Thermally stabilized iridium on an integrated, carbide-coated platform as a permanent modifier for hydride-forming elements in electrothermal atomic absorption spectrometry. Part 3. Effect of L-cysteine

Abstract

The effect of L-cysteine (0.2–2% m/v), sodium tetrahydroborate (0.05–0.4% m/v) and hydrochloric acid concentrations (0.01–0.15 mol l^–1) in an automated flow injection hydride generation system with in situ collection of hydrides of Sb, As, monomethylarsonate (MMA), dimethylarsinate (DMA), Bi and Sn in an electrothermal atomizer with an integrated platform pre-treated with 110 µg of Zr and 2 µg of Ir for permanent modification was studied. The hydride generation step was optimized by means of a full factorial design of the 3³ type, and the corresponding regression equations, response surfaces and contour plots were derived and are discussed with a view to the improved chemical yields and possible unified conditions for the simultaneous hydride generation/trapping of the three As species or all six analytes. The best characteristic masses for integrated absorbance measurements are 83, 35, 31, 32, 110 and 104 pg for Sb, As, MMA, DMA, Bi and Sn, respectively. The importance of the molar supply rates of the reagents (in µmol s^–1) and their ratios, rather than reagent concentrations, as well as the critical role of sample acidity, are emphasized.