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.
Vogeser
Michael
M
Institute of Clinical Chemistry, Hospital of the University of Munich, Munich, Germany. michael.vogeser@med.uni-muenchen.de
Schelling
Gustav
G
D001095:Arachidonic Acids / Q000032:analysis*; D063385:Cannabinoid Receptor Modulators / Q000032:analysis* / Q000592:standards; D002853:Chromatography, Liquid; D063388:Endocannabinoids; D005189:False Positive Reactions; D005990:Glycerol / Q000031:analogs & derivatives* / Q000032:analysis; D006801:Humans; D007536:Isomerism; D012680:Sensitivity and Specificity; D053719:Tandem Mass Spectrometry
D001095:Arachidonic Acids; D063385:Cannabinoid Receptor Modulators; D063388:Endocannabinoids; D005990:Glycerol