title: Determination of acid/base dissociation constants based on a rapid detection of the half equivalence point by feedback-based flow ratiometry.
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 approximately 3%) at a throughput rate of 56 s/determination.
authors.affiliation: Faculty of Pharmaceutical Sciences, Tokushima University, Shomachi 1-78-1, Tokushima 770-8505, Japan. htanaka@ph.tokushima-u.ac.jp
authors.forename: Hideji
authors.initials: H
authors.lastname: Tanaka
authors.forename: Takahiro
authors.initials: T
authors.lastname: Tachibana