Chromatography Forum

Hi everybody,

I have a problem in the analysis of residual methanol in API. I do manual headspace and I inject 0,5mL of headspace vapour into the GCMS. I dissolve the API in water at 80°C for 20min. The column is a capillary WAX 60m 0,25I.D. 0,25u.
Inj = 120°C SPLIT 40
Det = 210°C
Column flow 1,1ml/min

Column 40°C --9 min--
50°C/min 180°C --2 min--
-50°C/min 40°C --2 min--



The problem is that, after 2 weeks of work, the peak of methanol has started to tail. I've changed the wool in the liner and also the septum but nothing is changed...

Any suggestion?

Thanks for the help
Have a good day

REmove the front end of your Wax column, 1 to 5 meters. See if that helps. You have active sites that are causing the methanol to tail.

Any metal in the flow path can also be a problem.

Thanks for the reply...

I've tried to remove 50 cm of the front end of the column but nothing is changed... I think I don't have metal in the flow path (only in the bottom of the liner) because I'm doing manual injection.
What could have caused this problem?
Is better to use a pre-column like hydroguard or something like that?
Is better to use another type of column less sensitive to this problem?

Thanks again

Have a good day...

You have a damaged Wax column or contamination in the injector port.

Could be a piece of septa or you could have a mis-installed column.

I would still trim the front of the existing column by 5 meters, no 50cm.

Good luck.

Rod

I am wondering why you use glass wool for headspace injection?

Good point, sg.

I suspect the GC is used for other samples and the system is contaminated, thus causing the tailing.

Thanks for the answers,

about the wool in the liner, I use it to trap the pieces of septum in the liner not to reach the head of the column (I'm doing manual inj so the septum broke easily).

I think the problem is the column and I will try to cut the first meters...

Anyway there is another type of column that could retain methanol but is less susceptible to damage when working with headspace from water sample? What about 50-60%diphenyl - dimethylpolysiloxane?

Which column could I use to separate ethanol from dichloromethane?

Thanks again for the help,

Bye

SPB-1301

Call Supelco technical service for assistance if you deem it necessary.

This is a USP column for OVI residual solvents.