Application of multivariate techniques in the optimization of a procedure for the determination of bioavailable concentrations of Se and As in estuarine sediments by ICP OES using a concomitant metals analyzer as a hydride generator

A procedure has been developed for the determination of bioavailable concentrations of selenium and arsenic in estuarine sediments employing inductively coupled plasma optical emission spectrometry (ICP OES) using a concomitant metals analyzer device to perform hydride generation. The optimization of hydride generation was done in two steps: using a two-level factorial design for preliminary evaluation of studied factors and a Doehlert design to assess the optimal experimental conditions for analysis. Interferences of transition metallic ions (Cd2+, Co2+, Cu2+, Fe3+ and Ni2+) to selenium and arsenic signals were minimized by using higher hydrochloric acid concentrations. In this way, the procedure allowed the determination of selenium and arsenic in sediments with a detection limit of 25 and 30 μg kg−1, respectively, assuming a 50-fold sample dilution (0.5 g sample extraction to 25 mL sample final volume). The precision, expressed as a relative standard deviation (% RSD, n = 10), was 0.2% for both selenium and arsenic in 200 μg L−1 solutions, which corresponds to 10 μg g−1 in sediment samples after acid extraction. Applying the proposed procedure, a linear range of 0.08–10 and 0.10–10 μg g−1 was obtained for selenium and arsenic, respectively. The developed procedure was validated by the analysis of two certified reference materials: industrial sludge (NIST 2782) and river sediment (NIST 8704). The results were in agreement with the certified values. The developed procedure was applied to evaluate the bioavailability of both elements in four sediment certified reference materials, in which there are not certified values for bioavailable fractions, and also in estuarine sediment samples collected in several sites of Guanabara Bay, an impacted environment in Rio de Janeiro, Brazil.