Chemometric Determination of the Acidity Constant of Etodolac Using PARAFAC and MCR‐ALS Modeling of UV‐pH Spectral Dataset

Abstract The acidity constant (pKa) is a fundamental physicochemical parameter that affects a drug's solubility, permeability, and bioavailability. In this study, chemometric modeling strategies, parallel factor analysis (PARAFAC), and multivariate curve resolution–alternating least squares (MCR‐ALS), were applied to UV‐pH absorbance data of the nonsteroidal anti‐inflammatory drug etodolac. Spectral measurements across varying concentrations and buffer media were modeled to resolve acidic and basic species profiles. The calculated pKa values, 4.64 (PARAFAC) and 4.55 (MCR‐ALS), showed strong agreement and confirmed the reliability of these approaches. The results highlight the potential of multiway and bilinear modeling as rapid, titration‐free alternatives for precise pKa determination in pharmaceutical analysis.