Determining selenium speciation by graphite furnace atomic absorption spectrometry

A straightforward method for measuring two aquatic inorganic species of selenium, selenate, Se(VI), and selenite, Se(IV), was developed in this study. Selenium toxicity and bioaccumulation in food chain are strongly dependent on its speciation. Therefore, it is important to measure selenium species as part of any selenium risk assessment practice. In this method, total selenium was first measured using graphite furnace atomic absorption spectrometry, and then, chemical procedures in the literature were used to reduce selenite, Se(IV), to hydrogen selenide (H 2 Se). Total selenium of the same solution was measured again with the analytical instrument after stripping H 2 Se from the solution. The difference of total selenium measured gave Se(IV) concentration. The two main species in natural waters are Se(VI) and Se(IV). Therefore, it can be assumed that after removing Se(IV) from the solution, the remaining total selenium is Se(VI). The two inorganic selenium species of (IV) and (VI) in purified waters and synthetic irrigation waters both spiked with Se(VI) and Se(IV) were determined using this method. Recovery of spiked samples in diluted synthetic irrigation water was 97% for Se(VI) and 99% for Se(IV). Detection limits of the method were 0.32 µg L −1 for Se(VI) and 0.11 µg L −1 for Se(IV). The advantages of the method developed in this study are that it employs a straightforward simple chemical reaction combined with acidification and stripping, requires only one instrument (graphite furnace atomic absorption spectrometry), and does not require extensive sample pretreatment.