internal standard for organophosphate

[Etox]

Hi

I am running organophosphate pesticide residue analysis using LCMSMS (ES+). I will use ISTD for matrix effect study, TPP and ethoprofos are recommended in several papers to be used as internal standards. Do they have to be labelled or just conventional standards?

[carls]

I believe TPP is usually used as a process control, not an ISTD. The ISTD is usually something similar such as another organophosphate pesticide. If you are not looking for ethoprofos in your analysis you dont need the stable labeled ethoprofos. These methods assume the ISTD will act like the other compounds in the extraction, i.e. similar recovery, and will correct for instrument drift. However, they do not correct for matrix effects in LCMS. In pesticidce residue analysis there are typically many analytes so using stable label ISTDs for all analytes is not economically feasible.