Hi All,
I’ve recently become concerned about PFAS contamination from PTFE stopcocks when using a separatory funnel during A/B extractions.

PFAS stands for “polyfluoro alkyl substances” which consists of a bunch of short to medium chain (C4-C10 say) molecules with various polar ends (sulfonate, carboxyl). I think there’s potential for PFOS and probably other PFAS contamination from the PTFE stopcock.

From Wikipedia:
Because PTFE is poorly soluble in almost all solvents, the polymerization is conducted as an emulsion in water. This process gives a suspension of polymer particles. Alternatively, the polymerization is conducted using a surfactant such as perfluorooctanesulfonic acid (PFOS).

I checked out the LogP for PFOS using miLogP and the ionized (basified) version of PFOS (sulfonate) has a LogP estimated at 1.74 (for reference, DMT has a LogP of -1.22 when ionized (acidified) and 2.30 when neutral (basified) according to the model). LogP ranges typically are from -3 (polar) to 7 (nonpolar). So it sounds like PFOS and maybe similar PFAS would prefer the nonpolar solvent in an A/B? But PFOS is a surfactant - and a really good one, so I’m not sure miLogP is accurate. Octonol-water partition coefficients can’t be measured for PFOS because it just forms an emulsion.

I believe there’s a potential for at least some PFAS to be extracted by naphtha, be it PFOS or whatever PFAS might be present within the PTFE matrix. PTFE resistance to naphtha is rated as “B-Good” as opposed to “A-Excellent” meaning there’s at least some degradation/interaction occurring.

https://www.calpaclab.co...lon-ptfe-compatibility/

I guess there’s no way to know for sure without analytical data, and that will be tough to come by as PFAS analysis is done by isotope dilution and costs about $300 per sample.

There have been documented instances of harm where Teflon or PFAS coated pans were left unattended and began to smoke, with people having negative effects from the PFAS degradation fumes. These fumes are acutely toxic to birds, and there have been many documented cases of birds dying from being near fuming pans!

Overall I’m not familiar enough with the comparison between PFAS as dissolved, aqueous molecules vs the extractability of PFAS from PTFE (but something must be dissolved by the naphtha if PTFE is rated as "B-Good" resistance). I’m imagining you could only extract very short-chain (hydrophobic) PFAS from PTFE if present, and those short-chain PFAS (like 1-4 carbons) aren’t as toxic as the 7-9 carbon range, though they wouldn't have any polarity either. But they would seem to get into freebase products, especially if the naphtha is evaporated. Maybe the wise thing to do is finish with a defat step on the final product, then a mini A/B to freebase?

The tough part about making assumptions is the concentrations of interest. EPA and states are regulating PFAS compounds in drinking water these days at the 20-70 parts-per-trillion range! So 1 mg of PFAS in your 50 mg dose is only a 2% contaminant but waaaay more PFAS than you want to be exposing yourself to (at least the more toxic of the PFAS).
Interested to hear anyone’s thoughts/concerns!

That's a good question. But i don't think there's any data on this yet.

If the quantities of PFAS leaking into your product would indeed be in the milligram range, then it's easy to find out. But if it's way smaller quantities, then most people probably don't have the equipment to test if there's any PFAS in their product and if so in what quantities.

This is of very little comfort maybe, but those EPA safety margins set for PFAS are probably very strict. Authorities generally prefer to be very much on the safe side with these substances, just to be sure. Because i don't think a safe amount has been scientifically established yet.

The logic of PFAS regulations in europe is, that because we don't know exactly wich amounts of PFAS in drinking water are safe, we consider any amount that is detectable unsafe.

I wouldn't be surprised if EPA regulations are based on the same line of reasoning.

Maybe what you could do, if you have a very exact scale that can measure beyond the milligram range, is to soak a stopcock in naphta for about maybe a week or so, and open and close it a few times each day to simulate mechanic wear and tear. Then measure the exact weight before and after. I hope the weight of the stopcock you're using is small enough to be able to do this. Otherwise i think you should use a sample of material and think of something to simulate the wear and tear of opening and shutting.

But this method would only be as accurate as your scale is ofcourse.

Well, the EPA numbers are strict because they are set for a lifetime of exposure. So if the standard is set at 1 ppb, they're saying "we think the most vulnerable children can consume water with 1 ppb XYZ chemical for the rest of their life and not develop an illness."

So for less frequent exposures, like an occasional toke, the "safe" limit would be much higher than the drinking water limit, but also, there's almost no more direct exposure route than intentional inhalatation aside from IM/IV.

I find your idea of weighing the stopcock interesting. I think you'd need to weigh it before, and after, then weigh it every day until the weight no longer changes, because I think it would absorb some naphtha and that would need to offgas.

If you're gonna do this, then please share the results of this little experiment with us.

And ofcourse, if you don't notice any loss of weight, that probably doesn't mean there is no PFAS material leaking at all because it could still be microgram ammounts.

I don't know how big of a problem that would be. But the stuff stays in your body forever so it adds up over time. And there's plenty of evidence that these chemicals are not friendly. At all.

The half-life seems to be somewhere around a few years for PFAS, a little longer for PFOS. Some of the short-chain PFAS are eliminated more quickly, not sure how common they are though. In general I think they are rather persistent in the environment though.

If you are interested in contaminants, I'd be more concerned with FAAs (Fatty Acid Amides) and other leachables from LDPE plastic transfer pipets, if you use them at all. In practice, you'd be amazed at what comes out of those pipets when using organic or organic/aqueous combinations (or even just water sometimes).
My lab did 2 series of mass spec analysis of impurities leaching out of these pipets, sometimes totaling 3.0% of total extract. Pre-rinsing may help at first but sooner or later more of those FAAs will migrate out of the plastic and you'll keep getting contaminants.
Sorry I know you are talking about PFAS but FAAs can also be big players but aren't as much talked about

Hmmm FAAs don't sound particularly toxic though, are they? And I'm way too much of a purist/snob to use LDPE. I was under the impression that PTFE was inert, but now...