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 (500l) 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 600l, the analytical signal showed a very good linearity in the range 0.5–8.0gml−1
and 0.5–10.0gml−1, with detection limits of 0.09 and 0.14gml−1 for promethazine and trifluoperazine, respectively. R.S.D.s
(%) lower than 2% were obtained for both analytes.