Voltammetry and quantification of the contraceptive drug norethisterone in bulk form and pharmaceutical formulation.

The electrochemical behavior of norethisterone at the mercury electrode was studied in the universal buffer of various pH values using dc-polarography, cyclic voltammetry and controlled-potential electrolysis. Norethisterone was reduced at the mercury electrode via the consumption of two electrons corresponding to reduction of the 3-keto-delta-4-group in the A-ring of the molecule. The pK(a) value (8.7) of norethisterone was determined from the polarographic and spectrophotometric measurements. A fully validated, simple, sensitive, precise and inexpensive square-wave adsorptive cathodic stripping (SWAdCS) voltammetry procedure was described for trace quantification of bulk norethisterone. The stripping voltammetry peak current of norethisterone in a universal buffer of pH 5 following its accumulation onto the hanging mercury drop electrode (HMDE) at -0.6 V (versus Ag/AgCl/KCl(s)) for 130 s showed a linear response with the concentration over the range 5 x 10(-9) to 3 x 10(-7)M norethisterone. Detection and quantitation limits of 1.5 x 10(-9) and 5 x 10(-9)M bulk norethisterone, respectively, were achieved. The proposed procedure was successfully applied for the assay of norethisterone in Steronate tablets without interference from excipients.