A mixed hard- and soft-modelling approach for the quantitative determination of oxipurines and uric acid in human urine Original Research Article

A new treatment of kinetic-enzymatic data, joining the benefits of hard- and soft-modelling methods, is proposed for the kinetic resolution and simultaneous quantification of xanthine oxidase induced oxipurines (hypoxanthine and xanthine) and uric acid in human urine without any further separation. These three analytes show highly overlapped spectral bands in the range of 232–320 nm and urine contains absorbing species in this wavelength range that behave as a constant interference throughout the monitoring of the kinetic experiment. The proposed method allows the determination of the analytes in human urine by simultaneous analysis of the urine sample and a few (even only one) standards of pure analyte mixtures of hypoxanthine and xanthine in aqueous solution. An iterative mixed hard- and soft-modelling multivariate curve resolution (HS-MCR) algorithm, which includes a hard-modelling constraint based on the enzymatic model in the parent multivariate curve resolution-alternating least squares method (MCR-ALS), is applied to a data set formed by the standards and the urine samples. Hard-modelling is applied to the concentration profiles of the three analytes in the standards, whereas soft-modelling on the analytes and the urine in the samples gives the quantitative information. As a result, quantitative information similar in quality to that obtained by separation techniques (HPLC and HPCE) and other chemometric approaches (PLS and N-PLS) is obtained with less experimental effort and a much smaller number of standards in aqueous solution that do not need to contain the interferences present in the samples.