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

It is a common problem with purge and trap. I started a discussion on this years ago here

https://www.chromforum.org/viewtopic.ph ... l+standard

One thing I have found it that the total mass of analytes causes higher response for internal standards an surrogates and it seems to be related to some type of contamination that adsorbs small amounts of certain analytes. Once you overload those active sites you get better recovery of the analytes that are normally adsorbed. I haven't used the Atomix purge and trap, but with the Encon it seems to be in the Moisture Reduction Trap, which is just an empty silcosteel treated tube that is held at low temp when purging or desorbing then baked when the trap is baked. I reduced my Moisture trap bake temp and it happens less often. It is just my theory as I haven't been able to prove it, but I think over time some of the high boiling contaminates collect on these traps and become a thin layer of char due to the baking process, then result in a slight adsorption problem. Usually changing the traps will help as cleaning doesn't always work. If you can clean or change that trap in the Atomix, see if that will help. The other thing I found that helps was to increase the spike level of the internal standard and surrogate, so that the effect is not as pronounced, if your method or SOP allows for it.