Interference reduction by L-cystine in the determination of arsenic by hydride generation

Interference in the production of arsine from As(III) and As(V) by a number of transition elements has been eliminated by the use of a 3% solution of L-cystine in 5M hydrochloric acid. With this modification, arsenic can readily be determined at low levels in the presence of up to 10 000 mu g ml exp --1 of Co(II), Cu(II), Fe(II) and -(III), and Ni(II). At this level, the signal was reduced by < 10%. Interference from Ag(I), Hg(II), and Pt(IV) is eliminated at levels up to 1000 mu g ml exp --1 . Severe interferences from Au(III) and Pd(II) could not be eliminated above 10 mu g ml exp --1 for Au(III) and 1 mu g ml exp --1 for Pd(II). In the case of Hg(II), a strong memory effect, in addition to the interference effect, was eliminated by the use of L-cystine. Determinations of low levels of As in standard reference iron and steel by the standard addition method gave excellent results. The results also showed that standard addition need only be used for the most precise work. 25 ref.--AA