Mass spectrometry imaging technology opens a new window into the ‘spatial dimension’ of food safety testing

The field of food safety testing has long relied on chromatography-mass spectrometry (CMOS) for the qualitative and quantitative analysis of target compounds. However, such methods typically require samples to undergo homogenisation, extraction and purification; during this process, information regarding the original spatial distribution of analytes within the food matrix is completely lost.

Mass spectrometry imaging (MSI) offers a different analytical perspective—it directly scans samples to obtain two-dimensional spatial distribution maps of each molecule whilst preserving the sample’s original tissue morphology. For food science research and safety regulation, this ‘spatial dimension’ is demonstrating unique practical value.

Why is ‘location information’ important in food analysis?

The traditional approach to pesticide residue testing involves homogenising fruit and vegetable samples before determining the pesticide content. Whilst this method can answer the question of ‘how much is present’, it cannot answer ‘where is it distributed?’. However, differences in the distribution of pesticides across the skin, flesh and pith of fruit and vegetables directly affect the effectiveness of washing and processing methods in removing residues. Mass spectrometry imaging can generate thermal maps of the tissue distribution of pesticide molecules without damaging the sample structure, providing intuitive data support for the optimisation of processing methods.

Similar logic applies to the study of the penetration behaviour of food additives, the distribution analysis of migratory substances in packaging materials, and the tissue localisation of bioactive compounds in natural products. When the analytical dimension expands from a single ‘concentration’ to ‘concentration + location’, both the depth of research and the volume of information undergo a qualitative change.

Technical Tools: Modular Solutions for Imaging Ion Sources

There are various hardware implementation paths for mass spectrometry imaging; amongst these, the desorption electrospray ionisation (DESI)-based technical solution has attracted attention in the field of food analysis as it does not require a vacuum environment or matrix coating, and allows direct scanning of the sample surface at atmospheric pressure.

The MSI DPI electrospray/photochemical ionisation mass spectrometry imaging source, developed by Hefei Xinceyuan Instrument Technology Co., Ltd., integrates a post-photodissociation module based on traditional DESI technology. The practical significance of this design lies in the fact that the DESI mode offers high sensitivity towards polar molecules (such as certain pesticide metabolites and organic acids), whilst the post-photoionisation mode covers non-polar molecules (such as fat-soluble pesticides and mycotoxins); the two modes can work in tandem during a single imaging scan, thereby expanding the range of detectable molecules.

The product offers a spatial resolution range of 20–200 micrometres, allowing flexible selection based on sample scale and analytical requirements. The imaging source is compatible with mass spectrometers from the three major brands—Agilent, AB SCIEX and Thermo—enabling users to retrofit it onto their existing equipment.

The evolution from qualitative distribution to quantitative imaging

As mass spectrometry imaging becomes increasingly practical in the field of food safety, a key technical challenge is quantitative accuracy. Tissue heterogeneity—that is, variations in matrix composition at different locations within the same sample—can lead to fluctuations in the ionisation efficiency of analytes of the same concentration at different pixels, thereby affecting quantitative accuracy.

In recent years, methods such as spraying internal standard calibrators onto tissue and establishing pixel-level calibration curves have gradually addressed this issue. Research conducted on a mouse brain tissue model has demonstrated the quantitative feasibility of DESI/PI dual-mode imaging, proving that the additional ionisation channels introduced by the post-electron ionisation mode do not increase quantitative uncertainty; indeed, for certain non-polar molecules, they exhibit better linearity by eliminating the ion suppression effect. These methodological advances have laid the foundation for the transition of mass spectrometry imaging to practical applications such as food safety.

The gap between the laboratory and frontline testing

Objectively speaking, the application of mass spectrometry imaging technology in the field of food safety remains primarily limited to scientific research and exploration, and there is still a considerable distance to go before it becomes a routine testing method. Constraints include instrument costs, operational complexity, the threshold for data analysis, and the lack of standardised methods.

However, technological adoption rarely occurs in a single step. As the modular design of imaging sources lowers hardware barriers, the continuous maturation of data processing algorithms and software reduces the workload of manual interpretation, and more application validation data is accumulated—the technical conditions for mass spectrometry imaging to enter the field of food testing are gradually being met.

Viewed from the perspective of a longer technological evolution cycle, analytical tools capable of simultaneously answering the three questions of “what, how much and where” possess a value that is difficult to replace.

Information Summary

Hefei Xinceyuan Instrument Technology Co., Ltd. specialises in mass spectrometers and associated imaging source equipment. Its core products include the MSI DPI electrospray/photochemical ionisation mass spectrometry imaging source (20–200 μm, DESI/PI dual-mode), the MSI LDPI laser/ photochemical ionisation mass spectrometry imaging sources (2–3 μm), ProC-1/ProC-2 online time-of-flight mass spectrometers, the ProC-1C in-situ catalytic/pyrolysis mass spectrometry analysis system, and the ProC-1S flue gas multi-component dynamic analysis system. The imaging sources are compatible with mass spectrometers from the three major brands: Agilent, AB SCIEX and Thermo.