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An Alkaline Oxidation Method for Determining Total Arsenic and Selenium in Soils

Countrymark Cooperative (Central Laboratory), 950 N. Meridian St., Indianapolis, IN 46204

M. A. Tabatabai^*

Dep. of Agronomy, Iowa State Univ., Ames, IA 50011

*Corresponding author (malit{at}iastate.edu).

ABSTRACT

A simple, accurate, and precise method for determination of total As and Se in soils was developed. In this method, a mixture of soil and NaOBr solution was boiled to dryness in a sand bath (260–280°C), and the total amounts of As and Se were extracted with 1.25 M H₂SO₄ and 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 to 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 agreed closely with those obtained by the acid digestion methods of USEPA and USGS proposed for determination of As and Se in soils and geologic materials. The method gives quantitative recovery (96–103%) of As and Se in certified standard reference materials and of these elements added to soils (99–101%). Digestion of soil samples with NaOBr solution and determination of the extracted As and Se by hydridge-generation atomic absorption spectrometry permit rapid analysis of a large number of samples at one time. Tests with 13 metals indicated that, at the concentrations normally expected in soils, none of those metals interfered with determination of As and Se by the proposed method. A single operator can complete the oxidation and analysis of one element in 40 samples in a normal working day.

Journal Paper no. J-15918 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA, Projects 2710 and 3047. This work was partly supported by the Biotechnology Byproducts Consortium of Iowa.

Received for publication July 28, 1994.