Utility of π-acceptor reagents for spectrophotometric determination of sulphonamide drugs via charge-transfer complex formation

A simple, sensitive and accurate spectrophotometric method for the determination of sulphonamides (sulphamethoxazole (SMZ), sulphaguanidine (SGD), sulphaquinoxaline sodium (SQX), sulphametrole (SMR), and sulphadimidine sodium (SDD)) has been developed. The charge-transfer reactions between sulphonamides as n-electron donors and 7,7,8,8-tetracyanoquinodimethane (TCNQ), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), and 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid, p-CLA) as π-acceptors resulting in highly coloured complexes were studied. Experimental conditions for these CT reactions were carefully optimised. Beer’s law is valid over the concentration ranges from 4–280 µg mL−1, 4–260 µg mL−1, 4–200 µg mL−1, and 4–200 µg mL−1 of SMZ, SGD, SQX, and SDD using DDQ reagent, respectively. While the calibration curves are linear in the concentration ranges from 4–180 µg mL−1, 4–80 µg mL−1, 4–60 µg mL−1, 4–180 µg mL−1, and 4–60 µg mL−1 of SMZ, SGD, SQX, SMR, and SDD, respectively, using TCNQ reagent and from 4–380 µg mL−1 and 4–300 µg mL−1 of SQX and SDD, respectively, using p-CLA reagent, respectively. Different analytical parameters, namely molar absorptivity (ε), standard deviation, relative standard deviation, correlation coefficient, limit of detection, and limit of quantification, were calculated. The results obtained by the proposed methods are in good agreement with those obtained by the official method as indicated by the percent recovery values.