Development of a micro-flow titration method and application to acid-base titration

Abstract

A flow titration analysis method based on flow ratiometry was developed in this study from the viewpoint of simplicity, rapidity, automation, and cost efficiency. Sample and titrant solutions react while the solutions are continuously propelled by individual pumps at different flow rates. The flow rates are accurately controlled and changed independently, and the color change of an indicator gives an equivalent point. The concentration of analyte was determined by using the ratio of the flow rate and the equivalent point. The fundamental properties of the flow titration method were evaluated through acid-base titration, and compared with the conventional manual titration. When Phenolphthalein or Cresol Red was used as an indicator added in either the sample solution or the titrant solution, linear calibration graphs were obtained for all titrations examined, including strong and weak acids. The proposed method was applied to the titration of carbonate salt using Bromocresol Green and Phenolphthalein. Two isolated end-points were obtained in one sequential measurement corresponding to carbonate and bicarbonate ions. The proposed titration method was applied to the analysis of commercial vinegar samples. The results agreed well with the ones obtained by the conventional titration method; the relative standard deviations for the end point were within 0.3%. The volume of wastewater per one measurement can be reduced down to about 100 μl by the proposed method, while a practical method requires about 50 ml.