Exposure to manmade perfluoroalkyl and polyfluoroalkyl substances (PFASs) is of increasing concern due to their potential toxic effects and links to ecological damage and human health. These substances can be found in drinking, surface, waste and ground waters, but are also prevalent in food, household products, and even living organisms including fish and humans.
In this on-demand SelectScience® webinar, David Schiessel, Babcock Labs, and Richard Jack, Phenomenex, demonstrate the use of a dual, stacked WAX/GCB SPE method that uses a single step for C4-C18 PFAS compounds from waste-, surface- and groundwater extracts followed by LC-MS/MS.
Read on for highlights of the live Q&A session or register to watch the webinar at any time that suits you.
Q: What volumes of water are typically used to get low PPT detection?
DS: We typically use two different volumes during sampling. We collect 250 milliliters of water sample, but at the same time, we also collect a 50-milliliter portion so that if we have to do a smaller volume due to unreasonable matrix interference, we can do the lower volume of 50 milliliters. Typically, we attempt to do 250 milliliters to maximize sensitivity.
Q: Do you think even longer-chain sample preparation will be feasible?
DS: With the isotopically labeled standard, the C16, you do start to see some loss, that graphitized carbon black (GCB) does have some affinity for longer chain. I think if we have to continue to use GCB, then longer chains in C18 are probably not feasible. However, they're probably not found in environmental waters just because they would probably rather be with surrounding sediment or particulates that are in the matrix.
Q: Any issues with the DoD QSM requirements of ISTD recoveries being 50% to 150%?
DS: Yes of course, especially within matrix samples. As far as blank QC, LCSs, or what we call blank spikes, those should be free of interference, essentially. Those should be meeting 50%, 150% every time. However, with matrix that could be anything, wastewater is such a broad matrix type, so the bottom line is through multiple analysis, multiple extractions of the sample, if it's not meeting 50% to 150%, then that data is essentially qualified or flagged. The short answer is, yes, there typically are matrices that do not meet the 50% to 150%. Typically, if we see them not passing across the board, for example, 10% across the board, that's an immediate re-extraction. So, by either reanalysis or re-extraction, you can establish matrix interference.
Q: Are PFASs classified as endocrine disruptor, or pollutants?
RJ: I think, for the most part, they're pollutants. They haven't been linked to endocrine destruction. They certainly have toxicological effects, meaning that the long chain of the fluorinated carbon chain embeds in the membranes and causes them to become porous in the tissue of animals and that leads to their toxicity. But they're not so much linked to endocrine destruction such as the other pharmaceuticals.
DS: One thing I will add to that is if you follow, for example, the UCMR, the Unregulated Contaminant Monitoring Rule, there's been a lot of talk about a lot of these compounds and the lack of toxicity studies, and toxicological studies just simply haven't been done on all of these compounds. Definitely, they've been done with PFOAs and PFOS, but when you start adding all these oddball compounds, some of them have had zero studies done. That's where, perhaps, these other techniques like chemometric tests that the Office of Research is working on might be useful.
Q: What type of sample cleanup are you using for these samples?
DS: The DoD QSM requires GCB. It's just in this product that was presented, we have the GCB basically being done right after the solid-phase extraction. It's a stacked cartridge, and so it's done in one fell swoop. The alternative method that we were doing before was to add the GCB after the extraction, and that required an extra step of filtration. That added an additional cost of consumables, specifically finding filters that meet the requirement of the construction of material like polypropylene or HDPE filters.
Q: Could you walk through your SPE extraction procedure for this method again?
DS: Briefly, it's simply the conditioning — that is we condition with basic methanol. That’s methanol that we've added ammonium hydroxide to and then conditioned with just regular methanol and then water. At that point, we load the sample, which we've verified that the pH is within a particular range. We do get samples that have pH that is above seven, and the pKa of this particular product is approximately nine, and so if you let the sample get too much higher, then you can definitely have a loss of analyte. So, the sample is loaded at approximately 10 to 15 milliliters per minute, and then we elute with 10 milliliters of basic methanol. I believe it is a 2% volume of ammonium hydroxide in methanol, then we evaporate that sample down using nitrogen and bring that up to a final volume of 2 milliliters.
Q: Are you able to resolve some of the branched isomers with the columns you are using?
DS: Yes. It wasn't in one of the slides where we had the perfluorosulfonates. We do see the branched isomers for the C6 and C8, which is PFOS. We also see branched isomers for the N-methyl, N-ethyl FOSAAs. That's pretty much it, but it's not a requirement to resolve any specific isomers. It's just that you have to know that your system can see the branching and make sure your data system is taking those into account and quantitating those in standards and samples.
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