OPTIMIZATION OF THE INDIRECT IMPEDANCEMETRY TECHNIQUE - A HANDY TECHNIQUE FOR MICROBIAL-GROWTH MEASUREMENT

In the indirect impedancemetry technique, the CO2 produced during biol ogical activity reacts with potassium hydroxide (KOH) solution, provid ing negative conductance variation. In this work, this technique was o ptimized, on a rapid automated bacterial impedance technique (RABIT) a pparatus, developed by Don Whitley Sc. Ltd (UK). The KOH concentration and volume, as well as the temperature were tested. The dynamics of C O2 absorption and the ratio between the conductance variation and the amount of CO2 produced were examined. After injection of CO2 either di rectly in the KOH solution, or above the KOH solution, the best result s were obtained with a KOH volume corresponding to immersion of the el ectrodes (0.7-1.2 ml), and with KOH concentrations of up to 7 g/l, alt hough 5-6 g/l is preferred. Decrease of 280 mu S/mu mol CO:, was obtai ned at 27 degrees C for a KOH concentration ranging from 0.5 to 8 g/l. All these results were slightly affected by temperature. However, it would be preferable for the CO2 produced to be bubbled directly into t he KOH solution, in order to decrease the dynamic response of the syst em (gaseous transfer).