GC FID detector with high base line

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Iskandar
Iskandar's picture
GC FID detector with high base line

We have a problem with high base line above 150 pA with capillary column from phenomenex by using Nitrogen as carrier gas and FID detector. The problem does not occur if we use HP-5 column from agilent with the same condition where the base line below than 30 pA. Please help me how to solve the problem and what wrong with this phenomena.

Iskandar
Iskandar's picture
Any one can help me

Any one can help me

mbicking
mbicking's picture
There are many possible

There are many possible explanations. First, please provide more information:

Please tell us the name/type of the Phenomenex column, and also the dimensions (internal diameter, length, film thickness).

First, check all connections between the column and GC. Measure the flow through the column, at the detector. If the flow is not correct, check for leaks.

Is this a new Phenomenex column? All new columns contain small amounts of solvent from the manufacturing process. These solvents will cause a high baseline until they are removed. This is one reason why every column much be "conditioned" or "baked" before it is ready for use. Increase the temperature to about 10 degrees below the maximum limit for the column. Leave the column at this temperature for a minimum of four hours. Then change the temperature to your usual conditions and watch the baseline. Usually it is much better now.

If these experiments do not help, then please write to us again.

Iskandar
Iskandar's picture
Dear M. K. L. Bicking, Ph.D.

Dear M. K. L. Bicking, Ph.D.

Thank a lot for your valuable advise. I would like to follow your advise tomorrow. This a new column from phenomenex that I have been received last weeks with specification ;
7FD-G002-08
Zebron ZB-5 Capillary GC
Column 20m x 0.18mm x 0.18um
maximum temperature limit of column is 360 C
Column conditioning have been done for 3 hours with temperature 250 C. After reconditioned I have a plan to flush the column by using methanol and dichlometane please advise can we do on it.
The HP-5 column is the old one that have been applied more than 2 years.
Best Regards,
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mbicking
mbicking's picture
Iskandar:

Iskandar:

Is the new column the same size as the old column? Does the new column have the same internal daimeter? If the diameter is different, then the flow of carrier gas should be changed.

Check the installation of the column. If the end of the column is not at the correct location in the detector, you can have problems with your baseline.

I would not recommend that you flush out the column with solvent. Condition the column at 300 C. I do not think that cleaning with a solvent will help you.

Iskandar
Iskandar's picture
HP-5 specification is length

HP-5 specification is length 30m, Column ID 0.32 mm Film thickness 0.25 um. Carier gas flow for both column is around 0.8- 1 ml/min. we are still on going to condition the column at 300 C. the base line still stable on 192 pA. we follow the GC manual HP 6890 to install column to detector and column to injector

mbicking
mbicking's picture
If you are still having

If you are still having problems, I have some more suggestions.

Please check the actual flows for the detector gases (hydrogen and air). Do not trust the readings on the instrument; make the measurements with a flow meter.

You can remove the column from the detector and the detector will still operate. Do you get the same baseline problem with no column installed? If yes, then you have a detector problem.

Greg Pronger
Greg Pronger's picture
Iskandar wrote:We have a

Iskandar wrote:

We have a problem with high base line above 150 pA with capillary column from phenomenex by using Nitrogen as carrier gas and FID detector. The problem does not occur if we use HP-5 column from agilent with the same condition where the base line below than 30 pA. Please help me how to solve the problem and what wrong with this phenomena.

After looking at the thread, if I assume correctly that you can install the Agilent column and have a fairly low baseline and then install the Zebron column and have a higher baseline; reproducibly, then you simply have a column issue.

First, your Agilent column, due to its age is very well conditioned. Phenomenex offers a traditional 5% phenyl 95% dimethylpolydiloxane column as well as a "MS" style, which fairly universally among column vendors, is a low bleed version of the same column.

Again, assuming that you have isolated the problem to the column (you can switch back to the Agilent column and see lower bleed) then I would simply try conditioning the ZB-5 for a longer period of time. The ZB-5 has a pretty decent upper temperature limit, so if my application had a max temperature at 300C I would probably simply set it to 300C for the week-end. Before I did this though I would verify that I have no risk of running out of carrier over the week-end and that I am 100% positive I do not have an air leak on the inlet side. My concern simply is not to have the column at an elevated temperature either without carrier or with an air leak.

Extended conditioning times, do in fact, slightly shorten the column lifetime, however since in the scenario I've outlined above you are still fairly below the column maximum so there should be minimal impact.

Good luck,

Greg