Adsorptive cathodic stripping voltammetric determination of dexamethasone in formulations and biological fluids

The electrochemical behavior of dexamethasone at a hanging mercury drop electrode (HMDE) in a universal buffer series of pH 2-10 was studied using cyclic voltammetry. Based on the interfacial adsorptive character of dexamethasone onto the HMDE (electrode surface coverage = 1.4 x 10(-10) mol/cm2), a fully validated simple square-wave adsorptive cathodic stripping voltammetric method is described for its determination in bulk form with a limit of detection (LOD) of 3.1 x 10(-9) M. The described method was successfully applied to analysis of dexamethasone in its pharmaceutical formulations (deltasone tablets and fortecortin ampule) and in spiked samples of human urine, bovine urine, and protein-free bovine milk. The achieved LODs of dexamethasone in human urine, bovine urine, and protein-free bovine milk were 1.5 x 10(-8), 2 x 10(-8), and 9 x 10(-9) M, respectively. The mean percentage recoveries of 4 x 10(-7) M dexamethasone in bulk form, spiked human urine, bovine urine, and bovine milk, based on the average of 3 replicate measurements, were 99.8 +/- 0.25, 100.4 +/- 0.96, 99.6 +/- 0.79, and 100.1 +/- 0.26, respectively.