Unraveling the Complexity of PFAS Analysis in Food

Targeted Analysis for Known PFAS in Food

Targeted analysis focuses on determining specific PFAS compounds in food. These are often the PFAS named in relevant national or international regulations or those of particular interest to analysts. Techniques like liquid chromatography tandem mass spectrometry (LC-MS/MS) are used, and each PFAS analyte requires an existing analytical reference standard for quantitative analysis. As Dr. Stefan van Leeuwen mentioned, a triple quad mass spectrometer (TQMS) approach is one of the tools they use. It is very selective and sensitive, working well for routine analysis and dietary exposure assessment. For example, in their recent analysis of PFAS levels in fruits and vegetables grown in allotments up- and down-wind from a fluorochemical production plant near Dordrecht, PFOA and GenX were the most prominent PFAS observed. The highest levels were found in brassicas, leafy greens, and root vegetables directly down-wind of the plant.

This targeted analysis helps us determine the known PFAS in a sample. But what about the unknowns? That leads us to the next stage of the analytical process.

Mass Balance Analysis for Total PFAS Contamination Levels

To determine the total amount of PFAS contamination in a food sample, researchers use techniques like combustion ion chromatography (CIC). By burning and mineralizing the sample or extract and then determining the fluorine content using ion chromatography, they get a sense of the amount of organic fluorine present. Total extractable fluorine and the total PFAS burden are not exactly the same, as there may be other organofluorine compounds depending on the sample and matrix composition. However, it is widely accepted as a proxy measurement. If the PFAS levels measured during targeted analysis do not closely correlate with the total extractable fluorine levels, non-targeted analysis should be conducted.

This mass balance analysis gives us an overall picture of the PFAS contamination but leaves us with the mystery of the unknowns.

Unknowns Identification (Non-Targeted Analysis) for Novel PFAS

There are many ways to conduct non-targeted analysis for PFAS. In Dr. van Leeuwen's lab, they have developed a non-targeted screening approach called fragment ion flagging (FIF). When running an extract on a mass spectrometer, they get a large number of signals, often over 10,000 features. Data filtering is then used to extract the relevant PFAS data from the bulk. Looking at specific fragments of PFAS, which fragment in a specific way, helps in identifying the unknowns. The FIF data filtering procedure can be used with any high-resolution mass spectrometer (HRMS) system coupled with either gas chromatography (GC) or liquid chromatography (LC). This allows for the screening and discovery of novel PFAS.

With these three complementary methods - targeted, mass balance, and non-targeted analysis - researchers can detect the known, total, and unknown PFAS. Once an unknown PFAS is identified, it can be added to the known ones in the targeted methodology.