Previously I wrote about some applications of mass spectrometry and in particular of proton transfer reaction – mass spectrometry (PTR-MS). You can read old articles here (1, 2, 3, 4). Today I want to explain in details how PTR-MS works.
PTR-MS is called a “non-targeted approach”. Non-targeted approaches are used to investigate samples when marker molecules are not known and the aim is to study the global sample fingerprint. These approaches are very useful in authenticity and traceability analysis and represent a valuable tool for food safety authorities, which aim is to establish control over food products in market circulation.
PTR-MS was developed by professor Lindinger at the Institut für Ionenphysik at the University of Innsbruck.
It measures volatile organic compounds (VOCs) released by the samples and has several advantages. Samples do not need to be prepared prior to the measurement and can be analyzed directly, avoiding sampling and storage artifacts.
Now, a practical example: we have three types of grapes (see the figure above). Producers claim they belong to the same expensive and precious variety.
Food scientists analyze the grapes with PTR-MS (step 1) and the results are compared (step 2). By looking at the graph (step 3), it is clear that the three samples are different and therefore they cannot belong to the same variety.
Food scientists just performed a food authenticity analysis and discover a food fraud. Those producers were trying to sell at a higher price low quality grapes.
Abbas et al., 2018, “Analytical methods used for the authentication of food of animal origin”, Food Chemistry, vol. 246, pp. 6-17
Cavanna et al., 2018, “The scientific challenges in moving from target to non-targeted mass spectrometric methods for food fraud analysis: a proposed validation workflow to bring about a harmonized approach”, Trends in Food Science & Technology, vol. 80, pp. 223-241
Lindinger et al., 2008, “On-line monitoring of volatile compounds at pptv levels by means of Proton-Transfer-Reaction Mass Spectrometry (PTR-MS). Medical application, food control and environmental research”, International Journal of Mass Spectrometry and Ion Processes, vol. 173, pp. 191-241