What are the differences between EPA methods 533 and 537.1?

Jan 10, 2022 | Blogs, Food / Beverage, Food and Beverage | 0 comments

With the risk of per- and polyfluoroalkyl substances (PFAS) contamination and accumulation in humans and wildlife on the rise, it is important to continuously improve and demonstrate capabilities for accurate and precise low-level quantification in research and testing laboratories. This includes biomonitoring as well as analyzing exposure sources such as drinking water.

In December 2019, the EPA released its latest method for analysis of PFAS in drinking water. This current method, EPA Method 533, evolves from the previous methods, 537.1 and 537. It can be a challenge for testing laboratories to implement a new testing method and ensure that the entire process is aligned with the latest requirements. Luckily, the updates in 533 should only make testing easier for you and result in better data quality.

EPA Method 533 still uses solid-phase extraction (SPE) clean-up and concentration, which was also used in Method 537.1. It is an isotope dilution-based method, which accounts for losses during extraction and corrects for any ion enhancement or suppression during analysis to ensure better data quality. It also allows for a lower sample prep volume. Sample volumes can be in the range of 100–250 mL, potentially resulting in cost savings during sample shipping and sample storage. The required injection volume is also unspecified, allowing for greater method flexibility.

Method 533 also benefits from increased knowledge about prevalent chemicals in the environment and increases the scope of GenX-like compounds (for example, perfluorinated ether carboxylic acids) that are monitored. Method 533 testing includes 25 analytes. Some short-chain compounds and novel perfluoroether acids have been added to the list, including odd-chain length PFSAs (PFPeS, PFHpS), short-chain PFCAs (PFBA, PFPeA), FTS compounds (4:2, 6:2, 8:2), additional perfluoroether carboxylates (PFMBA, PFMPA, NFDHA) and sulfonates (PFEESA). Some compounds from 537.1 were removed from the list, presumably because they were shown to not be prevalent in testing real-world samples. This includes FOSAA acids (NEtFOSAA, NMeFOSAA) and long-chain PFCAs (PFTA, PFTrDA).

Previously, Trizma was added to drinking water samples as a preservative and was a requirement in EPA methods 537 and 537.1. Trizma suppresses the ionization of PFAS and can impact data quality. Now, ammonium acetate is used instead of Trizma preservative.

A notable change, with respect to QA/QC monitoring, is the absence of the asymmetry requirement for the first two eluting compounds. The previous EPA methods specified a vial composition of 96:4 methanol/water and frequently resulted in poor, asymmetric peak shape for the earlier eluting PFAS. However, Method 533 specifies a 80:20 methanol/water vial composition and largely mitigates this problem.

The good news is that all of the above changes do not make much of a difference in your day-to-day testing for PFAS. The biggest change in Method 533 is how results are reported.

Analyst software and SCIEX OS software can work together to generate a Method 533-compliant report that will quickly and easily provide you with only the specific information that the EPA needs. The detailed EPA Method 533 QA/QC calculations can be built within SCIEX OS software using the “calculated columns” module. Further, custom flagging rules can be created to quickly highlight samples that are out of tolerance. We know that maintaining high throughput and being able to flag samples quickly and accurately can be critical when it comes to water quality testing. SCIEX helps make this fast and easy.

Manually creating reports can be time-consuming, tedious, and prone to errors. Save time and money by creating your PFAS testing report with SCIEX, and focus on testing.

Read here to learn more about the EPA methods 533 and 537.1 for the analysis of PFAS contaminants in drinking water.



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Craig has worked in the mass spectrometry industry for over 20 years and has been with SCIEX since 2016. As a senior product application specialist, he works with customers to understand their targeted screening workflows and provide solutions using high-resolution accurate mass spectrometry technologies.


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