SINGLE STANDARD CALIBRATION AND DATA-PROCESSING IN FLOW-INJECTION TITRATION BASED ON CONCENTRATION GRADIENTS

This paper describes use of gradients of concentration generated in fl ow injection (FT) systems to perform determinations based on points wh ere the concentration of titrant and analyte are at stoichiometric rat io. Two procedures were developed. In one procedure the titrant is inj ected in a FI manifold and merges with the sample which is continuousl y pumped towards the detector. In the other procedure the sample is in jected and merged with the titrant which is continuously pumped. Both techniques make use of concentration gradients of the sample or titran t generated in FI manifolds that contain a mixing chamber. This gradie nt is calibrated employing only one standard solution (usually the tit rant) in order to convert any detector signal, obtained in the elapsed time after injection, to instantaneous concentration values. The flow system is microcomputer controlled and data are treated to locate poi nts where the concentration of titrant and analyte are at the stoichio metric ratio. These points are found in abrupt changes of the signal x concentration curves obtained in the presence of the reaction. The me thod has been evaluated for determination of Fe(II) and acetic acid by , spectrophotometric and conductimetric detection, respectively. Resul ts shore, a mean relative standard deviation bower than 1%, an average accuracy of 1% and a high sampling processing capability (40 to 60 sa mples pet hour).