Chromatography Forum

Hi
Could anyone help me?

I have GC 3900 connected to Galaxie software.
- 1- I have an enquiry about the chromatogram. when I inject a volume of pure of hydrogen gas, I notice the baseline doesn't return to zero and there is a negative peak in the begining of run, what do you think the cause??

Thank you in advance

What detector do you have, what column are you using, what is your carrier gas etc etc etc ?

Can you post an example of the chromatogram please.

Peter

Thank you Peter

I use TCD detector(120oC),
MS 13X packed column(50 oC),
The carrier gas is Ar (30 ml/min),
the temp. of injector is 50 and I need to do the calibration curve of known volumes of pure hydrogen.

I wish all information mentioned above is useful...
Thank you

It is my supposition that you injected a large amount of pure hydrogen onto your 13X column.

The tailing you are seeing is the hydrogen slowly eluting from the pores of the MS 13X.

When you try to measure hydrogen with a carrier gas that is close in thermal conductivity certain concentration effects can occur. This is known historically as the "w" effect.

This effect is published in the literature when using helium as a carrier. I suspect you went beyond the limits of hydrogen/argon mixture linearity when you injected your hydrogen sample, especially since it appears that you are not seeing a return to baseline.

While the use of Argon allows you to have a measurement of hydrogen and other gases concurrently, the dynamic linear range may not be adequate for your needs.

Another reason for the tailing is an amount of water or some other contaminant in your system or hydrogen gas sample which may be eluting slowly from the column.

This tailing diagnosis assumes that no defect is present in your packing material or in the packed column made from this packing material.

best wishes,

Rod

- I inject 0.05 ml of pure hydrogen gas, so this amount is low.
- The carrier gas is Argon and there is a significant difference between H2 and Ar in thermal conductivity.
- I am sorry i didn't understand what do you mean about (you went beyond the limits of hydrogen/argon mixture linearity when you injected your hydrogen sample).
-Do you recommend me to increase the rate flow of carrier gas or the temperature of column to elute H2 fast??
-I noticed also the baseline is noise and not straight.

I checked the conductivity values again and you are right, you should have no problems with hydrogen and argon carrier linearity.

I suspect that you have a leak in your gas supply that is contaminating your carrier or that your columns is not properly conditioned.

How did you condition your column before use?

best wishes,

Rod

How are you doing the injection? With a Valco six-port valve or something similar?

Hi there

I would like to say thank you for your replies.

GC I used has six-ports valve but I inject manually by the syringe.
The problem is solved.

The problem was in the syringe(26 gauge) which was not tight, so the injection was wrong. the insert of the injector was drilled to be wider to fit with a practical syringe (22 gauge), therefore, the Peak of pure hydrogen samples is very fine now.