As the precursor is different and sufficiently far from each other to avoid co-isolation in the first quad mass filter, I would assume it to be fine when quantified by MRM/SRM. Do they co-elute since your are concerned?

The internal standard - in your case and from a chromatographer's point of view - should elute in the vicinity of the analyte and must not coelute. In case it does, you should either look for a different component or consider using a labeled internal standard (ILIS).

Good luck with your research

Detlef.

Speaking from experience. If the precursor ion has a different mass there is no problem at all. One of ions will be selected in the first quad and will go to collision cell.

As suggested, difference in elution time would be an additional safety layer.

Hi,

For those having a cross-talk problem, it is better to choose the deuterium or carbon isotope dilution method for internal standard (IS) quantitation. If you cant provide the isotope synthesized molecule or co-elution exist and you cant improve the chromatographic resolution then I strongly suggest switching your IS with an analog molecule, which behaves like your target compound (Extraction yield, ionization suppression effects etc.) but also giving fragmentation product at different MW far away from your target fragments.

I am in agreement with @Michal, @Deltef.

As long as the precursor ions are different, no problems.

Concur Michael and Detlef on this.

LC-MS/MS is a hyphenated technique combining the separation power of HPLC, with the detection power of Mass Spectrometry. Triple Quad Mass Spec (LC-MS/MS) System can resolve any peak having a difference of ± 0.7 amu at the unit resolution.

Even if the both have same precursor ion, as they are different mass there is no problem. Detection would not be hampered, yes eluting at same retention time create problem, for that different HPLC parameters can be played on or change the IS.

This method was developed on LC MS/MS. The quantifier for both analyte and internal standard have same product ion

The perfect choice for an IS is a labeled version of the analyte (usually by means of at least 3-4 labeled 13C, 2H, 15N atoms depending on chemistry...in order to shift its isotopic pattern/envelope away from the analyte's). This choice usually leads to strong analyte/IS coelution (--> establish/test IS concentration to avoid suppression of analyte ionization), nonetheless the selectivity of the first quadrupole allows to avoid cross-contamination in detecting a common fragment.