DETERMINATION OF AMINO ACIDS AND SELENIUM IN FISH PLASMA * A. IORDACHE 1,2 , M. CULEA 2 , E. HORJ 2 , O. COZAR 2 1 National R&D Institute of Cryogenics and Isotopic Technologies – ICSI Rm Valcea, 4 Uzinei St., Rm. Valcea, 240050, Romania, E-mail: andres_iro2002@yahoo.com 2 Babes-Bolyai University, 1 M. Kogalniceanu St.,Cluj-Napoca, 400084, E-mail: mculea@phys.ubbcluj.ro, elenahorj@yahoo.com, cozar@phys.ubbcluj.ro Received September 10, 2010 Two different mass spectrometric methods were developed for amino acids and selenium monitoring in plasma. The stable isotope internal standard used was 15 N- Methionine for amino acids quantitation. The aim of this study was to evaluate the differences in plasma free amino acids and selenium occurred at a dietary Se- methionine level of 0.05 mg/kg in comparison with control carp plasma. Key words: GC-MS, ICP-MS, selenium. 1. INTRODUCTION Selenium is a very potent antioxidant protecting the body from damage due to oxidation by free radicals. Dietary supplementation with selenium in animals increased selenium content in several tissues. The antioxidant effect of selenium on lipid peroxidation, enzyme activities and biochemical parameters might be beneficial in antagonizing aluminum toxicity [1]. Oral nutritional supplements infusion improves duodenal protein balance in healthy humans [2]. Changes in the plasma amino acids (AA) pool reflect the nutritional state of fish, help us to understand the complex amino acids metabolism and to evaluate the quality of a diet. Isotopic dilution gas chromatography-mass spectrometry (ID-GC/MS) is a technique used for quantitative analysis of compounds from different biological specimens. Stable isotopes provide the ideal internal standards in quantitative information [3-6]. Inductively coupled plasma mass spectrometry (ICP-MS) is a relatively new and powerful technique for the determination of metals in aqueous solution. The aqueous sample is turned in aerosols by continuous nebulization, then is ionized in * Paper presented at the 11 th International Balkan workshop on Applied Physics, July 7–9, 2010, Constanta, Romania. Rom. Journ. Phys., Vol. 56, Nos. 7–8, P. 963–970, Bucharest, 2011