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- Posts: 44
- Joined: Wed Jul 11, 2012 1:45 am
- Location: California
I run EPA 8260 and have been experiencing a strange problem for months now. During calibration the first few points will be linear (.5-20 ppb) but the high points (50-100ppb) show extreme suppression of the chromatogram sometimes a highpoint will how a lower area count than a point below it. It happens to HP5890, 6890 and 5975c GCs, and to Tekmar 3100, and SOLATek 72 concentrators.
The problem arises suddenly, and is difficult to rid. For the older GCs reducing the purge time for 2 minutes to 30 seconds helped. For the newer GCs a full referb of the concentrator sometimes helps.
My first though was that it was a water issue, but increasing the split dramatically or letting it bake for 72 hours causes no change.
Some compounds show a significant increase:
Benzene
Chloroform
many show a huge decrease:
Styrene
Bromoform
Ethylbenzene
m,p-Xylenes
o-Xylene
Isopropylbenzene
1,1,2,2-Tetrachloroethane
Bromobenzene
Below is a comparison of a 75ppb run where that looks normal (black) and a suppressed one (blue). Only standards were run between these two runs.
Internal standard comparision for these runs, over 100% is an increase from normal:
Pentafluorobenzene 160%
1,4-Difluorobenzene 167%
Chlorobenzene-d5 120%
1,4-Dichlorobenzene-d4 20%
It is mainly happening to water instruments but has happened to one soil instrument. We purge with Nitrogen and run with Helium. Gas was tested by hooking everything directly to a new tank helium.
Please let me know if you have any ideas or would like any additional information