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  • Humans  (543)
  • Analytical Chemistry and Spectroscopy
  • Chemical Engineering
  • 1995-1999  (675)
  • 1999  (675)
  • 1
    Electronic Resource
    Electronic Resource
    Composition and Microstructure Determination of the Syndiotactic Copolymer of para-Methylstyrene and Styrene by Pyrolysis Gas Chromatography (1999)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 11-16 
    Details
    ISSN: 0935-6304
    Keywords: Pyrolysis gas chromatography ; microstructure determination ; syndiotactic copolymers ; styrenes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The composition and microstructure of syndiotactic para-methylstyrene/styrene copolymer was determined by a pyrolysis gas chromatography (Py-GC) method. This method uses the styrene and para-methylstyrene monomer peak intensities to determine the styrene and para-methylstyrene composition in the copolymer. The number average sequence length of styrene was calculated by using the triad peak intensities. Because of the low concentration of para-methylstyrene in the copolymer, the number average sequence length of para-methylstyrene was determined with formulas that incorporate the copolymer composition and the number average sequence length of styrene. The distribution of para-methylstyrene defined by the terms “percent of single units” and “percent of desired distribution” was calculated by the number average sequence of para-methylstyrene. This method has been tested with copolymers containing up to 24 mole% of para-methylstyrene. The composition results from Py-GC of para-methylstyrene and styrene copolymers used in this study were in excellent agreement with 1H-NMR results.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Superior ECD Performance through Design and Application (1999)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 24-28 
    Details
    ISSN: 0935-6304
    Keywords: Gas chromatography ; ECD ; Micro-ECD ; GC detector ; organochlorine pesticides ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A new ECD, the HP 6890 Series Micro-ECD, was designed to address inherent deficiencies in classical electron capture detectors (ECD), especially with respect to sensitivity, linearity, dynamic range, and ruggedness. Several novel technologies were incorporated in the totally new design and were refined through practical testing and user feedback. Validation of the micro-ECD performance was accomplished through side-by-side testing of the Micro-ECD with previous ECDs following US EPA Contract Laboratory Program methods for pesticides and PCBs. In addition, extensive interviews were conducted with early users of the Micro-ECD who also had experience with other designs running a variety of ECD methods. The design and resulting performance improvements are described.
    Additional Material: 6 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Experimentation with Chiral CE: The Application of Two Chiral Selectors and Partial Filling with Chiral Selector (1999)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 33-38 
    Details
    ISSN: 0935-6304
    Keywords: Capillary electrophoresis ; chiral separation ; negatively charged chiral selectors ; capillary filling methods ; dual systems ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Data on the use of two chiral selectors, namely 18-crown-6 tetracarboxylic acid and a negatively charged cyclodextrin derivative (sulfated-β-cyclodextrin or carboxymethyl-β-cyclodextrin), in the same background electrolyte are presented. The use of such dual systems has a considerable influence on the resolution, as illustrated for the separation of tryptophan derivatives. Reduction of the consumption of chiral selector without significant loss in resolution was obtained by only partly filling the capillary and applying a run buffer without selector. This is illustrated for the chiral separation of tryptophan hydroxamate and the diastereomeric and enantiomeric separation of the dipeptide α/b-AspPhe-OMe.
    Additional Material: 5 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Determination of Free Diterpenes in Green and Roasted Coffees (1999)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 43-46 
    Details
    ISSN: 0935-6304
    Keywords: Green and roasted coffee ; diterpenes ; cafestol ; kahweol ; 16-O-methylcafestol ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The three coffee diterpenes cafestol, kahweol, and 16-O-methylcafestol are mostly esterified with fatty acids. Little has been published about the diterpenes occurring in the free form. By means of gel permeation chromatography on Bio Beads S-X3, it is now possible to simultaneously analyze and quantify the small amounts of these compounds by RP-HPLC. In this way, free kahweol was first proved to be an ingredient of Robusta coffee. Various Arabica and Robusta coffees - both green and roasted - were investigated. Free diterpenes were found in green coffees in amounts below 200 mg/kg dry matter. In comparison to the respective total diterpene content determined by the same HPLC method after saponification of the coffee oil, the proportion of free diterpenes ranged from 0.7 to 3.5 %. During the roasting process, the three uncombined diterpenes behaved similarly: free 16-O-methylcafestol, cafestol as well as kahweol were degraded with increasing roasting temperature.
    Additional Material: 6 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Optimization through Factorial Planning of the Use of Ethanol : Water as a Mobile Phase for Reversed Phase HPLC (1999)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 52-54 
    Details
    ISSN: 0935-6304
    Keywords: Ethanol ; mobile phase ; factorial planning ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Levels of Organotin Compounds in Burbot (Lota Lota) from Norwegian Lakes (1999)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 177-180 
    Details
    ISSN: 0935-6304
    Keywords: Fresh water systems ; burbot ; organotin compounds ; speciation analysis ; GC-AED ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---No abstract
    Additional Material: 2 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    RP-HPLC and GC-MS Techniques for the Quantitative Analysis of Substituted 1,2,4-Trioxanes and their Thermolysis Products in Solution (1999)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 67-69 
    Details
    ISSN: 0935-6304
    Keywords: RP-HPLC ; GC-MS ; trioxanes ; thermolysis products ; quantitative analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    A Robust Thermal Modulator for Comprehensive Two-Dimensional Gas Chromatography (1999)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 3-10 
    Details
    ISSN: 0935-6304
    Keywords: Multidimensional Gas Chromatography ; orthogonal separations ; GC×GC ; comprehensive two-dimensional chromatography ; characterization of gasoline ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---In comprehensive two-dimensional gas chromatography (GC×GC), two capillary columns are connected in series through an interface known as a “thermal modulator”. This device transforms effluent from the first capillary column into a series of sharp injection-like chemical pulses suitable for high-speed chromatography on the second column. Dramatic increases in the resolving power, sensitivity, and speed of the gas chromatograph result. This paper describes the development of a robust and reliable thermal modulator for GC×GC.
    Additional Material: 5 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of Mobile Phase Components on the Separation of Polypeptides Using Carbon Dioxide-Based Mobile Phases (1999)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 74-78 
    Details
    ISSN: 0935-6304
    Keywords: Polypeptides ; subcritical fluid chromatography ; supercritical fluid chromatography ; carbon dioxide ; additives ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The effect of mobile phase modifier and additive on the chromatographic properties of various small polypeptides was explored under subcritical conditions. A polymeric column was used to separate various enkephalin analogs, bradykinin, and oxytocin using a carbon dioxide-based mobile phase with either an ethanol or a 2-methoxyethanol modifier. The role of the modifier was found to be secondary to that of the mobile phase additive. As progressively stronger acidic mobile phase additives were used, the peak profiles of the various polypeptides improved and retention decreased. Heptadecafluorooctanesulfonic acid was found to be the most useful additive for these types of solutes under near-critical conditions, while the potassium salt of heptadecafluorooctanesulfonic acid failed to elute any of the polypeptides. At low temperatures, pressure gradients with a carbon dioxide/ethanol/heptadecafluorooctanesulfonic acid ternary mobile phase produced reasonably good peak profiles with the polymeric column.
    Additional Material: 7 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    γ(δ)-Thionolactones - Enantioselective Capillary GC and Sensory Characteristics of Enantiomers (1999)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 89-92 
    Details
    ISSN: 0935-6304
    Keywords: Enantioselective gas chromatography ; heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin ; heptakis(2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin ; γ(δ)-thionolactones ; olfactometry ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The even numbered γ(δ)-thionolactones (C6-C12) were investigated, using heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)- and heptakis(2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin as chiral stationary phases in capillary gas chromatography. The odor characteristics of γ(δ)-thionolactone enantiomers were investigated by enantioselective gas chromatography/olfactometry.
    Additional Material: 4 Ill.
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