Chromatography Forum

Hello,

I recently did some runs on my GC and ended up with a ripple in the baseline, as seen here:



The only change that was made to the system was to install the column. The gas cylinders are all the same. I assumed the column was not properly installed, so I cut a bit off the ends and reinstalled it. It didn't solve the problem, so I have changed the septum and inlet liner as well, with no change to the chromatogram. Could it be a problem with the detector? I have not tried cleaning that yet.

I presume that you baked out the column (it's maxium isothermal temperature or as hot as your method will take you) after installation. If not, do that first. You didn't mention it so I thought I'd ask.

If that ripple continues at the hot temperature then I'd be looking elsewhere (injector, detector). If after a time it stabilizes, you should be good to go.

Hello,

I recently did some runs on my GC and ended up with a ripple in the baseline, as seen here:



The only change that was made to the system was to install the column. The gas cylinders are all the same. I assumed the column was not properly installed, so I cut a bit off the ends and reinstalled it. It didn't solve the problem, so I have changed the septum and inlet liner as well, with no change to the chromatogram. Could it be a problem with the detector? I have not tried cleaning that yet.

Are you sure that gases to your detector come from gas cylinders ?
Check whether your cylinder pressure regulators are set to adequate pressures.

Make sure they is plenty of pressure in the cylinders. If the cylinder pressure is getting down near the set pressure on the regulator then you could be getting uneven flows from surging as it tries to control the pressure.

What type detector are you using?

Also make sure the detector end is not installed too high up into the detector, it could cause uneven flow in there.

Is your inlet temperature above the isothermal maximum for your column, and do you have gas scrubbers on your carrier gas ?

Have you checked for leaks ? Did you clean the inelt body when you changed liners ?

Peter

Thank you for all of the suggestions.

I did bake out the column (I took that detail for granted, sorry!). I did it again yesterday for a longer time and it seemed to help a tiny bit. The ripple is still there, though.

The gas cylinders all are set properly, and have plenty of gas left. I have run this analysis many, many times before with this column and instrument. It was just after this recent installation that I have had problems.

The detector is an FID. I double checked the installation depths for both the detector and inlet when I reinstalled the column, as that was one of my first thoughts as well.

I will try cleaning the inlet body itself today and see if it makes a difference. I am also planning to try a different column, just to rule out that as a problem.

Thanks again!

I thought your FID was supplied with hydrogen from generator.
In my opinion it's an issue with gas supply to FID.
Check whether regulators are set to deliver gases to GC at pressure ca. 5 bar (including make-up).

Or ... you have power supply problems - sinusoidally fluctuating voltage (faulty UPS if applicable in your case, electric noise from high current load machines ?).

Cleanness is not the culprit I think.

Check your signal without flame , if it is electrical problem , you will continue to see it.

Check your signal without flame , if it is electrical problem , you will continue to see it.