Developing Metal Complexes for Captopril Quantification in Tablets Using Potentiometric and Conductometric Methods

Potentiometric and conductometric methods were successfully applied to elucidate the interaction of 10 ions, viz., Cr³⁺, Fe³⁺, La²⁺, Th⁴⁺, Co²⁺, Mn²⁺, Pd²⁺, Sr²⁺, Ti²⁺, and Zr²⁺, with the antihypertensive drug captopril (CAP) and its role to determine CAP in pure powder and tablet forms. The ionization constant of CAP and the generated complexes' stability constants (log K) were evaluated using potentiometric and conductometric methods at 25 ± 0.1 °C and 0.05 M ionic strength (I) of NaNO₃ aqueous solution, and CAP was then determined in pure powder and tablet forms. Complexes having metal:ligand ratios of 1:1, 1:2, and/or 1:3 were produced, regardless of the type of the ligand or metal ions. Both the suggested potentiometric and conductometric procedures were utilized to confirm the stoichiometry of the M-CAP binary complexes formed. These two different techniques were utilized successfully to determine CAP in pure powder and tablet forms. Using the standard addition method (SAM) based on the Gran plot, CAP was satisfactorily determined throughout the concentration range of 0.83-13.04 mg/mL (SD = 0.20, R = 0.9986 (n = 5)), with a detection limit of 0.64 mg/mL (SD = 0.20, R = 0.9986 (n = 5)). In the presence of common tablet excipients, no interferences were observed. The percentage of CAP recovered from various dosage formulations (tablets) varied from 95.88 to 99.92%.