Varian 4000 GC, Hardware Operation Manual

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Lack of Peak Size Reproducibility
Possible Cause Solution
Leaking or partially
plugged syringe Visually check that the syringe is pulling up the sample.
Check that the nut is tight. Flush the syringe with solvent.
Replace the syringe.
Leak at the septum Replace the septum regularly and ensure that the septum
nut is tight.
Improper installation of
column in the injector, or a
leak at the column inlet Check the installation of the column in the injector. Tighten
the capillary column nut.
Sample is being absorbed
by active surfaces in the
injector or column Change the injector insert. Remove the front 15 cm of the
column, or replace the column.
Incomplete vaporization of
sample in the injector Increase the injector temperature.
Injector splits too soon. Confirm that the switch time is chromatographically
optimized.
Correcting Peak Splitting (Particularly for Low
Boilers)
Possible Cause Solution
Sample flashing in injector
simulating two injections Lower the injection temperature.
Column is cracked Re-cut and install the column.
A piece of septum is stuck
in the injector insert. Replace the insert and septum.
Correcting Extra, Unexpected Peaks in the
Chromatogram
Possible cause Solution
Septum bleed Use high-temperature, low-bleed septa. Make sure
that the septum purge flow is set correctly.
Impurities from the sample vials
(e.g., plasticizers present) Confirm that this is indeed the case by running a
solvent blank with a new syringe. Use certified
sample vials, and keep the samples refrigerated.
Impurities from the carrier gas
present Install or replace the carrier gas filters.
Injector or GC pneumatics
contaminated Remove the column from the injector and bake it
out at elevated temperature, (e.g., 350 °C) using a
split vent flow of at least 20 mL/min.
Impurities present in the sample Confirm that this is indeed the case by running a
blank or standard.
Solvents are extracting impurities
from the septum. Switch to a new septum type, lower the injection
temperature, or reduce the injection volume.
Impurities present in syringe wash
solvent Use high purity grade solvents.
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