Microplastics are no longer just an environmental buzzword. They are increasingly part of a public conversation about water quality, consumer safety, and chemical exposure. Last week, the EPA published a list of microplastics and pharmaceuticals being considered for future drinking water regulation under the Safe Drinking Water Act. The draft list is open for public comment through early June.
That does not mean there is suddenly a nationwide testing strategy for microplastics in drinking water, or a final regulatory limit put in place. Instead, it means this question is becoming more urgent: if you want to measure microplastics in water, which analytical approaches will work?
For labs like Covalent, that is where things get interesting.
Why microplastics are analytically challenging
“Microplastics in water” sounds like one measurement problem, but it is really several. Are you counting particles? Identifying the polymer type? Estimating total plastic mass? Determining the size of the particles? Detecting small particles that may be missed by one method but captured by another?
Those are not interchangeable questions, and no single technique answers all of them equally well. Methods for detecting microplastics are still evolving and sampling and sample preparation are major parts of the challenge. Current best practice is often fit-for-purpose analysis: choose the method based on whether the goal is particle identification, size distribution, total particle count, or polymer mass.
What techniques are used to detect microplastics in water?
FTIR and Raman: identifying individual particles
FTIR and Raman spectroscopy are widely used for identifying microplastic particles because they can distinguish polymers based on their chemical signatures. In practical terms, these methods help answer: is this particle actually plastic, and if so, what kind?
Each has tradeoffs. FTIR is limited by long IR wavelengths which fundamentally limit the spatial resolution to 10 µm and cannot be applied directly to bulk water samples because the water signal would dominate, burying any plastic signal. This means FTIR analysis requires catching the particles in a filter, which is then analyzed. This step determines which particles are even available for analysis—making filtration one of the most critical and error-prone parts of the workflow. Raman, with its shorter wavelength, can push to smaller particle sizes (around 1 µm) and also benefits from weaker interference with water. This means Raman can handle wet samples. However, in practice, the low concentration of particles, difficulty of immobilizing particles for analysis, and fluorescence from other natural components in tap water often necessitate the same filtration and concentration steps used in FTIR workflows. Additionally, Raman scans can be slow.
In other words, although Raman can extend microplastics analysis to smaller particles and wetter conditions, both Raman and FTIR still depend heavily on sample preparation to turn a dilute, messy water sample into meaningful data. In the end, the biggest challenge is often not detecting microplastics but isolating them from the water matrix in a way that makes reliable analysis possible.
What about particle counting techniques?
For dilute environmental samples, techniques designed to detect and count individual particles, such as nanoparticle tracking analysis, Light Obscuration, Dynamic Image Analysis, or Electrical Sensing Zone, are often more relevant than bulk particle sizing methods. These approaches can measure particle concentration and size on a particle-by-particle basis, making them well suited to low-concentration systems like microplastics in water.
However, this method will size and count all particles, not just plastics. In tap water, there are many natural sediments and organic materials that cannot be differentiated by these techniques. In practice, particle counting techniques are most powerful when combined with spectroscopic techniques such as FTIR or Raman, which can confirm whether detected particles are plastic and identify their polymer type.
Pyrolysis-GC/MS: measuring polymer mass
If the real question is not “what does this one particle look like?” but instead “how much polyethylene, polypropylene, or polystyrene is in this sample?”, pyrolysis-GC/MS becomes very attractive.
Py-GC/MS works by thermally breaking polymers into characteristic fragments that can then be separated and identified. Recent comparative work in urban water samples1 showed that μ-FTIR and Py-GC/MS can provide complementary information: μ-FTIR is useful for particle-number data, while Py-GC/MS helps quantify microplastics in terms of mass concentration.
That distinction matters. A sample can contain many small particles with low total mass, or fewer particles with higher mass contribution. Depending on the application, one metric may be more useful than the other.
So what is the “best” technique?
Covalent’s answer is: the best technique depends on the question.
If the goal is:
- Particle identification → FTIR or Raman are often the strongest starting points.
- Bulk polymer quantification by type or mass → Py-GC/MS is often the better fit.
- Particle sizing and counting → nanoparticle tracking analysis, Light Obscuration, Dynamic Image Analysis, or Electrical Sensing Zone are the go-to techniques.
- A more complete picture → a combined workflow can be the smartest strategy, using one method to identify particles and another to quantify polymer load.
That is the real takeaway: microplastics analysis is less about finding one magic instrument and more about building the right analytical workflow.
Why this matters now
EPA’s latest move does not instantly create a standard national microplastics test, but it does signal growing regulatory and public-health attention. As that attention increases, labs will need methods that are not only sensitive, but also reproducible, interpretable, and matched to the decisions being made from the data.
For analytical scientists, this is a familiar story. The hardest part is not data generation, but instead it is choosing the technique that answers the right question. This is where Covalent can help.
In the case of microplastics, that may mean combining spectroscopic particle identification with chemistry-driven polymer quantification and laser particle sizing techniques to move from concern to defensible measurement.
Citations
- Sefiloglu, F. Ö., Stratmann, C. N., Brits, M., van Velzen, M. J. M., Groenewoud, Q., Vethaak, A. D., Dris, R., Gasperi, J., & Lamoree, M. H. (2024). Comparative microplastic analysis in urban waters using μ-FTIR and Py-GC-MS: A case study in Amsterdam. Environmental Pollution, 351, 124088. https://doi.org/10.1016/j.envpol.2024.124088