DIAGNOSIS
Observation Cause Remedy
All peaks in the chromatogram are becoming smaller. Sample flow unit is blocked.
Injection hole contaminated.
Clean injection hole, vapor-
izer and sample flow unit.
Replace gaskets if
necessary.
Peaks are becoming wide and shifted to longer times.
Baseline becomes neg. in pre-purging position of A column.
Vaporizer is contaminated.
Baseline becomes pos. in pre-purging position of A column. Leaky valve in vaporizer section.
Interruption in chromatogram: injection occasionally missing. Leaky pneumatic drive, grease
used up, O-rings damaged, control
pressure too low.
Clean pneumatic drive, re-
place O-rings, grease sliding
surfaces and O-rings.
Peaks too small and too wide, especially those of higher boil-
ing point.
Heating plate is faulty.
Vaporization temperature too low.
Replace heating plate.
Set higher equalization
temperature.
Injection quantity slowly rises until a double peak results (with
calibration medium).
Poor peak form, platform following peak. Increase in baseline.
Visible discharge of sample.
Worn gaskets and/or tappet. Replace gaskets or tappet.
The injection tappet is matt and rough in the vicinity 3 mm
around the injection volume, and often also dark. Material
wear is visible using a magnifying glass. The effect is signifi-
cantly less in the adjacent areas.
Corrosive sample Possibly replace injection
tappet by version made of
sapphire, ZrO
2
, Hastelloy or
Monel.
Starting from the location of the injection volume, furrows are
present in both directions, and end at the position where the
tappet no longer comes into contact with the gaskets (when
viewed using magnifying glass). The furrows may be very fine
and distributed uniformly around the circumference or very
marked and starting at the injection volume.
Particles in the sample not only damage the tappet surface,
they are also deposited in the hole of the soft Teflon gasket.
This can be recognized by the dark gray deposit in the gas-
ket.
Sample is contaminated by parti-
cles (most frequent case).
The groove tappet is more suscep-
tible since the sample is in contact
with the gasket over a larger area.
Check filter and replace if
necessary.
The space between the tappet and the inside wall of the va-
porizer is filled by deposits. This can block the supply of car-
rier gas.
In the final phase, deposits may result on the part of the tap-
pet which protects into the vaporization area. This directly re-
sults in large sealing problems between the sample and the
carrier gas.
In seldom cases, these deposits may also be produced on
the drive side of the injection tappet.
If brown deposits are present on the vaporizer gasket at the
outlet to the vaporization area, this is an indication of
non-volatile components.
The sample contains dissolved
salts and other non-volatile materi-
als.
The deposits in the vaporizer
must be removed mechani-
cally
(drill/reamer with 3.3 mm
diameter).
Assessment of filters
IMPORTANT: Checking the filter
If the above-mentioned effects occur, it is
essential to check the filter situation!
The filters must be regularly service accord-
ing to the degree of contamination.
If necessary, the flow must be reduce using
the filter and injection valve. Bypass opera-
tion is recommended!
Filters are required for liquid samples with a
separating capacity of 98% for 0.3- µm parti-
cles.
Siemens sample conditioning units contain
such filters.
CAUTION
The deposits on the tappet must be re-
moved extremely carefully. The tappet must
not be damaged. It is better to fit a new tap-
pet.
With this type of filter, the particles are not removed by
a filtering effect but are deposited on the inside of the
filter assembly. The filtering effect is based on the fact
that the settling forces of the particles are far greater
than the pulling forces of the sample. The result is a
high filtering effect and low flow resistances.
Such a filter is not blocked, but is punctured when its
surface is completely full. This can be recognized in
that the coloring of the filter reaches the outlet side in
the flow direction.
Register8.vp Stand: 20.11.2000 2-V
Liquid injection valve
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