Design a continuous microfluidic flow cell for turbidimetric-flow injection technology: A new approach for routine analysis of active pharmaceutical formulations

In this study, a new flow injection analysis (FIA) based on a microfluidic flow cell (MFC) with a sample capacity of 40 µL is described. A Tungsten lamp directs light from a typical 2100P Portable Turbidimeter apparatus into a quartz flow cell through a round sidewall aperture of 2.0 mm and emerges through the identical aperture on the opposite side of the flow cell, where a photodiode array (light detector) detects the passing light. When compared to a traditional cuvette (25 mm x 60 mm round) with the same nominal route length, this technique improves sensitivity by around 4.0. This improvement is due to the use of a short, narrow internal diameter microfluid as the flow cell, which reduces physical dispersion. The designed flow cell has been evaluated by developing a turbidimetric method for the detection of promethazine in pure form or pharmaceutical dosages. The developed method is based on forming of a yellowish ion-pair association complex due to the reaction of promethazine and sodium tetraphenylborate (STPB) in an acidic medium. At the flow optimum conditions, the calibration curve (CC) and the limit of detection (LOD) for promethazine were obtained 0.5-90 µg mL^-1 and 0.35 µg mL^-1. respectively (R² = 0.9955). The intra-day and inter-day precisions (RSD%) of the FIA-MFC method for measuring promethazine at concentrations of 20, and 50 µg mL-1 were achieved (2.0 and 1.6) and (0.8 and 1.2), respectively.