Antec Scientific VT-03, User Manual, Page: 8 / 36

8 VT03 flow cell user manual, ed. 8
In literature several ways are described to determined the detection limit. In
principle, it does not matter which definition of detection limit is used, as long
as the definition is precisely described.
In this manual the concentration detection limit (c
LOD
) for a certain compound
is defined as the analyte concentration that results in a signal that is 3 times
the standard deviation of the noise:
c =
3
signal
c
LOD
noise
A


where sigma-noise is 0.2 x peak-to-peak noise and c
A
is the concentration of
analyte injected.
In Fig. 3 a typical S/N ratio of a VT-03 glassy carbon flow cell with 2.74 mm
WE is shown. In this example the concentration detection limit for
norepinephrine based on three times the sigma-noise is 11 pmol/l (see Table
II for conditions).
Expressing the performance of a detection system by only the peak height
makes no sense. A system can easily be changed in a way that a larger peak
height is obtained. However, if the noise increases similarly, it has the same
effect as switching a recorder to a higher sensitivity: peaks appear higher but
the S/N ratio is the same.
Expressing the limit of detection in an absolute amount (i.e. in picomoles)
without mentioning the injection volume, makes a good comparison between
different systems difficult.
Fig. 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