Exploiting iminoquinone free radical production for thiol based drugs determination in pharmaceutical formulations

A spectrophotometric flow analysis procedure to determine Captopril (CPT) and N-acetyl-L-cysteine (NAC) in pharmaceutical formulations was developed based on the reaction with iminoquinone radical produced from the N,N-dimethyl-p-phenilenediamene (DMPD) oxidation in acid medium. The reagents addition order was evaluated and analytical parameters were optimized. The linear concentrations ranges were 2.5-90 and 5.0-50 mg L-1 for CPT and NAC, respectively. Limits of detection (3σ) were calculated at 0.22 and 1.8 mg L-1 and the relative standard deviation (N = 10) were lower than 1.0 and 2.1% for CPT and NAC, respectively. The procedure was employed for CPT and NAC determination in diverse pharmaceutical formulations and by applying paired t-test the results were in agreement with those obtained by reference methods for 95% confidence level.