Chromatography Forum

Hi, is there a possible way of diluting a gas sample using GC program, e.g. diluting to 50% by adding a measured amount of carrier gas? Currently we are diluting our samples manually using syringes and it is very time consuming and prone to contamination. Thanks

No, at least I did not hear about such system.

On the other hand, GC carrier gas amount (meaning volume) is not possible to measure using any standard GC hardware - volumetric flow is calculated from the measured pressure data and column dimensions entered (if the length/diameter numbers entered are wrong - calculated flow rate is also wrong).

The only possible solution of such kind would be custom made/programmed system using syringe - kind of modified CTC CombiPal, however this still does not solve contamination possibility because syringe can not be closed during transportation steps.

There are external gas standard generators/ dilutors available, but presumably these also are quite expensive.

Hi, is there a possible way of diluting a gas sample using GC program, e.g. diluting to 50% by adding a measured amount of carrier gas? Currently we are diluting our samples manually using syringes and it is very time consuming and prone to contamination. Thanks

Why not inject smaller volumes of gas samples no matter manually or by injection loop valve ?

Why not use split injection?

+1 on injecting less or splitting more. Make it easy on yourself!

Funny you asked, but about 10 - 12 years ago my co-worker Ed suggested we should create a macro using the CTC Combi PAL autosampler making out of a single vial a set of dilutions. We programmed the following steps: First, we flushed the syringe with carrier gas. At the end of the flush time, the plunger went down to 1mL (instead of going down all the way). Next, the syringe went down 10% (25%, 50%, 75%, 90%, 99%). At last, we picked up standard (at a vial stored in the agitator at equilibrium) and filled the syringe back to 1mL.

We intended to publish this at Pittcon in 2000 or 1999, but we missed the deadline and withdrew the poster at the end. But I'd be happy to share the macro. It was written using Cycle Composer.

Best Regards,
Ingo Christ
Autosampler Guys LLC
+1-703-780-1500
ingo@autosamplerguys.com

Thanks for your responses. Appreciated

Hiz

Get a gas cylinder for sampling. Put a quick connect (Swagelok) on both ends. Snap it onto a quick connect on tubing to a gas sampling (6 port Valco) valve. Using a split vent injector, life would be so easy. Have a nice day.