5975 gc/ms + OI internal std response

[danicrd]

Hi everyone
in our lab we are running Epa 8260 method with purge e trap OI Eclipse plus 6890/5975 msd.
The problem is IS area response: the area go down during the batch and is very unstable.
When we have a calibration control spiked at 5ppb rise, while with blank or clean sample go down.
The IS are added automatically from Archon Autosampler with Valco valve at 1 ppb final concentration.
Our system has turbo pump, and the source is just replaced with clean one.
The column is DB-624, 30m, and we work in split mode with 20 ml of flow.
Does anyone has some suggestion?
Thank you

[Steve Reimer]

I have seen this on both 5973inert and 5975.
Agilent has a bulletin on this: F05013.pdf
They claim that it can result from overloading the EM and recommend keeping the target abundance for ion 69 down in your bfb tune targets.

I have noticed it when the source, especially the repeller, is dirty or has had more than the normal amount of methanol exposure (purging 2% methanol in water). It affects fluorinated compounds more, thus you see it in fluorobenzene first, then diflurobenzene, and if it gets bad enough, bfb. It shows up in blanks and blank samples, but where there are other ions, e.g. spiked control samples, the affect disappears!

[AICMM]

Danicrd,

Have you tried turning off the IS addition at the OI and simply doing it yourself? Would help you identify problem with MS stability versus problems with autosampler.

Best regards.