SELENIUM DETERMINATION IN SOIL AND PLANT MATERIALS

Abstract

Selenium (Se) was determined in soil and plant samples after wet digestion with HNO₃ and HClO₄. The method included the usual steps, namely, the reduction of Se, complexing Se with 2,3-diaminonaphthalene, and the extraction of the piazselenol in cyclohexane followed by fluorometric measurements. The most important step, the stabilization of selenium at the oxidative state Se⁺⁴, was achieved by reducing Se⁺⁶ to Se⁺⁴ with 2 ml of 1 N HCl while the system was kept in a boiling water bath. For best results and adequate control of interfering ferric ions, the system was adjusted to pH 1.8, and a stabilizing agent consisting of 10% hydroxylamine hydrochloride in a 0.04 M EDTA solution was used. Fluorescence measurements obtained for soil samples gave average coefficients of variation and recovery percentages of 3.35 and 97.4, respectively. For radioactivity counts made on cyclohexane extracts, the coefficients of variation and the recovery percentages were 2.31 and 93.1, respectively. Similar results were obtained for plant materials. Major problems encountered in establishing the modified method are discussed.