Simple Extractive Colorimetric Determination of Tramadol Hydrochloride by Acid-Dye Complexation Methods in Solid Dosage Form

Two simple and sensitive ion-pairing spectrophotometric methods have been described for the assay of tramadol hydrochloride in pure form and in pharmaceutical formulations. The developed methods involve formation of colored chloroform extractable ion-pair complexes of the drug with Bromocresol Green (BCG) and Bromothymol Blue (BTB) in acidic medium. The extracted complexes showed absorbance maxima at 430, 424 nm for BCG, BTB, respectively. Beer's law is obeyed in the concentration ranges 5–40, 2–10 μg/mL with molar absorptivity of 7.2 x 10³, 1.8 x 10⁴, L mole⁻¹ cm ⁻¹ for BCG and BTB, respectively. These methods have been successfully applied for the assay of drug in pharmaceutical formulations. No interference was observed from common pharmaceutical adjuvants. Results of analysis were validated statistically and through recovery studies.