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EPA 524.2 Internal Standard/Surrogate Issue
Posted: Tue Nov 13, 2018 5:02 pm
by mduplease32
I've been running Purge and Trap GCMS for about a year now and am seeking answers to a problem that I've been having. When I run samples my internal standard (Fluorobenzene) and surrogates (BFB and D4) are for the most part consistent. However when I run calibration standards (0.5ppb to 20 ppb) and LFB (4ppb) my internal standard and surrogate responses increase. So much so that my surrogate recoveries for my samples sit between 50-70%. Currently, my internal standard response for samples is around 80,000 and my surrogate responses are around 18,000. My internal standard response for my LFB/CCV is around 108,000 and surrogate response is around 40,000. Also, I noticed that if I have a high concentration of a specific analyte in a sample it will cause the internal standard/or surrogates to increase depending on where the analyte elutes (For example I had a high abundance of THF come out of a sample and it only increased the internal standard and not the surrogates. I believe it's because THF elutes close to Fluorobenzene, which is causing it to be effected). Has anyone else had this problem/found a solution to it?
The equipment used includes: Aquatek 100, Lumin Concentrator (using VOCARB K Trap), 7890B GC, and 5977A MSD.
Re: EPA 524.2 Internal Standard/Surrogate Issue
Posted: Tue Nov 13, 2018 5:21 pm
by Steve Reimer
There have been several threads on this forum about increasing response overall for internal standards with increasing concentration of target analytes.
It is a common problem for me when I analyze nasty samples (water with visible creosote or a beads of PCE appear in some of my projects). The cure is to clean out the entire path from the vial to the GC inlet and the MS source.
Re: EPA 524.2 Internal Standard/Surrogate Issue
Posted: Tue Nov 13, 2018 5:46 pm
by mduplease32
The instrument was installed in May of 2016 and this problem has been going on from the start.
Re: EPA 524.2 Internal Standard/Surrogate Issue
Posted: Thu Nov 15, 2018 5:33 pm
by Steve Reimer
If you increase the split ratio, does the problem decrease?
Re: EPA 524.2 Internal Standard/Surrogate Issue
Posted: Tue Nov 27, 2018 7:42 pm
by LALman
Steve Reimer wrote:
There have been several threads on this forum about increasing response overall for internal standards with increasing concentration of target analytes.
It is a common problem for me when I analyze nasty samples (water with visible creosote or a beads of PCE appear in some of my projects). The cure is to clean out the entire path from the vial to the GC inlet and the MS source.
I agree with Steve. Its probably an active sites problem. It happens with metals analysis also. You can run a concentrated potassium signal and then rinse it down to nearly nothing. Then aspirate a high sodium standard and suddenly you have potassium showing up again.