Spectroscopy in the Modern Cannabis Laboratory

The rapid expansion of the medical and recreational cannabis markets has created an urgent demand for rigorous analytical testing.^1,2 To ensure consumer safety and regulatory compliance, laboratories must accurately detect toxic contaminants and quantify psychoactive compounds. Psychoactive compounds in legal cannabis include: Δ9-tetrahydrocannabinol (THC), tetrahydrocannabinolic acid (THCA), cannabidiol (CBD), cannabinol (CBN), tetrahydrocannabivarin (THCV), and trace cannabinoid degradation products such as Δ8-THC, along with other minor phytocannabinoids and terpenoid compounds.¹ Traditionally, this required expensive, complex, and time-consuming equipment.

Cannabinoids such as THC, THCA, CBD, CBN, THCV, and Δ8-THC are commonly analyzed using gas chromatography–mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC) for quantitative profiling, with liquid chromatography–tandem mass spectrometry (LC-MS/MS).

Fourier transform infrared spectroscopy (FT-IR), near-infrared spectroscopy (NIR), Raman spectroscopy/surface-enhanced Raman scattering (Raman/SERS), and quantitative nuclear magnetic resonance (qNMR) are also used for confirmatory analysis, rapid screening, and structural characterization.¹ However, recent advancements in spectroscopic techniques are revolutionizing the field by offering faster, greener, and more accessible, yet accurate alternatives.

In this Q&A, we explore how improved techniques like inductively coupled plasma–optical emission spectroscopy (ICP-OES), near-infrared (NIR) spectroscopy, and laser-induced fluorescence (LIF) are involved in reshaping cannabis science.

Why is heavy metal testing so critical for cannabis, and what are the primary challenges?

Cannabis and hemp plants are known for their unique chemical compositions and their ability to absorb elements from the soil.^2,3 This makes them susceptible to accumulating heavy toxic metals. Normally in cannabis analysis, there are four major toxic heavy metals found in cannabis, which include arsenic, cadmium, mercury, and lead.^2,3 Regulatory bodies, such as those in California and Colorado, have set maximum allowable limits (MAL) for these elements at extremely low concentrations, often in the parts-per-billion (ppb) range.³

Historically, inductively coupled plasma–mass spectrometry (ICP-MS) has been the gold standard for this analysis because of its extreme sensitivity.^2,3 However, the problem is that ICP-MS is complex to operate, expensive to maintain, and requires significant routine upkeep.^2,3

As a result of ICP-MS’s limitations, other spectroscopic techniques are replacing it.

How is ICP-OES becoming a viable alternative for detecting these trace metals?

Despite the sensitivity of ICP-MS, ICP-OES is simpler and more cost-effective. Recent innovations in sample introduction systems have closed the sensitivity gap.^2,3

A key breakthrough involves the use of high-efficiency nebulizers, such as the OptiMist Vortex, which utilizes a non-concentric design and an external impact bead to create a much finer, denser aerosol.² This system, combined with optimized microwave digestion to break down the organic plant matrix, allows ICP-OES to reach detection limits well below the strictest regulatory thresholds.^2,3 Additionally, ICP-OES can handle 10 times higher amounts of total dissolved solids (TDS) than ICP-MS, reducing the need for extensive sample dilution.²

What role does near-infrared (NIR) spectroscopy play in distinguishing hemp from cannabis?

NIR spectroscopy has emerged as a powerful screening tool for this purpose. Researchers from the National Institute of Standards and Technologies (NIST) and the University at Albany recently demonstrated that NIR can accurately classify cannabis samples into "low-THC" (less than 2%) and "high-THC" (2% or more) categories.⁴ Using chemometric models like partial least squares discriminant analysis (PLS-DA), they achieved a 98.9% accuracy in cross-validation.⁴ This method relies on spectral features related to both THC and CBD, as high-CBD profiles are often characteristic of hemp.⁴

How does NIR compare to traditional chromatography for potency testing?

Traditional methods like liquid chromatography (LC) or gas chromatography (GC) are highly accurate, but they come with significant drawbacks. LC and GC analysis can be time-consuming, require chemical solvents, and necessitate trained analysts.⁴ In addition, these techniques are destructive to the sample.⁴

However, NIR spectroscopy is not destructive and requires little to no sample preparation.⁴ It can analyze ground cannabis flower directly and produce results almost immediately. Because the statistical analysis can be automated, it does not require expert interpretation on-site, making it an ideal candidate for field applications, law enforcement, and agricultural testing.⁴

Can you explain the use of laser-induced fluorescence (LIF) in drug analysis?

LIF is another emerging technique favored for its simplicity, speed, and portability. It is particularly useful for analyzing optically dense substances like hashish (cannabis resin).⁵

By using a single wavelength excitation (such as 405 nm), researchers can identify unique fluorescence parameters, specifically the absorption coefficient (α), the quenching factor (k), and the concentration at maximum intensity.⁵ These parameters act as a "fingerprint," allowing for the rapid identification of drugs in the field where conventional laboratory tools might be unavailable.⁵

What is the future of these spectroscopic methods in the cannabis industry?

The shift is clearly toward high-throughput, reliable, and cost-efficient methodologies. Although techniques like NIR may still require confirmatory analysis via chromatography for final regulatory approval in some jurisdictions, they serve as essential "first-line" screening tools.⁴ As data sets grow and chemometric models are refined, spectroscopy will continue to reduce the cost and complexity of ensuring a safe, standardized cannabis supply.^2,4

References

1. National Academies of Sciences, Engineering, and Medicine. The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research, 2017. Available at: https://nap.nationalacademies.org/catalog/24625/
2. Leikin, S.; Phillips, A. ICP-OES as a Viable Alternative to ICP-MS for Trace Analysis: Meeting the Detection Limits Challenge. Spectroscopy 2023, 38 (10), 7–13. DOI: 10.56530/spectroscopy.do3475y9
3. Acevedo, A. Pittcon 2024: Detecting Toxic Metals in Hemp Samples Using ICP–OES. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/pittcon-2024-detecting-toxic-metals-in-hemp-samples-using-icp-oes (accessed 2026-04-10).
4. Wetzel, W. New Spectroscopy Method Offers Rapid, Reliable THC Classification for Cannabis Samples. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/new-spectroscopy-method-offers-rapid-reliable-thc-classification-for-cannabis-samples (accessed 2026-04-10).
5. Acevedo, A. Opium and Hashish Tested Using Laser-Induced Fluorescence Spectroscopy. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/opium-and-hashish-tested-using-laser-induced-fluorescence-spectroscopy (accessed 2026-04-10).