Chromatography Forum

This is driving me nuts! i have been running blanks for weeks and i can't get rid of a persistent benzene peak. i am running a Tekmar 3000 P&T concentrator with a 6890/5973 GCMS, and an EST autosampler with automatic standard injection.

I first sonicated the valves on the concentrator in methanol, changed the trap and flushed the transfer line with methanol. - still benzene.

I ran samples using a blank trap - still benzene.

I then ran samples through the glassware. - no benzene, so I turned my attention to the autosampler. I ran samples without standard addition - still benzene. I changed the water reservoir and filled the standard vials with pure methanol just to be sure. i also changed the pencil filter for the water supply. still benzene.

i have clipped the end of the transfer line from the autosampler to the concentrator and that does'nt seem to have made much difference.

Next thing i will try is to purge a vial of methanol to flush the system.

Does anyone know of any components that would release benzene into the system?

thanks

What material is in your trap in your P+T ?

best wishes,

Rod

It's a Vocarb® 3000 trap. I'm not sure exactly what material is used. I was pretty sure it's not the trap as I have used glassware and not seen contamination. However i think i will try changing the trap (again) as i can't imagine any other component releasing volatiles at such a constant rate.

You're definitely taking the right approach to troubleshoot this. If you using a Voacarb 3000 then you probably doing something similar to VOC 8260. It's usually pretty tough to find the source, but alot of the time it's stuck in a valve and slowly breaks off with each heating cycle.

You mentioned "I then ran samples through the glassware. - no benzene". Does that mean you transfered the sample amount (usually 5mL's) directly into the glass sparge tube and step the P&T to begin purging and continue the rest of the cycle and GC run. If that was clean, then it's starting from the P&T line to the autosampler would be where to begin. And just keep moving backwards along the sample pathway.

So next remove the line connecting the P&T and A/S at the A/S, and inject the sample amount through the line, then step to purge, etc. If that's clean, then take the next step backward in the sample pathway. Each backward step should incorporate more than one line and/or valve. Flow chart diagrams come in very handy here.

When you stated EST autosampler, would that be and 8100,Centurian or something else?

What level of benzene are you seeing (area or concentration)?

I'm more familiar with Tekmars, but I've dealt with the EST 8100's.