Presumptive Field-Testing During Narcotics Investigations

Presumptive field-testing refers to the initial testing of a substance to determine whether it is likely to be an illegal drug. These tests are designed to provide immediate results, indicating the presence of specific drugs or drug classes.

Presumptive field-testing is a crucial procedure in narcotics investigations, enabling law enforcement professionals to quickly identify suspected illegal substances found during searches, arrests, or routine patrols.  By identifying substances on-site, officers can expedite the investigative process, reducing the need for lengthy laboratory analyses initially. Positive presumptive tests can support probable cause for arrests and search warrants, aiding in the legal process. In addition, identifying substances quickly helps officers take necessary precautions, reducing the risk of exposure to dangerous drugs.

Two Common Presumptive Field Tests

We will discuss two types of presumptive field tests that are commonly used in narcotics and illicit drug identification and investigations:

Colorimetric Tests: Colorimetric tests involve adding chemical reagents to a sample, which change color in the presence of specific drugs. The color change indicates the presence of certain substances. For example, the Marquis reagent turns purple in the presence of heroin and brown with amphetamines.

Handheld Narcotics Analyzers utilizing Raman Spectroscopy: Raman spectroscopy involves shining a laser light on a sample and analyzing the scattered light to determine the molecular composition of the substance. Each type of molecule scatters light in a unique pattern, allowing for precise identification.  Handheld Raman spectroscopy devices can be used in the field for rapid, non-contact, non-destructive identification of narcotics.

Differences Between Raman Spectroscopy Analyzers and Colorimetric Test Kits in Identifying Drugs on the Street

Raman spectroscopy analyzers and colorimetric test kits are both used by law enforcement to identify drugs on the street, but they differ significantly in their technology, application, accuracy, and usability. Here is a comparison of some of their features.

Accuracy:
- Raman Spectroscopy: High precision with detailed molecular analysis. Provides highly accurate identification of substances based on their molecular structure. Can identify a broad spectrum of drugs, including complex mixtures and cutting agents.
- Colorimetric Tests: Moderate precision and provides quick, preliminary identification, however may produce false positives or negatives because the color change must be interpreted by the user. The colorimetric response produced is subjective and its interpretation can vary with the experience of the analyst, and the type or lack of lighting available when the test is performed.¹

Sample Integrity:
- Raman Spectroscopy: Non-contact, Non-destructive analysis for most samples. Raman analyzers do not alter or destroy the sample, preserving the sample for further analysis.
- Colorimetric Tests: Destructive. The sample is often altered or consumed during the test, which may limit further analysis.

Usability:
- Raman Spectroscopy: Handheld analyzers are portable with user-friendly interfaces. Reduces the risk of exposure to hazardous substances by quickly identifying them, even through plastic bags.
- Colorimetric Tests: Test kits are portable, and simple to administer with basic instructions. Interpretation of results can be subjective.

Time to Results:
- Raman Spectroscopy: Raman typically takes <1 minute to obtain results, enabling rapid decision-making.
- Colorimetric Tests: Sample prep of mixing reagents and waiting for a color changes typically takes a few minutes for colorimetric tests.

Admissibility:
- While Raman analyzers and colorimetric test kits are valuable tools for law enforcement, their admissibility in court varies. Raman analyzers, due to their higher accuracy, may have a stronger standing when supported by officer/expert testimony.² For specific references and case law, consulting legal databases, forensic science journals, and law enforcement guidelines is recommended.

Summary

Both Raman spectroscopy analyzers and colorimetric test kits are valuable tools for law enforcement in identifying drugs on the street. Handheld Raman narcotics analyzers offer high precision, non-destructive testing, and rapid results, making it ideal for detailed analysis and complex mixtures. Colorimetric test kits provide quick, preliminary identification, are easy to use, and are cost-effective, but may produce inaccurate results due to potential for false positives/negatives due to subjective misinterpretations. The choice between these technologies depends on the specific needs of the investigation, available resources, and the required level of accuracy.

Additional Resources & References

¹From Front Psychiatry, 2021 Feb 22;12:596895. doi: 10.3389/fpsyt.2021.596895, noted in the National Institutes of Health, National Library of Medicine.

²Accessibility Note: The Thermo Scientific TruNarc Delta and Tau capture all scan results, including time-and-date stamps and system self-checks to help expedite prosecution. Once a substance is analyzed, full results are automatically stored for reporting and evidence submission. Rapid results combined with automated reports can streamline the path to prosecution, reducing administrative burden and dramatically impacting the time and expense of drug-related arrests. Depending on the jurisdiction, the TruNarc Delta and Tau Handheld Narcotics Analyzers’ test results may be used as presumptive evidence in preliminary hearings.