Headspace oven temperature drift.

[pontiuspilot]

Hi everyone,

Any thoughts on this will be great.

I am running a Headspace method on an Agilent 7890A GC system and a 7697A headspace sampler unit.

I am running with a 3ml loop with the loop and transfer line temp set at 150deg. The sampler oven is set at 45deg.

The problem I'm having is that I once the gripper places the vial into the oven I see a drift in the oven temperature which puts

the sampler into a state of 'not ready'.

Has anyone seen this drift when the sampler oven temperature is low?

There is a provision in my method that says parameters can be varied slightly, based on scientific rationale, provided the system

suitability requirements are met and a comparable separation of all relevant compounds is demonstrated.

I would rather identify the source problem before I progress to this stage.

Thank you.

[Peter Apps]

I have seen this with the Agilent 1888 headspacer with the oven at 60C (from memory) - a temporary temperature drop when a room temperature vial dropped in. But it always recovered in plenty of time to equilibriate the vial (impact on other vials was a more complicated question !!).

What is your equilibration time ?

Peter

[pontiuspilot]

Hi Peter,

Many thanks for the reply. The equilibration time is 30 minutes.

Regards,
Kevin.

[Peter Apps]

Hi Kevin

If the temperature has not stabilised after 30 min then there is something wrong with your instrument - or does the problem affect the injection from an earlier vial in the queue ?. How long does it take for the temperature to return to set-point ?

Peter

[pontiuspilot]

Hi Peter,

I thought initially that I might have an instrument problem but I trialed the method on an additional two instruments with the same outcome.

I haven't worked many methods with a oven temp that low and a loop temp that high.

I've been on leave until this morning but I will be starting the project again this afternoon. I was thinking of lowering the loop temp. I can't think of a reason for it to be that high?
I'm thinking of lowering it to 110deg which is still high enough to prevent potential condensation of solvents from the headspace vapour.

The 'rational' is that the extreme high relative loop temp is a system function issue and that the loop temp is still adequately high to prevent potential condensation of solvents (and water) from the headspace vapor!!!

Does this sound feasible?

Thank you for your help.

Kevin.

[Peter Apps]

I agree that the loop temp is unusually high relative to the oven temp, but I cannot see why that would cause a problem with the oven temperature that was synchronized with the addition of vials to the oven.

Does the oven temperature rise or fall when a vial is added ?, and by how much ?

Peter

[pontiuspilot]

It is difficult to figure. I didn't anticipate this would be a problem at all !!

Once the vial has been placed into the oven there has been a gradual increase, over a space of approx ten minutes, where the temperature has reached 49.4 - 50.1 deg.

I have trialed on 3 separate instruments with the same outcome.

[Peter Apps]

Strange.

I presume that this is the first vial in a sequence, and that the headspacer was on standby before that ?

It is several years since I worked in these instruments but I have vague memories of their having a standby temperature setting that could be different from the sample equilibration temperature. That you can reproduce the problem on three different instruments suggests that they are somehow being told to behave like that.

Peter

[pontiuspilot]

Hi Peter,

Thank you for all your help.

I've lowered the loop temperature to 130deg and the oven temperature is holding and I am getting reproducible chromatography!!

I awaiting my QA department to allow me to proceed with these new parameters.

Thanks again.

Kevin.

[Peter Apps]

Great, thanks for the feedback.

Peter

[Mike H.]

I use an 1888 and have never experienced over drift. Once it's at temperature it is very stable. When was the last PM done?

[GasMan]

Which version of the 7697A do you have, the 12 vial single vial heating version or the 111 vial 12 vial heating version.

Gasman

[pontiuspilot]

Sorry I didn't reply. I've since completed the project. Thank you for your posts.