Fluorotelomer Sulfonates and Crosstalk
The commercially available isotope-labelled fluorotelomer sulfonates are typically labelled with 13C atoms on the non-fluorinated hydrocarbon atoms. This increases the mass of the fluorotelomer sulfonate by 2 Da, and causes crosstalk between the native +2 isotope and the mass-labelled isomer. The crosstalk occurs between the [M-HF]- fragment of the isotope-labelled fluorotelomer sulfonate and the [M-HF]- fragment of the +2 isotope. This causes the reponse of the isotope-labelled FTSs to increase as the concentration of the native FTS increases. The solution to this problem is to use the  fragment as the preferred transition for isotope-labelled FTSs.
M2-4:2 FTS 329.0>81.0 DP: -20 CE: -55
M2-6:2 FTS 429.0>81.0 DP: -20 CE: -70
M2-8:2 FTS 529.0>81.0 DP: -20 CE: -85