3.4. Effect of pH
The effect of pH on the response was investigated in the
pH range 4–8 at 25 ◦C. The response to standard solution
of 0.5mM ethanol was recorded and no significant differences
were registered in this pH range. This is a normal
behaviour taking into account that the sample is separated
from the yeast cell layer by the gas-permeable membrane,
which does not allow ion exchange between the external and
internal parts of the membrane. All further measurements
were carried out at pH 7.