Review: DART–MS In-Source Collision Induced Dissociation and High Mass Accuracy for New Psychoactive Substance Determinations
Emily C. Lennert
Keywords: new psychoactive substances, NPS, cathinones, bath salts, drugs, controlled substances, amphetamines, methamphetamine, direct analysis in real time, mass spectrometry, MS, DART, DART-MS, rapid, analysis, ambient, ionization, gas chromatography, GC, GC-MS, standard
Article to be reviewed:
- Musah, R. A.; Cody, R. B.; Domin, M. A.; Lesiak, A. D.; Dane, A. J.; Shepard, J. R.E. DART–MS in-source collision induced dissociation and high mass accuracy for new psychoactive substance determinations. Forensic Science International. 2014, 244, 42-49.
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.
New psychoactive substances (NPS) are designer drugs that are created and sold as alternatives to common drugs such as marijuana, methamphetamine, or ecstasy. Synthetic cathinones, also known as bath salts, are a class of designer drugs. These substances have a common core chemical structure, and adding different subgroups to the core structure can create new compounds, known as analogs. The new compounds may maintain their psychoactive properties while avoiding legal restrictions. These drugs are often marketed as legal alternatives, or “legal high” drugs, due to the vague nature of controlled substance laws pertaining to drug analogs. As the market is inundated with new drug analogs, drug laws are continuously modified in an effort to keep pace; however, challenges still remain in controlling the abuse and ease of access of these drugs in a timely fashion.
Current preliminary tests are generally insufficient for cathinones, color tests and immunoassays are either underdeveloped or are not fully effective for the broad range of cathinones available. Traditional confirmatory test methods, centered on gas chromatography – mass spectrometry (GC-MS), can also pose problems for cathinone analysis. Mass spectra produced by common methods of GC-MS analysis for cathinones show a high degree of fragmentation, with parent peaks being either weak or completely absent. In mass spectrometry, parent peaks are the peaks that represent the complete mass, or weight, of molecule. The mass spectra produced by GC-MS for different cathinones are often too similar to distinguish, due to the high degree of fragmentation and lack of parent peaks. Since many of the “legal high” products available include multiple cathinones, the difficulty in distinguishing between different cathinones by GC-MS can be problematic. The authors of this study sought to address this issue by studying the application of direct analysis in real time – mass spectrometry (DART-MS). DART-MS is a rapid method for analysis that provides high-resolution mass spectra of nearly all compounds present in a sample simultaneously. This method allows for the analysis of complex mixtures and identification of individual components within the mixture, all within a single mass spectrum, where each peak represents a different molecule. DART is a “soft” ionization method, meaning that minimal fragmentation occurs and parent peaks are easily observed. With DART, parent peaks will most commonly be observed as the protonated molecule, [M+H]+. M represents the molecule, or individual compound, and H is hydrogen. Most commonly, the parent peak observed will equal the exact mass of the molecule, M, plus the exact mass of hydrogen, H, that has been added to the molecule.
Three common cathinones were selected for analysis; 3,4-dimethylethcathinone (3,4-DMEC), 2,3-methylenedioxymethcathione (2,3-MDMC), and 3,4-methylenedioxy-N-benzylcathione (3,4-MDBC). Common cutting agents were selected for analysis as well; caffeine, lidocaine, and benzocaine. Each compound was analyzed individually, and mixtures were created to represent real world samples. The mixtures were created with equal proportions, by mass, of each component, with all components within the range of the concentrations found in real world samples. A Dipit-tubeTM system was used for semi-automated introduction of liquid samples, in the optimal sample introduction position. Solid samples were introduced directly into the sampling stream.
Each compound was analyzed individually prior to the analysis of the mixtures created by the authors. The expected parent peak of each compound, [M+H]+, was observed for each individually analyzed sample. Mixtures of the cathinone 3,4-DMEC with each of the cutting agents were also analyzed. In each two-component mixture, under the “soft” ionization, both parent peak for the cathinone and the cutting agent were easily identified as two different peaks. However, fragmentation is necessary to identify different cathinone analogs. At higher ionization energies, DART can fragment the molecule similar to GC-MS. The different peaks in the fragmentation patterns can indicate the structural differences that identify which cathinone analog is being analyzed. If fragmentation is desired, DART-MS parameters can be adjusted to promote the formation of fragments through a process called in-source collision-induced dissociation (CID). In in-source CID, an increase in voltage leads to an increase in kinetic energy that accelerates the molecular ions. The molecular ions then collide with the neutral molecules of the carrier gas, usually helium, and this collision leads to the fragmentation of the molecular ion.
Mixtures containing multiple cathinones and cutting agents were also analyzed, to represent combinations of multiple cathinones that have been observed in real world samples. 2,3-MDMC and 3,4-MDBC were individually added to existing mixtures of 3,4-DMEC and caffeine, in equal proportion to the 3,4-DMEC. In-source CID was used in the analysis of the new, two cathinone mixtures. Analysis of the 2,3-MDMC, 3,4-DMEC, and caffeine mixture showed that all three expected parent peaks were present, as well as the accompanying fragment peaks. Comparison of the peaks observed in the CID spectra for 2,3-MDMC alone and 2,3-MDMC in the more complex mixture show that the parent peak and fragment peaks are still easily identified in the complex mixture. Likewise, each component of the mixture of 3,4-MDBC, 3,4-DMEC, and caffeine can be identified. By comparison of the spectra of the mixture and 3,4-MDBC alone, the peaks of 3,4-MDBC can consistently be identified within the mixture.
- DART-MS is capable of analysis with no fragmentation of the molecular ion.
- Fragmentation in DART-MS can be induced by in-source CID.
- Fragmentation patterns observed in the mass spectra can allow for differentiation of compounds with similar structures and aid in the determination of structure.
- Cathinones can be identified rapidly, and with relative ease, using DART-MS.
- Using DART-MS CID, individual cathinones may be identified in complex mixtures, including mixtures that contain multiple cathinones or cutting agents.
Relevance: Current screening and analysis methods for cathinones are deficient, overall. Methods that allow for rapid analysis and the ability to differentiate cathinone analogs need to be developed to address the gap in current screening and analysis methods.
- DART-MS provides a rapid method for cathinone analysis.
- DART-MS CID provides a method by which cathinones may be differentiated within complex mixtures.