A Monosegmented Flow Titration for the Spectrophotometric Determination of Total Acidity in Vinegar

摘要

A monosegmented flow system involving sample and titrant sequential injections and the establishment of a tandem plug between two air bubbles is proposed for automated titrations. The end point is found after successive variations of the sample and titrant volumes, determined by an algorithm based on the one-dimensional optimization method of Fibonacci. The set up includes a multi-port solenoid valve with four inlets and one outlet. The feasibility of the system was demonstrated in the spectrophotometric determination of the total acidity in vinegar with NaOH and phenolphthalein used as the titrant and indicator, respectively. The sample throughput was ca. 30 h-1 and consumption of the sample and titrant was about 0.7 ml. The results were in agreement with the expected values, with relative errors lower than ±0.4%. After 12 successive analyses of typical samples with a 47.1 - 53.4 total acidity, expressed as g l-1 acetic acid, the relative standard deviations of the results were estimated within the 1.2 - 2.1% range.