Sequential Injection Analysis in Selenium Determination by HG-AAS: Optimisation and Interference Study

A sequential-injection hydride-generation atomic absorption spectrometry (SIA-HG-AAS) system for the determination of trace levels of selenium was designed and characterised. The system included on-line pre-reduction from Se(VI) to Se(IV) and used NaBH4 as reagent for the generation of the hydride. The operation of the system was optimised regarding the main operating variables by means of appropriate experimental designs. The analytical response was linear in the range 2.0 - 20 μg L-1 (Apeak = 0.0048 C, with C = concentration in μg L-1, r2 = 0.9973). Detection (3 s) and quantification (10 s) limits were 0.6 and 2.0 μg L-1 respectively with precision (repeatability, sr(%), n = 10) from 2.2% to 3.6% for concentrations between 5 and 20 μg L-1. Sampling frequency was 60 hour-1. An interference study was carried out comparing the performance of both the proposed system and an HG-AAS reference system involving batch generation of the hydride. As, Co, Cu, Fe(II), Fe(III), Hg, Ni, nitrate and Zn were chosen as potential interferents. Interference from As and nitrate was shown to be more severe in the proposed system than in the batch one. Co, Hg and Zn did not present any significant interference in either system. The presence of Fe(III) at the concentrations tried showed the same behaviour in the response for both systems. The range of concentrations of Cu, Fe(II) and Ni allowing an interference-free selenium determination was wider in the SIA-HG-AAS system than in the reference HG-AAS system.