Continuous flow titration system for the generation of multivariate spectrophotometric data in the study of acid—base equilibria

In the present work a continuous flow system to carry out spectrophotometric titrations is developed. The titrant solution is generated on-line from mixing two different stock buffer solutions. The composition of the titrant agent is sequentially varied along the titration by changing the ratio of flow rates of both buffer channels, and therefore the pH can be modified. One spectrum is recorded at each pH value when the absorbance achieves the steady state. The spectral data have been treated by means of a recently developed self-modelling multivariate curve resolution method (SPFAC procedure). This method has been applied to the study of the acid-base equilibria of 1,2-naphthoquinone-4-sulfonate (NQS). Four titrations with concentrations of NQS ranging from 1.6 × 10−4 to 7.3 × 10−4 M have been performed, and, in every case, 24 spectra at different pH have been registered. Three species are detected in the range of pH studied (6.9–12.3). Their distribution plot with pH and their unit spectrum have been obtained.