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  1. 1.3.9. Stirred Chamber & FI Titrations When the volume of a well-mixed chamber (Vm) is much larger than the combined volumes of injector connecting tubes and detector, the concentration gradient will decrease exponentially, as described by one tank (N=1) model. This type of well-defined gradient has been used to dilute concentrated samples prior to detection (Gisin 1986), and to automate and speed up titrations. An acid injected into a carrier stream comprising of a base and an acidobasic indicator will become neutralized and therefore the width of the concentration gradient ( ) will be proportional to the concentration of injected acid. Since the concentration gradient decreases exponentially with time, the width of the recorded peak will be proportional to log C of the injected acid. While fast and simple, the FI titrations are due to this log/C dependence, less precise than conventional titrations ( Ruzicka & Hansen 1988). INDICATOR Gisin M., Thommen C, Mansfield K.F. Anal. Chim. Acta 179, 1986 149. Ruzicka J, Hansen E,H,H, flow Injection Analysis 2nd Ed. p 309. J. Wiley & Sons 1988.

  2. SAMPLE: HCl BASE & Ind. 1.3.10 Fast Titrations for Process Control The previously described titration can be accelerated by removing the mixing chamber and decreasing the volume of the channel between injector and detector. Provided that there is a sufficient radial mixing (induced by coiling or by other means), the conduit will behave like a mixed tank, albeit producing a limited exponential decay curve. The system will still respond in logC vs fashion, but the linear range will be limited to two decades of C, which is less than obtained with a mixing chamber. The example shows superimposed titrations of HCl (0.01M, 0.02M, 0.04M, 0.06M, and 0.1M) with 0.001M NaOH using bromothymol blue as indicator. Sample volume 30mL,flow rate 1,46mL/min (Ramsing 1981, Ruzicka 1989). The same system was also used for EDTA titration of Zn with xylenol orange as an indicator, and for the redox titration of iodine with thiosulphate with starch indicator. By replacing the peristaltic pump with a syringe pump, or by redesigning the apparatus into SI Mode, the system will become robust, and thus suitable for process control applications. A.U. Ramsing, J. Ruzicka and E.H.Hansen, Anal. Chim. Acta. 129(1981) 1. J. Ruzicka and E.H.Hansen. Flow Injection Analysis 2nd ed. Willey 1989. p235- 237.