High Throughput Titration Based on Variable and Fixed Triangular Wave Controlled Flow Ratiometry with LED-Photodiode Detector

Unprecedented high throughput flow titration (maximally 43.1 titrations/min) has been realized by a triangular wave controlled flow ratiometry using an in-house LED-photodiode detector. The detector was fabricated mainly with quartz tubing, an LED, a photodiode and a DC power supply. While the total flow rate is held constant, a titrand (acid) is merged with a titrant (base) containing an indicator, the flow rate of which is linearly varied by the control voltage Vc supplied from a computer. Downstream, the intensity of the transmitted light is monitored with the detector and acquired in the computer as detector output voltage Vd. In the initial feedback-based mode, the lamp direction of Vc is changed from upward to downward, or vice versa, when the detector senses the equivalence point. In the subsequent fixed triangular wave controlled mode, the scan range and the scan rate of Vc are further limited and quickened, respectively, in order to increase the throughput rate. Equivalence point is determined by offsetting the effect of the lag time between the upstream merging and the downstream sensing. Although the present approach is an absolute method, calibration curves have been constructed for practical operation. The linearity of the curve is satisfactory (r2 › 0.993). The present method is well applicable to various titrations of acids and bases including acetic acid in commercial vinegars.