Baseline above normal value

[dolenjc2000]

Hi!
A problem...
I was runing a gc analyses on Agilent 6890 normal untill i changed empty bottle with full bottle H2 (5.0). After that the baseline from 5-6 pA rised do 30-35 pA. I called the gas service and told them my problem. They said that might be the problem beacuse they changed the gas filler. Today they brought me a new bottle of H2 (5.0) and the baseline is the same 35 pA.

Bellow you will see a chromatogram when i was changing the amunt of H2 in the gc. I started from my normal flow 50 ml/min (35 pA) and came to 10 ml/min (the minimum that is able that FID still runs) where baseline was normal for me 5 pA. Is normal that lowing of H2 causes such baseline fall or is it a problem that the H2 of this supplier still is not so pure.

Lowering of other gases (He, air) does not cause such an baselinefall.

THNX

[chromatographer1]

I suspect your Hydrogen lines are contaminated and will be for a while. Any traps you had may be overloaded and continue to contaminate your GC. Time to clean and replace. One dirty cylinder can cause a lot of trouble, no?

Good luck with your housecleaning.

best wishes,

Rod

[HW Mueller]

Well if I understand this correctly you lowered the amount of H2 burned. That lowers the flow of ions resulting in a lower baseline (higher resistance).

[AICMM]

dolenjc2000,

I think Rod's comment about cleaning gas lines is right on the mark. The beauty of the FID is the remarkable low noise since hydrogen and air flame does not generate any significant ionization. Your symptoms suggest the hydrogen line was (is) contaminated.

Best regards.

[HW Mueller]

AICCM, your baseline does not change when you extinguish the flame?

[AICMM]

HW Mueller,

Sure, your baseline will drop slightly when you turn off the flame but that is most likely because you are no longer burning contaminants found in the gases. My point is that hydrogen/air flames don't generate measurable ions which is why the signal in an FID at idle is so wonderfully low. Noise/background is due to such things as contamination, leakage currents and electronics more than the flame itself.

On a clean system, if you increase/decrease the hydrogen (or the air) you will hardly see any change at all in the baseline.

Best regards.

[chromatographer1]

I concur. Just a subtle baseline shift, but the sensitivity of the same sample when in the flame changes a good deal as the gas mixture is modified.

21 days until retirement ! woo hoo !

best wishes,

Rod

[skunked_once]

Code: Select all

21 days until retirement ! woo hoo ! [quote]

Rod,  Say it isn't so!!!  Who will provide us with your wisdom and knowledge?  Congratulations anyway!!  Will you continue contact with the forum?

[chromatographer1]

Thanks for the kind words.

I may be back less often as I may have distractions from the world of chromatography.

But links with my email address are here if anyone might like to say hi once in a while by email. (aim yahoo)

Rod

[Schmitty]

I heard of this new thing...the "internet". Rod should be able to help us out with any questions, regardless of location!

Best wishes.

[chromatographer1]

But Schmitty, my cane pole and rowboat don't have an installed computer.

I may not even turn my computer on at home.

I may be too busy digging worms for bait.

and then there are those chores that were put off for years 'cause I was too busy at work..........

well, you understand.



Rod

[dolenjc2000]

Hi Guys!

Finnaly solved the problem!
It vas the problem with the new gas supplier. They changed the gas bottles and the new ones seem to have some impurities. On the chromatogram you will see the change of the baseline when we change the bottle wit 5.0 H2 purity to 6.0 purity

Thnx for all your help and hope not to retire fully chromatographer1 aka. Rod