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- Posts: 4
- Joined: Wed Oct 11, 2017 3:36 pm
We are seeing two discrete siloxane peaks after routine maintenance on our GCMS. Peaks have ions 207 and 281. These peaks are interfering with our compounds of interest and we are looking for help to troubleshoot this issue.
Routine Maintenance steps:
1. Cleaned the Ion source, changed the inlet liner, and septum.
2. Changed the analytical and condensation trap in the Atomx Purge and trap. Also changed the sparge glassware and internal standards on the Atomx.
The MSD tuned went well and we started out by running a water blank and started seeing the two discrete peaks around the time of our internal standards.
We assumed it was the inlet liner or septum so we changed out the liner and septum. We continued to see this problem so we began thinking it was the column- exposure to oxygen perhaps. So we changed the column and gold seal. When the new column was installed, the tech was unaware that the new column should not be connected to the MSD while conditioning. So we cleaned the ion source again and disconnected the column and baked for 4 hours with 2ml/min flow and then baked out the MSD.
Again, we ran a water blank sample and the discrete peaks were still there. So we decided to isolate the issue and started with manual tune scan on the MSD. The MSD did not pick up any 207 ions. So next, we ran the GC only- no injection and we didn't see the peaks. Next, we ran methanol direct injection on the GC and did not see the siloxane peaks.
So we went back to our purge and trap. We changed the analytical trap and condensation trap again and baked them out at recommended temperatures. Peaks still there. We skipped through the purge right desorb stage and the peaks are present. We ran an empty vial and the peaks are there. We ran no internal standards and the peaks still remain. We are quite stumped at what to do next. Does anyone have experience with siloxanes coming from the purge and trap system and where to isolate?
The Atomx purge and trap is connected to the GC via transfer line which shouldn't have siloxanes.
Here is some of our instrument info:
5973 MSD Hewlett Packard
6890 Agilent GC
Column: 1st column was DB-624 Agilent 60m x 250um x 1.40um
2nd column was Rxt-624 Restek 60m x 250um x 1.40um
Pressure: 16.1, Flow: 1, Carrier gas: Helium, Constant flow
Inlet: Split
Temperature: 250, Pressure: 16.1, Split ratio 40:1, Split flow: 39.7, Total flow: 43.2, Gas saver off
Oven:
Initial 35 for 5 mins
Ramp 1: 104
Ramp 2: 142
Ramp 3: 230
for total of 30 mins
Internal standards used in Atomx: d4-dichloroethane, tolene-d8, and bromoflurobenzene.
Peak ions showing cyclotrisiloxane and cyclotetrasiloxane.
Any help is greatly appreciated!! We are out of ideas!!