Detecting Fluorinated Residuals Using Liquid Chromatography–High-Resolution Mass Spectrometry

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Scientists from the Chemours Company in Delaware and West Virginia, USA, have created a new process for tracking targeted and non-targeted fluorinated residuals using liquid chromatography–high-resolution mass spectrometry (LC–HRMS). Their findings were published in the Journal of Chromatography A (1).

Close up of a two stacks of blue plastic polypropylene granules on a table | Image Credit: © LS Visuals - stock.adobe.com

Close up of a two stacks of blue plastic polypropylene granules on a table | Image Credit: © LS Visuals - stock.adobe.com

Fluoropolymers are a type of high-performance plastic characterized by strong carbon-fluorine (C-F) bonds (2). This atomic structure offers various desirable properties, including chemical resistance, thermal stability, and electrical insulation. They are typically synthesized using free radical emulsion polymerization in an aqueous medium, where polymerization aids (PAs), such as surfactants, are utilized to stabilize emulsion by coating growing polymer particles and preventing agglomeration. As a rule, fluorinated PAs have been used because fluorocarbon radicals are highly reactive and the C-F bonds in fluorinated PAs are inert. However, while fluoropolymers are safe for their intended uses, hydrocarbon PAs can react with fluorocarbon radicals, causing unintended side reactions that produce low molecular weight residuals that are difficult to identify with standard analytical methods, making detection and quantification challenging.

LC–MS has become the standard method for detecting fluorinated residuals, offering the sensitivity and selectivity needed to resolve numerous analytes in complex matrices. A targeted approach using LC–MS/MS with triple quadrupole detection (LC–QqQ) enables straightforward interpretation of results, especially with appropriate sample preparation, such as spike recovery and repeatability testing.

For this experiment, the scientists investigated a polytetrafluoroethylene (PTFE) dispersion prepared with a hydrocarbon-based surfactant (DOSS) to measure process-specific fluorinated residues. DOSS, a hydrocarbon, is completely non-fluorinated, has low toxicity, a low environmental impact, potential for post-polymerization recycling, and is available in bulk quantities. The PTFE with DOSS dispersion was first extracted to isolate low-molecular-weight residuals. Then, the extract was analyzed using targeted and non-targeted LC–MS to assess the types and concentrations of fluorinated residuals generated.

Non-targeted analyses by liquid chromatography can investigate complex matrices at relevant concentrations, ensuring that residuals are measured and can be effectively abated to support responsible fluoropolymer production. Two main categories of residuals were observed in non-targeted analyses. The first category, referred to as Class #1, is made of low-molecular-weight oligomers produced during radical emulsion polymerization of fluoromonomers via chain transfer side reactions. Class #2 consisted of PA adducts that are homolog distributions differing by the addition of TFE(n) or other fluorinated monomers.

The study illustrates that using non-fluorinated surfactants as PAs can generate Class #1 and Class #2 oligomers, which are less sustainable for fluoropolymer production. Targeted LC–QqQ provides a screen for major analytes, but non-targeted methods are required to comprehensively evaluate process chemistries. The workflow consists of multiple steps:

  1. Screening sample extracts using available targeted LC–QqQ methods, including those developed for Class #1 residuals
  2. Starting non-targeted LC–quadrupole time-of-flight (QTOF) or LC–orbital ion trap screening for fluorinated analytes
  3. Estimating concentrations using calibration standards with similar chemical functionality, for example, for Class #2 residuals, the unreacted PA
  4. Putting the process through structural interrogation based on MS2 fragmentation
  5. Beginning targeted method development so analytes can be measured more accurately and precisely.

Overall, the scientists believe that residuals identified in non-targeted investigations must be incorporated; however, without non-targeted method applications, analytes can form and remain undetected, causing regrettable substitutions in different chemistries.

References

(1) Sworen, J. C.; Morken, P. A.; Smith, A. P.; et al. Interrogation of a Fluoropolymer Dispersion Manufactured with a Non-Fluorinated Polymerization Aid for Targeted and Non-Targeted Fluorinated Residuals by Liquid Chromatography High Resolution Mass Spectrometry. J. Chromatogr. A 2024, 1736, 465369. DOI: 10.1016/j.chroma.2024.465369

(2) Biering, D. What Are ‘Fluoropolymers’ and What Are Their Common Attributes. TriStar 2025. https://www.tstar.com/blog/what-are-fluoropolymers-and-what-are-their-common-attributes (accessed 2025-1-28).

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