Application of LC–MS/MS for quantitative analysis of glucocorticoids and stimulants in biological fluids

Edge plane pyrolytic graphite electrode (EPPGE) modified with single-wall carbon nanotubes (SWNTs) has been used as a sensor to determine triamcinolone, abused by athletes for doping. A comparison of the voltammetric behavior between SWNTs modified EPPGE and fullerene - C(60)-modified EPPGE indicated that SWNTs modified EPPGE is more sensitive. The electrode exhibited an effective catalytic response with good reproducibility and stability. The effect of several parameters such as pH, square wave frequency and steroid concentration were studied. The square wave voltammetric response of the electrode to triamcinolone is linear in the range 0.1-25 nM with a detection limit and sensitivity of 8.9 x 10(-10)M and 2.06 microA nM(-1), respectively. The method was applied for the determination of triamcinolone in several commercially available pharmaceuticals and real urine samples obtained from patients undergoing pharmacological treatment with triamcinolone. A comparison of the observed results with HPLC analysis indicated a good agreement. The product obtained after reduction of triamcinolone was also characterized using (1)H NMR and GC-MS and the site of reduction is found to be carbonyl group at position 20. The method described is rapid, simple and accurate and can be easily applied for detecting cases of doping.

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 enhancement 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 microM and the sensitivity of the method has been found to be 0.685 microA microM(-1). The detection limit is estimated to be 5.5 x 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 formulations 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.