Chromatography Forum

Hello,
I am planning to analyse benzyl alcohol and benzaldehyde using GC (FID). I installed RXi5MS column and trying to find the retention time for each chemical. But I am getting the double peak for each compound. I tried to change the injection volume but it didnt works. I set injector tempt.= 220 0C and tempt. program is 60 0C for 1 min and 10 0C ramp upto 100 0C and hold time 2 min and 40 0C ramp upto 240 0C and hold time of 2 min. I am using splitless mode.
another problem I faced is when I used split mode with ratio of 10 then it didnt detect any compound but if i used same program with splitless mode then peaks came for each compound but with ghost peak for each compound.
Please need suggestions to overcome this issue.

Thanks in advance.

It looks like you may not be getting any sample onto the column unless a large amount is used.

Make sure your syringe is clean and not clogged/damaged

Check that your liner is installed correctly and not broken: some people overtighten the inlet nut if using an older GC (5890/6890) and the liner shatters.

Then re check the column is installed correctly and not crushed or broken due to overtightening of the column nut ferrule.

Your syringe may have broken the column when trying to do a splitless injection.

To me ugly/split peaks and peaks appearing only at high volumes suggest damage or blockage at the inlet or column.

I tried to inject more sample volume but peaks are becoming broaden. I reinstalled column and tried but same results I got again. Is there any problem with column compatibility??

Does the chromatogram at the bottom help?

http://www.restek.com/Technical-Resourc ... l/env_A005

I don't have enough experience to say if that column will separate benzyl alcohol from benzaldehyde (maybe thats why you get double peaks?)

Thats an MS column you are using what is the column ID? Do you have the right ferrules for that size?

Could be the ID is too small and you are injecting too much onto the column, you probably need a 0.2 uL injection size and at least 100:1 split ratio...

You need to be able to do split injections, if you can't that suggests something is wrong in the inlet/column installation.

I used split mode but no peak was observed and when I used splitless mode i was able to detect the peak. Any suggestion on split and splitless mode?

You should have a split liner installed, see pic:

http://www.labexchange.com/products/tec ... age006.jpg