ANALYTICA CHIMICA ACTA Analytica Chimica Acta 312 (1995) 189-198 Continuous flow titration system for the generation of multivariate spectrophotometric data in the study of acid-base equilibria * J. Saurina, S. Hernhdez-Cassou *, R. Tauler Departament de Q&mica Analitica, Universitat de Barcelona, Diagonal 647, 08028 Barcelona, Spain Received 27 July 1994; accepted 4 April 1995 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSR Abstract 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 X lop4 to 7.3 X 10m4 M have been performed, and, in every case, 24 spectra at different pH have been registered. Three species are detected in the range bf pH studied (6.9-12.3). Their distribution plot with pH and their unit spectrum have been obtained. Keywork Flow system; Titrimetry; Chemometrics; Multivariate curve resolution; SPFAC procedure; 1,2-Naphthoquinone-4-sulfonate 1. Introduction Several methods have been described in the litera- ture to carry out titrations by using continuous flow methodologies [l-5]. These methods take profit of the advantages of flow systems such as the speed, reproducibility, high degree of automation and low expense of apparatus and reagents. Continuous flow IT Presented at the 6th International Conference on Flow Analy- sis, Toledo, Spain, June 8-11, 1994. The majority of papers presented at this conference have been published in Anal. Chim. Acta. Vol. 308. titration manifolds are mostly based on the mixing of analyte and titrant solutions in a reaction coil fol- lowed by on-line detection. The analyte usually flows at a constant flow rate while that corresponding to the titrant solution is modified. In this way, parame- ters of the medium such as pH can be modified by generating a gradient along the titration when this titrant flow rate is varied. Several acid-base systems have been studied, although redox or complexation equilibria are also available. The recently reported flow injection titrations [6-91 are based on the injec- tion of-variable volumes of titrant into the system in order to obtain the corresponding titration curve. In both continuous flow and flow injection titration l Corresponding author. methods the detection of the process is usually per- 0003-2670/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDI 0003-2670(95)00223-5