Knauer Azura ECD 2.1, Инструкция по эксплуатации

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58 Optimization of the working potential
AZURA® Detector ECD 2.1 Instructions, V6685
Fig. 44 Selectivity in LC-EC of compound X and Y is optimised by choosing
the working potential with the largest difference in peak height.
Electrochemical reactions are pH sensitive (Fig. 45). For norepinephrine
the I/E curve is shifted to a lower potential at higher pH. When the wor-
king potential is high (E2), and the signal is diffusion limited, an increase
in pH will result only in a small increase of the peak height. When the
working potential is lower (E1), and the signal is not diffusion limited, the
signal will strongly increase at higher pH. In both cases the background
current increases at a higher pH.
Fig. 45 At a higher pH the I/E curve of norepinephrine is shifted to the left.
Reaction kinetics predict that electrochemical detection is mass flow de-
pendent. When the LC flow is stopped in LC-EC, the analyte will be oxidi-
zed completely and the signal decreases rapidly. This means that the flow
rate not only affects temporal peak width and analysis time but also peak
height. Also the background signal is sensitive towards fluctuations in the
flow rate. Therefore, it is important to use a pulse-free solvent delivery
system.