Back Plunger Error

[stategc]

Hello - I am new to this forum so I hope that I am posting correctly. I have an HP 5890 GC that the lab got refurbished from another lab. The GC tower is about 10 years old, but had been working for over a year. Just recently I have been getting a "back plunger error" when starting a sample run. The GC tower is a 7673A (serial #2704A05665). The syringe will eject the solvent, but when it goes to pull up hexanes to clean the syringe, it gets stuck (the plunger will not move up) and the error message pops up. You can abort and the syringe will move up, the autosampler will remove the sample back to it's spot. Mechanically, everything looks OK - the belt is fine, the syringe is new. I called the company that originally made the GC but they are unable to help because it is so old. Any thoughts on what I should look for?

[tsoukalas1]

Hello,


http://www.chem.agilent.com/Library/Support/Documents/a15704.pdf

It's a diagnostic procedure for 7673 autosampler.

for me, there are 3possibilities of your issue :
a motor problem, so you will have to change it or,
your system is just jammed so you will have to clean it and grease it or,
you have a problem with the magnetic sensor, in this case you will have to change the electronic board

The diag procedure will help you to find the issue.

Good luck

Pierre

[Consumer Products Guy]

Make this happen again. When stuck, unscrew the screw holding the top of the syringe plunger, I bet there's still resistance, than with a little more force will then seem normal.

That sounds like the little motor above the syringe is bad, we've had those go out occasionally, pretty straightforward fix. Turn off power to control box. One electrical connector, a funky retaining wire, and the belt tension is adjusted by pressing the little plastic wedge in a little tighter. You'll want to take the rear cover off the tower.

Take photos before you start in, unless you have another tower to use as a model.

[cleh]

Agree with CP Guy. It's most likely the syringe motor. You said you're using hexane in your wash vials, but what solvents are you using with your samples and standards?

[stategc]

Make this happen again. When stuck, unscrew the screw holding the top of the syringe plunger, I bet there's still resistance, than with a little more force will then seem normal.

That sounds like the little motor above the syringe is bad, we've had those go out occasionally, pretty straightforward fix. Turn off power to control box. One electrical connector, a funky retaining wire, and the belt tension is adjusted by pressing the little plastic wedge in a little tighter. You'll want to take the rear cover off the tower.

Take photos before you start in, unless you have another tower to use as a model.

I did as you explained above, and there isn't any resistance when the plunger is not screwed in. With the plunger screwed in, more force is required than I think should be necessary to pull the plunger back up. This makes me think it is not the motor, but I am not sure. We did look at what we believe to be the motor above the syringe and the plastic wedge seems to already be in pretty tightly.

I received an email from Alpha Omega (the company that serviced the autosampler last year) and she believes that the injector will need to be serviced (bad plunger motor - which you mentioned above, or solenoid assy). Could it be some sort of an alignment issue? I have followed the directions for replacing the syringe so I do not believe that is the problem.

Thank you for your response - I am definitely willing to try anything that could potentially be the issue.

[stategc]

Agree with CP Guy. It's most likely the syringe motor. You said you're using hexane in your wash vials, but what solvents are you using with your samples and standards?

I am using methanolic KOH, BF3, and hexanes in the samples and ethanol in my standard.

[Peter Apps]

A sticky syringe plunger sounds likely. Does this ever happen with a new syringe, or if you take the syringe out after a jam, clean it by hand and then re-install it ?

Peter

[cleh]

I would try making injections of hexane. Clean the syringe by hand first with hexane and make sure the plunger moves freely or just install another new syringe and then run the instrument injecting hexane as samples using hexane in the wash vials. If this works, you would know that the autosampler is OK and it may be the syringe is binding due to something in your samples. If it still binds up, it's probably the motor or an electronic problem (solenoid, etc.). Please let us know what you find.

[MSCHemist]

I had some initial plunger errors when I pressed my 5890 with 7673 back into service. It would go to the rinse vial and just stop for no aparent reason and give the plunger error message.

I ended up wiping down all the belts and poles with methanol and cotton tips. It seems to have gone away.

[Consumer Products Guy]

The first thing to do with any plunger issues is to swap in a new syringe.

The second thing to do with any plunger issues is to swap in a new syringe.

Yes, wiping down the guide rails with alcohol for both the entire assembly and for the plunger assembly once a year is a good idea, part of routine maintenance. Don't use lubricants there, they'll pick up dust.

[stategc]

A sticky syringe plunger sounds likely. Does this ever happen with a new syringe, or if you take the syringe out after a jam, clean it by hand and then re-install it ?

Peter

This occurred after I installed a new syringe. The older one had not been used for a couple of months and I thought it would be best to start with a new one. I have taken the syringe out and re-installed it. Just did a thorough cleaning with alcohol as mentioned by those below and so far it seems to be working. It would be something so simple - I should have thought of that!

[stategc]

I had some initial plunger errors when I pressed my 5890 with 7673 back into service. It would go to the rinse vial and just stop for no aparent reason and give the plunger error message.

I ended up wiping down all the belts and poles with methanol and cotton tips. It seems to have gone away.

Thank you for giving me such a simple solution - one that I should have thought to do as a first step. I wiped everything down with alcohol, particularly the plunger since that is what seemed to get stuck, so far so good.

[stategc]

The first thing to do with any plunger issues is to swap in a new syringe.

The second thing to do with any plunger issues is to swap in a new syringe.

Yes, wiping down the guide rails with alcohol for both the entire assembly and for the plunger assembly once a year is a good idea, part of routine maintenance. Don't use lubricants there, they'll pick up dust.

Thank you - yes I did swap out for a new syringe and still got the same error message. However, as I mentioned below, it looks like cleaning with alcohol did the trick - at least so far. I will keep this in mind for maintenance.

[skunked_once]

Sticky plunger errors are common on the Agilent autosamplers (personal experience). I recommend adding a second syringe wash solution referenced in the June 2007 issue of LCGC North America, volume 25, No. 6, p. 572. The wash solution is N-Methyl-2-pyrrolidone. Please read the MSDS before use. Since I started using it, my sticky syringe errors have decreased dramatically. If you do use this solvent, you will have to test that it does not interfere with your sample analysis since the peak elutes at about 1.5 minutes on a 30-meter DB-23 column. Hope this helps!

[MSCHemist]

I find acetone followed by MeOH works well for me. I have some pretty sticky viscous samples. I simply do 5 acetone rinses post injection followed by 2 MeOH.

I do a lot of raw material quality analyses by injecting the neat raw material with a viscosity delay and a 500:1 split.