Pitfalls in measuring the endocannabinoid 2-arachidonoyl glycerol in biological samples

Background: The endocannabinoid 2-arachidonoyl glycerol (2-AG)
undergoes spontaneous isomerization to biologically inactive 1-AG.
This effect has not been adequately addressed in previous studies
that reported 2-AG concentrations in biological samples. Methods:
Liquid chromatography tandem-mass spectrometry (LC-MS/MS) was used
for 1-AG and 2-AG analyses. Results: Identical collision-induced
disintegration spectra were found for 1-AG and 2-AG. For specific
detection of both compounds, which share a common mass transition,
baseline chromatographic separation is mandatory, even when
applying MS/MS technology with its generally high detection
specificity. When using standard chromatographic conditions with
the very short run times typically used in LC-MS/ MS methods,
co-elution of 2-AG with 1-AG, which is present in human serum,
causes false 2-AG results. Conclusions: Our data highlight that the
analytical specificity of MS/MS can be limited by interference from
isobaric isomers with identical disintegration patterns. The
specificity of this technology must be carefully evaluated for each
individual application.