Externally buffered enzyme electrodes

In an externally buffered enzyme electrode (Fig. 45), substrate-free buffer is continuously pumped between the dialysis membrane and the enzyme layer (Cleland and Enfors, 1984), i.e., the sample is diluted before it reaches the enzyme. The intensity of the buffer flow may be used to adjust the measuring range and sensitivity. The configuration of the sensor permits it to be sterilized. While the membrane is protected by continuously flowing buffer, the rest of the sensor can be sterilized for 1 h in a solution of 95% ethanol and 5% H2SO4. 

Fig. 45. Externally buffered enzyme electrode. (Redrawn from Cleland and Enfors, 1984).

Figure 1441. Sampling from a fermenter for on-line analysis (after [366]). 1. Direct removal of fermentation broth (analyte A) 2. indirect sampling by ultrafiltration, dialysis, electrodialysis, per-vaporation, providing an analyte A of proportional concentration, normally diluted 3. indirect sampling by extraction of fermentation broth by external buffer 4. in situ measurement by means of an enzyme electrode or using a sterile housing with inserted electrode. F = fermenter, W = waste.

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