Automated, high-sensitivity analysis of residual fumigants for food safety testing by multi-step enrichment–headspace–trap (MSE–HS–trap) with GC–MS

This study shows highly sensitive detection of residual fumigants in seeds and spices by MSE–HS–trap developed on Centri 90, an automated sample concentration platform, coupled with gas chromatography–mass spectrometry (GC–MS). The MDLs obtained are as low as 0.0018 mg/kg, well below regulatory limits imposed by EU Regulation 2015/868 (0.01–0.05 mg/kg). Excellent chromatographic performance is achieved, with linearity R2 > 0.99 and relative standard deviations <10% for all compounds, indicating good reproducibility. Full automation with prep-ahead functionality provides high productivity with throughput of approximately 40 samples per system per day. A further enhancement in sensitivity when using single-ion-monitoring (SIM) is also demonstrated, with excellent linearity and reproducibility achieved on the same analytical system for ethylene oxide and 2-chloroethanol in seeds.

Fumigants are volatile, poisonous chemicals sprayed as gases or mists into an enclosed space to kill pests such as insects, rodents, fungi and bacteria. They are widely used on foodstuffs (among other products) to prevent spoilage during shipping or long-term storage, and are subsequently allowed to dissipate, so that (in principle) there is no risk to consumers.¹

However, residues may remain on the surface of foodstuffs that can have harmful effects when later ingested by consumers. This has led to regulatory bodies within the EU specifying maximum residue limits (MRLs) on the concentrations of residual fumigants that may be present in imported foodstuffs, to ensure consumer and food safety.² Excess levels above regulatory limits can lead to product recalls and rejects, such as the thousands of food products withdrawn from sale (at great cost to suppliers) since August 2020 due to the presence of alarming levels of ethylene oxide.³

There is therefore a need for a sensitive, robust and highthroughput extraction method for the detection of residual fumigants from foodstuffs. In this paper, we expand on previously published work, where we developed a method for determining ethylene oxide from sesame seeds.⁴ This involved a multi-step enrichment–headspace–trap (MSE–HS–trap) method, shown in Figure 1, using the Centri extraction and enrichment platform, with subsequent detection by gas chromatography–mass spectrometry (GC–MS). The method detection limits (MDLs) achieved were well below regulatory limits.

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