Baseline Increase

[hwright]

Hi all,

I have been having problems in the last couple of days with a jump in my baseline. Last Thursday before lunch my baseline was fairly smooth and consistent. After lunch I have seen this baseline-jump at around 10 to 12 minutes. Here is a chromatograph of a calibration gas mixture before seeing the baseline jumps.



And one with the baseline problem.



Peak 1: Oxygen
Peak 2: Nitrogen
Peak 3: Carbon Monoxide
Peak 4: Methane
Peak 5: Carbon Dioxide

Method Used: Initial 40 C. Hold 3 min. Heat Rate 8 C/min. Final Temp 250

Here is a chromatogram of a sample of Natural Gas with baseline problem:




I did a blank run at a constant oven temperature of 40 C and still saw baseline shift but at a much later time.



Can you guys tell me what is causing this? Thanks for all help.

[Don_Hilton]

What carrier gas?
What column?

And is there a chance you have been looking at some samples whith something so well retained that it is coming out a sample or two later?

[chromatographer1]

Your calibration gas contains ethane propane butane?

The Carboxen column appears to be holding a hydrocarbon or some other slowly eluting analyte.

Since the baseline upset first came out around CO2 I suspect water is the problem.

Good luck.

Rodney George
consultant USA

[hwright]

@Don_Hilton,

I should have mentioned that in my post. Carrier Gas is He and the column is a Restek ShinCarbon ST Micropacked. I don't believe that anything is being retained but I'm new to GC so anything is possible.

@chromatographer1,

Calibration gas is
5.00 % Carbon Dioxide
5.00 % Carbon Monoxide
4.01 % Hydrogen
4.01 % Methane
5.00 % Nitrogen
5.00 % Oxygen
Balance of Helium

AICMM also believes water could be the problem. He has suggested that I bake the column and see if on the next run there is any improvement. If so then I should use a temperature program that removes the water every run.

I am baking right now and will post results.

[larkl]

I'd be wary of using this column without either a stripper column or with a backflush arrangement. You might be able to work around it with time and heat (bake out), but it would be quicker in the long run to keep the water and any heavies in the sample off the column.