GC injection techniques (pointers)

[cbowen]

Hi,

I'm a fresh out of undergrad uni QC Chemist. I'm in my first week of work and getting used to all the instruments I only used once or twice during Analytical Chem 2 years ago!! Anyway I'm having difficulty getting good peak separation when I inject my standard into the GC. There are three compounds in the standard but instead of 3 nice peaks I get 2 nice ones and the third is split.

This is what I do to inject:
Pull ~1ul of standard into syringe, making sure there are no air bubbles.
Push syringe needle into septum.
Push down plunger and press start.
Count 5 seconds and pull syringe out quickly.

I'm looking for some pointers on how to better inject my standards. Thanks so much in advance!

-CB

[skunked_once]

CB,

Welcome to the wonderful world of chromatography with all of its potentials and pitfalls! The only thing I would change in your injection procedure is to wait only one second before pulling out the syringe. It's important to inject the sample as quickly as possible so that it enters the column as a single plug. Your problem with the split peak could be due to other factors also. If changing the injection procedure doesn't solve the problem, get back to us. Be sure to post as much information as possible, column, temperatures, flow rates, compounds, etc. so that we can do our best to help. There is also a lot of information available in the archives of this forum (use the search function) as well as on the web. I've included one source to get you started. Good luck!

http://www.dsbscience.com/freepubs/fore ... ode28.html

[cbowen]

Thanks for the help and welcome

I just finished a run and the peak looks a ton better. I think you were right that I was taking too long to inject. I waited only one second and I was quicker pushing the syringe in. I'm going to run a few more then I'll update you if I have a problem.

[JGK]

Hi,

I'm a fresh out of undergrad uni QC Chemist. I'm in my first week of work and getting used to all the instruments I only used once or twice during Analytical Chem 2 years ago!! Anyway I'm having difficulty getting good peak separation when I inject my standard into the GC. There are three compounds in the standard but instead of 3 nice peaks I get 2 nice ones and the third is split.

This is what I do to inject:
Pull ~1ul of standard into syringe, making sure there are no air bubbles.
Push syringe needle into septum.
Push down plunger and press start.
Count 5 seconds and pull syringe out quickly.

I'm looking for some pointers on how to better inject my standards. Thanks so much in advance!

-CB

Recommend purchasing an autosampler as an efficiency move

[cbowen]

I know! At school we did a manual injection just to see how it was done then the rest of the labs we used the auto injector. I couldnt believe they did it that way here haha! Oh well...maybe in the future?