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  • 1
    ISSN: 0935-6304
    Keywords: Liquid chromatography ; Supercritical fluid Chromatography ; Light scattering detection ; Pharmaceutical analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The evaporative light scattering detector (ELSD) has been used in pharmaceutical analysis by liquid and supercritical fluid chromatography. An ELSD equipped with interchangeable interfaces enables the use of various eluents (UV- or non-UV-absorbing) in isocratic or gradient mode. Analyses were performed on several non-UV-absorbing excipients and active substances. The narrow spread of the response factors of the various compounds investigated has indicated that the detector is suitable for direct raw quantitation of unknown samples in stability studies.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0935-6304
    Keywords: Liquid chromatography ; Beet ; Carbohydrates ; Light scattering detection ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An evaluation of the most commonly used HPLC system (reversed phase octadecyl sillica gel) was undertaken in order to determine the level of certain carbohydrates in molasses produced in the refining of sugar beet. Chromatographic parameters and purification operations prior to analysis are discussed in order to develop an analytical method permitting automation of sugar determination. A Zorbax ODS column (250 × 9.4 mm), water elution, and light scattering detection allow easy determination of glucose + fructose, sucrose, and raffinose in molasses using an internal standard (maltose).
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0935-6304
    Keywords: Liquid chromatography ; Carbohydrates ; Light scattering detector ; Automatic analysis ; Prepurification ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sugar analysis in the beet industry presents some difficulties due to the highly complex composition of the raw products. This is particularly important in molasses, which contains a considerable ionic component. However, precise determination of raffinose concentration is necessary to optimize the crystallization process. Purification of raw products on mixed-bed ion exchangers followed by passage through a ODS precolumn is performed before the actual chromatographic step. These steps must be automated in order to improve precision and productivity. A completely automatic system, designed for maximum stability of chromatographic columns and good analytical precision of results is presented.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0935-6304
    Keywords: HPLC ; Glucosinolate analysis ; Desulfated glucosinolates ; Synthetic glucosinolates ; Rapeseed ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The separation of new, artificial, non-sulfated glucosinolates and desulfated natural glucosinolates on different apolar (C8, TMS, phenyl) or weakly polar (CN) bonded stationary phases by gradient elution has shown that apolar or weakly polar bonded silica-based adsorbents, in addition to the C8 phase chosen for the standard procedure, can be used with benefit for the analysis of glucosinolate mixtures.The use of new artificial glucosinolates, not present in cruciferae, as internal standards for the standard HPLC method for the determination of the main glucosinolate composition and content of rapeseed is discussed.The main factors influencing the retention and selectivity toward several natural and artificial non-sulfated glucosinolates for different chromatographic systems have been studied, and for additional information the retention data have been analyzed statistically by factor analysis.The first results from this study show that the mechanism of the HPLC retention of glucosinolates is the sum of only two methematically independent physico-chemical phenomena. The first is associated with the hydrophobicity of compounds.A better understanding of the chromatographic behavior of glucosinolates has made it possible to investigate the synthesis of new, artificial standard glucosinolates with the intention of providing an ideal standard for every kind of analysis. It also supplies a tool to enable laboratories to choose the best chromatographic system for a particular selectivity problem.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The side-chain conformations of D- orL- Thr, D- or L-Ser, L-Asp, and L- His residues in cyclic and linear dipeptides in D2O or in DMSO-d6 are deduced from vicinal (1H,1H) and (13C, 1H) coupling constants. Vicinal (13C, 13C) coupling constants strongly depend on substituents and cannot be used without a more sound analysis. In cyclic dipeptides, the Thr and Ser side chains are folded above the DKP ring, with χ1 near 60°. The L-Asp side chain interacts more specifically with peptide bonds (χ1 near 300°). The L- His side chain is more flexible and its conformation depends on the proximity of a second side chain and on solute-solvent interactions. In all cases, this side chain is not completely folded. In linear dipeptides, the conformation of a C-terminal L-His residue is mainly influenced by the end carboxylic group. On the other hand, a N-terminal L-His residue interacts more easily with a neighboring L-Asp residue. In aqueous solution, the imidazole pKa depends on the proximity of terminal and lateral charged groups but does not reveal any specific interaction in cyclic dipeptides. A comparison between the conformations of cyclic peptides observed in solution, in the crystalline state and calculated by empirical methods, allows one to point out the discriminating role of the packing in crystals, and of solute-solvent interactions in solution.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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