Search

A new sensitive method for the determination of lipoic acid (LA) in selected food items based on its reaction with Mukaiyama reagent (2-chloro-1-methylpyridinium iodide, CMPI) was developed. It was stated that CMPI reacts with reduced form of lipoic acid (dihydrolipoic acid, DHLA) and the stable product is produced. The spectrum of the labeled form of DHLA exhibits new band at 312 nm. Based on its spectral characteristics new spectrophotometric and UV–high-performance liquid chromatography (HPLC) methods of LA determination were elaborated. Both methods allowed determination of the analyte in the concentration range of 5 × 10−6–1 × 10−4 mol L−1with limit of detection 0.39 × 10−6and 0.77 × 10−6 mol L−1for spectrophotometric and HPLC method, respectively. The practical usability of newly developed methods was checked by determination of lipoic acid contents in its pharmaceutical preparateRevitanerw. The proposed method was precise and accurate. The relative error of determination did not exceed ±0.067%. As chromatographic method allowed the determination of analyte in the presence of complex matrix, it was applied for assay of free fraction ofα-lipoic acid in selected food items. A procedure of LA isolation from biological matrix was developed. The extraction with dichloromethane allowed quantitative recovery at 102.94 ± 4.20%. The green barley appeared to be the richest source of LA. [ABSTRACT FROM PUBLISHER]

Abstract: The usefulness of the potassium tert-butoxide/dimethyl sulphoxide/ethyl iodide reaction with carbamate and phenylurea herbicides, and its application to phenoxy acids as a way to prevent hazards and toxicity of the sodium hydride/dimethyl sulphoxide/methyl iodide reaction was studied. Using factorial design optimization of this reaction was carried out. A solid-phase extraction method using dimethyl sulphoxide as eluent on-line with this reaction was developed to determine these herbicides in water samples by gas chromatography–mass spectrometry. Relative standard deviation values were lower than 10% for most of the herbicides in multicomponent trace determinations. Detection limits were in the 0.110–0.652ngL−1 concentration range. The validity of the method was confirmed by recovery studies from natural water samples. [Copyright &y& Elsevier]

• The esterification reaction of α-lipoic acid with 4-methoxybenzyl alcohol was studied. • The analytical usefulness of obtained ester was evaluated. • The GC–MS procedure was applied for determination of α-lipoic acid amount in real samples. The presented work is aimed to synthesize a new UV active derivative of α-lipoic acid (ALA) by its esterification with 4-methoxybenzyl alcohol (4-MBA, anise alcohol). The formation of ester was confirmed by 1HNMR, FTIR and UV spectroscopy. The analytical usefulness of the obtained compound for quantification of ALA in food items was examined using HPLC-UV and GC–MS systems. It was found that it is possible to assay ALA in the ester form in the concentration ranges: 5·10−6–1·10−4 mol L−1 by HPLC-UV and 1∙10−7–5∙10−5 mol L−1 by GC–MS techniques. The GC–MS procedure was applied for the determination of ALA in the food samples. [ABSTRACT FROM AUTHOR]