BUCHI ELS Detector C-650 - Manual (Page 41)

C-650 Operation Manual, Version B 6 Operation 41
Fig 6.27:Chromatogram with variing solvent quality
The mobile phase should not contain non-volatile solvent modifiers. Volatile solvent modifiers
(e.g. CHOOH, CH
3
COOH, CF
3
COOH, NH
4
Formate, NH
4
. Acetate, (C
2
H
5
)
3
N)…) can be used, but
they may increase the noise level at high gain settings. In addition, the solvent should not contain
preservatives, (e.g. Tetrahydrofuran may contain BHT as a stabilizer).
The wetted parts of the detector are made from PTFE, stainless steel, and glass. Make sure that
the solvents do not react with these materials.
NOTE
Depending on the mobile phase nature and flow rate, the suggested gas pressure 3.5 bar
(51 psi) may have to be adjusted in order to optimize the background noise and so Signal-to-
Noise ratio.
6.4.3 Sample pretreatment
If the sample contains any particulate matter, it should be filtered through a 0.2 µm or 0.45 µm
filter before injection.
6.4.4 Column treatment
The chromatographic column typically contains microparticles which are used to separate the
compounds of interest. Under certain conditions, the column packing will undergo chemical
and/or mechanical breakdown, this may lead to the introduction of particulate matter in the de-
tector, which may lead to an increase in the noise.
NOTE
When strongly retained compounds are slowly eluted from the column, excessive noise will be
observed.
The breakdown of the column packing is dependent on a variety of factors including the particle
size, type of column packing, the manufacturer of the column and the nature of the mobile phase
(high pH may degrade silica based columns).
When you install a new column, we suggest that you pump the mobile phase through it for few
minutes before connecting it to the detector. This will flush out the microparticles that remained
in the column after its manufacture. After installing a new column, we also suggest that you per-
form the Column Noise test (section 5.9.5) to obtain the baseline signal value corresponding to
this column.