Improvements in LC-MS/MS sensitivity and multiple reaction monitoring (MRM) capabilities are resulting in further adoption of LC-MS/MS technology in clinical settings. One specific clinical challenge with LC-MS/MS is the potential for matrix effects that cause interferences or impact ionization efficiency. As samples vary from patient to patient it can be challenging to anticipate and detect matrix effects.

Stable isotope-labeled internal standards are frequently used to compensate for matrix effects and to increase the accuracy of quantitation. A labeled internal standard that co-elutes with the drug being monitored can offset patient specific matrix effects (co-eluting concomitant medication, etc.) that may occur at the retention time of the analyte of interest.

Complications in the use of deuterium-labeled internal standards can arise from hydrogen-deuterium scrambling in solution or in the ion source at the selected transitions. In this study, we examined deuterium-labeled hormones and other compounds of clinical significance by LC-MS/MS at select transitions. We investigated reproducibility of the scrambling ratio and influences on scrambling from different LC-MS systems (tandem quadrupole vs. quadrupole time-of-flight), concentration, solution behavior, and deuterium placement in the internal standard.