AN ALKALINE OXIDATION METHOD FOR DETERMINING TOTAL ARSENIC AND SELENIUM IN SOILS

A simple, accurate, and precise method for determination of total As a nd Se in soils was developed. In this method, a mixture of soil and Na OBr solution was boiled to dryness in a sand bath (260-280 degrees C), and the total amounts of As and Se were extracted with 1.25 M H2SO4 a nd determined by an atomic absorption spectrophotometer, equipped with a hydride generation system, after reducing As(V) to As (III) and Se( VI) to Se(IV). With 12 soils analyzed, the As values ranged from 5.0 t o 14.3 mg kg(-1) soil and the Se values ranged from 0.5 to 5.5 mg kg(- 1) soil. The average results by the proposed NaOBr oxidation method ag reed closely with those obtained by the acid digestion methods of USEP A and USGS proposed for determination of As and Se in soils and geolog ic materials. The method gives quantitative recovery (96-103%) of As a nd Se in certified standard reference materials and of these elements added to soils (99-101%). Digestion of soil samples with NaOBr solutio n and determination of the extracted As and Se by hydride-generation a tomic absorption spectrometry permit rapid analysis of a large number of samples at one time. Tests with 13 metals indicated that, at the co ncentrations normally expected in soils, none of those metals interfer ed with determination of As and Se by the proposed method. A single op erator can complete the oxidation and analysis of one element in 40 sa mples in a normal working day.