Abstract
For fragmentation studies whole citrus peel extracts were obtained from organic Florida-grown Valencia oranges. The application of positive-ion Electrospray Ionization (ESI) Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) Broadband analysis identifies elemental compositions of thousands of basic species in each sample, based on mass resolving power (m/Δm50% > 300,000, in which Δm50% denotes mass spectral peak full width at half height) and high mass accuracy (better than 1 ppm), but molecular assignment alone does not reveal structure. Isolation of a species of interest and fragmentation with a CO2 laser allows for accurate mass assignments for precursor and product ions, aiding structural interpretation. Fragmentation of parent ions leads to common losses of CH2, H2O, CH2O, CH2O2, C6H10O4, C10H20O9, C14H10O5 and C6H10O5. Other unrepeated losses were observed. Several nitrogen-containing species were identified. Based on proposed structures of the parent and daughter ions these fragments were generated by three main pathways: acid-catalyzed dehydration, ether-to-ketone conversion by loss of unobserved radical or by ether-to-hydroxyl where rearrangement facilitates hydroxyl formation. Previously known constituents including hesperidin were identified with sub-100 ppb error.
For broadband analysis whole citric juice and peel extracts were obtained from organically grown fruits. The application of ESI FT-ICR MS Broadband positive-ion analysis serves to simultaneously confirm the presence and elucidate elemental composition of many phytonutrients while revealing elemental compositional differences between varieties and species, detected and characterized by their double bond equivalents (DBE = number of rings plus double bonds) and carbon number in an unfractionated (raw) sample. For a given citric fruit, characteristics of peel and juice are relatively similar; however, there is surprisingly pronounced variation between different citric fruits. Compounds with higher carbon number are more abundant in the juice than in the peel oil. The juices have higher O/C ratios than the peels; evidently the higher polarity of the high O/C ratio species compensates for the otherwise lower solubility of compounds with more carbon atoms. Peels show more species with higher DBE than do the juices. The results/trends will be discussed with respect to variation within and characterization of citric species, citric varieties, juices, and peels. Previously known constituents were identified with sub-100 ppb error. All species were detected and identified without the need for prior chromatographic separation.
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