Critical approach to flow injection gradient titration as a calibration method

An attempt was made to demonstrate that flow injection gradient titration should not be considered as classical titration but rather as the indirect calibration method. This was shown experimentally by exploiting indirect spectrophotometric determination of chlorite ions in the presence of iron(II) in an acid environment with measurement of absorbance for the coloured Fe(II)/o-phenanthroline complex at 512 nm. In such an analytical system, the peaks of a cut-off profile were obtained with two characteristic points corresponding to equivalent amounts of analyte and reagent, and peak widths were used as the analytical signal. The only difference between the approach presented and the classical flow injection titration procedure was not fundamental but of a technical nature and consisted in the fact that a sample loop of relatively great volume instead of a mixing chamber was installed into the flow injection system. The analytical performance of the developed calibration procedure is also presented and discussed.