Methods for Rapid Multi-element Analysis in the Field and Their Applications IV. Determination of Arsenic and Cadmium

In this paper, two micro-bead colorimetric methods for determinations of arsenic and cadmium have been developed respectively. Arsenic is determined by using ammonium molybdate as chromogenic reagent. In HNO_(3) medium As (V) reacts with ammonium molybdate to form As-Mo heteropoly acids and then the product is reduced to arsenomolybdate by SnCl_(2). Interference from Si, P and Ge can be eliminated by solvent extraction and the detection limit for As by this method is 10 ng with precision of 13.3% RSD (n=21). Cadmium is determined by using pyridyl-azonaphthol as chromogenic reagent. Interference from over 20 coexisting elements(Zn, Cu, Co, etc.) can be removed by solvent extraction with DAM-CHCl_(3) and KCN. The recovery of standard addition for Cd is 100%～106% with precision of 3.0% RSD (n=21) and the detection limit for Cd is 5 ng. The methods have been applied to the determination of trace As and Cd in geological standard reference materials with satisfactory results.