Air-segmentation approach has been introduced to a feedback-based and subsequent fixed triangular wave-controlled flow ratiometry to suppress axial dispersion in flow titration. Flow rate of a base solution containing an indicator is linearly varied with a control signal Vc supplied from a computer. The solution is merged with an acid solution under constant total flow rate. Air is introduced to the merged solution in order to segment the solution with air bubbles. Both phases are led to a UV/Vis detector without phase separation. Air signals are removed by a signal processing. The effect of lag time between the merging of solutions upstream and the sensing of corresponding signal downstream is offset by feedback-based upward and downward Vc scans, and thus the Vc that gives the equivalence composition is determined. Subsequently, fixed triangular wave control is applied to narrower Vc range with higher scan rate to enhance the throughput rate (maximally 11.8 titrations/min). Air-segmentation has found to be effective to reduce axial dispersion and to preserve the titrand/titrant composition on their just being merged. Consequently, applicable range extended especially to lower titrand concentration. The proposed method has successfully been applied to various acid-base titrations including nonaqueous titration of the Japanese Pharmacopoeia drug.

We propose a novel concept for detecting color transition by the inner product (IP) of RGB unit vectors. A digital microscope-based detector and a Visual Basic program were developed in-house. The concept is applied to indicatorbased flow titration. The IP is 1 or < 1 if the vector's direction is the same or different, respectively. The IP's change can be used as a criterion for the indicator's color transition. The present IP-based approach is simple, economical, and versatile because it is applicable to any color transition without selecting an analytical wavelength.

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