Abstract

A radiofrequency glow discharge (rf-GD) has been used as an ion source for mass spectrometry using gas chromatography as the sample introduction technique for the speciation of seleno amino acids. The use of helium as the plasma gas allowed the monitoring of selenium's major isotope (⁸⁰Se), interfered by polyatomic species when using Ar as the plasma gas. Optimization of the power and pressure of the source was undertaken to achieve the best sensitivity for selenium determination and detection limits of about 100 pg (as Se) have been obtained for the derivatized Se-methionine. Studying the cell pressure and power on the fragmentation patterns obtained for Se-methionine and Se-ethionine has also been undertaken to characterize the source. No significant variations were observed on the mass spectra under different operating conditions, although noticeable variation of the fragment intensities was observed. The system has been applied to the determination of Se-methionine in selenium-enriched yeast after enzymatic extraction of the corresponding species using Proteinase K to cleave the peptide bonds. The results obtained showed a Se-methionine content of about 78% in the enriched yeast.