INVESTIGATIONS FOR THE DETERMINATION OF TIN BY FLOW-INJECTION HYDRIDE GENERATION ATOMIC-ABSORPTION SPECTROMETRY

It could be shown that the pre- or double peaks which are frequently observed in the determination of tin by hydride generation atomic-absorption spectrometry are not due to reagent contamination or memory effects. Rather they originate from the silica material used to make the quartz tube atomizer. At elevated temperatures the tin diffuses to the surface and it can be volatilized and atomized only in the presence of hydrogen. The height of the pre-peak depends, among other things, on the time for which the quartz tube atomizer has been at a high temperature without hydrogen. The pre-peaks disappear when argon with 10% (v/v) hydrogen is used as the purge gas. In flow injection the pre-peaks can be separated in time from the analytical signal by using a program in which hydrogen is generated by reaction of sodium tetrahydroborate reductant solution with the acid carrier prior to the injection of the sample. Also investigated was the influence of the acid and sodium tetrahydroborate concentration on sensitivity and freedom from interferences. Best results were obtained when a saturated boric acid solution containing 0.1 M hydrochloric acid was used for standards, samples and carrier solution, and a 0.4% (m/v) sodium tetrahydroborate solution with 0.05% (m/v) sodium hydroxide as the reductant. Under these conditions tin could be determined accurately in the range 0.008-0.1% in low alloy steel standard reference materials, with matrix-free standard solutions for calibration.