Improving accuracy and precision of Gas Chromatographic injections
The accuracy and precision of Gas Chromatographic analysis depends on
significant extent on your skill to use the injection syringe. It is possible
to achieve a precision of
manual injection volumes less than 1% RSD once you
have gained mastery on sample injections.
Following the under-listed tips will help improve reliability of your analysis.
- Visually
inspect the syringe for any cracks in barrel or any other physical damage
such as bends, kinks or burrs in the needle. Do not use a damaged syringe.
- Syringes
should be used at ambient temperatures only. Allow hot or cold liquids to
attain laboratory temperature before making injections.
- The
syringe should be handled by the flange and plunger. Touching the barrel
can transfer body heat to the syringe.
- Rinse
the syringe several times with water, acetone or any other recommended
solvent for removal of residues of previous analysis before making the
sample injections
- Remove
any air bubbles by tapping gently and expelling the trapped air
- Wipe
the needle carefully with lint free tissue to remove any sticking droplets
before making injections into the GC.
- Rest
your forearms on the top of the GC at time of making injection so that you
assume same position for every injection.
- Insert
the full needle length into the septum
- Allow
the needle to heat up for 3-4 seconds before pushing the plunger in one
swift move of the index finger. Leave the needle fully inserted for about
4 -5 seconds before withdrawing the syringe in another swift move
The suggested tips will help achieve greater reproducibility and
accuracy of results. Syringe injection precision can be improved by maintaining
consistency of timings at different stages of injection. Several aids are
commercially available which help contribute to injection reproducibility.
These include syringe guides which prevent plunger bending or chances of it
being pulled out. Chaney adapter is another useful accessory which prevents
bending of plunger and also makes possible consistency of injections.
Autosamplers available on modern gas chromatographs free the operator
for other tasks and at same time eliminate human errors. However, mastering the
injection skills serves to boost your confidence as an expert chromatographer.
Lab training
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