ASTM Method D8591-24

ASTM D8591-24 is a standard test method for the detection and quantification of fluorotelomer alcohols (FTOHs) in air samples collected on thermal desorption (TD) tubes. The method was released in September 2024 and uses thermal desorption–gas chromatography with triple-quadrupole tandem mass spectrometry (TD–GC–MS/MS).

The need to monitor FTOHs: The dangers of PFAS precursors

FTOHs are volatile and semi-volatile precursors to perfluorinated carboxylic acids (PFCAs), and are widely used in the synthesis of surfactants and consumer products such as polymers, paints, adhesives, and cleaning agents.

Fluorotelomer alcohols can transform in the environment into PFCAs such as the banned compound perfluorooctanoic acid (PFOA), making the understanding of their presence and sources even more important. Like other PFAS products and their precursors, these are persistent organic pollutants that are dangerous to environmental and human health, and as such require careful monitoring.

FTOH analysis in accordance with ASTM D8591-24: Key challenges

FTOHs have previously been quantified using liquid chromatography–mass spectrometry (LC–MS). However, using this technique, sensitivity limitations arise due to ionisation methodology, and because adducts can form under the chromatographic conditions used to quantify other PFAS in the same run.

The TD–GC–MS/MS approach mandated in ASTM D8591-24 overcomes these difficulties by providing a method that is tailored to the monitoring of trace-level FTOHs, ensuring higher sensitivity, selectivity and reliability.

ASTM D8591-24 is validated for air samples collected from test chambers, such as Markes’ Micro-Chamber/Thermal Extractor, which allows rapid sampling of vapour-phase samples used in combination with sorbent tubes and thermal desorption–GC–MS. The same technique is also easily adapted to other types of air sample, and a wider range of PFAS chemicals and precursors.

What compounds are included in D8591-24?

The method has been validated for, but is not limited to, the following compound list, and may also be applicable to other volatile and semi-volatile PFAS chemicals.

• 1H,1H,2H,2H-perfluorohexan-1-ol (4:2 FTOH; CAS No. 2043-47-2)
• 1H,1H,2H,2H-perfluorooctan-1-ol (6:2 FTOH; CAS No. 647-42-7)
• 1H,1H,2H,2H-perfluorodecan-1-ol (8:2 FTOH; CAS No. 678-39-7)
• 1H,1H,2H,2H-perfluorododecan-1-ol (10:2 FTOH; CAS No. 865-86-1)

Complying with ASTM D8591-24

To comply with ASTM D8591-24, laboratories must use sorbent tubes validated for PFAS analysis, paired with a thermal desorption system and a GC connected to a triple-quadrupole mass spectrometer (TD–GC–MS/MS).

The sampling approach is very flexible – using a pump, air volumes ranging from 500 mL to 500 L can be collected onto a sorbent tube. Sorbent tubes can also be used to collect samples diffusively, further extending the applicability (although this isn’t covered by the method). Another advantage of using TD sorbent tubes is that they eliminate the variability of solvent extraction recovery, improving reproducibility.

TD tubes are desorbed and preconcentrated using a thermal desorption instrument, with the sample immediately (and automatically) transferred to a GC column for separation and analysis. This minimises the potential for sample loss or contamination, and significantly increases sensitivity for FTOHs.

Markes offers fully validated ‘PFAS Extended volume’ tubes for air volumes of up to 500 L, and which are ideal for large-volume sampling. For indoor or chamber air analysis, where lower volumes are typically required, we recommend our regular ‘PFAS’ tubes, which are validated to 300 L.

Robust TD systems to handle challenging samples

PFAS methods are very analytically demanding, and ASTM D8591-24 is no different. Markes’ systems are designed to help you overcome these challenges. All of our tube autosampler systems (listed below) have uniformly heated, low-volume flow paths, which have been proven not to contribute PFAS to sample flows. Markes’ systems are also platform-neutral, so whatever GC–MS/MS you’re using, you’ll be able to find a TD instrument to partner with it.

For labs interested in running ASTM D8591-24, Markes has three TD instrument options:

• TD100-xr: Dedicated, automated thermal desorber for 100 sorbent tubes, perfect for laboratories who only need to analyse sorbent tubes.
• UNITY–ULTRA-xr: Flexible system with capacity for 100 sorbent tubes, and which can be upgraded to nearly double the tube capacity (199 tubes) or to enable analysis of canisters and on-line air samples.
• Centri: Automated sample preparation system with capacity for 100 sorbent tubes, as well as headspace, SPME and sorptive extraction probes, making it ideal for laboratories who need flexibility.

In addition to these TD systems, Markes offers the Micro-Chamber/Thermal Extractor. This is a compact, standalone unit for dynamically sampling headspace volatiles from larger samples of materials onto sorbent tubes, making it ideal for rapidly acquiring PFAS emission profiles in accordance with ASTM D8591-24.

Managing interferents: A key hurdle for laboratories

Fluorinated compounds are commonly found in all types of materials, many of which can be found in analytical laboratories, from instrument components to consumables. It’s therefore critical to identify and manage the source of any interference prior to beginning the analysis, as indicated in section 6 of ASTM D8591-24. It is often the most significant hurdle labs face when beginning any PFAS analysis.

Markes International was one of nine organisations to participate in the interlaboratory study for this method, and we therefore have extensive experience in troubleshooting this application.

In addition, our equipment is fully compliant with ASTM D8591-24, and our specialists can support with method development and implementation. For more information on how to comply with this method in your lab, contact us.