The accuracy and precision of Gas Chromatographic analysis depends to a 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.
Proper handling and care of chromatographic syringes has been dealt with earlier. However, a few tips are proposed which 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.