3.5. Calibration
Response curves for ethanol concentrations between 0.02
and 50mM were recorded and calibration graphs were produced
using steady-state and kinetic methods. Fig. 3 shows
the graph for the steady-state method at pH 7 and 25 ◦C.
Each point represents the average for five determinations. A
linear calibration plot was obtained.
The linear regression parameters (y = ax + b) are
a = 139.0 ± 2.3, b= 26.51 ± 0.71
with the correlation coefficient R = 0.9978 (n = 40).
The slope of 26mV per decade shows a sub-Nernstain response
of the biosensor, a comparable sensitivity with the potentiometric
biosenser for sucrose [23]. The detection limit
corresponds to an ethanol concentration of 5.7 M.
A calibration plot for the kinetic method also shows a linear
relationship between the potential and the ethanol concentration
with the following parameters:
a = 62.0 ± 1.1, b= 12.85 ± 0.32, R= 0.9981
The sensitivity for the kinetic method is about half that
of the steady-state method but there was a good correlation
for both methods.