough volumes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A GC method is described for the determination of pollutants in aqueous samples by direct enrichment out of large sample volumes in a PTV injector. The vaporized water is eliminated through the split vent and the analytes are concentrated on an adsorbent inside the insert of the PTV. For the selection of suitable adsorbents, breakthrough volumes of selected pesticides and nitroaromatics on Tenax TA, Tenax GR, Chemipack C18 and graphitized carbon blacks have been determined by experiment. The determination of the breakthrough volumes was carried out directly in the PTV insert. Tenax TA proved to be the best sorbent with regard to the breakthrough volumes and its inertness to the analytes to be determined. As the result of the investigations, 500 μl of aqueous standard solutions of pesticides and nitroaromatics (concn.=0.02 ... 2 μg/l) were analyzed with an average relative standard deviation of 10%. The procedure was successfully applied for the analysis of real samples.
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  • 24
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Reversed-flow technique ; Absorption rate ; Air pollutants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple chromatographic method is developed to determine the rate constant for expulsion of an air pollutant from water or its diffusion parameter in the liquid, the rate constant for chemical reaction of the pollutant with water, its mass transfer coefficient in the liquid, and the partition coefficient between liquid water and air. From these physicochemical parameters, the absorption rate by sea water and, therefore, the depletion rate of a polluting substance from the air can be calculated, together with the equilibrium state of this absorption. The method has been applied to nitrogen dioxide being absorbed by triple-distilled water and by sea water, at various temperatures. From the temperature variation of the reaction rate constant and of the partition coefficient, the activation energy for the reaction and the differential heat of solution were determined.
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  • 25
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    Chromatographia 39 (1994), S. 645-648 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Headspace analysis ; Gonadotrophins ; Residual solvents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A headspace, gas chromatographic method for determining residual solvents in pharmaceutical products such as the gonadotrophin powders, has been developed. The method allows the determination of residual solvents by transferring the samples directly into a vial contianing 10 mL 2M sodium chloride; the analysis is carried out by sampling the headspace and separating by capillary gas chromatography using a programmedtemperature vaporizer (PTV) injector. The procedure described is simple, sensitive and reproducible. The lower limit of detection is 20 ppb for ethyl alcohol, 8 ppb for acetone and 0.5 ppb for diethyl ether.
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  • 26
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    Chromatographia 39 (1994), S. 210-215 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Correlation chromatography ; Concentration methods ; Polymer dynamic head-space sampling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Gas chromatography has been used to study the kinetics of evolution of volatiles from polypropylene samples (at 70°C). Correlation chromatography (CC) and the trapping of volatiles on Tenax sorbents and activated charcoal were employed to improve the detector signal. As a reference, the kinetics of gas evolution was studied by making a series of direct single injections of polymer head-space gas on a GC column. The results of trapping differed from those obtained by single injection. However, the data from single injections and CC were in good agreement. The CC method was found to offer far more operator convenience for dynamic head-space analysis than sample trapping, being less subject to operator errors.
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  • 27
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    Chromatographia 39 (1994), S. 265-270 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Triglycerides ; Packed vs. capillary columns ; Milk fat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Quantitative gas chromatography of triglycerides in conjunction with established triglyceride formulae can be used to determine various milk fat parameters. Since the evaluation of, for example, iodine number or content of non-milk fats (foreign fats) in milk fat requires only the separation of triglycerides by carbon number and since repeatabilities, especially of the highboiling triglycerides, have been less acceptable with capillary columns in the past, packed columns have been used exclusively. There is, however, an increasing demand for the use of capillary instead of packed columns and to that end the present investigation has been carried out. To achieve a suitable resolution, with this particularly exacting high-temperature application, a short 5 m capillary column of extreme temperature stability has been used. As well as modification of various analytical conditions different injection techniques have been investigated. On-column, PTV and split injection were compared with regard to repeatability. The cold-on-column injection technique was found to produce the best results, being comparable to the excellent precision of a packed column. Thus, a method is now available by means of which the determination of milk fat parameters by the triglyceride formulae, such as the amount of foreign fats in milk fat, can now be carried out with a standardized capillary column.
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  • 28
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    Chromatographia 39 (1994), S. 363-365 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Light hydrocarbons ; Stabilized crude oil ; Capillary guard column
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary This paper reports a quick, and simple method for quantitative determination of C2 to C6 hydrocarbons in stabilized crude oil without using a back flush system. A mixture of crude oil and internal standard is injected into a GC equipped with a 6 meter length of fused silica capillary as a guard column. The light hydrocarbons are separated individually up to the last peak of the hexane group with the heavier components trapped in the guard column. The total analysis time for each sample is 15 minutes. The base line is table for up to 15 consecutive analyses. The guard column and the injector port are then reconditioned by simply heating them for one hour at 300 °C.
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  • 29
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Liquid modified adsorption capillary columns ; Polar compound analysis ; Aqueous solution analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The preparation of graphite layer open tubular (GLOT) columns is described together with their application to the analysis of priority pollutants and polar compounds such as alcohols, free carboxylic acids, aliphatic amines and phenols at the sub-nanogram level. A specific application of GLOT columns is for the direct analysis of aqueous solutions avoiding solvent extraction procedures. Several chromatograms of critical separations are reported together with calibration curves. A study of the reproducibility of column preparation is reported in terms of the standard deviation of the capacity ratio and of the minimum HETP obtained.
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  • 30
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    Chromatographia 38 (1994), S. 679-688 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Stationary phases ; Phase constants ; Explanatory coefficients
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Explanatory phase coefficients according to Abraham et al. are calculated from McReynolds index differences and the phase constant B. The retention expression (log Vg)−A=BI/100 connects specific retention volumes and retention indices. McReynolds phase constants and Abrahams explanatory coefficients can be used with similar accuracy for the prediction of relative retention data and for the characterization of stationary phases in gas chromatography. The application of polarity constants for the characterization of stationary phases is discussed.
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  • 31
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Gas chromatography ; Particle beam MS detection ; Polycyclic aromatic metabolites ; Biodegradation in water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Two liquid chromatography-particle beam mass spectrometry (LC-PBMS) systems have been used for analysis of polycyclic aromatic hydrocarbon metabolites in water samples from a biological decomposition model experiment. The results were compared with those obtained by classical gas chromatography-mass spectrometry. Evaluation of spectral data indicated the presence of six main metabolites; 1H,3H-naphtho [1,8-cd]pyran-1,3-dione, 1-(hydroxymethyl)naphthalene, and 1,2-acenaphthenedione were identified by use of standard substances and spiking experiments. Enrichment of the investigated water samples with online pre-column (C18) concentration, freeze-drying, and solvent extraction led to similar results with only slight differences. The application of microbore separation columns proved to be a promising tool in particle beam LC-MS measurements.
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  • 32
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    Chromatographia 38 (1994), S. 151-157 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; C5−C12 hydrocarbons in air ; Cryogenic focussing ; Thermal desorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A homemade cryogenic system derived from readily available material is described, illustrating its usage as an accessory for adsorption/thermal desorption chromatography. A small Chromsorb-W-HP packing (1 cm) was introduced into a deactivated precolumn as a cryofocussing, preconcentrating unit. This was able to retain the analyte which had been thermally desorpted from a Tenax TA sampling tube at a relatively higher temperature (−80°C∼−90°C), with the analyte also reinjected on the analytical column in a relatively narrow band. Average overall recoveries for 24 hydrocarbons tested were 97.5%. Cryofocussing enhanced sensitivity and improved resolution. Field studies at a petroleum industry site were carried out and the accessory proved to be useful for complex C5−C12 hydrocarbon analysis in ambient air.
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  • 33
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    Chromatographia 38 (1994), S. 304-312 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Electron capture detector ; Theoretical model of ECD
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    Topics: Chemistry and Pharmacology
    Notes: Summary This paper reports a theoretical model of the ECD detector. The model presented here can be used to examine the influence of pulse parameters on the current and signal characteristics of the detector. On the basis of this model it was found that a space charge is created in the detector when it is supplied with pulse voltage. Due to the electric potential generated by the space charge, in the time between the pulses the electrons and negative ions move towards the detector electrodes. The ionization current of the detector is the sum of the electron current flowing to the anode under the influence of the supplied pulse voltage and the current flowing under the space charge potential in the time between the pulses. It was also found that the detector signal is the sum of the differences between those two currents caused by introducing the sample molecules to the detector. The model was tested for a detector with different electrode configurations which worked at temperature of 300 K or 573 K and which was supplied with nitrogen or Ar+10% CH4 as the carrier gas.
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  • 34
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Adsorption and partition columns in series ; Molecular sieves ; Isomers of benzene homologs
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    Topics: Chemistry and Pharmacology
    Notes: Summary The possibility of using short gas chromatographic columns packed with different molecular sieves (silicalite and aluminophosphates), showing definite selectivity to para-isomeric compounds, in series with columns containing a liquid stationary phase was investigated. The molecular sieves were of different origin, while 1,2,3-tris (2-cyanoethoxy)propane (TCEP) and polyethylene glycol adipate (PEGA) were used as the liquid stationary phase. Ortho-, meta- and para-isomers of xylene, chlorotoluene and dichlorobenzene were chromatographed on these columns. It is shown that the best separation is obtained on a combined column with silicalite containing pure silica gel as the molecular sieve, and 10% PEGA as the liquid phase. Molecular sieves of aluminophosphate origin show only weak selectivity toward the para isomers.
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  • 35
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    Chromatographia 39 (1994), S. 294-298 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Preconcentration ; Thermal modulator ; Cross-correlation ; Trace analysis
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    Topics: Chemistry and Pharmacology
    Notes: Summary The inside wall of an uncoated polyethylene capillary traps organic substances from a water sample pumped through it by a nitrogen gas stream. Heating the capillary in a chromatographic oven slowly releases the trapped organic substances from the wall. Nitrogen carrier gas transports sample substances released through a thermal desorption modulator and onto a chromatographic column. Pulsing the temperature of the modulator modulates the concentrations of sample components as they enter the column. Computing the cross correlation of the detector output signal against the applied modulation signal generates the chromatogram. Detection limits below 1 ppb are possible using a flame ionization detector. No sample pretreatment or cold trap is required.
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  • 36
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    Chromatographia 38 (1994), S. 689-693 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Enantioselectivity ; GC-MS ; GC-GC-MS ; Pinus peuce ; Monoterpenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Needles of the Macedonian Pine,Pinus peuce Griseb., a conifer growing in the Balkan mountains, were extracted by a Likens-Nickerson simultaneous distillation-solvent extraction device. The components of this essential oil were identified by the retention times obtained on two columns differing in polarity and by GC-MS. Because of the complex nature of such plant extracts, a multidimensional GC method for enantiomer analysis, using a non-chiral pre-column and a chiral main column has been developed. The enantiomeric ratios of five monoterpene hydrocarbons were estimated by GC-GC and GC-GC-MS.
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  • 37
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Chiral phases ; Phenylalanine tetraamides ; Amino acids
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    Topics: Chemistry and Pharmacology
    Notes: Summary A wide series of L-phenylalanine tetraamide selectors (Phe-n-O-TA) have been synthesized and used as stationary phases for chiral resolution of D,L-amino acids by capillary gas chromatography. The influence of length and polarity of the oxaalkanoyl bridge spacing the diamide chains of the selectors and the effects of steric hindrance on separating power were investigated. The characteristics of the chiral columns and the separation factors of D,L-n-butyl-N-trifluoroacetyl amino esters are reported.
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  • 38
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Curie-point pyrolysis ; Multivariate analysis ; Sodium dodecylbenzene sulfonate
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    Topics: Chemistry and Pharmacology
    Notes: Summary Multivariate analysis was used to develop a viable method for determination of sodium dodecylbenzene sulfonate (DBS) by Curie-point pyrolysis gas chromatography. The pyrograms obtained were normalized against a maximum peak area and peak height. Normalized values were used for Quantification IV, which is one of the multivariate analysis methods, to select useful values initially. Then cluster analysis was carried out using both the selected values and their deviations. This method corresponds to qualitative analysis and indicates which data-base is similar to the sample. On the basis of this data-base, calibration data-bases are chosen. Principal component analysis (PCA) was performed using the calibration data-base and a set of sample data simultaneously. The principal component scores and contribution coefficients obtained were used to construct a calibration curve from which the DBS content of the sample was calculated. The results are in fair agreement with theoretical values.
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  • 39
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Morpholine ; Hydrazine ; Boiler feed water and steam condensates
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    Topics: Chemistry and Pharmacology
    Notes: Summary Hydrazine, an oxygen scavenger in boiler water, was derivatised to the corresponding acetone azine and determined at the ng ml−1 level by gas chromatography. Morpholine, a corrosion inhibitor used in steam boilers, was estimated either directly (if 〉2.0 μg ml−1) or by quantitative preconcentration (0.1 ng – 2.0 μg ml−1). To obtain symmetrical peaks for these amines, the column packing was coated with KOH. Use of a nitrogen-specific detector improved accuracy of estimation of hydrazine and morpholine, giving a RSD of 1.9–3.6%. Chromatographic analysis of these amines in boiler feed water and steam condensate samples collected from boilers servicing a petroleum refinery is described. Environmental safety regulations calls for monitoring of hydrazine and the methods developed can easily be adapted for this purpose.
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  • 40
    ISSN: 1612-1112
    Keywords: Gas chromatography ; MSD, ECD and NPD ; Non-steroidal anti-inflammatory drugs (NSAIDs) ; Plasma samples
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    Topics: Chemistry and Pharmacology
    Notes: Summary The aim of this work was to compare the performance of the MSD, ECD and NPD systems when used for drug assay in biological fluids. As a practical test, six non steroidal anti-inflammatory drugs added to plasma samples were detected and quantified. The analyses were carried out after solvent extraction from an acidic medium and subsequent methylation. The linearity of response was tested for all the detection systems in the range of 1 to 25 ng/ml. Precision and accuracy were determined at 1, 5 and 10 ng/ml. The minimum quantifiable level for the six drugs was about 1 ng/ml with each of the three detection systems.
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  • 41
    ISSN: 1432-2285
    Keywords: Abies alba ; Abscisic acid ; Damage ; Gas chromatography ; Needles
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    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The amount of abscisic acid (ABA) in needles of silver fir from a natural location was investigated with regard to position in the crown, damage, seasonal variation, and needle age. Because of problems of quantification of ABA in coniferous needles, which contain numerous secondary plant products, a method for reliable determination of both isomers cis-trans-ABA (c-ABA) and transtrans-ABA (t-ABA) was developed. By means of gas chromatography (GC) using an electron capture detector (BCD) and a programmed temperature vaporizer (PTV) injector complete separation of both compounds was achieved. Two different pairs of fir were investigated — in each case a damaged and a healthy tree. Needles from both trees from the first and the second pair collected in September contained 500–1100 ng c-ABA/g fresh weight (FW), and the concentrations of t-ABA varied from 400 to 700 ng/g FW. Investigations from the second pair show highest amounts of 2900 ng/g Fw c-ABA and 1800 ng/g FW of t-ABA in May and June. For the first pair a higher c-ABA content was found in needles from the top of the crown than in those from the middle and the base. This difference could not be confirmed in the analysis of the second pair. Because of the strong natural deviation no statistically significant difference between the healthy and the damaged tree was found. The first pair of firs examined showed a higher t-ABA concentration than the second one. In this case the highest amount was found in the top of the crown. Methodical mistakes during the clean-up procedure and in quantification by gas chromatography could be excluded. The presence of c- and t-ABA in the purified extract was corroborated by mass spectrometry. With regard to the seasonal variation both isomers of ABA show an unequivocal trend. The maximum concentration is achieved in May to June, whereas the content is minimal in August/September. In any case the level of t-ABA is lower than that of c-ABA. No correlation between the amount of ABA and the needle age could be established.
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  • 42
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    Mycopathologia 124 (1993), S. 73-77 
    ISSN: 1573-0832
    Keywords: Assessment ; Cancer ; Humans ; Hydrazines ; Mushroom
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    Topics: Biology , Medicine
    Notes: Abstract This assessment focuses on the concentrations of some chemicals present in theAgaricus bisporus mushroom, the cancer-inducing doses of these chemicals or mushroom used in the animal experiments, the total amounts of these chemicals or mushroom needed to induce cancer in these mice, and the estimated total amounts of these chemicals or mushroom needed to induce cancer in humans. By adding the estimated amounts of chemicals needed to induce cancer and by comparing it with the amount of raw mushroom needed to induce the same effect, it becomes obvious that we have accounted for less than 2% of the carcinogenic components of theAgaricus bisporus mushroom. Since some unavailable data handicapped this assessment, it should be regarded as tentative and subject to further adjustment.
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  • 43
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    Chromatographia 35 (1993), S. 649-652 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Triglycerides in cheese ; Programme temperature (PTV) injection ; Silica capillary columns
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    Topics: Chemistry and Pharmacology
    Notes: Summary A rapid gas chromatographic method for the analysis of triglycerides in cheese on a capillary column with a programmed temperature vaporizer has been developed. Fat were extracted with hexane to dryness. The reproducibility of the method was assessed and the coefficient of variation for the total triglycerides was 2.50%. Recovery of individual triglycerides ranged between 87 to 105%.
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  • 44
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Curie-point pyrolysis ; Multivariate analysis ; Sodium dodecylbenzene sulfonate
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    Topics: Chemistry and Pharmacology
    Notes: Summary Multivariate analysis can be applied to quantitative analysis of sodium dodecylbenzene sulfonate (DBS) by pyrolysis gas chromatography. The pyrograms obtained from mixtures of DBS and polyoxyethylene lauryl ether (PEG) were normalized for the peak heights and areas of several internal standards which appeared in every pyrogram, against the characteristics peaks for DBS and PEG. This normalization method gave smaller experimental errors than when using one internal standard. The normalization values were used for cluster analysis unchanged. The values were calculated correlation coefficients and principal component analysis was performed using 11 data base and a set of sample data simultaneously. One calibration curve was calculated from the principal component scores. The DBS content of a sample was obtained from the calibration curve. Calculated values were in fair agreement with theoretical values.
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  • 45
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    Chromatographia 36 (1993), S. 187-190 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Solid-phase extraction disks ; Pesticides ; Soil analysis
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    Topics: Chemistry and Pharmacology
    Notes: Summary A systematic study comparing the methodology and analytical results obtained in an investigation of seven pesticide residues (Molinate, Atrazine, Carbofuran, Pirimicarb, Prometryn, Malathion and Tetrachlorvinphos) in soil samples is reported. Solid-phase extraction (SPE) using glass columns and 47 mm disks of octyl and octadecyl-bonded silica was used in the pesticide analysis. The best extraction efficiency and clearest extracts are obtained with C8 disks. The analyses were carried out by capillary gas chromatography with nitrogen and phosphorus detection. Recovery experiments were performed at ppb levels in spiked soil samples. The average recoveries of the compounds were 53–77%. Detection limits are between 5 and 30 ng g−1 based on 5 g moist soil sample. The method was validated by comparing it with conventional liquid-liquid extraction.
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  • 46
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Fatty acid methyl esters ; Diesel fuel substitute ; Glycerol
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    Topics: Chemistry and Pharmacology
    Notes: Summary A GC method for the determination of free glycerol in vegetable oil methyl esters used as diesel fuel is described. The sample preparation includes dissolving in dimethylformamide, silylation with bistrimethylsilyltrifluoroacetamide (BSTFA) and separation on a methyl silicone capillary column using either FID or MS detection. The recovery was tested using standard samples containing known amounts of glycerol. The results of the analysis of different samples were compared with those obtained by enzymatic determination. The method described offers a far more sensitive and quick determination of free glycerol compared to other methods.
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  • 47
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Electron capture detection ; Trichothecenes ; Cereal grain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Various analytical methods developed for trichothecene determination, including TLC, HPLC, GC, supercritical fluid chromatography (SFC) and enzyme immuno assay (EIA) are reviewed. In addition a new method is described for the simultaneous determination of the trichothecene mycotoxins deoxynivalenol (DON), nivalenol (NIV), 3-acetyldeoxynivalenol (3-ADON), diacetoxyscirpenol (DAS), T-2 toxin (T-2), HT-2 toxin (HT-2) and T-2 triol (TRIOL), in Austrian wheat and corn samples by GC-ECD. A clean-up procedure has been developed using a combination of liquid-liquid and liquid-solid extraction. Trichothecenes were detected as their heptafluorobuturyl esters or alternatively as trimethylsilyl ethers (only sensitive for deoxynivalenol and nivalenol) using nandrolone or chloramphenicol as internal standard. Four derivatization techniques using HFBI, HFBA+DMAP on polystyrene, TMSI and TMSI+BSA+TMCS have been studied and the advantages and disadvantages of each are discussed. Quantification of trichothecenes from 10 to 1000 ppb in cereals could be accomplished routinely.
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  • 48
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    Chromatographia 37 (1993), S. 215-217 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Unified retention indices ; Dimethylsiloxane stationary phases
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    Topics: Chemistry and Pharmacology
    Notes: Summary Gas chromatographic, unified retention-indices of 56 alkylbenzenes up to C15 on dimethylsiloxane OV-101 and SE-30 stationary phases are given. These values agree well with the corresponding experimental values used in the statistical treatment of the experimental data.
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  • 49
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    Chromatographia 37 (1993), S. 259-263 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Quantitative analysis ; Ethylene oligomer by-products ; n-Alkanes, n-alkenes and 2-alkyl-1-alkenes
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    Topics: Chemistry and Pharmacology
    Notes: Summary A gas chromatographic method using temperature-programmed poly-dimethylsiloxane OV-101 and poly(pheny ether) (5 rings) capillary columns was developed to separate and quantify the reaction by-products in ethylene oligomers. It was found that the content of 2-alkyl-1-alkenes, 2-alkenes and n-alkanes in the C8−C18 α-olefin fractions amounts to 29, 10 and 2.6% respectively.
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  • 50
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    Chromatographia 37 (1993), S. 211-214 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Organic solvents ; Routine analysis
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    Topics: Chemistry and Pharmacology
    Notes: Summary A gas chromatographic method for the analysis of organic solvents in chemical products is described. The analysis is performed by the use of a polar column, Supelcowax 10, and a non-polar column CP-Sil-5CB. Samples containing a non-volatile matrix or water were analysed by headspace analysis. The identification of the solvents in a sample, based on GC retention times on one column, is confirmed by GC of the sample on the second column. The method has been found to be suitable for the routine analysis of solvent mixtures.
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    Chromatographia 37 (1993), S. 264-270 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Temperature programmed ; Peak widths ; Polynomial interpolation
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    Topics: Chemistry and Pharmacology
    Notes: Summary Isothermal chromatographic measurements lead directly to ΔH v o and A (entropy term) of solutes, and three constants of an empirical relationship between peak width and column temperature. From the thermodynamic parameters ΔH v o and A retention temperatures have been computed by means of a theoretical model including temperature dependence of carrier gas viscosity, and subsequently retention times; programmed retention indices have been determined by linear and polynomial interpolations. By substituting the value of the calculated retention temperature in the above-mentioned relationship, peak width at half-height for a linear temperature may be estimated. Predicted retentions correlate with observed data, with a P-value ≤0.01; simulation accuracy is generally 6–10% for peak widths. Retention indices of some organochlorine species, separated on an OV-101 capillary column, may differ by as much as 26 units depending on the method of calculation. Polynomial-calculated indices are more consistent with the retention index scheme, and have smaller standard deviations and better constancy at different heating rates.
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  • 52
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Inverse gas chromatography ; Poly(ethylene glycol) 20M ; Retention mechanisms
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    Topics: Chemistry and Pharmacology
    Notes: Summary The properties of poly(ethylene glycol) 20M (PEG 20M) coated on the hydroxylated surface of Chromaton N AW were investigated by inverse gas chromatography. It was found that the solid form of PEG 20M exhibits partition as the retention mechanism even below its melting range. The contribution of adsorption to the specific retention volume was also determined. It was demonstrated that inverse gas chromatography establishes the existence of a polymer surface layer but precise determination of its thickness is difficult. The limitation of the applicability of inverse gas chromatography results from the structure of the investigated surface layer which is thin and not coherent so that solute molecules can penetrate it.
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  • 53
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    Chromatographia 35 (1993), S. 33-37 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Crown ether polysiloxane phases ; Selectivity mechanisms
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    Topics: Chemistry and Pharmacology
    Notes: Summary The phase recognition mechanism of nine groups of position isomers on four crown ether polysiloxanes, OV-1701 and PEG 20M has been investigsated by measuring various thermodynamic parameters. The high selectivity of crown ether polysiloxane phases is due to hydrogen bonding and the extent of fitting between the analytes and the crown ethe cavity. The effects on selectivity of cavity size, heteroatoms and substituent groups on the crown ether are discussed.
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  • 54
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Equilibrium headspace sampling ; Partition coefficient determination ; Theory of chromatography
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    Topics: Chemistry and Pharmacology
    Notes: Summary The new phase ratio variation method is described which represents a convenient way for the determination of gas-liquid partition coefficients for practical purposes, utilizing equilibrium headspace-gas chromatography (EHS-GC). This method is based on the relationship between reciprocal peak area and the phase ratio in the vial containing the sample solution; it involves regression analysis of the EHS-GC measurements of a number of sample vials containing the same sample solution but with a wide variation of phase ratios. Examples are given for both aqueous systems and systems consisting of a stationary (liquid) phase used as the solvent; comparison of the measured values with results obtained by other methods shows satisfactory agreement. A critical discussion of the conditions influencing the accuracy of the analytical results is given.
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  • 55
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    Chromatographia 35 (1993), S. 109-110 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Unified retention index ; Correlation of data ; Hydrocarbons
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    Topics: Chemistry and Pharmacology
    Notes: Summary Gas chromatographic unified retention indices for 43 hydrocarbons (alkanes and cycloalkanes) are given for squalane and OV-101. Comparison of these values and unified retention index increments are presented as linear regression equations with high correlation coefficients and acceptable standard deviations.
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  • 56
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    Chromatographia 35 (1993), S. 160-166 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Neural networks ; Classification ; Pattern recognition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Artificial Neural Networks are proposed for the classification of vegetable oils submitted to gas chromatography analysis through their FAME profiles. Three important neural networks are evaluated here: the Hopfield model as a content-addressable memory (CAM), the Hamming model and the multi-layer perceptron. A brief description of these nets is first presented and further implemented for the classification of known vegetable oils. After the learning step, unknown samples are presented to the nets and the identification step performed. The performances of these nets are compared for the recognition of popular vegetable oils, including several edible oils.
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  • 57
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Mass spectrometry ; Atomic emission spectroscopy ; Pulp mill effluents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Three chlorinated dimethyl sulfones and five chlorinated thiophenes have been identified in the alkaline extraction liquor from a bleach plant by gas chromatography with atomic emission detection (GC-AED) and with mass spectrometry (GC-MS). The information on elemental content obtained by GC-AED enabled a rapid screening of the sulfur compounds and provided important structural information complementary to the mass spectral data. Quantitation was accomplished by GC-AED based on universal calibration.
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    Chromatographia 35 (1993), S. 209-215 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Gas chromatography-mass spectrometry ; Tagetes ; Plant volatiles ; Extractions ; Natural insecticides ; Mosquitos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Volatiles from three species of the genustagetes, commonly called marigold have been isolated and characterized. Simultaneous steam distillation extractions (SSDE) produced consistently extracts of higher insecticidal activity than Soxhlet extractions. Methylene chloride was the best solvent. Volatiles isolated from theminutae species showed higher activity than those frompatula anderecta. Comparison of extracts from the flower, foliage and roots of the plant showed that most of the activity is located in the flower. The volatiles are highly effective toward both larvae and adult mosquitoes.
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    Chromatographia 35 (1993), S. 237-240 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Enantioselectivity ; Polysaccharide chiral stationary phase ; Amylose tris(n-butylcarbamate) ; Grob test
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    Topics: Chemistry and Pharmacology
    Notes: Summary Seven aromatic and alkyl amylose and cellulose carbamates have been tested as chiral stationary phases in gas chromatography. One of them, amylose tris(n-butylcarbamate) can be used for enantiomer separation.
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    Chromatographia 35 (1993), S. 290-294 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Solid phase extraction ; Organochloride pesticides ; Water analysis
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    Topics: Chemistry and Pharmacology
    Notes: Summary Gas chromatography of chlorinated pesticides in water is carried out after adsorption of a 50 mL sample using a cartridge containing 100 mg CN-bonded porous silica and extraction with 500 μL pentane. The average recovery for eight organochloride pesticides at 1 ppb was 〉95%. The procedure described is simple, selective and reproducible.
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    Chromatographia 35 (1993), S. 339-343 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Preconcentration techniques ; Trace gas analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The blanks in preconcentration methods for determining trace amounts of impurities in ultra-pure gases, which include the preconcentration volume of sample gases, carrier gas impurities and atmospheric contamination are discussed and three concentration methods for eliminating blank errors are proposed. These are, the differential volume method by concentrating at the same flow-rate but different times (DVMSF), the differential time method by concentrating the same volumes at different flow-rates (DTMSV) and the differential volume method by concentrating for the same times but different flow-rates (DVMST). DVMST is proposed as the best method for its ability to eliminate all blank errors described. The methods are used to determine trace amounts of Ar+O2 and N2 in ultra-pure hydrogen. Calculations demonstrate that the methods can effectively improve analytical accuracy.
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  • 62
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Micropacked columns ; Retention behavior ; LC silica packing materials ; Silanol groups
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    Topics: Chemistry and Pharmacology
    Notes: Summary Gas chromatographic retention of cyclohexane and benzene on microcolumns packed with silica-based materials for liquid chromatography has been investigated to elucidate the relationship with the surface properties of the packing materials. Differences in capacity factors (Δk′) for these two hydrocarbons were related to the surface area of the packing materials. For untreated silica gels, the Δk′ value increased with increasing total surface area of the column employed and measurement of Δk′ for chemically-bonded stationary phases allowed estimation of accessible residual silanol groups.
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  • 63
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Pesticides in groundwater ; Solvent extraction ; Multiresidue analysis ; Selective detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple multi-residue procedure has been developed and applied to the analysis of pesticides in groundwater samples from the Comunidad Valenciana, a predominantly agricultural area on the Mediterranean coast of Spain. The procedure includes a liquid-liquid extraction, after addition of NaCl on the samples, and a subsequent analysis by capillary gas chromatography using a dual detection system with electron capture and nitrogen-phosphorous detectors. This allows the determination of more than 30 compounds (organophosphorous, organochlorine and pyrethroid pesticides) at the low ppb (μg l−1) levels. Detection limits obtained varied between 0.01 μg l−1 (lindane, fonofos) and 0.5 μg l−1 (cypermethrin). An additional injection of the sample extracts into a gas chromatograph equipped with a column of different polarity and electron capture detector is used for the confirmation of chromatographic peaks. The recommended procedure has been applied to 66 ground water samples. Pesticides, including organophosphorus and organochlorine compounds were detected in 31 of them, in levels ranging from 0.02 to 0.7 μg l−1.
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  • 64
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Headspace sampling ; PTV-System ; Ethephon in drinking water
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    Topics: Chemistry and Pharmacology
    Notes: Summary An indirect GC method is described for the determination of Ethephon in drinking water on the basis of the headspace analysis of the ethylene formed from Ethephon. In order to reach the necessary detection limit, the entire volume of the static headspace distribution is transferred into a cold injection system (CIS). There, the ethylene is adsorbed on Carbosieve SIII at 10°C and, subsequently, desorbed at 300 °C. The water vapour included in the headspace is completely eliminated through the splitting system. By means of this technique, a detection limit of 0.05 μg/l water was reached.
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  • 65
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    Chromatographia 37 (1993), S. 399-401 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Viscosity ; Carrier gases
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    Topics: Chemistry and Pharmacology
    Notes: Summary Equations are derived for viscosities of H2, He, N2 and Ar for use at chromatographic temperatures which are accurate to within 0.3% for H2, and 0.1% for the other gases. The effect of pressure is usually negligible but may increase the viscosity of N2 or Ar by as much as 0.5% at 25°C or lower and 5 atm or higher.
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  • 66
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    Chromatographia 35 (1993), S. 503-505 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Silanol terminated Chirasil-Val ; Cross-linking with polyfunctional silanes ; Enantiomer separation
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    Topics: Chemistry and Pharmacology
    Notes: Summary A method for the immobilization of Chirasil-Val has been studied based on the cross-linking which takes place between terminal silanols of Chirasil-Val and polyfunctional silanes. A leached, dehydrated and tetramethoxysilane-treated glass capillary coated with silanol terminated Chirasil-Val containing 5% tetraacetoxysilane as a cross-linking agent showed a maximum extractability of 15% without any loss of chirality.
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  • 67
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    Chromatographia 37 (1993), S. 51-56 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Halogenated hydrocarbons ; Headspace sampling ; ECD detection
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    Topics: Chemistry and Pharmacology
    Notes: Summary Simple sampling and preconcentration technique for the analysis of volatile halogenated hydrocarbons in water is described. For the separation a selective capillary column is used in combination with an ECD. Quantitative data are given.
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  • 68
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Fused silica open tubular columns ; Serial coupled columns ; Phase ratio optimization
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    Topics: Chemistry and Pharmacology
    Notes: Summary There are a number of parameters which have to be chosen depending on the analysis being done in gas chromatography. While the choice of stationary phase material is based on the solutes to be separated, the thickness is dependent on the concentration and the volatility of the components to be analyzed. This study undertakes a coupled column phase ratio optimization by connecting a short piece of a particular column prior to a normal length of an analytical column. Various columns of different dimensions (phase ratio), but of the same stationary phase material (methyl silicone), are coupled together by a deactivated glass press-fit connector, and the efficiency and capacity are measured. The coupling of fused silica open tubular columns is optimized in efficiency by matching or decreasing the phase ratio of successive columns. Capacity optimization is accomplished by increasing the phase ratio of consecutive columns. Capacity and efficiency optimization are opposing each other; therefore, if some efficiency can be sacrificed a substantial increase in capacity is possible.
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  • 69
    ISSN: 1612-1112
    Keywords: Supercritical fluid chromatography ; Gas chromatography ; High speed analysis ; Thermal desorption ; Two dimensional analysis
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    Topics: Chemistry and Pharmacology
    Notes: Summary A two-dimensional supercritical fluid-gas chromatography system was constructed and evaluated. A 50-μm i.d. capillary column coated with a 50 % cyanopropyl polysilixane stationary phase was used as the firstdimensional column. Group-type separations of polycyclic aromatic hydrocarbons, based on the number of aromatic rings, were achieved using this column under SFC conditions. A 25-μm i.d. liquid crystal column was used as the second-dimensional column under GC conditions. The effluent from the first column (SFC) was received continuously by the second column (GC) through a thermal desorption modulator. The thermal desorption modulator (prepared at the head of the second column) generated a series of concentration pulses from the first column effluent. These concentration pulses served as injections to the second column, and were developed into a corresponding series of high-speed chromatograms. Grouptype sample bands from the first column were separated into individual components on the second column. All sample substances passed through both columns to generate two sets of retention data, which could be used for more accurate compound identification.
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  • 70
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Capillary column sampling ; Additivity of variance in GC ; Aqueous samples ; PAHs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The possibility of using capillary columns for both sampling and gas chromatographic analysis of aqueous micropollutants has been studied. Factors influencing gas chromatographic band dispersion of the solute were investigated and a mathematical relationship developed correlating the properties (ID, df) of the capillary columns to the degree of dispersion of adsorbed substances has been derived. The experimental results obtained with aqueous samples are in good agreement with the theoretically forecast data. The method developed allows gas chromatographic dosing of traces of organic substances, reducing inconvenience deriving from excessive sample handling to a minimum. Non-refocusing of the analyte does not, in any significant way, compromise column efficiency for substances that are not very soluble in water.
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  • 71
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Headspace analysis ; Steam distillation ; Phenols
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    Topics: Chemistry and Pharmacology
    Notes: Summary High-temperature headspace analysis performed under static conditions above 100°C increases the sensitivity of gas chromatographic determination of volatile phenols in aqueous solutions 20–100 fold and reduces the detection threshold, to 10 μg×1−1. To improve the sensitivity and reduce the threshold still further, preliminary concentration by high-temperature microdistillation at elevated pressure is proposed. A theoretical model of this process has been developed. The possibility of concentrating volatiles by high-temperature microdistillation has been experimentally confirmed.
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  • 72
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    Chromatographia 36 (1993), S. 215-217 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Polar columns ; Vegetable oils ; Sterols ; Unsaponifiable matter
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    Topics: Chemistry and Pharmacology
    Notes: Summary The analysis of both the total unsaponifiable matter and the sterol fractions in vegetable oils has been performed with a new polar column (TAP, Chrompack). The use of a polar column, which is characterized by high thermal stability, has led to the identification of a greater number of constituents than the use of a nonpolar column (i.e. SE 52, SE 54). The polar column enhances the separation of the main classes of unsaponifiable matter (sterols, 4-methyl sterols and 4,4′-dimethyl sterols). When used for the unsaponifiable and sterol fraction analyses, it offers a powerful tool for characterizing the lipid source.
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  • 73
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Liquid chromatography ; Mass spectrometry ; β-agonists
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    Topics: Chemistry and Pharmacology
    Notes: Summary Different chromatography — mass spectrometry techniques for the analysis of β-agonists have been compared. Gas chromatography — mass spectrometry (electron impact) has been used, as also has liquid chromatography coupled to the mass spectrometer by either thermospray or electrospray interfaces. The results obtained by the three method were compared in terms of sensitivity, selectivity, and richness of information provided by the analysis. It was found that using electrospray ionization, very powerful analysis could be achieved with high sensitivity, thus providing significant potential for the analysis of β-agonists.
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  • 74
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Crown ether polysiloxane phases ; Capillary columns
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    Topics: Chemistry and Pharmacology
    Notes: Summary Two crown ethers, di(tert-butylbenzo)-propyl-15-crown-5 polysiloxane (PSO-DTB-15C5) and dibenzo-propyl-15-crown-5 polysiloxane (PSO-DB-15C5) have been synthesized and coated onto fused-silica capillary columns. The chromatographic characteristics, including column efficiency, polarity, phase transition temperature, operating temperature range and selectivity, were studied. Excellent selectivity was obtained for the separation of polar position isomers, especially phenol and dinitrotoluene isomers. The separation mechanism is discussed.
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  • 75
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Retention indices ; Adsorption effects ; n-Tetradecenes ; n-Tetradecynes
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    Topics: Chemistry and Pharmacology
    Notes: Summary The correction of the reproducibility of retention indices on polar capillary columns with different film thickness, using more polar reference standards instead ofn-alkanes, was investigated. It was found that the replacement ofn-alkanes by 1-alkenes, 3-alkynes and n-alkylbenzenes as standards significantly improves the reproducibility of retention indices and diminishes their temperature increments forn-alkanes,n-alkynes and arenes on PEG 20M columns.
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  • 76
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    Chromatographia 35 (1993), S. 539-542 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Liquid crystals ; Diffusion coefficients ; Xylenes
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    Topics: Chemistry and Pharmacology
    Notes: Summary The molecular diffusion coefficients of xylene isomers have been determined at different temperatures in the three phases (smectic, nematic and isotropic) of 4,4′-bis(heptyloxy)azoxybenzene (BHOAB) by gas chromatography. The results obtained are discussed in terms of molar volume, polarity and length-to-breadth ratio of several isomers. The activation energy of diffusion processes of solutes in the three phases of the liquid crystal has been calculated.
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  • 77
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    Chromatographia 36 (1993), S. 225-233 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Selective ionization detectors ; Organic fuelled flames ; Lead, tin, phosphorus, halogens
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    Topics: Chemistry and Pharmacology
    Notes: Summary The selectivities of two flame-based ionization detectors identified as a Remote FID (RFID) and a Flame Thermionic Ionization Detector (FTID) have been improved by introducing methane as a fuel for the flame. Both the RFID and FTID feature a detector struture in which the ionization polarizer and collector are located several centimeters downstream of an oxygen-rich flame, rather than immediately adjacent to the flame as in a flame ionization detector. The RFID detects long-lived negative ions produced in the flame by the combustion of lead, tin, phosphorus, or silicon compounds. The FTID re-ionizes and detects neutral electronegative products generated by combustion of nitrogen, halogen, or phosphorus compounds. An organic-fuelled RFID can detect 1 pg Pb (Sn, P)/sec with a selectivity of the order of 106 versus hydrocarbons. An organic fuelled FTID is applicable to detection of compounds at nanogram and higher levels. FTID selectivity for PCB compounds in a transformer oil matrix is of the order of 105∶1. The improved selectivity achieved by using an organic-fuelled flame is also applicable to the detection of phospholipid and other non-volatile N, P, or Cl compounds using an FID/FTID detector accessory for a TLC/FID analyser.
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  • 78
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    Chromatographia 37 (1993), S. 105-106 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Occupational hygiene analysis ; Epichlorohydrin in air ; Trace analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new method has been developed for the determination of trace amounts of epichlorohydrin in workplace atmospheres. Collection is peroormed in two bubblers in series both containing dichloromethane. Optimum conditions for sampling and analysis have been established. The lower limit of determination is 0.05 μg/mL with an RSD of ±5%.
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  • 79
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    Chromatographia 37 (1993), S. 277-280 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Hydrogenation of 1,5,9-cyclododecatriene ; Retention index
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The separation of the products obtained by the hydrogenation of 1,5,9-cyclododecatriene stereoisomers on fused-silica capillary columns coated with dimethylsilicone and cyanopropylmethylsilicone stationary phases was investigated. Retention indices of cyclododecatrienes, cyclododecadienes, cyclododecenes and cyclododecane were determined at three temperatures. The respective standard deviations were 0.3 and 0.6 i.u. The influence of the polarity of the stationary phases on the chromatographic retention of these cyclic hydrocarbones is discussed.
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  • 80
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    Chromatographia 37 (1993), S. 250-258 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Retention data ; Stationary phases ; Phase constants ; Linear free energy relationships
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    Topics: Chemistry and Pharmacology
    Notes: Summary Specific retention volumes and retention indices for selected compounds can be predicted from different sets of stationary phase constants by multiple regression. Errors in the corresponding calculated retention times are between 5 and 15%. Intercept (A) and slope (B) values are given for 72 McReynolds stationary phases. The A value can be predicted from the retention index of benzene with a standard deviation of 9%.
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  • 81
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    Chromatographia 37 (1993), S. 546-548 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Headspace sampling ; Methyl methacrylate monomer ; Contact lens
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    Topics: Chemistry and Pharmacology
    Notes: Summary A modified gas chromatographic method is described for the determination of free monomer in contact lenses, irrespective of the method of production. It thus becomes possible to assess very quickly the conformity of such lenses with hygiene regulations. This method allows direct supervision of production or determination of the quality of a product of unknown origin in only 15 min. Production tests of new polymerization initiators, reactors for polymerization, etc. can also be carried out.
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  • 82
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    Annals of biomedical engineering 21 (1993), S. 489-499 
    ISSN: 1573-9686
    Keywords: Work of breathing ; Inspiratory pressure-time integral ; Respiratory modeling ; Dogs ; Humans
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    Topics: Medicine , Technology
    Notes: Abstract We hypothesized that the viscoelastic properties of the respiratory system should have significant implications for the energetically optimal frequency of breathing, in view of the fact that these properties cause marked dependencies of overall system resistance and elastance on frequency. To test our hypothesis we simulated two models of canine and human respiratory system mechanics during sinusoidal breathing and calculated the inspiratory work ( $$\dot W$$ ) and pressure-time integral (PTI) per minute under both resting and exercise conditions. The two models were a two-compartment viscoelastic model and a single-compartment model. Requiring minute alveolar ventilation to be fixed, we found that both models predicted almost identical optimum breathing frequencies. The calculated PTI was very insensitive to increases in breathing frequency above the optimal frequencies, while $$\dot W$$ was found to increase slowly with frequency above its optimum. In contrast, both $$\dot W$$ and PTI increased sharply as frequency decreased below their respective optima. A sensitivity analysis showed that the model predictions were very insensitive to the elastance and resistance values chosen to characterize tissue viscoelasticity. We conclude that the $$\dot W$$ criterion for choosing the frequency of breathing is compatible with observations in nature, whereas the optimal frequency predictions of the PTI are rather too high. Both criteria allow for a fairly wide margin of choice in frequency above the optimum values without incurring excessive additional energy expenditure. Furthermore, contrary to our expectations, the viscoelastic properties of the respiratory system tissues do not pose a noticeable problem to the respiratory controller in terms of energy expenditure.
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  • 83
    ISSN: 1434-4475
    Keywords: Gas chromatography ; Polyphenyl ethers ; Lubricants, synthetic
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    Topics: Chemistry and Pharmacology
    Notes: Summary The described synthesis of synthetic lubricants based on polyphenyl ethers requires an analytical characterization of the isomerization step, which is important to the process optimization. The separation of the intermediates succeeds with gas chromatography; the isomers are determined using a retention index system. The obtained results are compared with the composition of the final product, which was investigated by HPLC analysis.
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  • 84
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    Journal of molecular evolution 35 (1992), S. 7-16 
    ISSN: 1432-1432
    Keywords: Alu source genes ; Humans ; Gorillas ; Retrotransposition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A member of the young PV Alu sub-family is detected in chimpanzee DNA showing that the PV subfamily is not specific to human DNA. This particular Alu is absent from the orthologous loci in both human and gorilla DNAs, indicating that PV subfamily members transposed within the chimpanzee lineage following the divergence of chimpanzee from both gorilla and human. These findings and previous reports describing the transpositional activity of other Alu sequences within the human, gorilla, and chimpanzee lineages provide phylogenetic evidence for the existence of multiple Alu source genes. Sequences surrounding this particular Alu resemble known transcriptional control elements associated with RNA polymerase III, suggesting a mechanism by which cis-acting elements might be acquired upon retrotransposition.
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  • 85
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    Journal of molecular evolution 34 (1992), S. 336-344 
    ISSN: 1432-1432
    Keywords: Humans ; Mitochondrial DNA ; Nuclear polymorphisms ; Heteroplasmy ; Genetic differentiation ; Sickle cell ; Rain forest refuges
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The identification of genetically coherent populations is essential for understanding human evolution. Among the culturally uniform ethnic groups of west Africa, there are two geographically distinct populations with high frequencies of sickle-cell hemoglobin (HbS). Although the HbS mutation in each group is found on distinguishable chromosomes 11, these populations have been assumed to be parts of a single population. Analysis of mitochondrial DNA (mtDNA) in these populations demonstrated that the two populations identified by alternative chromosomes 11 bearing HbS have distinct distributions of mitochondrial genotypes, i.e., they are maternally separate. These studies also showed that, contrary to expectation, the mtDNA of some individuals is heteroplasmic. For nuclear loci, a comparison of the frequency of alternative alleles established that these populations are genetically distinct. Both the mitochondrial and nuclear data indicate that these populations have been separate for approximately 50,000 years. Although HbS in the two populations is usually attributed to recent, independent mutations, the duration of the separation and the observed geographic distribution of the population allow for the possibility of an ancient origin of HbS. Assuming an ancient mutation and considering the known biogeography, we suggest that HbS protected selected populations from malaria in rain forest refuges during the most recent ice age.
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  • 86
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Activity coefficients ; 18-Crown-6-ether and tetraethyleneglycol dimethyl ether ; Thermodynamic properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The thermodynamic properties of different solutes at infinite dilution have been determined at 323.15 K. Deviations from ideality are discussed in terms of different contributions. The activity coefficients are compared with the calculated values by the one group contribution method.
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  • 87
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    Chromatographia 33 (1992), S. 103-112 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Gas chromatography ; Chiral separations ; Allethrin ; Cypermethrin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Liquid and gas chromatographic separations of the pyrethroid insecticides allethrin and cypermethrin have been investigated with various achiral and chiral stationary phases. Diastercomeric and enantiomeric selectivity was observed for cypermethrin on a Pirkle-type chiral LC stationary phase, but very strong interactions and therefore long retention times prevented the separation of allethrin on this phase. Trans-allethrin isomers were separated on a chiral β-cyclodextrin RP-HPLC column while cypermethrin showed some difficulties on this phase due to isomerization. Diastereomeric but no enantiomeric selectivity by GC was achieved for cypermethrin with an apolar DB 5 capillary. GC separation of the diastereomers was used to study the selective photodegradation of cypermethrin isomers after forestry applications. Chiral β-cyclodextrin-based GC phases showed some enantioselectivity for cis- and trans-allethrin isomers. A separation of the eight isomers into six partially resolved peaks was achieved by GC with a coupled column consisting of chiral permethylated β-cyclodextrin and DB 1701 as stationary phases. This combination was used to characterize allethrin formulations intended for indoor use and to investigate allethrin products formed by ozonolysis of thin films of the insecticide.
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  • 88
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Free fatty acids ; Cheese ; Programmed temperature vaporizer
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    Topics: Chemistry and Pharmacology
    Notes: Summary A gas chromatographic method with a capillary column and a programmed temperature vaporizer injector has been used to analyze the individual free fatty acids in cheese. The lipids were extracted from an acidified cheese slurry with diethyl ether and treated with tetramethylamonium hydroxide (TMAH) to convert the free fatty acids to tetramethylammonium soaps (TMA-soaps), which were subsequently pyrolyzed to methyl esters in the injector. Carrying out injection at the initial column temperature resulted in lower dispersion of the results, but the solvent front prevented quantitative determination of butyric and caproic acids, and an injector temperature of 300°C was therefore employed. Under the conditions tested, trimethylamine (tma) flash-off did not affect the determinations. The accuracy of the method improved at higher free fatty acid contents (coefficient of variation of 0.53% for a total free fatty acid content of 9000 mg/kg as opposed to 7.0% for a total free fatty acid content of 1400 mg/kg). The recovery rate for individual free fatty acids ranged between 91 and 103%.
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  • 89
    ISSN: 1612-1112
    Keywords: Gas chromatography ; coupling capillary columns ; Selectivity optimization ; Dual oven tuning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A computer-assisted procedure is presented for optimization of selectivity of tandem capillary columns with the same apolar (SE-54) stationary phase by varying column temperatures. The procedure is based on a threshold criterion calculated from the required resolution factor in which the separating power of the columns as a function of temperature is incorporated. The validity of the procedure has been verified by the analysis of a sample containing 33 hydrocarbons on two 31 m×0.3 mm i.d. SE-54 capillary columns coupled in series and by varying the temperatures of both columns in the range 60–100°C. At the optimum temperatures (70°C for the first and 92°C for the second column) 26 compounds were resolved equal to or better than Rji=1.00 in 22.8 min.
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  • 90
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Carbon adsorbents ; Methyliodide ; Effect of KI on adsorption ; Thermodynamics of adsorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Gas chromatography has been used to measure the adsorption at zero surface coverage of methyl iodide on different types of carbon. The effect on the adsorption of methyl iodide of adding potassium iodide to the carbon samples was also studied. The differences observed in the behaviour of these samples for the adsorption of methyl iodide are explained on the basis of the textural characteristics of the samples. Thermodynamic functions of adsorption of methyl iodide at zero surface coverage are obtained.
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  • 91
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Partition coefficients ; Olive oil-nitrogen partition ; QSAR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A gas-liquid chromatographic method has been used for direct determination of the partition coefficients (KD) of alcohols, ethers and ketones between olive oil and nitrogen. Olive oil was characterised as a stationary phase for gas chromatography. The differential molar enthalpies of solution were also calculated from retention data. Correlations between log KD for olive oil — nitrogen and molecular connectivity indices, differential molar enthalpies of solution, biological activity and partition coefficients for blood-air were obtained.
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  • 92
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    Chromatographia 34 (1992), S. 621-626 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Methyl and ethyl chloroformate ; Derivatization in the presence of water ; Alkyl and alkoxycarbonyl esters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Phenolic acids, i.e. benzoic, phenylacetic, phenylpropenoic (cinnamic), phenylglycolic (mandelic), phenylpropionic and their variously substituted forms can be converted almost instantly to derivatives amenable to GC by treatment with methyl or ethyl chloroformate. The reaction, catalyzed by pyridine, proceeds even in the presence of water. The carboxylic group is esterified to the corresponding alkyl ester but even the alkoxycarbonyl ester (mixed anhydride) can be produced by altering the reaction conditions. Hydroxyl groups on the benzene ring or adjacent to the carboxylic group are converted to the alkoxycarbonyl ethers. Benzoic acid and some of its substitutents, unlike the other aromatic acids, shows a tendency to mixed anhydride formation even under conditions used for alkyl esters. A well deactivated capillary column with a thin film of stationary phase of low polarity enables even the mixed anhydrides to be analyzed successfully.
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  • 93
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    Chromatographia 34 (1992), S. 163-165 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Cyclodextrins ; Crown ethers ; Dimethylnaphthalene isomer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The twelve structural C2 isomers of naphthalene are resolved on a single capillary column using α, β, or γ cyclodextrin as the stationary phase. A change in elution order is seen upon going from α to β and then γ cyclodextrin which can be related to the size of the cyclodextrin cavity and the stereochemical fit of the isomer. A crown-ether column and a liquid-crystal column were found to be unable to separate all of the isomers.
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  • 94
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Headspace sampling ; Partition coefficients ; Multiple headspace extraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Equilibrium headspace gas chromatography has been applied to the determination of the partition coefficients of volatile compounds in water-air systems. Only techniques that are suited to a fully automatic headspace procedure using the pneumatic headspace sampling-technique have been considered. Particularly simple is the technique of “vapor phase calibration —VPC” where an external vapor standard is used to calibrate the concentration of the volatile analyte in the headspace, while the concentration in the sample is found from the difference in the total amount in the vial. This technique is described in detail for 2-butanone in water. Finally, the water-air partition coefficients of several selected volatile compounds at different temperatures are listed together with their temperature functions.
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  • 95
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    Chromatographia 34 (1992), S. 241-248 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Natural insecticides ; Marigolds ; Isolation of volatiles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The results of optimizing Soxhlet and Simultaneous Distillation-Extraction (SSDE) procedures for the isolation of natural insecticides fromTagetes erecta, Tagetes patula, andTagetes minuta, members of theCompositae family, are presented. Extraction procedures were developed and validated that produced the extract with the highest degree of biocidal activity. The highest activity was obtained with extracts isolated by SSDE using methylene chloride. Initial work was carried out on a micro-SSDE. Preparative SSDE was used to provide large quantities of extracts for bioassays. Bioassays were used to govern optimization procedures usingAedes aegypti andAnopheles stephensi adults and larvae as target organisms.Tagetes minuta was determined to be the most active of the three species studied. Evaluation of activity and recovery versus extraction time was investigated. It was determined that an extraction time of ten hours resulted in the highest activity and over 90% recovery of the oils. Finally, supercritical fluid extraction of the flowers with CO2 was compared to SSDE.
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  • 96
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Sociation constants ; Hydrogen bonding solutes ; Nearly ideal binary solvent theory ; Isosteric solvents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Gas chromatographic data measured on mixtures of 19,24-dioctadecyldotetracontane, A≡C78, and 18,23-dioctadecyl-1-hentetracontanol, POH, allow the determination of the standard chemical potential of a solute on an ideal stationary phase with primary alcohol groups at ideal dilution. The Nearly Ideal Binary Solvent Theory provides the link between these data and the sociation constant of the solute with the primary alcohol. The method was applied to calculate sociation constants of a series of hydrogen bonding solutes. Results are compared with those determined by spectroscopy and calorimetry.
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  • 97
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    Chromatographia 34 (1992), S. 398-410 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Reversed-flow technique ; Catalysis ; Hydrodenitrogenation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Many important parameters of surface catalysed reactions can be determined simultaneously, under nonsteady state conditions using Reversed-Flow Gas Chromatography. A simple, slightly modified gas chromatograph is required. The distorted diffusion bands, obtained experimentally for reactant and product(s), can be analysed mathematically, using simple PC programs, to give the pre-exponential factors and the exponential coefficients of a function consisting of the sum of two-four exponential functions of time. From these, and some geometrical and diffusional characteristics of the reaction cell, the values of adsorption, desorption and reaction rate constants, the overall mass transfer coefficients in the gas and in the solid catalyst, and the adsorption equilibrium constant, for both reactant and product(s) can be calculated. The above parameters were determined at various temperatures and over three catalysts for the hydrodenitrogenation of piperidine ton-pentane, an industrially important hydrotreating process. The results obtained can help to understand the mechanism of reactions on solid surfaces and to confirm experimentally theoretical calculations on adsorption and surface reactions.
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  • 98
    ISSN: 1612-1112
    Keywords: Gas chromatography ; High-pressure Soxhlet extraction ; Organochlorine residue analysis ; Supercritical fluid extraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The operational conditions of a high-pressure Soxhlet extractor (pressure, temperature, time and amount of sample) have been optimized, using carbon dioxide as extractant for the determination of organochlorine pesticides and polychlorinated biphenyls (PCBs) in certified potato, carrot, olive oil and lyophilized fish tissue samples. Good recoveries were obtained.
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  • 99
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    Chromatographia 34 (1992), S. 475-478 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Telomeric fluoroalkanols ; Retention index ; Regression equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The separation of fluoroalkanols with the general formula H(CF2CF2)nCH2OH (n=1–8) on fused-silica capillary columns coated with dimethylsilicone and cyanopropylmethylsilicone stationary phases was investigated. Retention indices were determined at three temperatures. A correlation between the retention index values, the molecular weights and the number of C and F atoms in the solute molecules was found.
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  • 100
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    Chromatographia 34 (1992), S. 461-467 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Allyl thiocyanate and isothiocyanate ; Plant extract ; Analytical artifacts ; Isomerization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Allyl thiocyanate and isothiocyanate were synthesized and could be analysed by gas chromatography without isomerization by keeping the injector at, or below, 50°C. Synthetic allyl isothiocyanate contained none of the isomeric thiocyanate but allyl thiocyanate contained 0.5% of isothiocyanate. The NMR spectra indicated both compounds to be free of the corresponding isomer. Analysis of extracts of stinkweed, mustard and horseradish by GC using non-isomerizing conditions showed that only the stinkweed extract contained allyl thiocyanate. Mustard and horseradish extracts contained allyl, and other, isothiocyanates but no allyl thiocyanate. Allyl thiocyanate previously reported in extracts of mustard and horseradish was most likely an artifact caused by partial isomerization of allyl isothiocyanate under the conditions of isolation and/or analysis.
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