Using NMR in Characterizing Cocaine

The recreational use of psychoactive substances due to their hallucinogenic and stimulatory effects has been commonplace for hundreds of years. In more recent times, however, the issue of drug addiction has become widespread around the world.

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The use of alcohol and caffeine for their mood-altering and stimulatory effects is widely accepted, though alcohol abuse does have the potential to lead to use of potent illegal substances for more intense effects.

A recent worldwide survey reported that over half of the population claimed to have used an illegal drug at least once,1 with estimates suggesting that more than 1 in every 100 people globally use stimulants, such as amphetamines, cocaine or ecstasy.1

Long-term use of illicit drugs can lead to extreme agitation and hallucinations, often resulting in unpredictable, unusual or violent behavior. It also poses severe health risks, including an increased chance of seizures, heart attacks, strokes, malnourishment or movement disorders.

Significant work is being done to reduce the availability of illegal drugs via the arresting of traffickers and suppliers. Cocaine itself is the second most trafficked illegal drug worldwide, but the huge variability in terms of illegally produced cocaine’s composition has considerably hindered the work of authorities analyzing seized samples to confirm the presence of cocaine.

Cocaine

Cocaine is a highly addictive stimulant derived from the leaves of the coca plant. While it has been approved for a limited number of medicinal purposes, the recreational use of cocaine remains illegal. Cocaine is sold on the street as a fine, white, crystal powder, often containing additional excipients, such as starch, sugars,  and flour.2

Cocaine is often mixed with caffeine and other drugs such as fentanyl and amphetamine. End-users are generally unaware of these additional ingredients, resulting in catastrophic consequences. The powder itself may be smoked by sprinkling it on tobacco, snorted, or dissolved and injected into the bloodstream for more rapid effects.

Cocaine’s effects include extreme energy and happiness, mental alertness, and paranoia, by raising the levels of dopamine in brain synapses. Because dopamine plays such a key role in the brain’s reward circuit, it has a high tendency to become addictive.

Additionally, because the reward circuit adjusts to the excess dopamine caused by cocaine use, the effects become weaker over time, prompting users to take increased doses in an attempt to achieve the same high while avoiding withdrawal symptoms.

The long-term use of cocaine can result in chronic, irreversible impact on the user’s health, and a cumulative negative effect on the whole of society.

Detection of cocaine in illicit drug samples

In order for action to be taken, cocaine must first be positively identified in a seized drug sample. This identification is not always straightforward, however, because many impurities and adulterants are usually also present.

Analytical methods capable of accurately detecting cocaine within a complex mixture are, therefore, imperative. Historically, an array of separation techniques has been utilized in the determination of suspected drug samples’ cocaine content.

These methodologies have largely been chromatographic in nature, such as capillary electrophoresis and high-performance liquid chromatography, in conjunction with mass spectrometry.4,5

Unfortunately, chromatographic techniques have a disadvantage in that they require the addition of a cutting agent, which has the potential to introduce variability in the results.

To overcome this need to separate all of a mixture’s constituents in order to determine the presence of cocaine, nuclear magnetic resonance (NMR) spectroscopy is rapidly becoming the tool of choice in the analysis of illicit drug samples.6

NMR detection of cocaine

When investigating complex mixtures like drug samples, NMR offers the key advantage of allowing concurrent identification of multiple constituents with no need for prior knowledge of the nature of the mixture, or for the separation of individual components. NMR has the added benefit of requiring minimal sample preparation.

Multidimensional NMR can also be employed to provide increased resolution. It achieves this by overcoming problems of resonance shifts and signal overlap due to variations in a chemical environment.7

Diffusion ordered spectroscopy (DOSY) NMR enables users to isolate spectra of a complex mixture according to the hydrodynamic radius. This technique has proven valuable in the detection of heroin.8 Maximum quantum (MaxQ) NMR offers the added benefit of being easier to interpret, since high resolution can be achieved using only a fraction of the data points normally required.9

Both DOSY and MaxQ NMR methodologies have been examined recently for their potential use in the detection of cocaine in illicit drug samples.10 Seven samples taken from illicit drug seizures were analyzed via both DOSY NMR and MaxQ NMR using a Bruker Avance III 600 MHz spectrometer fitted with a triple resonance high-resolution probe.

The NMR datasets were obtained, then processed using the integrated TopSpin 3.2 software. Parallel reference analyses were performed using gas chromatography in conjunction with ATR-infrared spectroscopy and mass spectroscopy.

Each of these NMR techniques was able to effectively identify both freebase cocaine and cocaine hydrochloride in the illicit drug samples, even when these were in the presence of several adulterants.10

A clear distinction of each of the different components in a complex mixture was not always possible with DOSY NMR, however. Assignment of each molecular fragment, and therefore compound identifications, was found to be simpler using MaxQ NMR when numerous constituents were present.

The 2D-MaxQ NMR technique was able to provide rapid detection of the presence of both forms of cocaine. The identification was achieved in under 3 minutes using non-uniform sampling acceleration. While intermolecular interactions of sample constituents did impact on the analysis result, these did not interfere with the quality of cocaine detection.

References

  1. Reed j. iSum 2019. Drug Use, Abuse & Addiction Statistics, Trends & Data. https://isum.com/drug-use-statistics/
  2. Evrard I, et al. Int J Drug Policy. 2010;21(5):399–406. https://doi.org/10.1016/j.drugpo.2010.03.004.
  3. Yemloul M, et al. Analytical and Bioanalytical Chemistry 2018; 410(5):1-8. https://doi.org/10.1007/s00216-018-1175-7
  4. Schneider S, Meys F. Forensic Sci Int. 2011;212(1–3):242–6. https://doi.org/10.1016/j.forsciint.2011.06.027.
  5. Debrus B, et al. Anal Bioanal Chem. 2011;399(8):2719–30.
    https://doi.org/10.1007/s00216-010-4282-7.
  6. Gama LA, et al. Microchem J. 2015;118:12–8.
    https://doi.org/10.1016/j.microc.2014.07.014.
  7. Pagano B, et al. Forensic Sci Int. 2013;231(1–3):120–4. https://doi.org/10.1016/j.forsciint.2013.04.028.
  8. Balayssac S, et al. Forensic Sci Int. 2014;234:29–38. https://doi.org/10.1016/j.forsciint.2013.10.025.
  9. Mobli M, et al. Phys Chem Chem Phys. 2012;14(31):10835–43. https://doi.org/10.1039/c2cp40174f.
  10. Zawilska JB. Int Rev Neurobiol. 2015;120:273-300.
    http://doi:10.1016/bs.irn.2015.02.009.

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Last updated: Aug 13, 2020 at 3:59 AM

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