Chromatography Forum

Hi all, I have recently started using Varian GC 3800. The column equipped is BR MS 5A, FS 30 m long and 0.53 mm ID. I'm operating at 25C column oven temperature at a flow rate of 10 mL/min. It is able to separate gases under these conditions. But there is a slight tailing of the peaks. Could anyone suggest, is this the right column to be used or else, which is the best column for my GC?

You are separating fixed gases on a molecular sieve 5 Angstrom capillary column.

At 10mL per min you are a little fast, but this probably helps with the tailing.

You did not state what gases you are separating. But as a guess only choosing capillary columns, you probably have a suitable column. What are the goals of your analysis? The matrix, the detection limits, and the separations required. Don't you think we on the Forum should know this before giving you a recommendation?

I would prefer a micropacked MS 5A column but to each his own. Are you splitting your sample, injecting manually, or with a sampling valve?

Are your using a PDD or a TCD?

best wishes,

Rod

Tailing on a column like this is often due to too much sample injection. What volume of injection are you using, and what sort of concentrations of analytes?

Hi Rod,

Thanks for the reply.

I am doing experiments with hydrogen and oxygen gases. I'm injecting them separately and recording their retention times. Currently, H2 elute at 1.4 min and O2 at 1.9 min.

A sampling valve is used for injection and the detector is TCD.

Thanks,
Jyothi

You have a suitable column for your needs.

Rod

Thats great! Thanks Rod, for the information.

Best,
Jyothi

Also make sure your column cut is flush. A jagged cut can lead to tails.

Tailing maybe caused by dead volumes. Consider to use a direct injection liner. There are "uniliners" available which minimize dead volumes by design.

Also be aware that Hydrogen response in a helium carrier gas may give some strange peak shapes due to an anomaly in conductivity of H2/He mixtures. Often for correct H2 measurement, argon is used as carrier gas. If argon is chosen, it will compromise sensitivity for O2.

adsorbents will alsways give a tailing peak when overloaded. This tail already starts at the top of the peak. If the tail is at the bottom, it's probably dead volume.

Jaap de Zeeuw, restek corporation