45
Noise suppression: ADF™
AZURA® Detector ECD 2.1 Instructions, V6685
Typically in chromatography narrow peaks are in front of a chromatogram
while peaks with longer retention times get wider. As a consequence
frequencies are not constant but vary between 0.1 – 0.01 Hz, which corre-
sponds to 10 – 100 s peak width.
Fig. 30
Typical chromatogram with peak widths between 10 – 100 s.
Noise in chromatography can come from different sources. Pump pulsa-
tions are typically shown as a very regular noise pattern, while electronic
noise has a more random character. This is illustrated in Fig. 31 where a
noise trace is shown with an overlay of a 10 and 0.4 Hz sine.
Fig. 31
Typical random noise in chromatography (lower trace). Both frequen-
cies (0.4 and 10 Hz) can be recognised amongst others.
Looking closely to the lower noise trace both frequencies (and others)
can be recognised. This is typical for noise in chromatography: a collec-
tion of more or less random frequencies.
Low pass noise filters
The way noise filters work is by suppressing certain frequencies in the
acquired signal. Typically low pass filters allow chromatographic peaks
(low frequency) to pass, while high(er) frequency noise is attenuated. No
matter how advanced, it is impossible to use a low pass filter successfully
if there is no difference in frequency of signal and noise.
ADF
-2000
98000
198000
298000
398000
498000
598000
698000
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
min
h
40 s
0.025 Hz
10 s
0.10 Hz
-5
0
5
10
15
20
30
31
32
33
34
35
36
37
38
39
40
t (s)
I (pA)
sine f = 10 Hz
sine f = 0.4 Hz
Summary of Contents for Azura ECD 2.1
Page 1: ...HPLC Detector ECD 2 1 Instructions Document No V6685 ...
Page 32: ...28 ECD 2 1 controller AZURA Detector ECD 2 1 Instructions V6685 Pulse mode ...
Page 33: ...29 ECD 2 1 controller AZURA Detector ECD 2 1 Instructions V6685 Scan mode CONFIC menu ...
Page 34: ...30 ECD 2 1 controller AZURA Detector ECD 2 1 Instructions V6685 DIAG menu ...
