Talanta 71 (2007) 1669–1674 The electrocatalytic examination of cephalosporins at carbon paste electrode modiﬁed with CoSalophen E.S. Jamasbi a , A. Rouhollahi a,∗ , S. Shahrokhian b , S. Haghgoo c , S. Aghajani d a Chemistry Department, Faculty of Science, K.N. Toosi University of Technology, Tehran 15418, Iran b Chemistry Department, Sharif University of Technology, Tehran 11365-9516, Iran c Quality Control Lab Ministry of Health & Medical Education, Iran d Ofﬁce No. 1529, Ministry of Jahad-e-Agric, Main Building-Keshavarz Bul, Tehran, Iran Received 15 April 2006; received in revised form 26 July 2006; accepted 27 July 2006 Available online 25 September 2006 Abstract The electrocatalytic oxidation of cephalexin and cefazolin has been studied at a carbon paste electrode modiﬁed with cobalt salophen (CoSal) by cyclic voltammetry. The selectivity of the carbon paste modiﬁed with CoSal in detecting cephalexin and cefazolin was examined. To suggest the electrocatalytic mechanism for electro-oxidation of cefazolin, the electrochemical behavior of ceftriaxone was investigated which has a thiol group out of the beta lactam ring. The electrocatalytic oxidation of these antibiotics is shown to be irreversible at the CoSal modiﬁed electrode. Scan rate dependence of cefazolin, which is a sulfur-containing compound, has been examined. The results indicated that the electrocatalytic oxidation of the compounds is diffusion controlled. The responses of the modiﬁed electrode were compared with those of unmodiﬁed electrode and it has shown that the modiﬁed electrode has better sensitivity than unmodiﬁed electrode to the detection of cefazolin. The overall number of electrons contributed to the oxidation of cefazolin is obtained 1 by chronoamperometry; the number of electron involved in the rate-determining step was 1. The results of differential pulse voltammetry (DPV) using the modiﬁed electrode with high sensitivity were applied for the determination of cefazolin in human synthetic serum samples. The linear range was obtained from 1 × 10 -5 to 1 × 10 -3 M for DPV determination of cefazolin in buffered solutions (pH 3.0). © 2006 Published by Elsevier B.V. Keywords: Cephalosporins; Carbon paste electrode; Modiﬁed electrode; Cobalt salophen; Cyclic voltammetry; Chronoamperometry; Differential pulse voltammetry 1. Introduction Cephalosporins are widely used in clinical therapy for the treatment of sever detection because of their antibacterial and pharmacokinetic properties [1–5]. Up to now several meth- ods have been reported to study cephalosporins such as spec- trophotometric [6–8] and chromatographic [9–13] techniques. However, the detection of these sulfur-containing compounds by spectrophotometry is not effective, because these sulfur- containing groups do not absorb light [14] and derivatization of sulfur-containing compounds is sophisticated [15,16]. So apply- ing a simple and easy technique has been urgently desired to detect cephalosporins. Electrochemical methods, due to rapidity, ∗ Corresponding author. Tel.: +98 21 22853308; fax: +98 21 22853650. E-mail addresses: rouhollahi@kntu.ac.ir (A. Rouhollahi), shaghgoo@hotmail.com (S. Haghgoo). simplicity and high sensitivity in analysis, have been consid- ered to study of the compounds such as cephalosporins and cepfamycins [17]. Although the electrochemical study of sulfur-containing compounds has been reported using carbon, platinum, mer- cury and gold as a working electrodes [18,19], but the sever detection conditions can damage the electrode and cause ﬂuc- tuating background currents [14]. To reduce these problems, some researchers used the modiﬁed electrodes. Transition metal complexes are well known as electron mediators in the elec- trocatalytic oxidation of sulfhydryl compounds. Application of Schiff base complexes of cobalt in the matrix of carbon paste electrode has been reported for the sensitive electro- chemical detection of sufhydryl compounds, e.g. cysteine [20], penicillamine [21], propylthiouracil [22] and captopril [23]. Carbon paste electrode modiﬁed with cobalt phthalocyanin is used for voltammetric detection of some sulfhydryl compounds [24,25]. In these investigations, the modiﬁed carbon paste elec- 0039-9140/$ – see front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.talanta.2006.07.058