Second-order multivariate curve resolution applied to rank-deficient data obtained from acid-base spectrophotometric titrations of mixtures of nucleic bases

Rank-deficient data matrices, obtained from simulated spectrophotometric acid-base titrations of mixtures of up to four nucleic bases (adenine, cytosine, hypoxanthine and uracil), were analyzed by second-order multivariate curve resolution. The analysis of these individual mixture data matrices gives a rank value of n + 1, where n is the number of nucleic bases present in the system. This number is, however, lower than 2n, the number of spectrometrically active species theoretically present in the systems under study, since each nucleic base is expected to give two species, a protonated and a deprotonated species. This rank deficiency is solved when more than one titration is simultaneously analyzed by second-order multivariate curve resolution. Full rank recovery is achieved when the titration of the mixture of n nucleic bases and other n - 1 titrations, each one corresponding to a different base, are simultaneously analyzed. Results obtained by second-order multivariate curve resolution indicate that for a total resolution of the system full rank is necessary. However, resolution and quantitative determinations of individual nucleic bases in mixtures in the presence of interferences can be achieved (with a prediction error lower than 2% in most cases) even in the case of rank deficiency.