Chromatography Forum

Hi Everyone,

I'm currently having an issue with my 7890 GC auto sampler. After about 200 injections, my syringe plungers are breaking. This hasn't been an issue until a new column was installed and over tightened. The tightening was enough to crack the silver seal. Needless to say the proper repairs were made but I'm still having an issue. Not sure if this has caused the issue or not but it was the last thing changed before this issue arose.

I've also noticed a fair amount of septum building up in wash vial. I had a service tech from the manufacturer come in and he told me this was a normal amount but I feel like it's enough to be drawn up.

Just an FYI I have a PTV inlet. I have tried the following to eliminate suspected culprits.

1. Injected only methanol to eliminate sample matrix build-up. Syringe still breaks after 200 injections.
2. Tried a different auto sampler tower and different lot of 5 uL syringes. Syringe still breaks after 200 injections.
3. Have now tried a merlin micro seal to see if septum is root cause. Will post later to see if syringe failed.

Other Current Method conditions.

Wash 6 solvent wash prior, 3 sample pumps, 6 solvent after, 6 water washes after.
I use red septum from Agilent.

Please let me know if you need any other information.

Thank you in advance.

Syringe plungers breaking ? Bending yes, but breaking ?? And after 200 injections repeatably ?

Cracked the silver seal ? Agilent inlets have a gold seal at the bottom. It is solid metal, whoever managed to crack it has probably misaligned the whole inlet, causing the syringe to scrape the inlet nut. This would result in bent needles though, not broken plungers.

I have been doing GC for a very long time, and I don't think that I have ever seen a septum fragment in a wash solvent, far less a build up of septum fragments, so that is certainly not normal. It is a sign that the needle is punching cores out of the septum, which is a symptom of the wrong needle or too much pressure on the septum. Once again though, this will lead to bent needles (and a host of other problems related to septum fragments in the inlet), not broken plungers.

The exact 200 injection limit is very suspicious. If you let a syringe run for 180 injections, and then take it out, can you feel that the plunger is not moving easily ?

What is the source of the water for the water wash ?

Peter

Hello

It happens when you have injection speed set up too fast. Just go to "config" ALS and change it from default value (as I remember it is 600) to 200-300 which is enough for injection speed.
I think that plunger is too thin when you have tight septa or high pressure inlet.

Regards

Tomasz Kubowicz

Hello,

When we experimented using 5uL syringes, in an attempt to improve RSD%,
we found that the 5 uL syringe plungers would bend once there was a little bit
of binding in the syringe bore, as the plunger diameter is smaller than the 10uL
syringe plunger.

So we ended up going back to the 10uL syringes.

If you have septum in your wash, you would then be getting septum pieces in your liner too
which will affect your chromatography.

In my wash bottles, I use the same solvent as my sample in Wash A and Isopropyl Alcohol in Wash B
,as IPA doesn't evaporate as quickly, and acts as a lubricant too


regards
Alex

Septum building up in wash bottle means septum particles entering inside the syringe barrel.
This may cause the syringe plunger to stick and bend , try different type of septum.

Thanks everyone for the reply. Currently having the service engineer come out again going to have him check over the entire inlet system alignment.

Peter: I have a PTV inlet not a split/splitless see below. The silver seal is a small washer different from a gold seal. The 200 limit isn't necessarily a limit. I take the syringe off and notice the barrel of the syringe is appearing to be scored and the plunger is slightly bent before catastrophic failure pictured below occurs. Source of water is milli-q.

kubowicz.tomasz
Post subject: Re: GC 7890 Syringe Breaking Issues Reply with quote
Hello

It happens when you have injection speed set up too fast. Just go to "config" ALS and change it from default value (as I remember it is 600) to 200-300 which is enough for injection speed.
I think that plunger is too thin when you have tight septa or high pressure inlet.

Regards

Tomasz Kubowicz

Haven't tried this yet will try it.

Alex: Will try the IPA thanks for the advice.

Scoring the barrel can only be from abrasive particles. Is the instrument in a dusty atmosphere ?

From the picture the plunger is bending when it is nearly fully withdrawn from the syringe, so this is not a problem with injection speed per se, but might be to do either with the speed of ejection during washing or with the plunger being pulled too far up. Try slowing things down and reducing the wash volume.

Peter

I will try this after the tech comes and checks the alignment. Thanks again for your input Peter, I'll be sure to update when there is a resolution.

Two things come to mind, is your septa nut too tight, and are your wash bottles full?