Ethylene oxide (EO) has a broad array of applications across many industries. One of the most important is as a fumigant pesticide for the preservation of dry food products, such as seeds, milled cereals, spices, and herbs. However, upon consumption, ethylene oxide can have significant impacts on human health, adversely affecting the nervous system and mucous membranes, and exhibiting mutagenic and carcinogenic potential. Moreover, in food, EO readily degrades into 2-chloroethanol (2CE), which is itself considered toxic.
Such health concerns have driven a spate of strict regulations on EO’s usage in food production across the globe. Most notably, EO is now banned for use in food in many countries, including all of those in the European Union (EU), where it has been banned since 1991. Currently, the EU has set maximum residue levels (MRLs) for EO at 0.02 to 0.1 mg/kg, depending on the commodity, where EO is defined as the sum of both EO and 2CE (Reg. (EU) 2015/868). Despite the ban, there have been a number of recent reports of the presence of EO residue in food products in the EU, primarily owing to inconsistent regulations globally. Between January 1 and July 31 in 2022 alone, there were 119 EO contamination alerts published in the Rapid Alert System for Food and Feed (RASFF).
This volume of alerts demonstrates the critical importance of more accurate and frequent monitoring of food for contamination with EO and its degradation products. Using current analytical methods, however, EO analysis is incredibly challenging. In this article, we will provide an overview of the current difficulties of EO determination and explore how these can be effectively overcome using an optimized gas chromatography with tandem mass spectrometry (GS-MS/MS) workflow.
Grappling with Ethylene Oxide Determination
Because of the significant health risks posed by EO residues and owing to the low permissible MRLs set by the EU, methods for the analysis of food products for EO residues must be sensitive, precise, and accurate. At the same time, food testing laboratories must have the capability to meet the continuous and growing testing demand. In practice, this means that food laboratories must deliver an increase in sample throughput and shorter analysis turnaround times.
However, meeting these requirements using current methods—typically triple quadrupole gas chromatography mass spectrometry (GC-MS)—is challenging on several fronts due to the lower MRLs stipulated and the inherent hurdles of EO analysis.
Many of the challenges in EO analysis stem from the inherent physical and chemical properties of EO itself. For example, EO is a highly volatile compound, with a boiling point of just 10.7°C. If careful precautions are not taken during sample preparation, analysts risk EO evaporation, which could lead to an underestimation of the extent of EO contamination. This means potentially unsafe food samples could make it to consumers. EO’s volatility also means that it cannot be retained at all on some generic chromatographic columns and is only weakly retained by others. EO, therefore, elutes shortly after the void time, bringing a risk of interferences from other poorly retained compound that are present, which means that EO cannot be separated from the matrix. As a result, there is a significant risk of either missing EO residues or inaccurately determining the level to be safe in a given sample, when in fact it is not.
The low molecular weight of EO and its fragmentation products presents another analytical hurdle—increased susceptibility to interferences. One notable compound that commonly interferes with EO is acetaldehyde (AA), which has the same ion transitions as EO. Because of these non-selective ion transitions, insufficient chromatographic separation of the analytes (i.e., co-elution) can lead to overestimation of EO contamination in a sample. In the worst-case scenario, analysts can get a false negative result from the interference between EO and AA.