Isotopes nitrogens

There are a number of methods that have been used for the separation of nitrogen-15 and these have been reviewed [36]. The two most important, that 

Other chemical exchange reactions that have been used for the fractionation of nitrogen isotopes include ammonia and anunonium nitrate solution [45], ammonia and ammonium carbonate [46], and ammonia and its complexes with aliphatic alcohols [47]. 

Nitrogen isotopes have been separated by gas chromatography. The separation of from was effected on a graphon column at 77°K [51 ], a partial separation having been previously obtained on glass capillary columns [52]. A laser-induced dissociation reaction of s-tetrazine has been reported to show separation of nitrogen-14 and -15, and of carbon-12 and -13 [53]. 

Thermal diffusion of nitrogen afforded 98.95% of the N N species [48]. It has also been used to prepare nitrogen at 99.8 atom% N [49], the N N molecules being randomised by the action of an electric discharge. Other work has been reported using chemical exchange of nitric oxide and nitrogen dioxide in a thermal diffusion column [50]. 

Consumers of terrestrial foods generally have bone collagen d N values of 10%c 

In arid areas, where rainfall is less than about 400 nun per annum, terrestrial systems, too, may yield elevated d N. 

Carbon and nitrogen isotope analyses today are a routine part of the study of human skeletal remains. They are usually calculated along with radiocarbon measurements at dating laboratories. There are other isotopes that may also be of interest in the study of diet such as hydrogen and sulfur, but these are less well understood. 

There are other methods for investigating past diet as well and our first example discussed below illustrated one of them - the use of antigen-antibody reactions. This is a very special case where the preservation of unusual human remains makes possible the preservation of proteins that reveal evidence for cannibalism. 

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Some nitrogen isotope separation is also observed (6). 

Discovery of a nitrogen isotope N by S. M. Naudd following the discovery of isotopes of O and C by others earlier in the same year. 

Important additional evidence for aryl cations as intermediates comes from primary nitrogen and secondary deuterium isotope effects, investigated by Loudon et al. (1973) and by Swain et al. (1975 b, 1975 c). The kinetic isotope effect kH/ki5 measured in the dediazoniation of C6H515N = N in 1% aqueous H2S04 at 25 °C is 1.038, close to the calculated value (1.040-1.045) expected for complete C-N bond cleavage in the transition state. It should be mentioned, however, that a partial or almost complete cleavage of the C — N bond, and therefore a nitrogen isotope effect, is also to be expected for an ANDN-like mechanism, but not for an AN + DN mechanism. 

What was the solution The reaction had to be carried out with a diazonium ion labeled with one or two atoms of the nitrogen isotope 15N in the presence of large concentrations of unlabeled nitrogen molecules (14N2), quenched before completion, and the remaining diazonium ion analyzed for 15N content if this had decreased relative to the initial value, the dogma would be falsified. 

One way to determine just where a given reaction stands on the El-E2-ElcB spectrum is to study isotope effects, which ought to tell something about the behavior of bonds in the transition state. For example, CH3CH2NMe3 showed a nitrogen isotope effect of 1.017, while PhCH2CH2NMe3" gave a corres-... 

A smaller number of individuals, 132 samples, was analyzed for stable isotopes of nitrogen. There were two objectives to the nitrogen isotope analysis 1) to determine the amount of animal protein in the diet and to look for variation between the sexes and 2) to determine when infants were weaned from the breast. These objectives were addressed by selecting at least ten individuals, when available, from a number of age classes. Figure 1.1 illustrates the age distribution of the sample. Table 1.3 shows the results of these analyses. Individual 5 N values are provided in Herring et al. (1998). 

Fogel, M., Tuross, N. and Owsley, D.W. 1989 Nitrogen isotope tracers of human lactation in modem and archaeological populations. Annual report of the Director Geophysical Laboratory, 1988-1989. Washington, D.C., Carnegie Institution ofWashington 111-117. 

Katzenberg, M.A. and Pfeiffer, S. 1995 Nitrogen isotope evidence for weaning age in a nineteenth century Canadian skeletal sample. In Grauer, A.L., ed.. Bodies ofEvidence. New York, John Wiley Sons, Inc. 221-235. 

Katzenberg, M.A., Saunders, S.R. and Fitzgerald, W.R. 1993 Age differences in stable carbon and nitrogen isotope ratios in a population of prehistoric maize horticulturists. American Journal of Physical Anthropology 90 267-281. 

Schurr, M.R. 1997 Stable nitrogen isotopes as evidence for the age of weaning at the Angel Site A comparison of isotopic and demographic measures of weaning age. Journal of Archaeological Science 24 919-927. 

The 8 C values of the Preclassic humans at Cuello (Table 2.1) average -12.9 0.9%o (n = 28) in collagen, -9.8 1.0 in bone apatite (n = 16), and -8.7 2.3%o in tooth enamel apatite (n = 33) the S N values in collagen average 8.9 1.0%o (n = 23). The discrepancy in the number of specimens is due to the fact that more teeth were available than post-cranial material, while some of the specimens contained insufficient collagen to measure the nitrogen isotope ratios. Additional bone apatite analyses are in progress. 

Table 2.1. Carbon and nitrogen isotope values of animal and human skeletal remains from the Predassic archaeological deposits at Cuello. Belize.

Figure 2.2. Carbon and nitrogen isotope values of marine fauna from Belize, Ecuador (van der Merwe et al. 1993), and the southwestern Cape coast of South Africa (Sealy and van der Merwe 1986).

Table 2.3. Carbon and nitrogen isotope values in hair of modern human and canid residents of the Cuello area Orange Walk, Belize. 1992.

Figure 2.3. Carbon and nitrogen isotope values of human bone collagen at Maya sites in Belize. The value for the modem sample has been corrected for collagen-hair spacing and the Industrial Effect. Boxes represent isotopic means one standard deviation.

Figure 2.4. Carbon and nitrogen isotope values in human bone collagen from Preclassic Belize (Cuello and Lamanai) and from the Preclassic Peten (Altar de Sacrificios and Seibal).

Keegan, W.F. and DeNiro, M.J. 1988 Stable carbon- and nitrogen- isotope ratios of bone collagen used to study coral-reef and terrestrial components of prehistoric Bahamian diet. American Antiquity 53 320-336. 

Reed, D.M. 1994 Ancient Maya diet at Copan, Honduras, as determined through the analysis of stable carbon and nitrogen isotopes. In Sobolik, K.D., ed., Paleonutrition The Diet and Health of Prehistoric Americans. Occasional Paper 22, Center for Archaeological Investigations, Carbondale, University of Southern Illinois 210-221. 

The interpretation of the factors mentioned above in the context of palaeodietary research is not straightforward a lack of nitrogen isotope data in relevant plant species makes the situation even more complicated. The observed variability in plants, even within ecosystems, is so extensive and so unpredictable that modelling of the behaviour of natural nitrogen abundances in plants is fraught with difficulties because there are no simple, universal laws governing the site-specific details of the N cycle, there will be no simple, universal laws of 8 N (in plants) (Handley and Raven 1992 Handley and Scrimgeour 1996). 

Nitrogen is mainly taken in by humans in the form of proteins, so there is no possibility for ambiguity here nitrogen isotopic ratios must reflect those of the protein in the diet. 

Ambrose, S.H. 1986 Stable carbon and nitrogen isotope analysis of human and animal diet in Mrica. Journal of Human Evolution 15 707-731. 

Effects of diet, climate and physiology on nitrogen isotope abundances in terrestrial... 

Climate and habitat reconstruction using stable carbon and nitrogen isotope... 

Delwiche, C.C. and Steyn, P.L. 1970 Nitrogen isotope fractionation in soils and microbial reactions. Environmental Science and Technology 4 929-935. 

DeNiro, M.J. and Epstein, S. 1981 Influence of diet on the distribution of nitrogen isotopes in animals. Geochimica et Cosmochimica Acta 45 341-351. 

Handley, L.L. and Raven, J.A. 1992 The use of natural abundance of nitrogen isotopes in plant physiology and ecology. Plant Cell Environment 15 965-985. 

Macko, S.A., Estep, M.L.E., Engel, M.H. and Hare, RE. 1986 Kinetic fractionation of stable nitrogen isotopes during amino acid transamination. Geochimica et Cosmochimica Acta 50 2143-2146. 

Mariotti, A., Mariotti, F., Champigny, M.L., Amarger, N. and Moyse, A. 1982 Nitrogen isotope fractionation associated with nitrate reductase activity and uptake of NO3by pearl millet. Plant Physiology 69 880-884. 

Schoeninger, M.J., DeNiro, M.J. and Tauber, H. 1983 Stable nitrogen isotope ratios of bone collagen reflect marine and terrestrial components of prehistoric human diet. Science 220 1381-1383. 

Sealy, J.C., Van der Merwe, N.J., Lee-Thorp, J.A. and Lanham, J.L. 1987 Nitrogen isotopic ecology in southern Africa implications for environmental and dietary tracing. Geochimica et Cosmochimica Acta 51 2707-2717. 

Some environmental parameters, such as aridity and dietary stress, also seem to increase nitrogen isotopic abundances at each trophic level (Ambrose and DeNiro 1986 Heaton et al. 1986 Sealy et al. 1987 Ambrose 1991). 

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