Application of two- and three-way chemometric methods in the study of acetylsalicylic acid and ascorbic acid mixtures using ultraviolet spectrophotometry

In this work, mixtures of acetylsalicylic acid (ASA) and ascorbic acid (AA) were studied by ultraviolet spectrophotometry (210-300 nm) using parallel factor analysis (PARAFAC) and partial least square (PLS). The study was carried out in the pH range from 1.0 to 5.5 and with a concentration range from 1.0 x 10(-5) to 1.0 x 10(-4) mol l(-1) of both analytes. PARAFAC was used for spectra deconvolution, pK(a) estimation for both acids and to check the presence of salicylic acid (SA), due to the possible ASA decomposition. The estimated first pK(a) was equal to 3.41 and 4.10 for ASA and AA, respectively. Multivariate calibration models using PLS at different pH and N-way PLS were elaborated for simultaneous determination of ASA and AA in pharmaceutical samples. The best models for the system were obtained with N-way PLS2 and PLS2 at pH 1.1. The results obtained for simultaneous determination of ASA and AA in samples were in agreement to the values specified by the manufacturers and the recovery was between 97.6 and 103.6%. Nevertheless, these models failed to predict ASA decomposition to SA in simulated samples. Thus, a new PLS-pH1 model considering SA was built and applied successfully in simulated samples. (C) 2000 Elsevier Science B.V. All rights reserved.