Model-based rank annihilation factor analysis for quantitative analysis of mixtures of monoprotic acids using multivariate spectrophotometric acid-base titrations

A new application of rank annihilation factor analysis (RAFA) method is proposed for the quantitative determination of monoprotic acids in complex samples based on spectrophotometric acid-base titrations. The inclusion of a hard-modeling constraint based on the acid-base equilibrium model in the RAFA method allowed for the correct quantitation of the analyte in a sample mixture. An intrinsic difficulty in the analysis of spectrometric titration data is the presence of rank deficiency due to the closure for the mixtures of two or more compounds. Using the proposed approach, accurate quantitation is possible even in the presence of this rank deficiency. The presence of unknown and uncalibrated interferences in the samples does not affect the quantitative determination of the analyte of interest. Extra titration of standard and augmentation with sample matrix and also the matrix effects are avoided in the proposed method. The procedure was successfully applied to the analysis of mixtures of chlorophenols as model compounds.