Poly(2,5-dimethoxyaniline) based pH sensors Nophawan Paradee ...

91 NU Science Journal 2009; 6(S1)
2. Potentiometric Measurements of PDMA-modified Electrodes
2.1 Potentiometric Responses to pH Change
Figure 4 presents the calibration plot of the PDMA-modified electrode. A
response slope was found to be a sub-Nernstian slope of 49.31 ± 6.1 mV/pH (28 o C)
with the linear regression correlation coefficients greater than 0.997 over the pH
range of 2 to 8. The evolution of potential as a function of measuring time for the
PDMA-modified electrode in buffer solutions revealed that approximately 98% of
the steady response occurred in less than 10 seconds indicating a short response time
of the PDMA-modified electrode. As seen in Figure 4, however, a large deviation is
observed above pH 8. This suggests that the PDMA-modified electrode may not be
an effective pH sensor for basic solutions.
E (mV) vs. Ag/AgCl
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pH
Figure 4 Potentiometric responses to pH change of the PDMA-modified electrodes
A comparison of pH measurements in various solutions, including buffer pH
4, buffer pH 7, Pepsi, Sponsor, orange juice and water, was performed using the
PDMA-modified electrode and a commercial glass pH electrode. It can be seen in
Table 2 that the PDMA-modified electrode shows an acceptable difference for all
tested solutions, except water. It is important to note that the PDMA-modified
electrode is not suitable for basic solution as mentioned earlier.