ORIGINAL PAPER Electrocatalytic determination of reduced glutathione in human erythrocytes Rita de Cássia Silva Luz & Flavio Santos Damos & Paulo Guimarães Gandra & Denise Vaz de Macedo & Auro Atsushi Tanaka & Lauro Tatsuo Kubota Received: 1 September 2006 / Revised: 17 November 2006 / Accepted: 28 November 2006 / Published online: 3 January 2007 # Springer-Verlag 2007 AbstractThe determination of reduced glutathione (GSH) in human erythrocytes using a simple, fastand sensitive method employing a glassy carbon electrode modified with cobalt tetrasulfonated phthalocyanine (CoTSPc) immobilized in poly( L-lysine) (PLL) film was investigated. This modified electrode showed very efficient electrocatalytic activity for anodic oxidation of GSH, decreasing substantially the anodic overpotentials for 0.2 V versusAg/AgCl. The modified electrodepresented better performance in 0.1 mol l −1 piperazine-N,N′-bis(2-ethanesulfonic acid) buffer at pH 7.4. The other experimental parameters, such as the concentration of CoTSPc and PLL in the membrane preparation, pH, type of buffersolution and applied potential, were optimized. Underoptimized operational conditions, a linearresponse from 50 to 2,160 nmol −1 wasobtained with ahigh sensitivity of 1.5 nA l nmol −1 cm −2 . The detection limit for GSH determination was 15 nmol l −1 . The proposed sensor presented good repeatability, evaluated in terms of the relative standard deviation (1.5%) for n=10. The modified electrode was applied for determination of GSH in erythro- cyte samples and the results were in agreement with those obtained by a comparative method described in the literature The averagerecoveryfor thesefortified samples was 100±1)%. Applying a paired Student’s-t testto compare these methods, we could observe that, at the 95% confide level, therewas no statistical differencebetweenthe reference and the proposed methods. Keywords Electrocatalytic determination . Reduced glutathione . Erythrocyte samples Introduction Reducedglutathione (γ- L-glutamyl- L-cysteinyl-glycine, GSH) is the most abundant low molar mass thiol found in mammals cells [ 1]. In the human body, the most important physiological function of GSH is protecting cells from free radicals and reactive oxygen species, keeping an adequate intracellular redox status. GSH is also an important cofacto in the biological processes of metabolism, catabolism and transport [2]. Severalstudieshavealso indicatedthatlow GSH concentrations in HIV-infected patients may contribute to theirimmune deficiency [3]; thus,the analysis of GSH in biological samples is of significant interest owing to its potential for disease diagnosis [3]. For this, several metho are available for determination of GSH, such ashigh- performance liquid chromatography [ 4, 5], spectrofluorim [6, 7], spectrophotometry [8, 9] and potentiometry [10]; however, mostof them show some difficulties with sample preparation, the necessity for derivatization of molecules or the lack ofsufficient detectability, limiting their utility [11]. Electrochemical methods for the determination of GSH have received growing attention in recent years owing to theirsimplicity,low cost, high detectability and easy miniaturization. However, not withstanding the fact that Anal Bioanal Chem (2007) 387:1891–1897 DOI 10.1007/s00216-006-1053-6 R. C. S. de Luz : F. S. Damos : L. T. Kubota (*) Institute of Chemistry, UNICAMP, P.O.Box 6154, 13084-971 Campinas, SP,Brazil e-mail: kubota@iqm.unicamp.br P. G. Gandra : D. V. de Macedo Institute of Biology, UNICAMP, P.O.Box 6109, 13084-971 Campinas, SP,Brazil A. A. Tanaka Departament of Chemistry, UFMA, Avenida dos Portugueses s/n, 65085-040 São Luís, MA, Brazil