EPA Method 327: A technical perspective on ethylene oxide monitoring

EPA Method 327: A technical perspective on ethylene oxide monitoring

In the run-up to the release of the newly introduced US EPA Method 327 the team at Markes and I have been delving into the details of the analysis and how it will be implemented in the field. This method represents a significant step forward in ethylene oxide (EtO) monitoring from fugitive and area sources. While the method provides much-needed standardisation, implementing it presents some new technical challenges worth exploring for anyone monitoring volatile compounds in air.

The critical nature of ethylene oxide monitoring

What makes this method particularly important is the extreme toxicity of ethylene oxide. The US EPA has established that EtO presents a 100-in-1-million cancer risk at just 11 parts per trillion – an incredibly small concentration that pushes the boundaries of analytical instrument capabilities. Prior to the release of Method 327 there was simply no validated way to measure this compound in air.

Technical hurdles

Whilst Method 327 is fully validated for the measurement of ethylene oxide, the process from sampling to analysis is by no means simple. Understanding this from the outset can significantly reduce development time.

One of the most challenging aspects of Method 327 lies in the sampling process. EtO can form spontaneously inside the canisters used for sampling, even under carefully controlled conditions. This phenomenon can lead to sampling bias—a problem we have observed both in our own work and in the laboratories of our customers.

The chromatographic separation presents another layer of complexity. EtO is prone to co-elution with other VOCs that have similar structures or masses. For example, compounds such as acetaldehyde, methanol, and trans-2-butene can all act as chromatographic interferents. Overcoming this requires careful method optimisation, particularly as the molecular characteristics of EtO result in a relatively weak response in the MS instrument, which significantly impacts the achievable detection limits.

Refining the analytical approach

After assessing the challenges, we focused on the two main analytical hurdles: interferents and sensitivity. Using Markes International’s UNITY–CIA Advantage-xr™ system, combined with the Kori-xr™ water management module, we developed a highly sensitive method for EtO analysis without the need for liquid cryogen. However, it should be noted that cryogenic cooling of the oven may still be necessary to manage interferents co-eluting on the column. Minimising cryogen usage makes the analysis more cost-effective and reduces downtime.

The unique back-flushed focusing trap on the UNITY-xr enables sampling volumes of up to 1.5 L. This volume exceeds what is required to reach the detection limit of 11 ppt but gives analysts the flexibility to achieve even lower detection limits in the future, without needing costly system upgrades, such as replacing the mass spectrometer.

Practical considerations for implementation

Based on our experience helping laboratories implement Method 327, we have identified two critical areas that require special attention:

1. Sample handling protocol: This includes well-validated canister conditioning and strict contamination control measures, including blanks for every canister taken into the field. The CIA Advantage-xr autosampler comes with 14 channels as standard and can be upgraded with a further 13 if required, providing ample capacity to meet standard operating procedures (SOPs) that require blanking every canister.
2. Quality control: Instrument blanks, calibration checks, and the use of internal standards all play a crucial role in this analysis. On the Markes system, a gas-phase internal standard can be added with every run, and the high-capacity autosampler makes it easy to incorporate additional blanks and calibration checks as part of the SOP.

Looking ahead

The introduction of Method 327 will support the HON rule in the USA, where industries will be expected to monitor for this chemical, if applicable, from April 2026. Outside the US, ethylene oxide monitoring at the fenceline will also be important, and this method will play a significant role in supporting those regulatory efforts.

The path to reliable EtO monitoring is not straightforward. Having a background in trace VOC analysis already puts laboratories in a much stronger position to begin offering this type of analysis to industry. If you are interested in learning more about trace VOC analysis and ethylene oxide in particular, reach out to me or Markes’ team of global experts, read one of our application notes, or watch our webinar on the subject.