Two simple, sensitive and extraction-free spectrophotometric methods are described for the estimation of risperidone (RSP) in both pure and in pharmaceutical preparations. The proposed methods are based on the formation of ion-pair complex between RSP and the dyes, bromophenol blue (BPB) in method A and Phenol red (PR) in method B at room temperature to form yellow colored products which show maximum absorbance at 410 and at 400 nm in methods A and B, respectively. Beer's law was obeyed in the concentration range of 0.5-10 and 0.5-25 μg mL-1 in methods A and B with apparent molar absorptivities of 3.43 × 104 and 0.85 × 104 L moL-1 cm-1, respectively. The limit of detection for method A is found to be 0.0056 and for method B is 0.132 μg mL-1. The composition of the ion-pairs was established by Job’s method and it was found to be 1:1 for both the methods A and B. The proposed methods have been applied successfully to the determination of RSP in pharmaceutical preparations. The results were statistically compared with those of a reference method by applying the Student’s t-test and F-test. The methods developed were validated for accuracy and precision by performing recovery experiments via standard addition technique

The aim of this work was to develop a simple, sensitive and extraction free spectrophotometric method for the quantitative estimation of valsartan in both pure and in pharmaceutical preparations. The developed method is based on the charge transfer complexation reaction between valsartan (VRT) as n-electron donor and pchloranilic acid (p-CA) as π-acceptor. VRT reacts with p-CA in methanol to produce a bright pink colored complex with a maximum absorption at 530 nm. Beer's law was obeyed in the concentration range of 5-50 µg/mL. The linear regression equation of the calibration graph is A = 0.0081+0.0092C with a regression coefficient (r) of 0.9976 (n = 7). The molar absorptivity is calculated to be 2.06 × 10 3 L mol -1 cm -1 and the Sandell sensitivity is 0.1025 μg cm -2 . The limits of detection (LOD) and quantitation (LOQ) values are calculated according to ICH guidelines. The method developed is successfully applied to the determination of VRT in dosage forms.