Labware Evaluation for Selenium Sorption Experiments.

Selenium (Se) is an essential trace element that is toxic at small concentrations. The United States Environmental Protection Agency has established a maximum concentration of 50 µg L^-1 in drinking water and 5 µg L^-1 as a chronic life criterion. Environmentally relevant concentrations are very low — 0.02 µg L^-1 in freshwater, 0.08 µg L^-1 in saltwater and 0.01-2 mg/kg in soil. Therefore, labware must be carefully selected in order to prevent changes in sample composition over time as a result of interactions between sample and container. Our objective was to assess four materials (glass, silanized glass, Teflon, and polypropylene) for use in Se sorption studies. All glass containers were acid washed in a two stage acid bath for 24 hours per stage. Varying selenium stock solutions (0, 10, 25, and 50 µg L^-1) were prepared in 0.1 M NaNO₃ and delivered to each container. Samples were sealed and allowed to equilibrate for 6, 12, 24, or 48 hours to evaluate the ability of the material to suitably hold samples for sorption studies. Statistical analysis was completed on blank-corrected sample concentration because hydrochloric acid used in procedural work contains trace levels of Se. Statistically significant factors (time, treatment, and treatment with time) varied with each sample concentration as determined by p-values. Based on these p-values, the length of time during which a sample is held is significant for samples with greater than 8 µg L^-1 Se. Tukey’s Method for Least Squared Means was used to determine differences in sample material using the 40 µg L^-1 Se sample, the only sample that was statistically different with treatment type. Silanized glass was statistically different than other materials and corresponded to the greatest least squares means. In sorption studies, silanized glassware is recommended as it enhances sample integrity through limited losses to the material itself.