Figure 16–3: Typical S/N ratio for norepinephrine measured with a VT-03 glassy carbon
flow cell (peak height: 80 nA, peak-to-peak noise: 1.5 pA)
The amount injected is 20 pmol (1.0 µmol/L). The concentration detection limit based on three
times the sigma-noise is 11 pmol/L.
16.1.5 Working electrode diameter
The size of the WE is an important factor in LC-EC; it affects both the signal and the noise. For
the VT-03 flow cell, several glassy carbon WE diameters are available (0.7, 2, and 3 mm). In a
standard LC system, the signal and the noise increase linearly with the WE diameter. This means
that the S/N ratio remains more or less the same. In micro-LC, an increase in WE diameter
increases the noise more than the signal. In micro-LC, a decrease in WE diameter results in a
better S/N ratio.
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