Naturally occurring isotopes of an analyte can interfere with doubly deuterated internal standard measurement

Abstract

Background: Internal standards are essential in quantitative mass spectrometry (MS) assays to correct for variability in sample extraction and ionization at the source. In liquid chromatography MS assays, analogues of the analyte with several atoms replaced by their stable isotopes, e.g.2 H (D, deuterium) are often used as internal standards.

Quantification of cortisol and 6 beta-hydroxycortisol in human urine by LC-MS/MS, and gender-specific evaluation of the metabolic ratio as biomarker of CYP3A activity

“…This may incorrectly increase the amount of internal standard detected, when high concentrations of analyte are present with low concentrations of internal standard. Following the procedure published by Duxbury et al for cortisol and [ 2 H 2 ]cortisol [16], we therefore chose the concentration of the internal standard high enough to avoid deviation from linearity of the calibration curve.…”

The role of liquid chromatography–tandem mass spectrometry in the clinical laboratory

“…C13 atoms, on the contrary, are typically located in the backbone of a molecule and are less prone to exchange and differences in chromatographic behaviour. In order to prevent the natural isotope ions of the target analyte contributing to the intensity of the molecular ions of the internal standard, with subsequent underestimation of the true value, it is advised to choose the mass of the internal standard at least 3 amu above that of the analyte [50].…”

Late‐Stage 18O Labeling of Primary Sulfonamides via a Degradation–Reconstruction Pathway

“…Synthetic reagents containing the traditionally used isotopes 2 H, 13 C, and 15 N can also be costly and only provide one mass unit increase for each atom. Although advances have been made in utilizing hydrogen‐isotope exchange (HIE) catalysts as a late‐stage labeling option for primary sulfonamides, 2 H isotope is not typically desirable for bioavailability studies as deuterium is often labile to metabolic pathways, and can also exhibit problematic chromatographic behavior by failing to co‐elute with the non‐labeled analyte of interest…”