Multidimensional-Constrained Suspect Screening of Hydrophobic Contaminants Using Gas Chromatography-Atmospheric Pressure Chemical Ionization-Ion Mobility-Mass Spectrometry

Suspect screening
strives to rapidly monitor a large
number of
substances in a sample using mass spectral libraries. For hydrophobic
organic contaminants (HOCs), these libraries are traditionally based
on electron ionization mass spectra. However, with the growing use
of state-of-the-art mass spectrometers, which often use alternative
ionization approaches and separation techniques, new suspect screening
workflows and libraries are urgently needed. This study established
a new suspect screening library for 1,590 HOCs, including exact mass
and a combination of measured and model-predicted values for retention
time (RT) and collision cross section (CCS). The accuracy of in silico predictions was assessed using standards for 102
HOCs. Thereafter, using gas chromatography-atmospheric pressure chemical
ionization-ion mobility-mass spectrometry, a suspect screening workflow
constrained by the full scan mass spectrum of (quasi-)molecular ions
(including isotope patterns), RT, CCS, and fragmentation mass spectra,
together with a continuous scoring system, was established to reduce
false positives and improve identification confidence. Application
of the method to fortified and standard reference sediment samples
demonstrated true positive rates of 79% and 64%, respectively, with
all false positives attributed to suspect isomers. This study offers
a new workflow for improved suspect screening of HOCs using multidimensional
information and highlights the need to enrich mass spectral databases
and extend the applicable chemical space of current in silico tools to hydrophobic substances.