Spectrophotometric Determination and Thermodynamic Parameters of Charge Transfer Complexation Between Stavudine and Chloranilic Acid

Purpose: The official assay methods for most antiretroviral drugs are limited by cost and unavailability of good test equipment in several developing countries. Therefore, this study investigates the use of charge transfer complexation in the spectrophotometric assay of stavudine as an alternative method to conventional methods. Methods: Charge transfer complex formation between stavudine (n-donor) and chloranilic acid (π- acceptor) in 1,4-dioxan using a spectrophotometer was employed. Thermodynamic parameters of the complex formed were determined. The proposed method was employed in the analysis of commercially available stavudine dosage form. Results: The wavelength of maximum absorption (λmax) of the complex was at 526 nm compared to 457 nm for p-acceptor alone. Beer’s law was obeyed in the range of 5 - 40 mg % while the stoichiometry of the complex was found to be 2:1. The complex formed was still stable 24 h later. Its formation was spontaneous with a ΔH° of -3.78×10^3 J/mol. The standard entropy change was from 12.18 ± 0.78 to 11.08 ± 1.23 cal/deg/mol over the temperature range of 30 - 60 °C while molar absorptivity decreased from 2.45×10^5 to 1.2×10^5 over the same temperature range. The assay result of the standard stavudine solution was of high accuracy with a recovery value of 99.85 ± 1.95 %. Conclusion: The proposed method is reliable and reproducible and should be suitable for the quality control of stavudine in bulk and dosage forms.