LRA, Vol. 11, pp. 207–216 207 Study on the Implementation of Flow Titrations in Sequential Injection Analysis J. M. Estela, F. Mas, A. Cladera, and V. Cerda ` Department of Chemistry, University of the Balearic Islands, 07071 Palma de Mallorca, Spain Received 11 November 1998; revised 12 January 1999 ABSTRACT: Several variables that affect flow spec- trophotometric titrations in sequential injection analysis (SIA) systems were studied by using titration of a strong acid with a strong base as a model; blue bromothymol was used as an indicator and distilled water was used as a carrier. Both possibilities of per- forming titrations on SIA systems according to the aspiration sequences (a) titrant B/sample/titrant A and (b) titrant/sample are considered. In case (a) the possibilities regarding the use of different volumes and/or different concentrations of titrant reagents were studied and are discussed. The established methodology allows hydrochloric acid determina- tions with 0.1 M sodium hydroxide within the range 32–1000 mM by means of logarithmic calibration curves. The analysis rate is of 5 min/sample.  1999 John Wiley & Sons, Inc. Lab Robotics and Automa- tion 11: 207–216, 1999 INTRODUCTION In 1977 Ruzicka et al. [1] presented a new approach to continuous flow titrations based on studies of dis- Correspondence to: V. Cerda ` Contract Grant Sponsor: Spanish Comisio ´ n Interministerial de Ciencia y Tecnologia, Project AMB94-0534.  1999 John Wiley & Sons, Inc. CCC 0895-7533/99/040207-10 persion patterns called FIA titrations. Although this denomination has been the issue of controversies mainly due to the fact that it does not strictly conform with the definition of titration given by IUPAC [2] and according to the conclusions drawn from the studies performed by Pardue and Field [3], the for- mer technique has been successfully used in FIA in numerous applications for all kinds of analytes, by means of acid–base, redox, complex formation, etc. reactions. In FIA, two variants of the technique were chiefly used. In the first, a gradient chamber [4] is used in addition to a manifold involving one or two chan- nels, with which a large reproducibility of the sample dispersion is attained. In the second variant [5–8], a sample volume in a titrant flow is injected, giving rise to two dispersion zones at both sides of the sampling zone in a manifold of a sole channel. A disadvantage of the latter over the former variant is less precision, however, the advantages that have made this variant especially attractive include a greater simplicity of the manifold, smaller sample volumes, higher anal- ysis rates, and a higher sensitivity, because the gra- dient chamber that can give rise to a large dilution of the sample is not used. All of the FIA titrations are based on the mea- surement of the peak width, which is defined by the location of a pair of equivalent points detected by the