Chromatography Forum

Hello,
Just have had a series of about 10 needle plungers bent by the injector. I disconnected the injector and looked carefully at the plunger action. I saw nothing out of ordinary. I am at a total loss. Has anyone here had similar problems?
I have noticed a slight movement when the plunger hits the second stop before injection. As always, I haven't seen the plunger being bent. When I replaced the last syringes, I watched about 10 injections without a problem. Today I arrived and found the plunger fault and a slightly bent plunger. I removed the syringe and pushed and pulled. A slight resistance. I washed a little toluene down the plunger barrel and the movement seemed fine. I straightened the plunger out as best I could and placed in service. 10 injections later, still working.
The GC is ASTM 3606 Benzene in Gasoline 6890N. The instrument has been operating for 3 years no problems.

The problems I have seen with bent plungers have generally been due to build-up in the syringe barrel. You might try periodically checking the syringe after it has made a few injections to see if the plunger still moves freely. Have you changed your rinse solvent? Have the parameters for the rinse steps after the injection been changed? If toluene rinsed out the syringe well, you may want to use it as an initial syringe rinse solvent then use a second one if the toluene would cause a problem with your method.

Good advice Russ. I checked the needle barrel. There seemed to be gum left in the barrel. Now this needle was only in service for a few injections. That is what is very strange. I've not run across this problem in such a short time. Over longer periods, yes that occurs, but not just a few shots.
I've added the toluene and iso-octane as a rinse pre and post injection. Since I measure toluene in the method, I've made that a post run rinse. I also changed the needle from a 5ul to a 10ul. Hopefully the added barrel size and the rinses will help with the gum build up.

As I am sure you are aware, "gasoline" is unfortunately not a pure chemical or consistent blend. It can vary depending on the season, where it is going to be sold, or even refinery, among others. You may be running samples with different additives or blends from what you have run in the past. I couldn't tell from your post, but I think you could do a toluene rinse followed by an iso-octane rinse post injection. Don't know if that would clear out the toluene better. If you haven't already done so, you might want to make an injection of iso-octane to make sure you are getting rid of the toluene from the rinses.