The Analytical Demands of PFAS Analysis

When we think about instrumentation to measure PFAS, the first thing that we need to consider is, “what's the goal and how long do we need to measure that?” What I like to say is you can't manage what you can’t measure. Measurement is ultimately critical for us. If the measurement is not accurate and reliable, you're not going to be able to have management remediation treatment or regulatory options. 

If we take an example of a regulation, say, in water, typically we're looking at PFAS at the low nanograms per liter level (ng/L). One ng/L  is pretty much the equivalent of one drop of water in around 20 Olympic-sized swimming pools. This is an extremely low level that we are having to measure PFAS. The most common analytical tool used for routine regulatory testing would be an LC-MS/MS.

But, what we are realizing is there are actually several thousand PFAS, and some of them are pretty volatile. Because of this, we have to use GC-MS/MS instruments as well. Then, to identify some of the new PFAS, researchers need to use s high-resolution mass spectrometer, such as a Q-TOF. 

There really isn't one silver bullet tool; you need a set of complementary measurement suites to really capture the entire known amount of PFAS.

Analytical instruments are critical for identifying PFAS and measuring their concentration. When we generate that information, we can help other scientists study the effects, the removal and the treatment, and how to get rid of PFAS from the environment.

We are seeing an increased use of different instruments for the analysis of PFAS. For example, ion chromatography. With ion chromatography, you can analyze the fluoride that is attached to the PFAS molecules, as well as other chemicals like pesticides and pharmaceuticals. Additionally, GC-MS systems—whether single quadrupole or triple quadruple—are becoming more prevalent for the analysis of volatile and semi-volatile PFAS. It’s also a popular choice for researchers trying to understand what happens when samples that have PFAS are burned or combust in incineration or other treatment processes that rely on heating up the molecules.

LC-MS is often the core of the analytical work for analyzing PFAS due to sensitivity. In particular, the triple quadrupole LC-MS is essential for detecting PFAS at the increasingly low levels that EPA regulations are requiring for screening methods.

A single quadrupole is a very good instrument because you're able to do remediation or QC checks with a less expensive instrument and find out whether or not PFAS are present. If there is a hit, then you can go to a more sensitive instrument, such as the triple quad to then that those analytes that have a hit. In the world of unknowns, we are still finding out that there are many, many kinds of PFAS. In this case, a high-resolution mass spectrometer is perfect, such as a QTOF. When you're using a nominal mass spectrometer like a triple quad, you might find out that a particular analyte has a mass of 376 or so. Once you look at the charged analyte, if you look at a library, you'll have hundreds if not thousands of hits. But a high-resolution mass spectrometer is amazing in that you can get down to 369.0001 or whatever it might be, and then you're looking at two or four hits in your library. This kind of high resolution is able to identify truly unknown unknowns from a matrix. And then we're able to determine the unknowns of not just PFAS, but the universe, with these advanced mass spectrometers. It's really helping us determine not only how to address issues like PFAS, but other environmental and public health concerns.

There have been advancements throughout the entire laboratory in terms of sensitivity. We're getting down to the part per trillion level—single digits. That's remarkable considering how low of a level that is. Imagine a grain of sand and an entire football field. That's essentially the levels we're looking at for part per trillion levels. We predict that those levels will continue to become more and more sensitive as new regulations and new methods come out from regulatory agencies in terms of the matrices, whether that be a solid liquid air or even tissue. We have instruments that are able to extract things from these matrices or even analyze the matrices themselves. It's incredible to see what analytical instrumentation is able to do in our current age.

It really comes down to what the laboratory or the team is looking to test in regard to the sample type, as well as how many PFAS compounds they want to look for. In general, I would break it down into three workflows, and we see these referenced throughout the regulatory requirements as well. 

The first is the use of combustion or ion chromatography. This is a technique that screens for the total organic fluoride concentration. We know PFAS compounds contain a significant amount of fluorine, so this screen captures the baseline or the aggregate amount of potential pitfalls and other fluorinated compounds, such as pesticides. In addition to this technique—and one we're seeing commonly used in the recent drinking water methods—is the use of targeted mass spectrometry. PFAS quantitation labs typically use a triple quadrupole LC or even GC-MS to perform this test, and they can accurately detect PFAS concentration levels down to parts per trillion levels.

Finally, a workflow that is getting a lot of attention recently as more and more PFAS compounds are discovered is the use of high-resolution mass spectrometry. This technique allows researchers to leverage a very sensitive and accurate workflow, but also use a very extensive PFAS library database to confirm the presence of up to 40,000 additional PFAS compounds or fragments.

Overall, we're seeing a lot of challenges in the laboratory now because of the background issues labs have due to how prevalent PFAS materials are. Really great care needs to be made when evaluating all the consumables, even the solvent grade that researchers use for these workflows as they can attribute a fairly significant signal of PFAS in the sample. Researchers need to consider the overall cleanliness of the lab and understand what technology and consumable choices are best fit for their workflow.

When we think about challenges to analyze PFAS, I would say there are four of them. The first one—and what I think is the biggest—is PFAS are everywhere. How do you ensure that when you're measuring for PFAS, you're not actually accidentally introducing PFAS from your background or in the lab? As manufacturers, we've spent a lot of time trying to make sure we can eliminate this, but that remains one of the biggest challenges.

The second challenge in PFAS testing is we constantly see evolving and new regulations. That means testing for new PFAS, testing for new levels. You constantly have to stay up to date and create new analytical methods to capture all of those. 

The third would be extremely low levels. We are measuring a low nanograms per liter levels, so you require highly sophisticated, sensitive analytical instruments and corresponding software to do.

The last is, at this point, we don't even know the exact number of PFAS that are out in the environment. Some people say it could be 1,000, some say over 5000, some say as many as a 1 million. So how do we analyze that? Mass balance is where we need high resolution mass spectrometry or other mass tools to do this forensic analysis so that we can actually identify new PFAS and monitor accordingly.

The challenges labs face are tied to both correct methods and correct technology. To use a correct method, you need the correct technology to implement it. One of the big hurdles I’ve seen is the use of LMS/MS for environmental testing. These instruments were not widely used prior to the explosion of PFAS testing, so labs don't have a lot of experience with them. This can make it difficult for labs to initially start their PFAS testing journey.

To make it more complicated, there are so many different PFAS around that a targeted approach can't catch everything. Thus, laboratories have to also employ high resolution mass spectrometry to identify and characterize PFAS. There’s also a technique called adsorbable organic fluorine that can be used to quantify a total fluorine amount—which then can potentially be related to a total PFAS exposure. In addition to these instrument-based techniques, specific sample prep and sample collection techniques are key as well. For water samples, solid phase extraction is the standard for most analysis. As you move away from water sampling into things like air sampling, absorbance or air canisters can be used to sample PFAS.

It's really about employing the correct method with the correct technology.

Labs are dealing with two main challenges when analyzing PFAS. The first is that we need to agree which PFAS we need to analyze. There are thousands—in fact, we don't even agree on how many. We also need to decide which levels we need to determine and which concentrations are relevant. Once we agree on that, we have the technology and the means to modify workflows so that laboratories can achieve the necessary concentrations, and also prepare the workflows so we can eliminate PFAS that could be in the background coming from instruments or consumables.