Review: DART-MS as a Preliminary Screening Method for “Herbal Incense”: Chemical Analysis of Synthetic Cannabinoids

Emily C. Lennert


Category: Chemistry

Keywords: herbal incense, spice, synthetic cannabinoids, marijuana, cannabis, alternative, designer drugs, DART-MS, direct analysis in real time, ambient, mass spectrometry, GC-MS, gas chromatography

Article to be reviewed:

  1. Lesiak, A. D.; Musah, R. A.; Domin, M. A.; Shepard, J. R. E. DART-MS as a preliminary screening method for “herbal incense”: Chemical analysis of synthetic cannabinoids. Journal of Forensic Sciences. 2014, 59(2), 337-343.

Disclaimer: The opinions expressed in this review are an interpretation of the research presented in the article. These opinions are those of the summation author and do not necessarily represent the position of the University of Central Florida or of the authors of the original article.

“Herbal incense” or “spice” is a marijuana alternative made from plant material spiked with synthetic cannabinoids. These cannabinoid and plant mixtures are marketed as “legal alternatives” to marijuana. Many synthetic cannabinoids are scheduled substances; however, suppliers circumvent regulations by synthesizing new, similar synthetic cannabinoids that have not yet been characterized or scheduled. Smoked similarly to marijuana, the synthetic cannabinoids within the plant material bind to cannabinoid receptors in the brain, producing similar or greater effects than marijuana. Synthetic cannabinoids have been associated with adverse medical affects, such as increased anxiety, rapid heart rate, and heart attacks. Large backlogs exist in crime labs; many labs do not possess the expertise to perform analysis, and procedures may not yet be developed and validated for use in these crime labs, due to the novel nature of many of these substances. Additionally, hundreds of known cannabinoids exist and share structural similarities, making the development and validation of methods and procedures challenging. Due to the challenges of synthetic cannabinoid analysis, priority is often given to conventional drug cases, like controlled substance cases regarding cocaine, heroin, etc., contributing to the backlog.

When synthetic cannabinoids are analyzed, traditional screening methods are often inadequate and not capable of detection for the wide range of analogs, or structurally similar compounds, that exist. Due to lack of adequate screening, many unnecessary samples may be sent for analysis. Analysis is commonly performed by gas chromatography – mass spectrometry (GC-MS), which requires time consuming sample preparation and extraction. After the sample is prepared, analysis by GC-MS is also lengthy, with a single sample injection running upwards of 10 minutes and a full run can take hours, depending on the number of samples or desired number of replicates. The time and effort required for GC-MS analysis also contributes to backlog. A rapid and accurate screening procedure for synthetic cannabinoids is therefore desired to reduce backlog and prevent unnecessary GC-MS analysis. Direct analysis in real time – mass spectrometry (DART-MS) is a rapid method of analysis that allows for analysis of a sample directly with no need for extraction and little to no preparation. Within seconds, a sample can be introduced and results can be observed immediately; a full run of a sample with replicates can be performed in less time than required for a single GC-MS sample injection. Rapid screening and the decrease in analysis of unnecessary samples can serve to reduce backlog, as well as help in prioritizing samples for analysis. The rapid nature of DART-MS makes it an ideal screening tool for use prior to confirmatory testing.

The authors obtained six unregulated “spice” samples from retailers, as well as standards of synthetic cannabinoids, oleamide, a previously identified component in “spice”, and 13-docosenamide, a structural analog of oleamide. The standards were analyzed for reference purposes, to confirm the identification of compounds in “spice” samples. “Spice” samples were first analyzed by holding a small segment of plant material in tweezers and introducing the sample directly into the DART-MS sample stream. To account for variation within samples, each sample was analyzed 3-5 times, and samples included both leaf and stem segments. No variation in the synthetic cannabinoids identified was observed between sample replicates. Samples were then extracted according to a defined extraction procedure and confirmatory analysis by GC-MS was performed. Calibration curves using two synthetic cannabinoid standards were created by GC-MS to allow for quantitation of the synthetic cannabinoids in the samples. Results were compared to Scientific Working Group for the Analysis of Seized Drugs (SWGDRUG) library, containing reference information for synthetic cannabinoids and other drugs.

In DART-MS, sample spectra were dominated by cannabinoid peaks. In five of the six samples, two cannabinoids were identified, and one cannabinoid was identified in the sixth sample. In all samples, the plant material contributed little to the spectra and did not interfere with the peaks originating from the cannabinoids. However, in some cases, structural analogs were not distinguishable with DART-MS, and tentative identifications were made. These structural analogs share the same molecular formula, and therefore have the same molecular mass. However, the atoms within the molecule are arranged differently, and normally analogs can be differentiated based on the GC-MS fragmentation patterns. This makes GC-MS a confirmatory method of synthetic cathinone analysis. Although differentiation of analogs is required for confirmatory analysis, it is not required for the purpose of screening prior to confirmatory analysis. Therefore, DART-MS appears to be a viable screening option for synthetic cannabinoids. Samples extracts were analyzed by GC-MS and the identifications and tentative identifications made via DART-MS were confirmed. Additionally, traces of other substances were found in both DART-MS and GC-MS results. Oleamide and 13-docosenamide were identified in three of the six samples. Oleamide is a compound that acts similarly to cannabinoids and has been identified in “spice” before, and 13-docosenamide is an analog of oleamide that, to the authors’ knowledge, has not been reported in synthetic cannabinoid products.

Other studies, cited by the author, have shown that collision-induced dissociation (CID) with DART-MS can be used for confirmatory analysis of synthetic cannabinoids. CID produces fragmentation of the molecules, and the resulting fragmentation patterns observed in the mass spectra is similar to what is obtained with GC-MS. Therefore CID by DART-MS can be used to determine the structure of a molecule in addition to its molecular mass, which is typically obtained in normal DART-MS spectra. Using CID, structural analogs that are not typically differentiated by regular DART-MS analysis may be distinguished from one another. GC-MS, a “gold standard” for confirmatory analysis, works in a similar fashion, producing fragmentation that is observed in the mass spectra and used to differentiate structures. Through CID, DART-MS may have the potential to be used as a rapid confirmatory technique.

Scientific Highlights:

  • “Spice” and “herbal incense” contain synthetic cannabinoids that are comparable to or much stronger than cannabinoids found in marijuana.
  • Screening methods and presumptive tests are inadequate to test for the wide variety of synthetic cannabinoids that exist. The lack of adequate screening contributes to increasing backlog of suspected synthetic cannabinoid case samples, due to unnecessary submission of samples for confirmatory GC-MS analysis.
  • The sample preparation and lengthy analysis time required for GC-MS may contribute to the backlog of suspected synthetic cannabinoid case samples.
  • Identifications of synthetic cannabinoids by DART-MS were confirmed by subsequent GC-MS analysis.
  • DART-MS was demonstrated to be an effective, rapid screening tool for synthetic cannabinoids.
  • Some structural analogs of synthetic cannabinoids could not be differentiated by this DART-MS method; however, other research has indicated that analogs may be differentiated by CID, creating the potential for confirmatory analysis by DART-MS.

Relevance: The development of a rapid screening method for synthetic cannabinoids may assist in decreasing the current backlog of suspected synthetic cannabinoid cases. Additionally, the use of DART-MS as a screening method may save time and money by preventing unnecessary GC-MS analysis.

Potential Conclusions:

  • DART-MS is a viable screening method for synthetic cannabinoids that required no sample preparation and little time.
  • The use of DART-MS as a screening tool may assist labs in eliminating and preventing backlog of suspected synthetic cannabinoid case samples.