Any one has experience with 1 GC with 2 columns??

[Cest]

[/quote]
Then probably it's not detector gas flows related.
The simplest method of diagnosing would be to change the column. If new column has similar pattern then you would have to investigate further.
If new column has flat baseline then the old one is deteriorated.

BTW - this baseline is acceptable for me [/quote]

So far, the samples' results are comparable with those before this happened. And the GC has to keep running. We can't pause for trouble shooting right now. But would like to try when things slow down, just out of curiosity.
Thanks all for help!

[AICMM]

Cest,

I have seen such a baseline ripple with contaminated FID air before. Was on a high temp SidDis application but if you just watched
the baseline you got a ripple similar to yours. Try changing out air to a completely different lot.

Best regards,

AICMM

[Peter Apps]

The other possible cause of ripples like that is poor temperature control on inlet or oven. If it is the inlet it probably means that there is a lot of dirt in there. How often do you do inlet maintenance, and what do you do ?. If is was the oven I would expect the ripples to get higher as the temperature increased, so that is a less likely culprit.

Peter

[CE Instruments]

Whilst the baseline is slightly worse on the second trace the peaks are better, no tails that you see on the last of the night before on some peaks. That it did not improve during the day indicates that it is not a function of how the GC was left overnight.

[Cest]

Cest,

I have seen such a baseline ripple with contaminated FID air before. Was on a high temp SidDis application but if you just watched
the baseline you got a ripple similar to yours. Try changing out air to a completely different lot.

Best regards,

AICMM

Thanks AICMM. But I tried the 100m column using the same air cylinder the past weekend. The baseline was all good..

[Cest]

The other possible cause of ripples like that is poor temperature control on inlet or oven. If it is the inlet it probably means that there is a lot of dirt in there. How often do you do inlet maintenance, and what do you do ?. If is was the oven I would expect the ripples to get higher as the temperature increased, so that is a less likely culprit.

Peter

Unfortunately, the lab mate said she never cleans the inlet unless a tech support who is visiting helped to clean, which was a long time ago.
I think you have a good point! Do you have instructions on cleaning the inlet?

[Cest]

Whilst the baseline is slightly worse on the second trace the peaks are better, no tails that you see on the last of the night before on some peaks. That it did not improve during the day indicates that it is not a function of how the GC was left overnight.

I agree with you, CE Instruments. Thanks for your thought.

[Peter Apps]

The other possible cause of ripples like that is poor temperature control on inlet or oven. If it is the inlet it probably means that there is a lot of dirt in there. How often do you do inlet maintenance, and what do you do ?. If is was the oven I would expect the ripples to get higher as the temperature increased, so that is a less likely culprit.

Peter

Unfortunately, the lab mate said she never cleans the inlet unless a tech support who is visiting helped to clean, which was a long time ago.
I think you have a good point! Do you have instructions on cleaning the inlet?

That sounds like a recipe for poor performance for sure.

Basically you have to let the inlet and oven cool down, remove the septum nut and septum and throw the septum away, remove the glass liner and throw that away, on an Agilent remove the gold seal and throw that away, then put in a new gold seal, new liner and a new septum. The details of what you have to loosen and tighten differ from instrument to instrument, so have a look in the users manual under routine maintenance. It is not difficult and this is the kind of operation that you really need to know how to do yourself unless you have a lot of money to waste on service call outs.

Peter

[Peter Apps]

The other possible cause of ripples like that is poor temperature control on inlet or oven. If it is the inlet it probably means that there is a lot of dirt in there. How often do you do inlet maintenance, and what do you do ?. If is was the oven I would expect the ripples to get higher as the temperature increased, so that is a less likely culprit.

Peter

Unfortunately, the lab mate said she never cleans the inlet unless a tech support who is visiting helped to clean, which was a long time ago.
I think you have a good point! Do you have instructions on cleaning the inlet?

That sounds like a recipe for poor performance for sure.

Basically you have to let the inlet and oven cool down, remove the septum nut and septum and throw the septum away, remove the glass liner and throw that away, on an Agilent remove the gold seal and throw that away, then put in a new gold seal, new liner and a new septum. The details of what you have to loosen and tighten differ from instrument to instrument, so have a look in the users manual under routine maintenance. It is not difficult and this is the kind of operation that you really need to know how to do yourself unless you have a lot of money to waste on service call outs.

Peter

[Cest]

The other possible cause of ripples like that is poor temperature control on inlet or oven. If it is the inlet it probably means that there is a lot of dirt in there. How often do you do inlet maintenance, and what do you do ?. If is was the oven I would expect the ripples to get higher as the temperature increased, so that is a less likely culprit.

Peter

Unfortunately, the lab mate said she never cleans the inlet unless a tech support who is visiting helped to clean, which was a long time ago.
I think you have a good point! Do you have instructions on cleaning the inlet?

That sounds like a recipe for poor performance for sure.

Basically you have to let the inlet and oven cool down, remove the septum nut and septum and throw the septum away, remove the glass liner and throw that away, on an Agilent remove the gold seal and throw that away, then put in a new gold seal, new liner and a new septum. The details of what you have to loosen and tighten differ from instrument to instrument, so have a look in the users manual under routine maintenance. It is not difficult and this is the kind of operation that you really need to know how to do yourself unless you have a lot of money to waste on service call outs.

Peter

Peter, I also have experience with Agilent only. I will figure it out based on PE's manual. Thank you!