Sensitive kinetic spectrophotometric determination of captopril and ethamsylate in pharmaceutical preparations and biological fluids

A highly sensitive kinetic spectrophotometric method was developed for the determination of captopril (CPL) and ethamsylate (ESL) in pharmaceutical preparations and biological fluids. The method is based on a catalytic acceleration of the reaction between sodium azide and iodine in an aqueous solution. Concentration range of 0.1-1.5 microg ml(-1) for CPL and 0.3-3 microg ml(-1) for ESL was determined by measuring the decrease in the absorbance of iodine at 348 nm by a fixed time method. The decrease in absorbance after 5 min was markedly correlated to the concentration. The relative standard deviations obtained were 1.30 and 1.87 for CPL and ESL, respectively, in pure forms. Correlation coefficients were 0.9997 and 0.9999 for CPL and ESL, respectively. The detection limits were determined as (S/N = 3) were 20 ng ml(-1) for CPL and 50 ng ml(-1) for ESL. The proposed procedure was successively applied for the determination of both drugs in pharmaceutical preparations and in biological fluids.