Antec Scientific VT-03, Руководство пользователя

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CHAPTER 1 The electrochemical flow cell 9
amount injected is 20 pmol (1.0 µmol/l). The concentration detection limit
based on three times the sigma-noise is 11 pmol/l.
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 increases linearly with the WE diameter. This means that he S/N ratio
remains more or less the same. In case of micro -LC an increase of the WE
diameter will increase the noise more than the signal. Therefore, in micro-LC
a decrease of the WE diameter will result in a better S/N ratio.
Table III. Flow cell recommendations.
Column diameter (mm) Recommended flow cell
3 and higher 3 mm GC
3 - 1 2 mm GC
1 and below 0.7 mm µGC
The choice for a flow cell is primarily based on the HPLC column diameter
(Table III). This way the best possible detection limit for a standard,
microbore or capillary column is warranted.
The recommended combinations are giving the best S/N ratios. It should be
kept in mind that other combinations are possible that still result in acceptable
sensitivities for many applications. All VT-03 flow cells are individually tested
and meet our high standards of quality and detection sensitivity.
Spacer thickness
The thickness of the gasket affects the linear flow velocity in the cell. With a
thinner spacer the cell volume is decreased (Table IV), resulting in a higher
linear flow velocity. The signal increases with thinner spacers while the noise
remains more or less constant (Fig. 4).
Several authors have described the relation between the layer thickness (i.e.
spacer thickness) in a thin layer flow cell and the measured current (S) as S
= k b
-2/3
where b is the spacer thickness and k a constant. Also for the VT-03
flow cell the relation between S and b
-2/3
results in a straight line (Fig. 5).