DETERMINATION OF ARSENIC BY GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY COMBINED WITH LIQUID-LIQUID-EXTRACTION OF ARSENOMOLYBDIC ACID

Graphite furnace atomic absorption spectrometry coupled with liquid-liquid extraction was investigated for the determination of ng ml-1 levels of arsenic. Arsenic(III, V) was converted into arsenomolybdic acid in 1 M hydrochloric acid and extracted quantitatively into isobutyl methylketone. The extract was injected into a graphite furnace atomizer and arsenic was determined using the 193.7-nm arsenic line under optimum conditions. By matrix modification, i.e., the formation of the heteropoly acid, the loss of arsenic which is apt to occur during the ashing stage was suppressed. When the aqueous to organic phase volume ratio was 2.5:1 (v/v), the sensitivity (1% absorption) and relative standard deviation [n = 10, 1.5-mu-g of arsenic(III)] were 0.58 ng ml-1 and 2.1%, respectively. The proposed method was applied to the analysis of steel, mine water and river water samples. The results were in good agreement with those obtained by a spectrophotometric procedure.