Simple and extraction-free spectrophotometric methods for risperidone in pure form and in dosage forms

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.