LC-MSMS - Points of attention when using isotope labelled standards

The use of isotope labelled internal standards is of common use in LC-MS/MS analysis of antibiotics and other veterinary drugs. The advantages are various like extraction recovery correction and elimination of matrix effects during LC-MS/MS analysis. However, there are some points of attention when using isotope labeled internal standards. If the number of labeled atoms is too low or when the number of C-atoms of the analyte is high, it’s is possible that the unlabeled analyte of interest will contribute on the signal of the internal standard. For that reason, it’s advisable to consider if the concentration of the internal standard is appropriate in relation to the concentration of the native compound.