Chromatography Forum

I am running drinking water VOC's on an Agilent 7890/5977 GC/MS and an ATOMX purge and trap autosampler. For the last several months I have been having an issue with my surrogates. When I run my curve the responses of my surrogates increases as the standard concentration increases. My curve samples pass just fine but it puts the "average" of my surrogate responses high enough that the surrogates in my samples and blanks (which don't have a whole lot of compounds in them) are reading to low and not passing my QC (they need to be between 80 and 120% recovery and mine are down around 75%). The P&T people are blaming the GC/MS people and the GC/MS people are telling me it is a P&T issue. I don't know what. I've tried cleaning the source, changing the liner, cleaning the mount. I replaced all of the tubing in the P&T to the GC twice but I can't find anything that fixes the problem

I get that when I run nasty samples, especially methanol extracts. You don't mention changing your trap, if you haven't already, swap that out.
For me the cleaning includes the transfer line and the everything before it. On my Eclipse it includes the water management fitting.
My Atomx isn't reliable enough to run the creosote soaked samples so I don't know its hiding places for residue.

I agree with Steve that it might be your trap. Sometimes I start seeing poor ISS behaviour when the bottom fitting on my trap starts to leak. The ferrules are teflon and the heat eventually gets to them and the joint gets loose.

I'm still strictly 8260 VOC's using an Archon autosampler and Tekmar 3000 P&T unit. But our Archon came with a system to automatically add the IS and surrogates. We had terrible drift over time even when doing a calibration. Then we ran a set where we loaded all the vials with IS an surrogates by hand and it was nearly perfect with no drift.

Bottom line, if a new trap does not fix things, I would take a look at your surrogate addition module. Maybe there is a problem with the valves or a blockage in delivery lines affecting the delivery precision. We never did figure out why ours were messing up. Once we had success running in soil mode, we never looked back.

Oh, and one more thing, if your P/T switching valve is loose or too worn, that will also give you variation in your surrogate recoveries. I recently had my Tekmar P/T valve resurfaced and it made a huge difference.