Rank annihilation factor analysis for multicomponent kinetic-spectrophotometric determination using difference spectra

In this work rank annihilation factor analysis (RAFA) is used to analyze difference spectra of kinetic-spectrophotometric data. Annihilation of the contribution of one chemical component from the original data matrix is a general method in RAFA. However, sometimes RAFA is not suitable for studying rank deficient data such as kinetic-spectrophotometric measurements. On the other hand, in order to apply RAFA for the determination of an analyte in an unknown sample, a standard two-way matrix of the analyte with rank one should generally be available. This is not usually attainable for kinetic-spectrophotometric monitoring of complexation reactions. Processes monitored by difference spectroscopy always have the spectrum of the initial stage subtracted from each spectrum in the data matrix. In this work we show that, for kinetic-spectrophotometric data of complexation reactions, the spectrum of ligand (reactant) itself can be used as initial spectrum for subtraction. The obtained difference matrix of sample and that of analyte of interest will be full-rank and rank 1, respectively. Therefore the system can be analyzed by RAFA. The proposed method was investigated with simulated data at the first stage. The method was then applied in the analysis of experimental kinetic-spectrophotometric data of a complexation reactions of Co(II) and Ni(II) with chromogenic reagent 1-(2-pyridylazo) 2-naphthol in order to do multi-component determination of these ions in various real samples. Copyright (C) 2009 John Wiley & Sons, Ltd.