Troubleshooting GC Syringe Issues

I think we all have experienced various syringe issues at one time or another, and of course, problems seem to occur at the worst times. Hopefully this post will help you quickly correct two of the most common issues we get asked about in tech service.

Probably the #1 issue is coring of septa. That problem was covered in a post titled "Troubleshooting Injection Port Septa".

 

The #2 issue is a sticking plunger. This occurs when the sample/solvent dries from inside the syringe and leaves behind sticky residue, which basically “glues” the plunger to the barrel. To fully understand why this happens, think about how a syringe works. For liquid syringes with a bare metal plunger and glass barrel, the liquid works its way between the plunger and the barrel to create a seal. Once the syringe is properly wetted and the seal is formed, it allows the plunger to pull up the liquid sample. Even though the syringe is usually rinsed with clean solvent after a sample injection, if the sample contains “sticky” material, not all of it may get rinsed out. If this happens, and the liquid dries, the remaining residue may bind the plunger to the barrel.

So the obvious question is, how can this issue be prevented? Below are a few suggestions.

1. Try using a Gas-Tight syringe, which contains a PTFE tip on the bottom of the metal plunger. Unlike a bare-metal plunger, the seal is formed by the tight contact of the PTFE and the syringe barrel. As a result, the sample/solvent is not able to get between the metal plunger and the barrel, so rinsing the syringe after a sample injection seldom leaves behind any residue. However, if you allow the plunger dry while inside the syringe barrel, it may become difficult to remove, and sometimes the PTFE tip will dislocate from the metal plunger and become stuck in the syringe barrel. To prevent this, remove the plunger from the barrel while the PTFE tip is still wet and store the plunger separately from the syringe barrel (if possible).

Please note that PTFE-tipped plungers rarely last as long as bare metal plungers, so replacing every liquid syringe with a Gas-Tight one may not be economical for your lab.

2.   Substitute a different rinse solvent; one with a higher boiling point. As I mentioned, when the liquid dries inside the syringe, sticky residue may “glue” the plunger to the syringe barrel. Instead of rinsing the syringe with just the same solvent as your sample, use a higher boiling-point solvent for the final rinse (one which will not evaporate out of the syringe between sample injections). For example, let’s say your samples are in methylene chloride (approx boiling point 40°C), and you notice your plunger is drying out between analyses. As your final syringe rinse, try using toluene (approx boiling point 110°C). Just remember to rinse the toluene out of the syringe before injecting your next sample. If your autosampler has two rinse vials, this can easily be done.

3.   If you do end up with a stuck syringe plunger, Hamilton has a few suggestions to try (I pasted this information directly below). However, just in case you are not successful in freeing the plunger, you may want to keep a few extra spare syringes available.

The plunger in my syringe is stuck. What can I do to free it up?

Frozen plungers are caused by improper care of your syringe. Here are a couple of suggestions to save your syringe: Soak the syringe in alcohol, acetone or warm water. Do not soak them for longer than 5 minutes. Sonic cleaners can sometimes help to free up the plunger. If the plunger does not start to move after this, you will need to replace the syringe. Proper cleaning will help prevent frozen plungers. Especially when the syringes are being used for life science applications, where sugary or protein based sample are required. We recommend using a like solvent to dissolves the sample. Rinse the syringe thoroughly and then remove the plunger and allow the syringe and plunger to air dry separately. MICROLITER Syringe Plunger Types Standard Microliter Plunger Stainless steel with a stainless steel button staked to the plunger rod. This type plunger is individually fitted to the syringe barrel. Interchanging plungers between syringes will permanently damage syringes.

Hopefully you have found this information helpful.  If so, you may also want to review Troubleshooting GC Syringe Issues – Part 2.

If you have any questions, give us a call.