istd LOST

[Glad23]

hello everybody,

I need help: on differents analyses I have huge variations or sometimes totaly lost of deutereted Internal standards on LCMSMS. It's seems to be sample dependant but i think it's too huge to be matrix effect. I have this problem mainly with urines sample and mainly with a SPE sample prep. I don't know if I could be condident in my results when the ISTD is 100 time decrease and give me a high result. Does somebody has the same problem or any explications, I find nothing in the literature?

Thank you verry much

Glad

[James_Ball]

Do you make your extracts strongly acidic?

I have seen in the past, loss of deuterium when samples are brought to pH less than 2, especially when brought down to pH 1.