MICROCHEMICAL JOURNAL 58, 325–336 (1998) ARTICLE NO. MJ971565 Selenium Determination in Biological Matrices Paola Borella, 1, * Annalisa Bargellini,* Eva Caselgrandi,* Antonio Menditto,² Marina Patriarca,² Andrew Taylor,‡ and Gianfranco Vivoli* *Department of Biomedical Science, Section of Hygiene and Microbiology, University of Modena, Modena, Italy; ² Laboratorio di Biochimica Clinica, Istituto Superiore di Sanita `, Rome, Italy; and ‡Robens Institute, University of Surrey, Guildford, England In this study, we discuss some relevant aspects concerning the determination of selenium in biological materials with special reference to fluorometry and hydride generation atomic absorp- tion spectroscopy (HG-AAS) techniques. The two methods may be applied without modifications to the analysis of Se in a wide spectrum of specimen types, and we describe their reliability in serum and hair analyses. Thirty-six independent control serum samples, the concentrations of which were unknown to the analyst, were analyzed in duplicate using both techniques in the Italian External Quality Assessment Scheme (EQAS). Accuracy was assessed by comparing Se values with those previously assigned by the organizers of the scheme using graphite furnace atomic absorption spectrometry (GF-AAS), which is the most frequently used technique for selenium determination in serum among the participants in the Italian EQAS. The results con- firmed that fluorometry has a higher degree of accuracy than HG-AAS: the mean differences between observed and expected values were 1.5 mg/liter (95% confidence interval, 01.06 to 3.97) for fluorometry and 01.1 mg/liter (95% confidence interval, 05.05 to 2.76) for Hg-AAS. We also report some results obtained for the determination of Se in hair. Since a critical step in hair preparation is the pretreatment for removal of external contamination, we compared six different washing procedures. In general, Se is poorly leached from hair, but the efficiency of removal differed with the substance used, ranging from 0 to 13% of the original content. A nonionic detergent like Triton X-100 offers the advantage of safe working conditions and a substantial reduction in costs compared with organic solvents. Lastly, in a consistent group (n Å 131) of women, Se in hair was found to be strongly reduced by the use of dye (389.9 ng/g vs 498.7 ng/g, P õ 0.001). We recommend recording information on cosmetic treatments when hair is collected to evaluate Se reference values in epidemiological studies.  1998 Academic Press INTRODUCTION Se is essential for humans, but it is also very toxic, showing adverse effects in many species, which depend mainly on the type of compound, route of absorption, and, for humans, type of diet (1, 2). Because of the wide range of biologically relevant Se concentrations and chemical forms, the determination of Se in biological samples has been problematic, leading to the development of many methods suitable for specific sample types. The concentration of Se in most human materials is between 0.01 and 1 mg/g, and the most frequently used analytical techniques for determining nano- and microgram amount of Se are fluorometry; atomic absorption spectrometry, both hy- dride generation (HG-AAS) and graphite furnace (GF-AAS); and inductively coupled plasma atomic emission spectrometry (ICP-AES). 1 To whom correspondence and reprint requests should be mailed: Dipartimento di Scienze Biomediche, Sezione di Igiene e Microbiologia, Via Campi 287, I-41100 Modena, Italy. Fax: /39 /59 428340. E-mail: p.borella@unimo.it. 325 0026-265X/98 $25.00 Copyright  1998 by Academic Press All rights of reproduction in any form reserved.