Hello
we are using a GC-MS (ion trap) for our routine analysis. Since a few days we observed a "strange" randomly occuring problem:

let me explain:
if we are running real samples it looks "always" nice. here we are not interested in absolute amounts of the anlytes, just in ratios. It seems, that the performance of the instrument is stable for this kind of samples.

if we are running standards, it happened that we loose almost all of the sensitivity. But, this occurs not every time, that means it happened that we injected the same sample twice, once we found the expected amount and at the other one we have seen more or less nothing!

We have tried preparing standards by adding a matrix (addition of some buffer), it seems that this helps, but we haven't done this before, so why shall we start with this now?

I believe the problem is up to the injector, here we have changed the syringe, septum, liner. we also heated up the injector and we changed the gas clean filter. No use at all!

Maybe you have observed similar problems? Any suggestions?

thank you!

Mikro