Analytical Sciences

High-Throughput Photometric Titrimetry Based on a Feedback-based and Subsequent Fixed Triangular Wave-controlled Flow Ratiometry

Hideji TANAKA* and Tsutomu BABA**

*Institute of Health Biosciences, Tokushima University, Shomachi 1-78-1, Tokushima 770-8505, Japan
**Faculty of Pharmaceutical Sciences, Tokushima University, Shomachi 1-78-1, Tokushima 770-8505, Japan

The principle of flow ratiometry for high-throughput titration, which we recently proposed for potentiometric titration, was extended to photometric titration. The flow rate (F_B) of a base solution containing an acid-base indicator was linearly varied in response to a control voltage (V_c) generated from a computer. With the total (acid + base) flow rate (F_T) being kept constant, the base solution was merged with an acid solution, which was aspirated to the confluence point at a flow rate of F_T - F_B. Downstream, the relative transmittance of the mixed solution was measured at the maximum absorption wavelength of the base form of the indicator. Initially, a feedback-based control was applied, where the scan direction of V_c was reversed from upward to downward, and vice versa, whenever the transition of the indicator at the equivalence point (EP) was sensed. Next, the scan range of V_c was further limited to the range just around EP by using fixed triangular waves. These processes avoided scanning in a range of no interest. Thus, an unprecedentedly high throughput rate (maximally 34 titrations per minute, corresponding to 1.76 s per titration) was realized with reasonable precision (RSD < 0.5%).

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