Biosensors and Bioelectronics 24 (2009) 1649–1654 Contents lists available at ScienceDirect Biosensors and Bioelectronics journal homepage: www.elsevier.com/locate/bios Fullerene-C 60 -modified edge plane pyrolytic graphite electrode for the determination of dexamethasone in pharmaceutical formulations and human biological fluids Rajendra N. Goyal ∗ , Vinod K. Gupta, Sanghamitra Chatterjee Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India article info Article history: Received 30 May 2008 Received in revised form 11 August 2008 Accepted 14 August 2008 Available online 26 August 2008 Keywords: Fullerene-C60-modified pyrolytic graphite electrode Dexamethasone Blood plasma Doping Square wave voltammetry abstract Electrochemical behaviour of dexamethasone at the fullerene-C 60 -modified pyrolytic graphite electrode (PGE) has been investigated using Osteryoung square wave voltammetry (SWV). Compared to a bare PGE and fullerene-C 60 -modified glassy carbon electrode (GCE), the fullerene-C 60 -modified edge plane PGE exhibited an apparent shift of the peak potential to less negative potentials with a marked enhance- ment in the current response of dexamethasone. The peak potential was linearly dependent on pH with dE p /dpH as 59 mV/pH. Calibration plot having good linearity with a correlation coefficient 0.9983 is obtained in the concentration range of 0.05–100 M and the sensitivity of the method has been found to be 0.685 A M -1 . The detection limit is estimated to be 5.5 × 10 -8 M. The electrode showed good sensitivity, stability and reproducibility. The practical analytical utility of the method is illustrated by quantitative determination of dexamethasone in several commercially available pharmaceutical formu- lations and human blood plasma of patients being treated with dexamethasone. HPLC method was used to compare the results obtained for the quantitative estimation of dexamethasone in biological fluids. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Glucocorticoids are adrenocortical steroids, both naturally occurring and synthetic, which are readily absorbed from the gastrointestinal tract. 9-Fluoro-11,17,21-trihydroxy-16- methylpregna-1,4-diene-3,20-dione, commonly known as dexamethasone is a synthetic adrenocortical steroid which is practically insoluble in water. Dexamethasone is considered as a doping agent as it is frequently abused by athletes in sports such as cycling and horse racing to improve the performance. To prevent its misuse related to euphoria and pain suppression, the use of dexamethasone is controlled and restricted by some sport federations (Deventer and Delbeke, 2003; Colmain, 2006; Fluri et al., 2001; http://www.asada.gov.au). In 2005, Polish cross country skier Justyna Kowalczyk was disqualified from the Under 23 (U23) OPA (Alpine nations) Intercontinental Competition in Germany and issued a 2-year suspension for her doping offenses on dexametha- sone (FIS, 2005). Dexamethasone is a potent glucocorticoid which acts as an anti-inflammatory and immunosuppressant (Zhang et al., 2007; Abraham et al., 2006; Lutsar et al., 2003). It is used for the treatment of various cancers, viral infections, respiratory diseases, ∗ Corresponding author. Tel.: +91 1332 285794 (O)/274454 (R). E-mail address: rngcyfcy@iitr.ernet.in (R.N. Goyal). liver disorders, gastrointestinal diseases, skin disorders and ner- vous system abnormalities (Rajkumar et al., 2002; Fabunan, 2007; Kim et al., 2004; Jost-Price et al., 2003; Hayes and Ettigi, 1983; Esel et al., 2004). It is useful to counteract rheumatoid arthritis, septic shock and for the treatment of tuberculous meningitis (Wang et al., 2007; Zhang, 2006; Wu et al., 2005; Chatterjee et al., 2007; Thwaites et al., 2004). Since, dexamethasone has strong efficacy against the diseases, the dose of the drug is much smaller than those of other synthetic corticosteroids. Therefore, a sensitive method is required for its determination in plasma after administration for efficient and safety use of the drug. Several methods involving radioimmunoassay (English et al., 1975), liquid chromatography–tandem mass spectrometry (Yu- Luan et al., 2002; Yang et al., 2008; Gao, 2003), stable isotope dilution mass spectrometry (Kasuya et al., 2006) and high perfor- mance liquid chromatography (Kumar et al., 2006; Yun-Kyoung et al., 2004) have been reported for the determination of dex- amethasone in human plasma. Although the radioimmunoassay methods are very sensitive, they require chromatographic purifica- tion to avoid cross-reaction with other endogenous corticosteroids. The chromatographic methods require sample pre-treatment and time-consuming extraction steps. Literature survey reveals that very few attempts have been made to determine dexamethasone using voltammetric techniques. Thus, the aim of this study was to develop a simple and rapid method for the analysis of dex- 0956-5663/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.bios.2008.08.024