Simultaneous Determination of the Acid Dissociation Constants of Phenolics by Multivariate Analysis of pH and Ultraviolet-Visible Spectrophotometric Measurements

Abstract

In the development of new commercial products in the pharmaceutical and food industries, acid dissociation constant (K_a) values of active and inactive ingredients are important factors for the estimation of the biological activity. In this regard, new spectrophotometric approaches based on parallel factor analysis (PARAFAC) and multivariate curve resolution-alternating least squares (MCR-ALS) to pH-absorbance dataset are described for the simultaneous determination of the acid dissociation constants of the phenolics ferulic acid, 4-hydroxybenzoic acid, syringic acid, protocatechuic acid, vanillic acid, and isovanillic acid that have more than one dissociation equilibrium without using classical titration procedures. The acid dissociation constants were determined by the pH profiles obtained by bilinear MCR-ALS and trilinear PARAFAC decomposition of pH-ultraviolet and pH-ultraviolet-visible spectroscopic datasets of the phenolics. For the quantification of the acid dissociation constants with the MCR-ALS and PARAFAC approaches, the estimated spectral profiles provided an opportunity for the direct observation of the individual spectral bands of each phenolic without the use of additional software. The results showed that MCR-ALS and PARAFAC applications to spectrophotometric measurements at various pH values were alternatives for solving acid dissociation constant problems that cannot be determined by classical methods.

Keywords:

• Acid dissociation constant
• multivariate curve resolution
• parallel factor analysis
• phenolics
• ultraviolet-visible spectrophotometry

Additional information

Funding

This work was carried out within the Chemometrics Laboratory of Ankara University, Faculty of Pharmacy, which was founded by Ankara University Scientific Research Projects Coordination Unit (Project 10A3336001). The authors acknowledge the financial support by the Research Fund of Necmettin Erbakan University (Project Number: 182015001) and the Ankara University Scientific Research Projects Coordination Unit (Project Number: 16H0237006).