Two- and Three-Dimensional Strategies for Determining Consecutive Acidity Constants of Ciprofloxacin and Enrofloxacin Using Fluorescent Excitation-Emission Measurements

Multidimensional analysis is getting more popular by the day thanks to technical improvements of analytical instruments and development of chemometric methods. Here, we describe the application of two different chemometric methods to the analysis of three-dimensional spectrofluorimetric dataset for green determination of dissociation constants of ciprofloxacin and enrofloxacin with minimal use of consumables. Three-dimensional spectrofluorimetric datasets of both drugs were obtained by recording excitation-emission matrices of only six sample solutions having different pH values. Parallel factor analysis (PARAFAC) and multivariate curve resolution (MCR) methods with the use of three components were used to decompose three-dimensional excitation-emission-pH arrays. The number of components support the presence of two pKa values. The individual profiles of H(2)A, HA(-) and A(2-) species in excitation, emission and pH modes were obtained by the application of PARAFAC and MCR. The intersection points in the pH modes were used to predict pKa values. pKa(1) and pKa(2) of ciprofloxacin was reported as 6.35, 9.15 and 6.42, 9.40 by PARAFAC and MCR-ALS, respectively. For enrofloxacin, consecutive pKa values were predicted as 6.11 and 9.06 by PARAFAC and 6.10 and 9.10 by MCR. A detailed comparison to literature was done for the estimated pKa values.