Flow injection spectroelectroanalytical method for the determination of promethazine hydrochloride in pharmaceutical preparations Original Research Article

The first flow injection spectroelectroanalytical method for the determination of promethazine hydrochloride has been developed. It is based on the in situ detection of a colored cationic radical formed during electroxidation at a gold electrode in sulfuric acid medium (0.1 mol l−1) and it offers a number of advantages in terms of simplicity, rapidity, selectivity and sensitivity over many other approaches. The determination of promethazine hydrochloride in pure form or in pharmaceutical formulations was investigated, considering the amperometric and the absortiometric signal. Although the amperometric signal alone can be used for the determination of promethazine in simple formulations like Fenergan (Rhodia-Farma), the photometric signal might become decisive when other electroactive compounds, such as dipyrone, are present in the formulation, e.g. in Lisador (Farmasa). Promethazine was quantified in Fenergan and Lisador. The results obtained using either conventional calibration curves or standard additions, were equivalent to those obtained with the official method recommended in the British Pharmacopoeia (BP) and in agreement with the labeled composition, for Fenergan. For Lisador, the results for promethazine were within 2% of the nominal value informed by the producer and the official method could not be applied due to dipyrone interference.