13C natural abundance

Fig. 17. Photofragment ion images of C6H5CD3 in three different mass regions. Image of m/e = 76 in (b) resulted from two-photon dissociation. Image of parent molecule m/e = 95, and m/e = 96, 97 due to the 13C natural abundance are shown in (c).

Skjemstad JO, Le Feuvr RP, Prebble RE (1990) Turnover of soil organic matter under pasture as determined by 13C natural abundance. Aust J Soil Res 28 267-276... 

Collins HP, Paul EA, Blevens RL, Bundy LG, Christenson DR, Dick WA, Huggins DR (1999) Soil organic matter dynamics in corn-based agroecosystems of the central USA results from 13C natural abundance. Soil Sci Soc Am J 63 584-599... 

Martin A, Mariotti A, Balesdent J, Lavelle P, Vuattoux R (1990) Estimate of organic matter turnover rate in savanna soil by 13C natural abundance measurements. Soil Biol Biochem 22 517-523... 

An important benefit of the isotopic approach is that below-ground biomass values are not required. The 13C natural abundance isotopic carbon budget approach is based on C3 plants having lower 13C value than C4 plants (Ehleringer 1991 Clay et al. 2006) and that the signatures can be tracked by placing C3 plant residue into a soil derived from C4 plants or vice versa. In these calculations, several definitions are needed. These definitions include... 

Balesdent J, Mariotti A (1996) Measurement of soil organic matter turnover using 13C natural abundance. In Boutton TW, Yamasaki S (eds) Mass spectrometry of soils. Marcel Dekker Inc., New York, pp 83-112... 

Although ubiquitin displays very favorable relaxation properties, these spectra indicate the potential for performing these experiments at 13C natural abundance for smaller proteins. 

For mass-limited samples, small-diameter (conventional) probes present an attractive alternative to cryogenic probes. In collaboration with Hoffmann-La Roche, Bruker has recently developed a 1 mm probe with a sample volume of 5 pL. This probe offers a mass sensitivity that typically is fourfold higher than a conventional 5 mm probe. An example displaying a [13C, 1H]-HSQC of 1 pg Ibuprofen at 13C natural abundance is shown in Fig. 3.6 below [25]. 

Raymond, P.A., and J.E. Bauer. 2001. Use of 14C and 13C natural abundances for evaluating riverine, estuarine, and coastal DOC and POC sources and cycling A review and synthesis. Organic Geochemistry 32(4) 469-485. 

Wang L, Schjoerring JK (2012) Seasonal variation in nitrogen pools and 15N/13C natural abundances in different tissues of grassland plants. Biogeosciences 9 1583-1595... 

Microbial transformations of DOM were also studied by incubation experiments. The DOM extracted from maize straw and forest floors was incubated for 90 days and samples taken before and after incubation were analyzed by Py-FIMS and complementary UV absorbance, fluorescence emission spectroscopy, FTIR-spectroscopy, 1H NMR spectroscopy, and 13C natural abundance (Kalbitz et al., 2003). The Py-FI mass spectra showed increases in the proportions of phenols and lignin monomers at the expense of lignin dimers and alkylaromatics during... 

The 13C-H spin coupling constants of thiazole have been determined on samples with 13C natural abundance or on samples specifically enriched in the 2-, 4- or 5-positions (Table 8). The 13C chemical shifts of benzothiazole are reported in Table 9. 

Although it is possible to measure one-bond 13C-13C coupling constants in unenriched samples (13C natural abundance is 1-108%), (28, 29) such measurements are not routine on most spectrometers. Most of the reported data on C-C coupling in the past two years have been obtained from 13C labelled compounds. 

---