Methanol Tailing with RTX-502.2

[curtis.bond]

I'm running a method for methanol determination in water using an RTX-502.2 column phase. My column dimensions are 105m x 0.53mmID x 3um. My carrier gas is helium and my solvent is water. I use 1-butanol as an internal standard. The remainder of my method parameters are as follows:

Injection size: 0.5 ul
Injector temp: 200 C
Detector temp: 200 C
Oven Time Program:

Initial Temp 1: 50 C
Initial Hold 1: 3 min
Rate 1: 10 C/min
Final Temp 1: 140
Final Hold 1: 0.1 min
Rate 2: 25 C/min
Final Temp: 250 C
Final Hold: 10 min.

Total Run Time: 26.5 min.

For almost every injection, the 1-butanol internal standard peak is perfectly symmetrical, while the methanol peak exhibits extreme tailing (including certain "humps" at the tail end of the peak that resemble interference). Are there any parameter tweaks that you would recommend? I was thinking that perhaps I would raise the initial temperature from 50 C to 60 or 70 C. Perhaps that would help in eliminating the tailing? What do you guys think?

Curtis

[Steve Reimer]

Peak tailing is often a problem when the oven start temperature is below the boiling point of the injection solvent, in this case water. The water and methanol don't wet the column phase so you have a bit of LC going on in the front. Try a higher start temp, >100 C.
Are you doing a split injection?

[James_Ball]

Water and Methanol elute very close together on the Rtx-502.2 column. It is one of the problems you run into even when doing purge and trap analysis. I used that column for years doing 502 and 8260 analysis with a GCMS and Jet Separator setup. If you can change columns I would suggest using a Wax phase column for doing alcohols with a water injection, it would be much better.

Once you go above the boiling point of methanol you are not going to retain it very much, and starting the run at 100c to account for the water probably won't help too much since you will be shooting them both right through the column on the Rtx-502.