Development and validation of fluorescence spectrophotometric method: Quantitation of chlorpheniramine maleate in pharmaceutical formulations

Ion-pair complex of the chlorpheniramine maleate with eosin Y was achieved because of the interaction of protonated drug with dianionic eosin Y. The stoichiometry of the reaction was studied by mole ratio method which showed 2:1 ratio for drug and eosin Y. This lead to the quenching of eosin Y which was the basis for the quantitation of chlorpheniramine maleate by fluorescence spectrophotometry. The fluorescence intensity was recorded at 544.02 nm after excitation at 257.96 nm. The linear dynamic range was obtained in the concentration range of 1-8 μg mL− 1. The quenching rate constant was calculated and found to be 8.2 × 1013 L mol− 1 s− 1 which is more than 2 × 1010 L mol− 1 s− 1 indicated that the proposed method has followed static quenching. The enthalpy change and Gibb's free energy were calculated and found to be negative. The same results were also obtained by computational calculations using Gaussian. Various variables such as reaction time, temperature, buffer solution and solvent were optimized and the proposed method was successfully applied for the assay of active chlorpheniramine maleate in commercial tablets.