Carryover of heavy compounds on purge and trap GCMS

[tangaloomaflyer]

O.K., riddle me this:

i am running a purge and trap GCMS. After installing a new column I started using a VOC method (USEPA 8260). After the high level of the calibration i got significant carryover of the heavier compounds. I have changed the transfer line from the concentrator to the GC, the transfer line from the autosampler to the concentrator (and flushed with methanol), cleaned the sparge needle of the autosampler, cleaned both valves of the concentrator and i'm still getting carryover.

I've just changed the trap again, and I am getting a lot of alkanes (C12-C16) coming out, which I think happened last time. Could this be a sign of insufficient trap conditioning? (I baked it for an hour at 260c). could insuffiecient conditiong be the cause of the carryover?

Any ideas?

i have'nt tested the new trap for carryover yet as I am still waiting for the alkanes to clear, I'll report back when I have.

cheers

[Ron]

The heavier hydrocarbons you mentioned are probably from Diesel fuel. Purge and trap is designed to analyze compounds more volatile than this, so the carryover is a function of the samples. Turning up the valve and transfer line temperatures may help, but I doubt if this will eliminate the problem.