Baseline Drift and Carrier Purity

Chromatography Forum: GC Archives: Baseline Drift and Carrier Purity
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Steve C on Friday, July 30, 2004 - 04:23 am:

When hydrogen is used as a carrier I understand that gas of the highest purity must be used to minimise column degradation.

However, I am interested to know the effects of using lower purity hydrogen carrier (contaminated with water and oxygen only) on the appearance of the chromatogram, and in particular on baseline stability, when an FID is used.

I read that the FID is insensitive to water and oxygen. This explains why purity is not a big issue for hydrogen used as FID fuel gas.

However, I have recently observed chromatograms using hydrogen carrier contaminated with up to 10ppm of water and oxygen where baseline stability is awful.

How can this be when apparently the FID is insensitive to water and oxygen. Can the effect be explained by the detection of the products of column degradation?

Please help.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By chromatographer1 on Friday, July 30, 2004 - 10:18 am:

Many phases are not stable to water and oxygen. When they break down bleed can increase and a very noisy baseline will be the result.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By GC user on Saturday, July 31, 2004 - 09:31 am:

With modern bonded, crosslinked phases water stability is usually not an issue, however oxygen is one of the worst things to introduce into a GC column. Oxygen starts the breakdown of the siloxane structure, and after the reaction starts it tends to be auto-catalytic. Column degradation products are definately detectable by FID.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Mark on Wednesday, August 4, 2004 - 02:42 pm:

Steve,

Oxygen and water in the carrier are both bad news. The newer bonded and cross-linked columns can handle water injections usually but having it in the carrier is a real problem. Using a good hydrogen generator with a good water trap and an oxygen/water trap in the carrier gas line just ahead of the GC should work very well.

Regards,
Mark


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