Last Month's Most Accessed Feature: Zombie drug identification solved by cold ionisation

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  • Published: Oct 3, 2017
  • Categories: Gas Chromatography
thumbnail image: Last Month's Most Accessed Feature: Zombie drug identification solved by cold ionisation

Multiple synthetic cannabinoid compounds pose an analytical challenge

An increasing number of synthetic cannabinoids, most of unknown toxicity, have appeared in many countries over recent years, known by names such as ‘spice’ and ‘black mamba’. These so-called ‘zombie drugs’ have been linked with a number of deaths. Legislation has struggled to keep abreast with the numerous analogues available on the black market.

These closely related compounds also pose an analytical challenge. Often law enforcement agency analysts rely on GC-MS with electron ionisation (EI) to detect such compounds, but this is a ‘hard ionisation’ technique, giving high fragmentation and weak or non-existent molecular ion peaks. Closely related compounds, even when not isomeric, can therefore give very similar spectra, since no signals may be present for the molecular ions and the main fragmentation ions may be identical. Possible alternative methods, such as LC-MS, may give stronger molecular ions, but are more expensive than GC-MS and are not compatible with the extensive databases covering the EI fragmentation patterns of drugs.

The Jerusalem researchers analysed several similar synthetic cannabinoids using cold EI. In this method a supersonic molecular beam (SMB), made up of analyte and helium gas, is produced at the interface between the GC and MS, emerging from a specially designed nozzle. The result is less energetic analyte molecules and stronger molecular ions. The typical fragmentation patterns of normal EI are largely retained, giving compatibility with existing spectral libraries.

Cold EI applied to synthetic cannabinoids

Fifteen synthetic cannabinoids were examined by GC-MS with cold EI. An Agilent 7890A GC system and an Agilent J&W DB-5ms column were used, with a temperature gradient running from 240 to 290 °C. The mass spectrometer was an Agilent 7000A triple quadrupole instrument, fitted with a 5975 SMB ion source. The instrument was run in total ion chromatogram (TIC) mode for initial identification of the compounds, in selected ion monitoring (SIM) mode for their quantitative evaluation and in multiple reaction monitoring (MRM) mode to examine the fragmentation patterns.

The mass spectra of the cannabinoids showed stronger molecular ions than those seen with conventional ‘hot’ EI. Compounds that gave virtually identical mass spectra with ordinary EI, such as FUB-PB-22 and FDU-PB-22, could now be clearly distinguished, since definite molecular ion peaks were present. The overall fragmentation pattern was similar to that seen with standard EI, although some fragment ions became more intense. The limits of quantification (LOQ) were low, varying between 8 and 133 μg/L for the 15 compounds examined. The electron energy, lens voltage and transfer-line temperature were optimised.

The researchers used their system to examine 10 samples of seized drugs, which were in the form of herbs spiked with synthetic cannabinoids. The samples were extracted with acetonitrile prior to GC-MS. Synthetic cannabinoids were detected in all the samples: six samples containing one synthetic cannabinoid, three samples containing two compounds and one sample containing three. MRM transitions were established for both the 15 compounds and the compounds in the seized samples. The use of MRM allows the detection of low levels of cannabinoids in such materials.

Cold EI gives better differentiation between synthetic cannabinoids

Cold EI gives stronger molecular ions than conventional EI, and thus allows synthetic cannabinoids that cannot be distinguished by the latter method to be differentiated. The system was shown to be applicable to ‘real-life’ seized samples. The method could doubtless be more widely used, since it should be applicable to many other classes of compounds.

Related Links

Drug Testing and Analysis, 2017, Early View paper. Smolianitski-Fabian et al. Discrimination between closely related synthetic cannabinoids by GC-cold-EI-MS.

Rapid Communications in Mass Spectrometry, 2015, 29, 1954-1960. Amirav et al. Soft Cold EI – approaching molecular ion only with electron ionization.

Wikipedia, Gas Chromatography-Mass Spectrometry

Article by Ryan De Vooght-Johnson

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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