SIM or MRM

[semia]

Hello everyone,

I've made an infusion for digoxin (in MeOH, ACN/H2O acidified with 0.1%HCOOH) and I've tried MRM mode but I couldn't see the MW ion in the profile, before that I've done it in SIM mode and I saw only the 803.5 ion but the parent mass is 780.4 and my standard is pure (digoxin HPLC grade) so I have no salt there and still I think there is the Na adduct formed. My lab glass is clean (acid washed 10%HNO3) so I can't understand how is it possible? For SIM mode the LLOD is 10ppb but i need for calibration 0.2ppb. if tried to breakdown the adduct but nothing, is there a chance if I use an ammonium or sodium buffer to obtain another adduct? or how am I going to concentrate my samples if I use SIM for 803.5, because i this conditions I have no linearity if I go down.


Thanks,

[Alexandre]

Even not advisable, adduct ions are used for quantification, don’t worry.
Some people use ESP with ammonia or Cs, or use ESN.

Yes you will have another adduct with a different salt, the logic is simple thermodynamic equilibrium, the higher concentration of one ion the more equilibrium will be shifted to formation of this adduct.

What instrument do you have, 0.2 ppb is hard to achieve.

[semia]

I'm using an 1200LC-320 MS TQ from Varian
But how can I concentrate my samples to obtain that level?
because my calibration has to be in 0.3-5 ppb

[semia]

is it possible that my droplets to be charged by electrostatic effects and the compound carries charge by association with the sodium adduct?
practically what involves this process?

Thanks,