Development and applications of spectrophotometric methods for quantitative determination of caroverine in pharmaceutical pure and tablet formulations

This paper describes two simple and novel analytical methods by using spectrophotometric technique for the determination of caroverine a spasmolytic drug in pharmaceutical formulations. The first (A) is a direct method in which analysis of the pure drug was carried out at its λ_max 304 nm in ethanol solvent. The method was linear from 0.5 to 18 μg/ml with correlation coefficient of 0.999 and molar absorptivity of 5.55 × 10⁴ L mole⁻¹ cm⁻¹. Limit of detection and limit of quantification were 0.44 and 1.47 μg/ml. While the second method (B) is based on the charge transfer reaction between caroverine as n-electron donor and 7,7,8,8-tetracyanoquinodimethane (TCNQ) as pi-acceptor resulting in highly colored stable complex, which showed maximum absorption band at wavelength of 525 nm. The thermodynamic parameters were calculated as association constant K_CT of 7.53 × 10⁴ mol⁻¹ and Gibbs free energy ΔG° of −6.72 kJ mol⁻¹. Different variables affecting the charge transfer reaction were carefully studied and optimized. At the optimum reaction conditions, Beer’s law was obeyed in a concentration range of 1–35 μg ml⁻¹ with molar absorptivity of 1.17 × 10⁴ L mole⁻¹ cm⁻¹ and correlation coefficient of 0.9999. The proposed methods were validated according to ICH guidelines.