Determination of Se in urine by flow injection hydride generation electrothermal atomic absorption spectrometry with in-atomizer trapping
Abstract
Following digestion of the sample in a mixture of bromate and hydrobromic acid, the inorganic selenium produced was quantified by trapping hydrogen selenide, formed when a 500 ml sample volume injected into a hydrochloric acid carrier stream merged with a stream of sodium borohydride solution, on the iridium-pretreated interior of a graphite furnace atomizer. A number of parameters relating to the digestion, flow injection manifold and trapping in the atomizer were investigated, including a study of factors affecting the detection limit. It was found necessary to heat the digest under reflux at a temperature of 150C for 2 h. Quantitative recoveries, from a human urine matrix, of selenite, selenate, trimethylselenium, selenocystine, selenopurine and selenomethionine spikes were obtained. The efficiency of hydride generation, transport and trapping was 75%. The major factors affecting the detection limit were the reagent purity and the volume injected. For high-purity hydro-bromic acid and borohydride free of caking agent, the detection limit, based on three times the standard deviation of the blank, was 0.06 mgl− 1 for a 1000 ml injection volume corresponding to a detection limit of 3 mgl− 1 for a urine sample. The method was validated by the accurate analyses of Standard Reference Material 2670 from the National Institute of Standards and Technol-ogy, and urine samples from an interlaboratory comparison program. The procedure avoids the need for perchloric acid and produces selenium in the + 4 oxidation state and thus no reduction is needed prior to generation of the hydrogen selenide. The use of a graphite furnace atomizer avoids the need for frequent reconditioning of the atomizer surface and the need for the standard additions method, both of which are drawbacks of procedures which make use of the quartz tube atomizer. All sample handling procedures following the digestion were automated by the use of flow injection technology.