Written by Luca Rota, Application Specialist | 24 November 2025

Milestone Introduces a Faster, More Reliable Solution for PFAS Extraction in Compliance with EPA 1633A

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Comparing conventional extraction with microwave-assisted extraction

Environmental laboratories are under growing pressure to deliver high-quality PFAS data while keeping pace with rising sample volumes, labor shortages, and increasingly complex regulatory requirements. Among the most challenging tasks is the extraction of PFAS compounds from solid matrices such as soils, sediments, and biosolids, an essential but time-consuming step that directly affects analytical quality and turnaround time.

Our new application study demonstrates that the Milestone ETHOS X microwave extraction system, equipped with the XTR-44 rotor, provides a powerful alternative to the traditional shaker-table extraction method described in EPA 1633A. The research, carried out by Advanced Environmental Laboratories (AEL), compares conventional extraction with microwave-assisted extraction, highlighting major gains in efficiency, consistency, and analytical performance.

Microwave extraction

The extraction prescribed by EPA Method 1633A often becomes a bottleneck, its long duration and manual handling steps limiting throughput and reproducibility.
EPA Method 1633A allows laboratories to optimize extraction parameters under Section 9.1, opening the door to workflow improvements without compromising regulatory acceptance.
Microwave-assisted extraction follows the same principles as the original method but eliminates repeated transfers, long agitation steps, and the risk of analyte loss. The ETHOS X achieves full extraction in only 15 minutes, reducing total sample-prep time by up to 70%, significantly lowering labor needs, and simplifying onboarding for new operators.

Validation Procedure

To validate the microwave-assisted extraction (MAE) as an alternative to the shaker table procedure, a comparative study was performed following the quality assurance framework outlined in EPA Method 1633A, Section 9.1. According to section 9.2.1 of the method, laboratories may introduce modifications to the extraction, concentration, or cleanup steps provided that equivalent precision and recovery are demonstrated and all performance criteria are met. The validation included the following steps:

Initial Precision and Recovery (IPR) with method blank
Low-Level Ongoing Precision and Recovery (LLOPR) for LOQ verification
Batch analyses including blank, LLOPR, OPR, MS, MSD, and samples for comparison
Method Detection Limit (MDL) studies (not performed here, as MDLs are laboratory-specific)

For reproducibility assessment, three samples were extracted in triplicate using both the shaker table and the microwave-assisted approach. The evaluation criteria followed Method 1633A Tables 7.0 and 8.0, which define recovery and precision limits for target PFAS and extracted internal standards (EIS).

Extraction Procedure

Shaker Table Extraction
Following Method 1633A, 5 g of Ottawa sand (for blanks and QC samples) or soil were weighed into 50 mL polypropylene centrifuge tubes, spiked with extracted internal standard (EIS), and allowed to stand for 30 minutes. The samples were extracted three consecutive times using 0.3% ammoniacal methanol (10 mL + 15 mL + 5 mL). Each extraction consisted of 30 minutes of shaking at 200 rpm, followed by centrifugation at 3000 rpm for 10 minutes and decanting of the supernatant into a clean tube.

Microwave-Assisted Extraction (MAE)
For MAE, 5 g of sample were weighed into 50 mL polypropylene tubes, spiked with extracted internal standard (EIS), and allowed to stand for 30 minutes. After adding 15 mL of 0.3% ammoniacal methanol and a rare-earth stirring bar (uncoated NdFeB), the tubes were placed into the XTR-44 rotor and then into the ETHOS X. The microwave program consisted of a 5-minute ramp to 65 °C, followed by a 10-minute hold with active stirring. After a brief 5-minute cooling, samples were centrifuged at 3000 rpm for 10 minutes and the supernatant transferred to clean tubes for further processing.

Post-Extraction Processing
Both extraction types followed the same downstream procedure: Activated carbon treatment, solvent concentration at 60 °C (Organomation™ nitrogen evaporator) to a volume <10 mL, and dilution to 50 mL with PFAS-free water. The final extracts underwent solid-phase extraction (SPE) cleanup using Phenomenex Strata-AW 33 μm PFAS Weak Anion Exchange cartridges. Extracts were then spiked with Non-Extracted Internal Standards (NIS) and transferred to autosampler vials for LC/MS-MS analysis.

LC/MS-MS Analysis
Extracts were analyzed on an Agilent 1290/6495C LC/MS-MS equipped with a Advanced Materials Technology (AMT) HALO 90 A, PFAS, 2.7um, 2.1X100 mm analytical column and an AMT guard column, HALO, 90A, C18, 2.1X5mm with the AMT HALO, 160A, and PFAS 2.7um, 3.0X50mm delay column. 4.0 uL of the extract was injected. The acquisition method was 0.4ml/min using this gradient: 0min – 98% A/2% B; 0.1min – 98% A/2% B; 18min – 10% A/90% B; 21min – 10% A/90% B; 22min – 98% A/2% B; 29min – 98% A/2% B. A mobile phase is 95/5 2mM ammonium acetate/LCMS acetonitrile; B mobile phase is LC/ MS acetonitrile. Data processing was performed using Mass Hunter software.

RESULTS

The validation study demonstrated that the microwave-assisted extraction (MAE) approach fully meets the precision, recovery, and reproducibility requirements established in EPA Method 1633A. All performance criteria were satisfied using the Milestone ETHOS X system equipped with the XTR-44 rotor, confirming that MAE provides a reliable and compliant alternative to the shaker table extraction.
Across all studies, microwave extraction achieved recoveries and precision fully within the method’s acceptance limits, with improved consistency across replicates and higher recoveries for strongly adsorbed PFAS such as PFTeDA and PFOSA. These findings confirm the robustness of the MAE process and its suitability for a wide variety of solid matrices.

Read the complete report with data

The validation performed by Advanced Environmental Laboratories (AEL) demonstrates that microwave-assisted extraction provides a fully compliant and more efficient alternative to the traditional shaker table procedure described in EPA Method 1633A. The ETHOS X system ensures robust, reproducible, and faster extractions across a variety of solid matrices, allowing laboratories to increase analytical throughput while maintaining data integrity and regulatory compliance.

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Read the AEL case study

AEL provides soil and biosolids PFAS analyses under EPA Method 1633A. Each batch of 20 samples requires about three hours to extract, a process that can add pressure on resources and make expedited turnaround more demanding as client needs continue to grow. Milestone’s ETHOS X with XTR-44 has provided AEL a solution to their challenges and as an early adopter allows them to provide efficient extractions in a fraction of the time while meeting EPA 1633A QA.

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