Emily C. Lennert
Keywords: drugs, controlled substances, amphetamines, methamphetamine, ketamine, date rape drug, GHB, nimetazepam, urine, spiked, drink, beverage, 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:
- Chen, T.H.; Hsu, H.Y.; Wu, S.P. The detection of multiple illicit street drugs in liquid samples by direct analysis in real time (DART) coupled to Q-orbitrap tandem mass spectrometry. Forensic Science International. 2016, 267, 1-6.
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.
Author’s Note: It is highly recommended that the reader reviews the information regarding DART-MS that is provided in Review: DART–MS In-Source Collision Induced Dissociation and High Mass Accuracy for New Psychoactive Substance Determinations, prior to this reading this review.
Illicit drugs are often found in nightclubs and bars. These drugs can include stimulants such as methamphetamine or ketamine, as well as drugs used in sexual assaults, also known as “date rape drugs”, such as g-Hydroxybutyrate (GHB) and nimetazepam. The authors of this study sought to evaluate direct analysis in real time – mass spectrometry (DART-MS) for the identification of these illicit drugs, as compared to more common means of analysis, such as gas chromatography – mass spectrometry (GC-MS). GC-MS is a common method of drug analysis, but it is not without disadvantages. Sample runs in GC-MS can be lengthy; each sample injection takes at least 10 minutes or more to run, and to run several samples with replicates could take hours. Sample preparation can also be time consuming; liquid samples often require extractions and derivatizations prior to analysis. Derivatization is a process by which a target compound is modified to produce a similar compound that is easier to analyze. Sample preparation is particularly important in complex liquid samples such as urine, which contain many other compounds in addition to any trace amount of drug or drug metabolite that is present. DART-MS, by comparison, requires little to no sample preparation, with no need for derivatization. Samples can be analyzed immediately by DART-MS, and a sample run can be completed, with replicates, in less than minutes.
In order to evaluate the utility of DART-MS for illicit drug identification, a number of drugs were evaluated. Nine drugs were selected for analysis: p-chloroamphetamine, p-fluoromethamphetamine, g-hydroxybutyrate (GHB), ketamine, methamphetamine, 3,4-methylenedioxypyrovalerone, p-methylethcathinone, methylone, and nimetazepam. Each drug was made into a solution, analyzed by DART-MS, and a limit of detection (LOD) was then determined. The LOD indicates the lowest concentration of the substance that the analytical method, DART-MS, can detect with confidence. The LOD for each drug can be found in Table 2 within the study. All of the drugs studied were reported to have very low limits of detection, with most falling near or below 150 parts per billion (ppb). The authors indicate that the LODs observed are of reasonable levels to allow for detection of trace amounts of the drugs.
The authors then evaluated the application of DART-MS for trace detection of drugs in more complex mixtures. Coca cola, lemon tea and orange juice were also used to create samples representative of beverages spiked with drugs. Spiked samples of each beverage were created with methamphetamine, ketamine, nimetazepam, 3,4- methylenedioxypyrovalerone, and p-fluoromethamphetamine. The authors reported that in each sample, the drug used to spike the beverage is still easily identifiable on the mass spectra.
Two real world samples of liquid drug mixtures were obtained. The real world samples had been seized by law enforcement officials during police inspections of night clubs and bars, and subsequently given to the researchers by the Criminal Investigation Bureau, Forensic Science Center, Taiwan. In the first sample, p-methylethcathinone and methylone were identified through DART-MS. Analysis by GC-MS confirmed the identifications previously made using DART-MS analysis. In the second sample, p-chloroamphetamine, methylone, and nimetazepam were identified through DART-MS analysis, and subsequently confirmed by GC-MS. The authors concluded that similar results are obtained by GC-MS and DART-MS.
The authors also further addressed the issue of derivatizations. Previous studies have reported that, in GC-MS, GHB is commonly converted to g-butyrolactone in the GC injection port or column, due to heat. g-Butyrolactone is not an illicit drug; therefore, derivatization to convert GHB to di-trimethysilyl-GHB (di-TMS-GHB) is required to prevent the conversion and confirm the presence of an illicit drug. The authors examined GHB by DART-MS and determined that no conversion, such as the one observed in GC-MS, takes place. Therefore, in DART-MS analysis, derivatizations are unnecessary.
- DART-MS is effective in the rapid identification of trace amounts of illicit drugs.
- DART-MS allows for identification of trace amounts of illicit drugs in complex mixtures with no sample preparation.
- In the identification of drugs, DART-MS performs comparably to the more common, but more time consuming, GC-MS methods.
- DART-MS circumvents the need for derivatizatons that are often required for GC-MS.
Relevance: While GC-MS is a common, standard method for drug analysis, it requires extensive sample preparation and does not allow for rapid analysis. DART-MS provides a rapid means of analysis, and requires little or no sample preparation.
- DART-MS is a viable option for the identification of illicit drugs in simple and complex samples.
- DART-MS can provide comparable results to GC-MS with less sample preparation and in far less time.
- GC-MS methods may convert some samples into other, similar compounds, leading to the need for derivatization prior to analysis to prevent this conversion. DART-MS maintains the original composition of the sample, eliminating the need for derivatizations.