Determination of the AcidityConstant of Drugs Usingthe Hard–Soft Net Analyte Signal Method.

The newly proposed hard–soft net analyte signal(HS-NAS)method was employed to determine the acidity constants of drugs. Thespectrophotometricdata obtained through monitoring of the pH-metric titrations of theacids (both experimental and simulated data) were analyzed by theHS-NAS method, and accurate results were obtained. As experimentaldata sets, tetracycline as a triprotic acid and p-aminobenzoic acid, m-aminobenzoic acid, and piroxicamas diprotic acids were studied. In addition, the acidity constantsof the drugs were determined in the presence of Triton X-100 as aninert light-absorbing interference. The data for such systems, whichare rank-deficient in nature, were successfully analyzed by the HS-NASmethod. This method is based on changing the acidity constants ofthe drugs to maximize the correlation coefficient between the NASvector obtained for one species of the reaction and the theoreticalconcentration profile of that species. Unlike existing methods, itneeds neither previous information on the pure spectra of the species(as required for rank annihilation factor analysis) nor the hard modelsof all species contributing to the absorbance of the solution (asneeded for the hard modeling method). [ABSTRACT FROM AUTHOR]