Determination of Acid/Base Dissociation Constants Based on a Rapid Detection of the Half Equivalence Point by Feedback-Based Flow Ratiometry

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Abstract

Acid dissociation constants (Ka) were determined through the rapid detection of the half equivalence point (EP1/2) based on a feedback-based flow ratiometry. A titrand, delivered at a constant flow rate, was merged with a titrant, whose flow rate was varied in response to a control voltage (Vc) from a controller. Downstream, the pH of the mixed solution was monitored. Initially, Vc was increased linearly. At the instance that the detector sensed EP1/2, the ramp direction of Vc changed downward. When EP1/2 was sensed again, Vc was increased again. This series of process was repeated automatically. The pH at EP1/2 was regarded as being pKa of the analyte after an activity correction. Satisfactory results were obtained for different acids in various matrices with good precision (RSD ≈3%) at a throughput rate of 56 s/determination.

Journal

  • Analytical Sciences

    Analytical Sciences 20 (6), 979-981, 2004

    The Japan Society for Analytical Chemistry

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