Why do Int Stnds not need reference ions In MRM LCMS?

[PeterPopoff]

Why is it that when I look at a premade method that for a specific compound it uses the target and reference ions to identify it, but for its dueterated internal standard there is only one peak, ie, not reference ions peaks? I know this is probably a dumb question but thanks.

[MaryCarson]

The reference ions are there to confirm that you found the compound you think you found. Not needed for the I.S. because you KNOW it's there--after all, you added it to the sample.

[James_Ball]

I usually build my own methods for LCMSMS and I include the second ion for the Internal Standards just for extra insurance there are no problems with the analysis. I have seen a lot of methods posted the do not use them, but coming from EPA GCMS background it have always just carried over the fact you have to have them.