Bead injection spectroscopy-flow injection analysis (BIS-FIA): an interesting tool applicable to pharmaceutical analysis. Determination of promethazine and trifluoperazine

A bead injection spectroscopy-flow injection analysis (BIS-FIA) system for the spectrophotometric detection of promethazine and trifluoperazine is developed. The sensor is based in the oxidation of the phenothiazines by Fe(III) which is later determined by formation of the complex between Fe(II) and Ferrozine, FeFz₃]⁴⁻. Immediately, this complex is retained on a homogeneous bead suspension of Sephadex QAE A-25 resin (500 μl) which has been injected previously in the system to fill a commercial flow-cell (Hellma 138-OS). The use of BI with respect to the use of a reusable flow-through sensor is justified because the complex is so strongly retained on the beads that the regeneration of the solid support becomes extraordinarily difficult in the proposed method. At the end of the analysis, beads are automatically discarded from the flow-cell, by reversing the flow, and transported out of the system. The analytical signals are measured at a wavelength of 567 nm, corresponding to the absorbance of the complex. Using a sample volume of 600 μl, the analytical signal showed a very good linearity in the range 0.5–8.0 μg ml⁻¹ and 0.5–10.0 μg ml⁻¹, with detection limits of 0.09 and 0.14 μg ml⁻¹ for promethazine and trifluoperazine, respectively. R.S.D.s (%) lower than 2% were obtained for both analytes. The proposed method is highly selective in the presence of other species that are normally encountered with these analytes. The sensor was satisfactorily applied to pharmaceutical preparations.