Extractive spectrophotometric determination of five selected drugs by ion-pair complex formation with bromothymol blue in pure form and pharmaceutical preparations

Simple, precise, selective, and expeditious spectrophotometric methods have been developed for the determination of itopride (ITO), midodrine (MID), diclofenac (DIC), mesalamine (MES), and sumatriptan (SUM) in their pure form as well as in pharmaceutical preparations. The method was based on ion-pair complex formation between the drugs and anionic dye, bromothymol blue in an acidic medium (pH 2.0–4.0). The yellow colored complexes formed were quantitatively extracted into chloroform and measured at 411, 410, 413, 412, and 414 nm wavelength for ITO, MID, DIC, MES, and SUM, respectively. Beer’s law was obeyed in the concentration range of 3.0–30 μg/mL for ITO, 1.0–20 μg/mL for MID, 1.5–40 μg/mL for DIC, 1.2–12 μg/mL for MES, and 0.5–15 μg/mL for SUM. The stoichiometry of the complexes formed between the drugs and the dye was 1:1 as determined by Job’s method of continuous variation. The association constant (KIP) of the ion-pair complexes formed was evaluated using Benesi–Hildebrand equation. Limit of detection, limit of quantification, and Sandell’s sensitivity of the methods were also estimated. The proposed methods were successfully employed for the determination of these drugs in their pharmaceutical dosage forms. *Corresponding author: Pranav S. Shrivastav, Department of Chemistry, School of Sciences, Gujarat University, Navrangpura, Ahmedabad 380009, Gujarat, India E-mail: [email protected]