Forensic Drug Analysis Using NMR Spectroscopy

When presented with drug samples, forensic scientists across the globe must find out what drug it is, and its level of purity.

These scientists need a reliable and rapid technique that will offer specific identification and precise quantitation. Although several methods are available, a majority of them need complicated instrumentation and time-consuming sample preparation.

Since SWGDRUG recognizes NMR spectroscopy as a Category A analytical method, it has become an extremely valuable technique for forensic chemists. Moreover, NMR is intrinsically quantitative, enabling the purity and identity of the sample to be determined with a single measurement. But high-field NMR systems are expensive, and need regular maintenance, thus limiting its use in forensics as a standard method.

The Spinsolve Benchtop NMR spectrometer from Magritek has a small footprint, excellent performance, and simple sample preparation, thus it addresses the drawbacks of high-field NMR and could be the perfect solution for forensics laboratories.

What is This Drug?

The advantage of using NMR for the identification of drugs is that it offers a specific fingerprint for every compound. This enables a database to be used to identify known compounds. Spinsolve has 13C and 19F capability, which is an added benefit that can offer additional proof to confirm the identity.

Structural elucidation of new drugs can be achieved by utilizing Spinsolve's 2D and multinuclear capability.

It is possible to use NMR as additional Category A evidence to support a proposed identity, as well as to differentiate between isomers or related compounds that can be difficult using GC-MS or IR spectroscopy.

Proton spectrum of a cocaine base street sample

Proton spectrum of a cocaine base street sample

How Pure is it?

In an NMR spectrum, the intensity of signals is proportional to the number of nuclei, and for each nucleus, the response remains the same. Therefore, the need for high-cost and timely calibration is eliminated. Sample preparation can be accurately carried out in a simple manner and, with the help of an internal standard like maleic acid, a simple comparison of integrals is performed to establish the purity.

Purity measurement of a caffeine sample with TCNB as internal reference. From the peak integrals, the purity is calculated to be 97.8%.

Purity measurement of a caffeine sample with TCNB as internal reference. From the peak integrals, the purity is calculated to be 97.8%.

The accuracy for Spinsolve purity measurements using an internal standard is usually around 1%. This is roughly the same as what can be realized at high field. The accuracy for purity measurements with an external standard is nearly 2.5%.

Multiple Nuclei

Spinsolve has the potential to measure a wide range of nuclei such as 1H, 13C, 19F, and 31P that can add to the analysis.

For instance, the 19F NMR spectrum of 4-fluoroethcathinone offers added evidence for the structure.

Proton spectrum of 4-Fluoroethcathinone

Proton spectrum of 4-Fluoroethcathinone

Fluorine spectrum of 4-Fluoroethcathinone

Fluorine spectrum of 4-Fluoroethcathinone

Related Compounds

The specificity of NMR enables Spinsolve to differentiate between related compounds, for example, the synthetic cannabinoids illustrated below.

Spectra courtesy of Forensics Laboratory

Spectra courtesy of Forensics Laboratory

The byproducts or degradation in a real sample of heroin, can be differentiated and identified.

Spectra courtesy of Forensics Laboratory

Spectra courtesy of Forensics Laboratory

Isomers

In a majority of cases, it is difficult to differentiate between isomers using IR and GC-MS. These methylmethcathinone (MMC) isomers that are found in real street samples can be easily identified using NMR. The distinct splitting patterns of the aromatic protons close to 7.5 ppm, caused by the methyl group’s position, can be noticed in the spectra illustrated in the figure below.

Spectra courtesy of Forensics Laboratory

Spectra courtesy of Forensics Laboratory

In the same way, it is possible to differentiate ephedrine from pseudoephedrine.

Spectra courtesy of ESR

Spectra courtesy of ESR

Cutting Agents

Cutting agents are contained in several street samples. The figure below illustrates an example of amphetamine cut with caffeine, and the two authorized reference standards for comparison.

Spectra courtesy of Forensics Laboratory

Spectra courtesy of Forensics Laboratory

Base or Hydrochloride Salt

Many drug compounds exist as the base or hydrochloride salt, with different properties, therefore they are used differently. For instance, the hydrochloride salt of cocaine is in the form of a powder that is often taken intranasally. By contrast, the base of cocaine has a lower melting point, and thus can be smoked. NMR can be used to differentiate between both forms.

Spectra courtesy of Forensics Laboratory

Spectra courtesy of Forensics Laboratory

Benefits of the Magritek Spinsolve

  • Excellent sensitivity
  • Very user-friendly
  • High spectral resolution
  • High stability with external lock
  • No deuterated solvents are required
  • Multiple nuclei options are available (1H, 13C, 19F, and 31P)

This information has been sourced, reviewed and adapted from materials provided by Magritek.

For more information on this source, please visit Magritek.

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