Send Orders of Reprints at reprints@benthamscience.net 296 Current Analytical Chemistry, 2013, 9, 296-304 Sequential Injection Analysis in Selenium Determination by HG-AAS: Optimisation and Interference Study Alicia Mollo* 1 , Sergio Luis Costa Ferreira 2 and Moisés Knochen* 1 1 Cátedra de Química Analítica, Universidad de la República (UdelaR), Facultad de Química, Av. Gral. Flores 2124, 11800 Montevideo, Uruguay 2 Grupo de Pesquisa em Química e Quimiometria, Universidade Federal da Bahia, Campus Ondina, Instituto de Quími- ca, CEP: 41.195.001 Salvador, Bahia, Brazil Abstract: A sequential-injection hydride-generation atomic absorption spectrometry (SIA-HG-AAS) system for the de- termination of trace levels of selenium was designed and characterised. The system included on-line pre-reduction from Se(VI) to Se(IV) and used NaBH 4 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 g L -1 (A peak = 0.0048 C, with C = concentration in g L -1 , r 2 = 0.9973). Detection (3 s) and quantifi- cation (10 s) limits were 0.6 and 2.0 g L -1 respectively with precision (repeatability, s r (%), n = 10) from 2.2% to 3.6% for concentrations between 5 and 20 g L -1 . Sampling frequency was 60 hour -1 . An interference study was carried out com- paring 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 sig- nificant 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 deter- mination was wider in the SIA-HG-AAS system than in the reference HG-AAS system. Keywords: Hydride generation, interference analysis, multivariate factorial design, SIA. INTRODUCTION Selenium determination is often accomplished by hydride generation coupled with atomic absorption spectrometry (HG-AAS). Selenium hydride is released in acidic solution when the sample reacts with a chemical reductant, NaBH 4 being used almost exclusively for this purpose. In order to achieve the reaction, selenium must be in the Se(IV) oxida- tion state. A pre reduction step is then necessary. For this purpose, some reference methods propose the use of hydro- chloric acid digestion heating in a water bath for at least 20 minutes [1-3]. Aiming at the various advantages of flow-based tech- niques, a number of research papers have been published showing different flow systems designed to carry out the generation of selenium hydride with detection by atomic absorption [4-6], atomic fluorescence [7, 8], and atomic emission [9] spectrometry. Some of these systems [4,9] in- clude an online pre-reduction step. Atomic Fluorescence Spectrometry (AFS) is the preferred detection technique be- cause of its extremely low detection limits. However, Atomic Absorption Spectrometry (AAS) is more widely *Address correspondence to these authors at the Cátedra de Química Analí- tica, Universidad de la República (UdelaR), Facultad de Química, Av. Gral. Flores 2124, 11800 Montevideo, Uruguay; Tel: +598 29241808; Fax +598 29241906; E-mails: amollo@fq.edu.uy, mknochen@fq.edu.uy available and is thus preferable as long as detection and quantification limits obtained with a given method are fit for the purpose. Atomic spectrometric techniques such as AAS and AFS benefit from hyphenation with flow techniques such as Flow Injection Analysis (FIA) [10]. In this way they become ame- nable to automation and the goals involved in the concept of Green Analytical Chemistry [11] can be accomplished and thus lower amounts of hazardous chemicals are employed and the volume of harmful wastes is decreased. Sequential injection analysis (SIA) [12, 13] is a flow technique featuring low consumption of reagents and sam- ples. However the use of this technique for the determination of selenium by hydride generation atomic spectrometry is not widely reflected in the literature [14, 15]. Since a number of interferences may arise during the hydride generation step, and they depend heavily on the technique used for sample and reagent introduction, further research is necessary in order to determine the main interferences occurring when SIA is hyphenated with hydride generation spectrometric techniques. This work presents the development and optimisation of a system for the determination of total selenium based on sequential injection hydride-generation atomic absorption spectrometry (SIA-HG-AAS) attempting to low sample con- 1875-6727/13 $58.00+.00 © 2013 Bentham Science Publishers