CHAPTER 6 Pulsed amperometric detection
57
different from the noble metals. The capacitance of the electrode material is
very high, such that the charging current is not stabilised before start of the
next potential step. This pattern makes detection impossible.
Fig. 21. Change in cell current during PAD. The cell current of the noble
metals gold (Au) and platinum (Pt) is stabilised faster than the cell current of
glassy carbon (GC), due to a much lower capacitance of the noble metals.
For Pt and GC the negative peaks run far off-scale, however the profile is
similar to the mirror image of the positive peaks.
Examples of carbohydrate analyses are given in Fig. 17. Typical PAD pulse
settings are given in Table X and
Table XI, these settings may be used as starting point for further optimisation.
Carbohydrates are oxidised at a pH of 12 or higher, which puts specific
demands on the HPLC system used (see above).
Table X. Potential settings for PAD of carbohydrates at a gold working
electrode.
s 1 2 3
t (ms)
100
400
200
200
E
(mV)
+150 +750 -800
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