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Breathomics and its Application for Disease Diagnosis: A Review of Analytical Techniques and Approaches
Published in Raquel Cumeras, Xavier Correig, Volatile organic compound analysis in biomedical diagnosis applications, 2018
David J. Beale, Oliver A. H. Jones, Avinash V. Karpe, Ding Y. Oh, Iain R. White, Konstantinos A. Kouremenos, Enzo A. Palombo
Spectroscopy is based on the measurement of absorption of electromagnetic radiation by a compound, or compounds of interest. Spectral fingerprints of compounds in breath span the UV to the mid-IR spectral regions. Typically, exhaled breath samples require pre-concentration prior to analysis via SPME, a suitable absorbent material or by direct cryofocusing (Miekisch and Schubert, 2006). Compounds present in exhaled breath that are IR or UV active such as ammonia, carbon monoxide, carbon dioxide, methane, and ethane absorb light at wavelengths characteristic of the bonds present in the molecule and these absorption bands can be used to identify specific molecular components and/or to allow identification of a compound via reference library matching. Stable isotopomers of IR active molecules can also be accurately detected, making it possible to follow specific metabolic processes. While infrared spectroscopy data are not as detailed as those from NMR or MS-based methods, the technique has the advantages that it is quick, simple, non-destructive and does not require extensive sample preparation; near real-time data can be obtained and the instruments are much lower in cost that NMR or MS instruments. The disadvantages are that spectroscopy is not as sensitive or selective as MS, with detection limits in the ppm to ppb range and the technique is also limited in the number of chemical species it can distinguish.
Determination of the natural deuterium distribution of fatty acids by application of 2H 2D-NMR in liquid crystals: fundamentals, advances, around and beyond
Published in Liquid Crystals, 2020
The isotope ratio value (2H/1H) using (fresh) ocean water molecules (known as V-SMOW value: Vienna-Standard Mean Ocean Water) has been set at 1.5576 × 10−2% (155,76 ppm) for hydrogen atoms. This value was promulgated by the International Atomic Energy Agency (based in Vienna) in 1968, and is still used as international standard value [10]. However, in natural hydrogenated compounds, significant changes in the isotope ratios (2H/1H) (up to 50%) can be observed at its different hydrogenated sites. This non-statistical intramolecular distribution of hydrogen isotope means that the content of different monodeuterated isotopomers depends on the deuterium-substituted position. These site-specific intramolecular variations define the isotopic fractionation of a molecule and characterise its isotopic profile. These profiles are unique molecular fingerprints that can be related to the geographical or botanical origin of a compound, and hence provide data sources in the fight against counterfeiting (adulteration, substitution, imitation of premium products), for instance [11]. From a theoretical point of view, the analysis of the isotopic profiles of a substrate/product pair can also makes it possible to study the primary or secondary kinetic isotopic effects (KIEs) [12], to identify hydrogen deuterium) sources, and thus to understand the enzymatic mechanisms leading to the synthesis/transformation of natural compounds [13–16].