Direct Mass Spectrometry Method to Detect Xenobiotics in Fruit

Direct analysis in real time mass spectrometry (DART-MS) is useful in assessing food quality and authenticity. In a recent publication, researchers applied direct DART-MS to detect and differentiate xenobiotics and post-harvest compounds present in fruit peels.¹ The researchers investigated this method on ten diﬀerent food samples purchased from a local market in Spain including: three apples (one Fuji and two Royal Gala), two oranges (Valencia Late), one lemon, one grapefruit, one tomato, and one potato. The fruit peels were analyzed in 1x3cm³ sections held by adjustable, self-closing tweezers directly in front of the DART ion source. The DART source was coupled to an LTQ Orbitrap Velos (Thermo Scientific) and the peels were exposed to ionizing gas at 0.2 mm s−1. To determine the limits of the DART-MS system, the researchers investigated and optimized the DART gas heater temperature and pressure, source-to-MS distance, and sample velocity. The detection capabilities and the limits of detection of the DART-MS system were analyzed using methanolic standards and extracts. The DART-MS spectra were analyzed using Xcalibur (ver. 2.1). Qualitative Xcalibur enabled the researchers to determine the elemental composition of major peaks, and the best matching chemical formula. The spectral peaks obtained from different pieces of the same type of fruit proved that the results could be duplicated with an acceptable standard deviation (6-14%) Farré et al. also compared the direct DART-MS approach to other methods widely used to analyze fruit peels. They obtained methanol extracts through ultrasonication. The extracts were then analyzed using DART-MS and ultrahigh-performance liquid chromatography (UHPLC) coupled to the Orbitrap mass spectrometer. As a whole, the data obtained through the UHPLC−Orbitrap-MS analysis was in agreement with those results obtained from the direct DART-MS and DART-MS on extracted samples. The identities of the post-harvest compounds were all detected with an exception of sucrose. The researchers note that the methanol extraction method might not be effective at extracting sugars, which adds more value to the direct DART-MS approach since no extraction steps were needed. The researchers determined that DART-MS is straightforward and can accurately and efficiently analyze fruit peel samples and detect xenobiotics, metabolites and/or degradation products. DART-MS also has the added advantage of eliminating cross contamination between runs while allowing for a high throughput of samples. Reference: 1. Farré, M., Picó, Y., & Barceló, D. (2013) “Direct peel monitoring of xenobiotics in fruit by direct analysis in real time coupled to a linear quadrupole ion trap-orbitrap mass spectrometer.”, Analytical Chemistry. 2013 Mar 5;85(5), (pp. 2638-44) doi: 10.1021/ac3026702. Epub 2013 Feb 14.