Analysis of Perfluoroalkyl Pollutants with the High Field 21 Tesla Magnet FT-ICR Instrument.

[NNadir]

Last edited Sat Feb 19, 2022, 10:15 PM - Edit history (1)

Recently I was giving a short lab tour to high school students during which I was describing isotopic distributions and their relevance to mass spectrometry. I was trying to interest kids in STEM careers. (It feels as if that part didn't go well.)

Also, as part of my job, I've also been researching software tools utilizing Kendrick Mass Defect Analysis in hopes of utilizing its features to understand a certain metabolic pathways using heavy stable isotope labeled intermediates.

It was thus with pleasure that I came across this paper utilizing a very, very, very high resolution mass spec analysis of a very serious set of pollutants resulting from products formerly used to protect fabrics from stains, from certain fire fighting foams, and a host of other products that were widely used until recently, perfluoroalkylated substances (PFAS): PFAS Analysis with Ultrahigh Resolution 21T FT-ICR MS: Suspect and Nontargeted Screening with Unrivaled Mass Resolving Power and Accuracy Robert B. Young, Nasim E. Pica, Hamidreza Sharifan, Huan Chen, Holly K. Roth, Greg T. Blakney, Thomas Borch, Christopher P. Higgins, John J. Kornuc, Amy M. McKenna, and Jens Blotevogel Environmental Science & Technology 2022 56 (4), 2455-2465.

The PFAS molecules interest me because at least one of the routes to their destruction is radiolytic, particularly with solvated electrons under some circumstances, and direct homolytic cleavage in others, would depend on access to gamma radiation which might, arguably present the least problematic approach to their destruction in flow systems.

The "'National' High Magnetic Field Laboratory" is located in Floridastan, a small nominally American country led by a banana Republican member of the Ignorance and Racism Party who is trying to declare himself "Governor (and/or) President for Life where hatred of science and scientists is official government policy; nevertheless one of the world's greatest scientific instruments, the 12 Tesla FT-ICR Mass spectrometer is located there and is available for use by citizens of foreign countries like the United States, in this case scientists from Colorado, California, and New Mexico. Go figure.

The 12 Tesla magnet used in FT-ICR (Fourier Transform Ion Cyclotron Resonance) mass spectrometer, gives the highest mass resolution in the world, particularly useful in analyzing PFAS and their desfluorometabolites and decomposition products, some of which may be more toxic than their parent molecules.

From the paper's introduction:

Per- and polyfluoroalkyl substances (PFASs) are a complex chemical family comprising thousands of individual species. Because of highly valued water-, oil-, and heat-resistant properties, PFASs have been used in an endless number of industrial applications and consumer products. (1,2) The pervasive use of PFASs has led to their widespread environmental release from many sources such as manufacturing, wastewater treatment plants, landfills, and the application of aqueous film-forming foams (AFFFs) for firefighting. (3−9)

Currently, targeted quantitative mass spectrometry methods for PFAS regulatory compliance are limited by reference standard availability to dozens of PFASs out of thousands possibly present. These methods, while valuable, require an a priori determination of what to target and quantify, which is sensible for regulatory compliance but unsuitable for comprehensive sample characterization. A more holistic approach to PFAS speciation in AFFFs, natural waters, and other complex mixtures is needed to more thoroughly assess environmental transport and transformation, source attribution, additive or synergistic health effects, and other issues associated with PFAS contamination. (10−14) Consequently, many previous and ongoing research efforts have employed nontargeted analytical techniques using high-resolution time-of-flight (TOF), Orbitrap, and ion mobility mass spectrometers to discover novel PFASs. (4,10,15−20)...

We're Orbitrap people in our laboratory, which gives rather remarkable mass resolution but being something of a pig, I can't help having mass resolution envy.

Anyway, a little more text:

Kendrick mass defect (KMD) analysis is commonly used to group and assign formulas to homologous series in petroleum hydrocarbon and natural organic matter samples, (39,40) and has been successfully used to identify homologous PFAS series. (4,41) KMD analysis produces a mass scale that is normalized by the ratio of the characteristic repeating unit’s nominal and accurate masses (e.g., CH2: 14.0000 Da/14.01565 Da). (42) As a result, the KMD of the repeating unit is zero, and the KMDs of homologous compounds, which have identical core structures and various numbers of repeating units, are approximately identical (within the mass spectrometer’s level of precision when computed with measured masses (43))...

...Kendrick-analogous mass difference networks (KAMDNs) extend the KMD approach by creating network graphs that connect detected ions to each other by one or more characteristic mass differences. (40,46,47) For example, in Figure 1, the black nodes (or vertices) represent known PFASs identified during suspect screening, the gray nodes represent detected ions that remain unidentified, and the links (or edges) between them represent certain characteristic mass differences: a CF2 repeating unit (blue), a chlorine-for-fluorine substitution (green), (48) and the presence of a 37Cl isotopologue (orange)...

Figure 1:



The caption:

Figure 1. Conceptual diagram of a Kendrick-analogous mass difference network (KAMDN) for identified and unidentified PFASs. The legend at the bottom shows characteristic mass differences for a difluoromethylene repeating unit (−CF2− ), a chlorine-for-fluorine substitution (+Cl/–F), and a 37Cl isotopologue (+37Cl/–35Cl).

Workflows:

Figure 2. Summary of the data analysis workflow for this study.

Briefly another excerpt:

Negative mass defects (exact mass – nominal mass) are useful when screening for PFASs. (63,64) Substantial F-for-H substitution causes many PFAS molecules to have low or negative mass defects because F has a negative mass defect, H has a positive mass defect, and 12C has no mass defect by definition. As a result, 43.5% of the compounds in the known PFAS database have negative mass defects (Figure S2). In this study, 17.6% of the detected peaks in the AFFF sample had negative mass defects (Figure S3), compared to 4% of the detected peaks in the NOM sample (Figure S4). In the AFFF sample, the proportion of peaks with negative mass defects is far greater than that in the NOM sample but far lower than in the known PFAS database. This suggests that many of the AFFF constituents are not PFASs or they contain enough hydrocarbon substituents to yield positive mass defects. In fact, hydrocarbon surfactants are known constituents of many AFFFs. (65)

The "negative" and "positive" mass defects derive from the definition of carbon 12 as having exactly a mass of 12.000000...

I believe this differs from the "mass defect" associated with the masses of neutron and proton summed and composite nuclei, but I never looked at this level of detail to see if this is true.

Anyway, this is a very cool paper, if esoteric, and I probably should find some time to spend with it.

Have a nice weekend.

[MyOwnPeace]

1. And I was going to post a 'cute puppy' video......

Wow! This stuff is just SO beyond my comprehension and understanding - but America is great BECAUSE we have people that DO understand this - and work to use that understanding to make things better.
Unfortunately, we also have people, especially in government positions, that work to "make things better" for just a selected few.

Education can and will make it all make sense - if society allows it to do so.

If not - we're screwed.............

[eppur_se_muova]

2. To think the Francis Bitter Magnet Lab at MIT was once designated as our Nat'l Magnet Laboratory ...

... but it were unfair, all them librul 'litists gettin' all them Fedr'l funds, so FL engineered a grab of the new expanded facility.

Somewhere, I saved a document summarizing the political horsetrading that went on to bring about this unnecessary relocation. I notice that Los Alamos is officially part of the facility -- apparently FL's university personnel couldn't provide the necessary consultation and support, which for some reason MIT was perfectly able to do without outside help.



But agree that the application of the magnet is cool. So when do they adapt the 30T magnet ?

[NNadir]

3. I just noticed I posted the title with a bit of dyslexia. It's 21T not 12T.

I'll fix it.

One can purchase a 12 T FT-ICR from Bruker. I've actually discussed this with the Bruker representative, but only in an offhand kind of way. Bruker also sells a nice TOF instrument with a rather intriguing ion mobility system, the TIMS-TOF. I've seen some amazing papers come off that instrument, in particular out of the Ge lab in Wisconsin. Someday, assuming I live long enough and my company agrees with it, I might get serious about one of these TIMS-TOF instruments.

Orbitraps fit our needs for now. Lots of people use them, and they can do amazing things.

As for Florida; I believe it used to be part of the United States and reasonably civilized at one time. How it turned into a third world banana Republican stronghold is somewhat surprising to me, but I guess if you want to work at 21T, you have to travel through dangerous provinces these days. I'd guess the Mag Lab is a kind of bubble in Tallahassee, where the science can distract one from primitives like DeathSentance.

Cambridge is a very expensive place to live we've learned, a cool place, but perhaps not a place where one can live decently - these days - on a graduate stipend. It might be easier to live in Tallahassee.

The cost of living, as well as access to outstanding equipment, if one can have both, as well as amazing mentors who can offer one attention, played a role in my son's choice. He stepped back from MIT.