GC043 Using a Syringe

When using an autosampler, it should be programmed to inject the sample as fast as possible.

For manual injections, some guidelines are useful:

Exclude all air initially: can be achieved by repeatedly drawing and expelling out liquid sample into the syringe. Special care must be taken with very viscous liquid samples. A better alternative is to dilute them with an appropriate solvent.

When handling the syringe manually, fill it with more liquid than the desired volume for the injection. After that, hold the syringe pointing up and the air in the syringe will go to the top of the barrel. Soft taps can be used to aid in this process. After that, press the plunger up to the desired injection volume. Wipe off the needle with a tissue and now add some air to the syringe. This serve two purposes: first it will often give a peak in chromatograms, which can be used to measure tM. Second, it prevents losing sample if the plunger is accidentally pushed.

Injection technique require the use of both hands. One of them guide the needle into the septum, the other is used to provide force to pierce the septum and to avoid the plunger from being blown out of the GC when the pressure inside of it is high. The whole process should be usually done as fast as possible.

Between different injections, the syringe must be cleaned. High-boiling liquids are best washed with volatile solvents, like methylene chloride or acetone.

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