Per- and polyfluoroalkyl substances (PFAS) are a family of synthetic chemicals known for their unique properties, including water and oil repellency and heat resistance. They have been widely used in various products such as nonstick cookware, food packaging, and firefighting foams. However, PFAS are soluble in water and persistent, leading to global contamination in the environment, food, and even in humans and wildlife.
The most hazardous PFAS compounds have faced global and EU-level restrictions for over a decade. And by January 2024, the European Union (EU) Commission is set to adopt Directive EU 2020/2184, a new set of technical guidelines for analyzing PFAS in drinking water. This new legislation specifies a limit of 0.1 µg/L for a group of 20 PFAS of highest concern. The cumulative maximum concentration for all PFAS compounds will be set at 0.5 μg/L of water.
To monitor and meet these regulatory requirements, updated analytical methods are crucial. A new application note by Anja Grüning from Shimadzu Europa describes a means to facilitate routine PFAS analysis in drinking water laboratories using a Shimadzu LCMS-8060NX triple-quadrupole mass spectrometer paired with a Nexera X3 UHPLC system (Figure 1). It presents the analysis of 44 types of PFAS compounds and 22 internal standards using an on-line solid-phase extraction (SPE) approach that minimizes sample preparation steps.
Methods and Materials
Forty-four PFAS standards and one IS-mixture (ISO 21675-LSS) were procured from suppliers then diluted with methanol to create individual stock solutions, each with a final concentration of 1 ng/µL per compound. Subsequently, further dilutions of this stock mixture were prepared and spiked into Evian water to generate calibration samples for the analysis of drinking water. The calibration samples covered a concentration range from 0.5 ng/L to 100 ng/L. Bottled Evian water was selected as the matrix for the drinking water analysis, as no noticeable PFAS were detected in the blank samples. To maintain consistency, all samples (excluding blanks) were spiked with IS to achieve a final concentration of 20 ng/L.
Traditional SPE involves performing extraction and purification steps separately from the analytical chromatographic instrument. On-line SPE, however, uses compact cartridges placed within the eluent flow path, allowing for direct elution onto the HPLC column. In this application note, 1 mL of sample is injected directly on a SPE-trap column, with no further sample preparation required.
Analysis was performed within 15 minutes using multiple reaction mode (MRM) acquisition to characterize PFAS compounds. At least two transitions for each compound were recorded where available. Analytical conditions are listed in Table 1. The optimized MRM transitions are available in the full application note.
Given that PFAS may exist in reagents, glassware, pipettes, tubing, degassers, and various components of the LC-MS/MS instrument, the use of a solvent delay column becomes imperative. In this method, compact C18 columns are strategically positioned between the mixer and the autosampler, as well as between the mixer and the valve, to mitigate potential PFAS contamination and separate it from sample-derived PFAS.
Long-chain PFAS are more likely to adsorb to surfaces due to factors including their larger molecular size and extended environmental stability compared to shorter-chain complexes. To reduce PFAS adsorption effects, this method uses LabTotal Vials with PP-caps and aluminum septa on vial surfaces.
Results
Calibration curves were constructed using weighted linear regression, with data points weighted based on the inverse of their concentration (1/conc).
- The method's linear range spans from 0.5 ng/L to 100 ng/L for most PFAS compounds;
- For some PFAS, such as PFNS (a specific PFAS compound), the linear range is from 0.5 ng/L to 50 ng/L;
- An R² of at least 0.99 suggests a high degree of linearity and accuracy for all PFAS compounds within their respective concentration ranges;
- The lowest calibration point (0.5 ng/mL) can be determined in 77.3% of all PFAS.
Exemplary calibration curves and MRM chromatograms at 1 ng/L are available in the full application note.
The study involved analyzing control samples three times, each at concentrations of 5 ng/L and 25 ng/L, to assess the consistency of analytical results. In most cases, the variability in the measurements, represented as the percentage relative standard deviation, was less than 20% for over 95% of the compounds and quality control samples.
Conclusions
Shimadzu's on-line SPE LC-MS/MS method for drinking water analysis offers an efficient solution for monitoring PFAS compounds, including those targeted by the EU Directive EU 2020/2184. By utilizing an innovative approach that minimizes sample preparation steps, this method simplifies routine PFAS analysis in drinking water laboratories. With a focus on precision and accuracy, it covers 44 PFAS compounds and 22 internal standards. The study demonstrates the effectiveness of this method through robust calibration curves, high linearity, and consistent analytical results, ensuring compliance with the evolving regulatory landscape.
This article is featured in our October publication, 'PFAS: Unraveling the Analytical Challenges.' From cutting-edge analytical methods to the unexpected avenues of PFAS exposure in everyday items, explore the multifaceted challenges and solutions surrounding these pervasive contaminants.
