High-pressure microwave digestion for the determination of arsenic, antimony, selenium and mercury in oily wastes

Abstract

The determination of arsenic, antimony and selenium by hydride generation and mercury by the cold vapour technique, following acid digestion of oily waste samples, can be very difficult if there is any residual organic matter. The preparation stage usually requires prolonged digestion to oxidize the organic matter. The situation is exacerbated if these metals are present as the organometallic derivatives. A method has been developed in which the organic matrices of oily waste samples, after solvent extraction, are completely oxidized. This has been achieved through the use of a newly designed microwave system that uses special high-pressure vessels capable of withstanding internal pressures in excess of 82.2 bar (1200 psi)(1 bar = 10⁵ Pa). The relative standard deviation using organometallic standards ranged from 5.4 to 6.6% and the recoveries for four spiked oily waste samples ranged from 89 to 105%.