Automatic Stepwise Potentiometric Titration in a Monosegmented Flow System

 An automatic stepwise potentiometric titration carried out in a monosegmented flow system is proposed. A tubular hydrogen ion-selective electrode without inner reference solution was employed as sensor. The titration procedure was implemented by exploiting continuous variations in volumetric fractions achieved by inserting different sample and titrant aliquots into the analytical path and maintaining the sample zone volume. Every sample plug was separated from the carrier solution by air bubbles to minimize dispersion and to distinguish each sample plug signal. The flow set-up comprised a set of computer-controlled three-way solenoid valves, and the software was written in Quick BASIC 4.5 allowing end-point determination while the titration was in progress. The feasibility of the system was ascertained by analyzing soft drinks, isotonic beverages, alcohol free beers and industrial fruit juices. Results were in agreement with those obtained by a conventional titration, and no significant difference at 95% confidence level was observed. Other profitable features such as a 1% standard deviation (n = 10), and an analytical throughput of 22 samples per hour were also achieved. Received January 24, 2000. Revision June 16, 2000.