Chromatography Forum

Hi Everyone
I am wondering if anyone has encountered a similar problem to mine before and if so how it was fixed. I am using an Agilent 6850 Autosampler and about 30 injections into a run the plunger screw will loosen and then obviously no sample will be injected (very frustrating when your samples degrade after 20 hours).

This is not the first time this has happened but previously we believed the cause to be overfilling of vials and improper septa use (we use screw caps and users were placing septa upside down in caps). This time the caps and vials are Agilent spec. and none are over or under filled. Also the plunger screw was tightened correctly just before the run was started and this is a new syringe.

Does anyone know of a cause for the loosening screw? My next port of call is the injector port septum but we are using the septa with a thru hole so this shouldn't be causing the needle to catch and thereby loosening the screw.

Any suggestions would be welcome.
Thanks
Ciara

Hi Everyone
I am wondering if anyone has encountered a similar problem to mine before and if so how it was fixed. I am using an Agilent 6850 Autosampler and about 30 injections into a run the plunger screw will loosen and then obviously no sample will be injected (very frustrating when your samples degrade after 20 hours).

This is not the first time this has happened but previously we believed the cause to be overfilling of vials and improper septa use (we use screw caps and users were placing septa upside down in caps). This time the caps and vials are Agilent spec. and none are over or under filled. Also the plunger screw was tightened correctly just before the run was started and this is a new syringe.

Does anyone know of a cause for the loosening screw? My next port of call is the injector port septum but we are using the septa with a thru hole so this shouldn't be causing the needle to catch and thereby loosening the screw.

Any suggestions would be welcome.
Thanks
Ciara

Plunger screw has nothing in common with vials nor with septa.

Try to screw in a little bit harder. Check whether the thread is in proper condition. If demaged, you won't get stable connection.


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Edit /

In 7683 inj. tower there is a spiral spring under the head of the screw. It reduces the tendency to self unscrewing of the screw.

I've got over 20 years experience with at least six 7673A autosamplers, and have NEVER had a plunger screw come loose on its own.

Be sure it's seated in the "recess" of the plunger knob.