A monosegmented flow titration for the spectrophotometric determination oftotal acidity in vinegar

A monosegmented flow system involving sample and titrant sequential injecti ons and the establishment of a tandem plug between two air bubbles is propo sed for automated titrations. The end point is found after successive varia tions of the sample and titrant volumes, determined by an algorithm based o n the one-dimensional optimization method of Fibonacci. The set up includes a multi-port solenoid valve with four inlets and one outlet. The feasibili ty of the system was demonstrated in the spectrophotometric determination o f the total acidity in vinegar with NaOH and phenolphthalein used as the ti trant and indicator, respectively. The sample throughput was ta. 30 h(-1) a nd 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 to tal acidity, expressed as g l(-1) acetic acid, the relative standard deviat ions of the results were estimated within the 1.2 - 2.1% range.