A false positive finding in liquid chromatography/triple quadrupole mass spectrometry analysis by a non-isobaric matrix component: the case of benzotriazole in urine for human biomonitoring.
Multi-residual methods employing liquid chromatography coupled to triple quadrupole mass spectrometry (LC/MS/MS) with selected reaction monitoring (SRM) are attractive also for human biomonitoring (HBM). A new process is determined that can lead to false positive findings by matrix components that are not isobaric to the analyte of interest.



Benzotriazole (1H-BT) was false positively detected in 87 human urine samples analyzed by ultra-high-performance-(UHP)-LC/MS/MS. The quantifier/qualifier ratio (Q/q ratio) did not match. This was further confirmed by negative results with an optimized gradient. Investigations were performed by UHPLC/high-resolution (HR)MS and model compounds to reveal the identity of the disturbing matrix compound and the way that it interfered with 1H-BT detection.



A formula of C7 H5 NO (m/z 120.0444) was found at the retention time of 1H-BT (m/z 120.0556) belonging to an in-source product ion of a heavier co-eluting compound. Product ion spectra and Q/q ratios of model compounds indicated a benzene sub-structure with a carbonyl and amine functional group in the ortho- or para-position. Finally, folic acid was confirmed as the disturbing urine component, exhibiting an in-source fragment with the nominal mass of 1H-BT and the same product ions as used in the SRM mode for UHPLC/MS/MS monitoring.



Interferences in SRM detection need not be due to co-eluting isobaric matrix compounds, but can originate from in-source fragmentation of heavier ions. Rigid quality control measures are recommended for LC/MS/MS analysis, especially for small molecules in complex sample matrices to overcome the selectivity limits of SRM. Copyright © 2016 John Wiley & Sons, Ltd.
Helmholtz Centre for Environmental Research - UFZ, Department of Analytical Chemistry, Permoserstrasse 15, 04318, Leipzig, Germany.
Linda
L
Schlittenbauer
Helmholtz Centre for Environmental Research - UFZ, Department of Analytical Chemistry, Permoserstrasse 15, 04318, Leipzig, Germany.
Bettina
B
Seiwert
Helmholtz Centre for Environmental Research - UFZ, Department of Analytical Chemistry, Permoserstrasse 15, 04318, Leipzig, Germany.
Thorsten
T
Reemtsma
D002853:Chromatography, Liquid; D004784:Environmental Monitoring; D006801:Humans; D053719:Tandem Mass Spectrometry; D014230:Triazoles / Q000652:urine*
D014230:Triazoles; C012771:benzotriazole