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- Posts: 3
- Joined: Tue May 09, 2023 2:12 pm
- Location: United States
We are using a HAPSITE ER GCMS (dimethyl polysiloxane column) system to analyze TO-14 analytes (chloroethene through hexachlorobutadiene). The internal standard is Bromopentafluorobenzene, but we calibrate using a commercial cylinder containing the TO-14 compounds (just got a brand new cylinder and new IS canister). During the last few rounds of biannual calibrations, we've begun to notice that the MSD response factor (RF) is concentration-dependent for the higher boiling point (B.P.) analytes only (i.e., the RF is concentration-independent--as it should be, for the lower B.P. compounds). For the high B.P. compounds, the RF is higher at high concentrations and lower at low concentrations of the standard injections.
We're trying to determine potential reasons for this problem with the higher B.P. compounds. Could the quadrupole not be conducting the heavier mass fragments to the detector efficiently? Could the electron ionizer be failing to properly ionize the heavier compounds? Could the column be spent (and would this be a symptom of a column that is past its prime?). The column (and the whole system in general) is pretty old and we do run the oven temp all the way up to the highest column operating temperature (200 deg C) for 90 seconds at the end of each run which isn't how I'd do things, but I just started here 3 months ago.
If anyone has ideas about how we might diagnose this issue and identify the failing component in this process, I'd be very grateful! About our injector: the HAPSITE units have a heated inlet with a triple-adsorbent bed concentrator (which we just tried changing out & which didn't solve the issue). We inject our standards using gas-tight glass syringes.
Thanks so much for your input!