Evaluation of thermodynamic ionization constants by computation of spectrophotometric and potentiometric experimental data obtained simultaneously from a flow system.

A method is proposed for the direct and simultaneous determination of the thermodynamic ionization constants of bifunctional substances, with (microscopic) and without overlap in the ionizations, with computational treatment of spectrophotometric and potentiometric experimental data obtained simultaneously in a flow system. For monofunctional substances, potentiometric data are enough. The data are obtained at very low values of ionic strength, which is variable throughout the experiment because no inert electrolyte is added. The MICROTER program, written in FORTRAN 77, is based on an algorithm of mathematical optimization with a controlled-descent movement. The ionization constants of the following substances of pharmacological interest were determined: cysteine, penicillamine, ofloxacin, and norfloxacin (bifunctional with overlap); cephalexin and cephapirin (bifunctional without overlap); and tolazoline, naphazoline, and oximetazoline (monofunctional).