Chromatography Forum

Hello Forum!
On an Agilent GCMS system (7890A/5975C) we weekly check if the recommended PFTBA- fragmentation conditions (69mz: 100%, 219mz:~50%, 502:~1%) are met, which was the case for months.

After cleaning the ion source and a following tuning procedure however, the PFTBA fragmentation pattern changed and now turns out to be: 69mz:100%, 219:~90%, 502:~10%.

Has anyone experienced this phenomenon before?

Hello Forum!
On an Agilent GCMS system (7890A/5975C) we weekly check if the recommended PFTBA- fragmentation conditions (69mz: 100%, 219mz:~50%, 502:~1%) are met, which was the case for months.

After cleaning the ion source and a following tuning procedure however, the PFTBA fragmentation pattern changed and now turns out to be: 69mz:100%, 219:~90%, 502:~10%.

Has anyone experienced this phenomenon before?

After cleaning the source you gained proper sensitivity for high masses.

Also if there is still some water hanging around in the analyzer it will bias the high mass abundance. I usually let mine pump down overnight before tuning, and then after a week do it again just in case. It takes a while for all that metal to come to a thermal equilibrium, but once it does it holds for a long time.

Solved!

It turned out that a wrong/different tune file caused these issues. stune and atune were somehow mixed up and falsely attached to the current method.

Air/Water checks are performed weekly, and indeed, after maintenance on the MS, an adequate amount of time is given for proper equilibration.

Thanks.

Solved!
It turned out that a wrong/different tune file caused these issues. stune and atune were somehow mixed up and falsely attached to the current method.
...

But you don't invoke tuning procedure from analytical method, do you ?
Then, no matter what tune file is attached to the analytical method you may stune or atune instrument.

Solved!
It turned out that a wrong/different tune file caused these issues. stune and atune were somehow mixed up and falsely attached to the current method.
...

But you don't invoke tuning procedure from analytical method, do you ?
Then, no matter what tune file is attached to the analytical method you may stune or atune instrument.

Could be the tune file that the method uses for operating parameters.

But you don't invoke tuning procedure from analytical method, do you ?
Then, no matter what tune file is attached to the analytical method you may stune or atune instrument.

No. The tuning is done manually.