Spectrophotometric Quantification of Valsartan in Pure Substance and Pharmaceutical Formulations through Ion-Pair Complexation with Bromophenol Blue and Methyl Red without Extraction

Two environmentally friendly, quick, and straightforward non-extractive spectrophotometric techniques have been developed for the quantitative estimation of valsartan in tablet formulations. The procedures rely on the formation of ion-pair complexes between valsartan and the acidic dyes bromophenol blue (BPB) and methyl red (MR). The drug interacts selectively with these dyes, generating colored complexes—yellow with BPB at pH 5.5, showing maximum absorbance at 424 nm, and red with MR at pH 4.3, with λmax at 494 nm. Optimal analytical conditions were determined for both methods. A linear correlation was observed between absorbance and drug concentration within the ranges of 8–24 µg/mL for BPB and 4–20 µg/mL for MR. The regression equations were found to be y = 0.0102x + 0.01636 (BPB) and y = 0.0222x – 0.0063 (MR), with excellent correlation coefficients (R² = 0.9988 for BPB and R² = 0.9991 for MR), confirming adherence to Beer’s law. The limits of detection (LOD) and quantification (LOQ) were determined as 1.03 µg/mL and 3.43 µg/mL for BPB, and 0.68 µg/mL and 2.26 µg/mL for MR, respectively. Accuracy, precision (both intra- and inter-day), and robustness studies demonstrated satisfactory results. The validated methods were successfully utilized for the determination of valsartan in three marketed tablet brands. Evaluation using the Analytical Eco-Scale indicated that both approaches represent excellent green analytical procedures, each achieving a score of 89.