Continuous flow titration based on complementary variation of titrant and sample concentrations

A novel automated titration procedure with spectrophotometric detection, based on opposite variations in titrant and sample flow rates under constant total flow, was developed. Concentrations of sample and titrant were varied simultaneously, from the original concentration to zero, and vice versa, by continuous change of flow rate (from 100% of the selected flow rate to 0, and conversely) of pumps. The procedure does not require conventional calibration; however, periodic calibration of the flow system is necessary to determine the titrant dilution factor at the titration end point under identical instrumental conditions. The procedure was evaluated by determining the citric and tartaric acids using NaOH as the titrant. Both acids were determined with very good precision and trueness (coefficient of variation, CV, lower than 1.6% and relative error, RE, lower than 3.1%, respectively). The procedure was successfully applied to determine the total acidity in non-alcoholic beverages and wines. The titration was completed in about 2 min, and 1.0 mL of each, the titrant and the sample, was consumed.