Troubleshooting GC Syringe Issues – Part 2

In an earlier post titled "Troubleshooting GC Syringe Issues", I discussed several things to try if sticking plungers are the problem.  In this post, I’ll discuss what to do if the syringe is not pulling up the sample properly (or at all).

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So what can cause a syringe to have problems pulling up a sample?

 

The sample is too viscous.

If your sample is viscous, slow the plunger draw speed.  Many autosamplers have this functionality.

If this still doesn’t solve the issue, you may need to dilute your sample.

 

The syringe needle is plugged, or partially plugged.

Find out what is plugging your syringe needle.  Is it the sample or septa?

If it is particles in your sample, you may need to add a filtering step before injecting.  

If you discover it is a piece of septum plugging your needle, try a different needle point style (Pt style #5 with side-hole are the least likely to plug).  

 

The plunger is not making a good seal with the syringe barrel.

How worn is the syringe?

Eventually the plunger to barrel sealing performance of syringes degrades as it gets older and worn-out.  This is especially true when using Gas-Tight syringes which have PTFE-tipped plungers. 

Tip:  Never use a PTFE-tipped plunger which has not been prewetted with a solvent.  When not in use, do not leave the plunger inside the syringe barrel.  Instead, remove the plunger and store separately from the rest of the syringe.  When needed, wet the PTFE tip before inserting into the syringe barrel.  

Most syringe manufacturers recommend that you do not use a plunger from one syringe in another (unless using Gas-Tight syringes where plungers are usually interchangeable).

 

There is a leak between the needle and barrel.

If using a removable needle syringe, make sure the PTFE seal between the needle and barrel is installed properly and not worn out.

If using a fixed needle syringe, verify that the cement holding the needle to the barrel hasn’t degraded.

 

The autosampler is not working properly.

Watch the autosampler as it tries to inject the sample.  Is the autosampler programmed properly?  Does it actually penetrate the sample vial deep enough to withdraw an aliquot?  Does the autosampler actually lift the plunger?

 

Hopefully one of these suggestions will help you out the next time your syringe is not pulling up a sample.  Thanks for reading.