Methyl groups, analytical determination

Laszlo A. Heredy There is NMR spectroscopic evidence for the presence of both a- and /3-CHa groups in coal, based on depolymerization work with phenol-BF.3 reagent. For example, isopropyl groups were shown to be present in a high volatile bituminous coal. Is there a distinct difference in the behavior of these two types of CHs groups with respect to the reagent used in wet analytical methyl group determination ... 

Various modern products may serve as sources for trace amounts of PAA. The origins, known hazards, release restrictions and environmental fate of PAA derived from azo dyes have been reviewed2. The metabolism of nitroarenes is closely linked to that of aromatic amines, as shown in a simplified way in equation 369. Gloeophyllum trabeum cultures spiked with TNT show formation of nitroaromatic amines such as 2-ami no-4,6-dinitrotoluene, 4-amino-2,6-dinitrotoluene and 2,4-diamino-6-nitrotoluene. Also, autoxi-dation of the methyl group of TNT or its metabolites may take part in the degradation process, as shown by the presence of Schiff bases and oligomeric and polymeric species detection and determination of the analytes after LLE and concentration were by HPLC-UVD or GC-MS70. 

This review will describe the analytical methods available to determine the structural components of pectin. These features determine the important physical, chemical, and biological properties of pectin. Included will be discussion of galacturonic acid determinations, degree of esterification with methyl groups, the neutral-sugar composition, and analysis of some less-common entities, such as 0-acetyl and 0-feruloyl linkages. 

The 14C label provides a sensitive analytical method for determining the extent of reaction and detecting subtle differences in the response of coal, and the sites of methylation can be established from the solid-state 13C NMR spectra of the 13C-enriched coal derivatives. To further characterize the types of reactive sites, the methylated coals were subjected to base hydrolysis with n-Bu4NOH in aqueous THF (12). The number of base-labile methyl groups was taken as a measure of the maximum number of methyl esters formed during the alkylation. The results from this study are presented in Table I. 

The central analytical problem is to determine the chirality of methyl groups generated or modified in biochemical reactions. The solution is dazzlingly ingenious. First, samples of chiral acetic acid [as 1.26)] of known absolute configuration were synthesized. All molecules of acetic acid contained deuterium (and hydrogen) but, as is customary, only very few molecules were also labelled with tritium. Only very few molecules were therefore chiral. Since the analysis is for tritium, however, this does not matter. [Subsequently an economical and supremely elegant synthesis of chiral acetic acid has been developed (Scheme 1.8), which involves two stereospecific... 

Erythromycin, a macrolide antibiotic, lacks a significant chromophore. Detection sensitivity was enhanced by using a wavelength of 200 nm and selecting an injection solvent of lower conductivity than the BGE. In order to facilitate the separation of erythromycin and its related substances, 35% (v/v) ethanol was incorporated into a 150 mM phosphate buffer pH 7.5. Resolution of all of the compounds was achieved in approximately 45 min. The method was employed as an assay method for erythromycin and for impurity determination. Peptide antibiotics, such as colistin and polymyxin, are mixtures of many closely related compounds. A validated CZE method for impurity analysis of polymyxin B was described, employing 130 mM triethanolamine-phosphate buffer at pH 2.5 to reduce the adsorption of analyte onto the capillary wall. Methyl-/l-cyclodextrin (M-/1-CD) and 2-propanol were found to be necessary for selectivity enhancement. Using similar buffer additives, the same group developed and validated a method for colistin analysis. ... 

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