GC-MS and Isotope Ratio Mass Spectrometry

Although GC-MS has been losing its monopoly that it held before LC-MS(/MS) was routinely available to doping control laboratories, a number of detection assays still rely on this technique due to the considerable resolving power of GC columns, the robustness of El sources, and the comparably low susceptibility to matrix effects, as well as the flexibility to interface various different analyzers to GC systems/  

MODERN MASS SPECTROMETRY-BASED ANALYTICAL ASSAYS 

1 mLof6MKOH K2C03/NaHC03 until pH = 9.6 1 mL of ferf. butanol 5 mL of TBME 3 g of Na2S04 shaking (10 min) 

The following GC-MS analysis is commonly done using a 12-16 minute HP5MS capillary GC column (inner diameter 0.2 mm, film thickness 0.33 pm) with helium as carrier gas operated at constant pressure (approximately 12psi) with 0.8-1.0mL/min. The temperature gradient of the GC usually starts from 100°C to 300°C with 15°C/min. The 

Due to the option to omit derivatization of analytes when using LC-MS/MS procedures, several analytes of the above mentioned screening procedures were implemented in other, alternative assays however, based on these sample preparation principles, also very recent GC-MS-based screening procedures were established, combining the goals of Screening I, II, and IV (see section A comprehensive 

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The innovations in Es-GC analysis have concerned not only the development and applications of distinct CSPs but also the development of distinct enantioselective analytical techniques, such as Es-GC-MS, Es-GC-0, enantioselective multidimensional GC (Es-MDGC), Es-MDGC-MS, Es-GC hyphenated to isotopic ratio mass spectrometry (Es-GC-IRMS), and Es-MDGC-IRMS. 

More recently, enantiomer ratios have been used as evidence of adulteration in natural foods and essential oils. If the enantiomer distribution of achiral component of a natural food does not agree with that of a questionable sample, then adulteration can be suspected. Chiral GC analysis alone may not provide adequate evidence of adulteration, so it is often used in conjunction with other instrumental methods to completely authenticate the source of a natural food. These methods include isotope ratio mass spectrometry (IRMS), which determines an overall 13C/12C ratio (Mosandl, 1995), and site-specific natural isotope fractionation measured by nuclear magnetic resonance spectroscopy (SNIF-NMR), which determines a 2H/ H ratio at different sites in a molecule (Martin et al 1993), which have largely replaced more traditional analytical methods using GC, GC-MS, and HPLC. 

Authenticity evaluation has recently received increased attention in a number of industries. The complex mixtures involved often require very high resolution analyses and, in the case of determining the authenticity of natural products, very accurate determination of enantiomeric purity. Juchelka et al. have described a method for the authenticity determination of natural products which uses a combination of enantioselective multidimensional gas chromatography with isotope ratio mass spectrometry (28). In isotope ratio mass spectrometry, combustion analysis is combined with mass spectrometry, and the 13C/12C ratio of the analyte is measured versus a C02 reference standard. A special interface, employing the necessary oxidation and reduction reaction chambers and a water separator, was used employed. For standards of 5-nonanone, menthol and (R)-y-decalactone, they were able to determine the correct 12C/13C ratios, with relatively little sample preparation. The technical details of multidimensional GC-isotope ratio MS have been described fully by Nitz et al. (29). A MDGC-IRMS separation of a natural ds-3-hexen-l-ol fraction is... 

FIGURE 35.13 C18 0 and C16 0 fatty acids formed via hydrolysis of triacylglycerides are ubiquitous archaeological residues indicative of the presence of animal fats and often identified using GC-MS. Natural abimdance isotope ratio mass spectrometry can be used to distingmsh between species via differences in 5 C content ([117] figure reproduced with kind permission). 

Isotope ratio mass spectrometry (IR-MS) is used with GC for the high-precision measurement of isotopic ratios of D/H, C/ C, and from organic mixtures. In general, gas chromatography is coupled to isotope ratio mass spectrometry via a combustion furnace [9]. 

In another approach using stable isotopes to measure retinoids in human serum, Parker and coworkers (296,297) studied the absorption and metabolism of C-labeled P-carotene using GC-isotope ratio mass spectrometry. Retinol and retinyl esters were separated using HPLC, the retinyl esters were hydrolyzed to retinol, and each retinol sample was analyzed using GC-isotope ratio mass spectrometry. As the retinol peak eluted from the GC, it was combusted to carbon dioxide, and the C02/ C02 ratio was measured using an isotope ratio mass spectrometer. In a similar way, lutein isolated from C3 and C4 plant sources was hydrogenated to perhydrocarotene which was subjected to GC-combustion-inter-faced isotope ratio-mass spectrometry (GC-C-IR-MS) to determine natural abundance C in lutein (298). 

Spectroscopic techniques used in essential oil analysis comprise ultraviolet and visible spectrophotometry, infrared spectrophotometry (IR), mass spectrometry (MS), and nuclear magnetic resonance spectroscopy (NMR), including the following H-NMR, C-NMR, and site-specific natural isotope fractionation NMR. Combined techniques (hyphenated techniques) employed in essential oil analysis are GC/MS, liquid chromatography/mass spectrometry, gas chromatography/Fourier transform infrared spectrophotometry (GC/FT-IR), GC/FT-IR/MS, GC/atomic emission detector, GC/isotope ratio mass spectrometry, multidimensional GC/MS. 

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