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High-Resolution, Accurate-Mass Forensic Toxicology Screening in Blood Samples Using a Q Exactive Mass Spectrometer
Conclusion
The Q Exactive MS provides high confidence with high-resolution
capabilities (up to 140,000 FWHM) for forensic screening.
Data processing is performed using ExactFinder 2.0 software. Compounds
are identified and confirmed using the exact mass of the precursor, the
isotopic distribution, the retention time and the exact mass of up to 5
fragment ions.
HRAM LC/MSMS method identified more compounds for forensic
toxicology than Diode Array Detection and Triple Quadrupole Targeted
SRMs methods.
Additional information such as metabolites identification can be easily
obtained by extracting the theoretical
m/z
values for predicted
biotransformations
This HRAM method also allows for retrospective data analysis.
A new HRAM database
(https://www.mzcloud.org/) will soon be available to
perform targeted and also unknown identification.
“For
Forensic Toxicology Use
Only”
Comparison between the different approaches: DAD detection, targeted
screening using a triple quadrupole, HRAM screening using the Orbitrap
technology
We’ve analyzed and compared 39 samples using the 3 different technologies. Overall,
the HRAM approach allowed identification of a higher number of analytes than the
other approaches. We have been able to identify 143 compounds with the HRAM
approach, 121 with the six targeted forensic screening methods performed on the
triple quadrupole MS and 69 compounds using the DAD. Some of the results are
reported in Figure 7 where we compare for 40 analytes (among the 77 identified) the
number of positive hits obtained for each approach.
DAD Approach
Fewer analytes have been identified using this approach despite the size of the library
(612 analytes). Sensitivity is certainly the main concern with this technique. Moreover,
DAD may provide in some cases some false positive results. For example estazolam
has been identified in DAD but not confirmed using the MS technologies. This
approach is well known for its poor sensitivity in benzodiazepines analysis. As reported
in Figure 7, alprazolam is not detected with DAD but is confirmed using the other two
approaches.
Triple Quadrupole Approach Using the Six Targeted SRM Methods.
This approach gives good results in terms of positive hits identified. THC was identified
using this approach as the sample preparation was done in acidic conditions unlike the
other approaches where basic conditions were used. There are still some limitations.
The identification is confirmed using six different SRM methods which means that we
may have to inject the same sample several times. Moreover these six methods
contain only 97 analytes. The run is performed in SRM mode and for this reason there
is no capability for retrospective analysis and potential metabolite identification.
HRAM Approach Using the Q Exactive MS
This approach is able to identify the largest number of analytes with the 650 analytes
library. But there are still some limitations to overcome. Precursor selection was done
in the data-dependent operation mode where the most intense ion of the previous
scan was selected for fragmentation. So we may, in some cases, have to add the
compounds in the inclusion list in order to not miss the MS
2
acquisition. Some of the
analytes listed are isomers (eg: maprotiline, paroxetine and EDDP). As they have
exactly the same exact mass, we have to make sure they present different fragment
ions in MS
2
or elute at different retention times. All data have been processed though
ExactFinder 2.0 software with a 5 ppm mass accuracy. In this version of the software,
the mass accuracy is set and can’t be adjusted. For this reason, low mass fragments
like the one we have with paracetamol at
m/z
110.0595 are in some cases not properly
identified with an accuracy of 5 ppm. This limitation is nevertheless going to be
overcome with the launch of Thermo Scientific™
TraceFinder
™ 3.0 where the mass
accuracy is set by the user and can be expressed in ppm or milli-amu.
TOXI-TUBES is a trademark of Agilent Technologies. UPLC Acquity is a trademark of Waters Technologies. All
trademarks are the property of Thermo Fisher Scientific and its subsidiaries unless otherwise noted.
This information is not intended to encourage use of these products in any manner that might infringe the
intellectual property rights of others.
ed among 39 samples
screening in SRM, DAD
6
8
10
DAD
SRM
Q-Exactive
f