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Speciation of selenoamino acids and selenium compounds by GC-AED and HPLC-ICP-MS
The increasing demands for speciation in nutrition, clinical chemistry and toxicology have made the sole determination of the total element in a sample unsatisfactory. It is important to determine the chemical form (species) of the element; most often its oxidation state or its organometallic or complexed nature, since different species of the same element can range from harmless to essential to toxic. In order to address this challenge, a separation technique (gas chromatography, GC) that usually focuses on qualitative analysis was effectively interfaced with an element specific detection technique, atomic emission spectrometry (AED). Likewise liquid chromatography (HPLC) was interfaced to inductively coupled plasma mass spectrometry (ICP-MS) for the characterization of selenium compounds. ^ The consumption of selenium nutritional supplements has been reported to provide anticarcinogenic benefits that are selenium compound dependent. The separation and identification of these selenium species is important in order to understand their activity and metabolism. In this study, methods were developed for the characterization of selenium species in selenized yeast, breath and urine samples. Enzymatic digestion of selenized-yeast samples followed by ethylchloroformate derivatization was used to dissolve amino acids and convert them to volatile compounds suitable for subsequent GC analysis. Volatile selenium species exhaled in breath were trapped on Tenax, then revolatilized by heating and sampled by solid phase microextraction. Gas chromatography with atomic emission detection (GC-AED) or gas chromatography with mass spectrometry (GC-MS) was employed for their detection. Selenium species in urine were characterized by ion-pair chromatography with ICP-MS detection. ^ The monitoring of chromatographic eluents with element specific atomic spectroscopy detectors enabled the determination of selenium species in the enzymatic digests of selenized yeast, breath and urine samples. The analysis of archived selenized yeast samples by GC-AED and GC-MS revealed the presence of a previously unknown aminoacid, S-(methylseleno)cysteine. Low molecular weight organoselenium and mixed organosulfur-organoselenium compounds were identified by GC-AED in exhaled human breath samples from volunteers taking selenium nutritional supplements. Trimethylselenonium ion was identified in the urine of these volunteers by HPLC-ICP-MS. ^
"Speciation of selenoamino acids and selenium compounds by GC-AED and HPLC-ICP-MS"
(January 1, 2004).
Electronic Doctoral Dissertations for UMass Amherst.