Chromatography Forum

I am running 1mg/L-air benzene sample using headspace manual injection. I am using HP GC5971A. I wonder why my benzene peak is braod. It is a clear and broad benzene peak. Is there anyone could help me with this?

Thanks!

Hong

Without any description of your instrument configuration, injection size, or other conditions, it is a bit hard to guess. I would suggest that you look at your initial column temperature - are you focusing the peak at all?

Manual headspace injection can be a bit tricky. In most cases you need to run in split mode to get good peak shape. I'm guessing you are doing a splitless injection, and if you are using a 1 mL sample volume and injecting with a 1 mL/min column flow you will get slow loading onto the column and a vey broad injection peak. If you use a 20:1 split ratio the column loading will be much faster, the injection band will be much narrower, and the peak shape should be much better.

hong_2009,

I would agree with Don. I have a customer doing a similar analysis out of water on a 60 meter column and the benzene peak is broader than all the others. If you can move to a thicker film or start much cooler, you might be able to affect a better peak shape.

Best regards.

Hi everyone, thanks for all your suggestions! Actually, you guys are right. It was because i injected too big sample. I increased the split ratio and it all turns out good. Thanks!