Selenium can be toxic to aquatic life at very low concentrations, even though it is an essential element to many organisms. Selenium-laden agricultural drainwater in the Imperial Valley of California may be affecting the survival of endangered desert pupfish, which inhabit the waters of that region. It is becoming increasingly important to ensure an appropriate balance between selenium deficiency and toxicity when developing new water quality criteria for the protection of aquatic life. Because the bioavailability and toxicity of selenium are dependant on its chemical forms, the primary goal of this dissertation research was to develop methods for routine speciation analysis of selenium in tissues, which has been identified as a critical data need in the derivation and interpretation of selenium residues in fish and waterfowl.

Initial experiments were conducted to optimize the selenium determination for dynamic reaction cell (DRC) ICP-MS using methane as the reaction gas. In the DRC mode, the Ar-Ar background signals could be reduced greatly but at the price of a large loss of net selenium signal intensities. Overall, the results were less satisfactory than expected and the added complexity for the DRC mode seemed unwarranted. Therefore, a method for total selenium using on-line stable isotope dilution analysis with conventional ICP-MS (SIDA-ICP-MS) was developed. Masses at 77, 78, 79, 81, and 82 were monitored and quantitation of Se was determined based on both ⁷⁸Se and ⁸²Se. SIDA-ICP-MS was successfully applied to the determination of total selenium in biological materials, such as selenized yeasts, certified reference materials, lab-cultured oligochaetes and desert pupfish.

Although cation-exchange chromatography separation proved to be feasible, separation and quantitation of seleno-amino acids was best accomplished by ion-pairing reversed-phase liquid chromatography (RPLC). For either separation method, ICP-MS detection at mass 82 using the standard mode produced good results. The efficiencies of different extraction methods were evaluated and the chromatographic conditions were investigated using selenomethionine-dosed samples and a reference yeast certified for selenomethionine content. It was found that methanesulfonic acidic hydrolysis demonstrated a higher extraction efficiency of selenomethionine than enzymatic digestion. Selenomethionine (SeMet) was the only significant Se-containing species detected in the biological samples that were examined.