Isotopes differentiation

Such a measurement can tell us about the chemical evolution of oxygen, such as whether the isotopes differentiated via a thermal cycle in which lighter leO fractionates from the heavier lsO, much as Vostok ice-core oxygen ratios reveal the Earth s prehistoric climate. From this fixed point of the Sun s oxygen ratios, we can then trace the history of water in other planetary bodies since their birth in the solar nebulae through the subsequent cometary bombardment [13]. In NASA s search for water on the Moon, important for the establishment of a future Moon base, such isotopic ratios will determine whether the water is a vast mother lode or just a recent cometary impact residue. 

Stoll PM, Stokes PE, Okamoto M (2001) Lifiiium isotopes differential effects on renal fimction and histology. Bipolar Disorders 3 174-180... 

Nitrate originates from gaseous emissions of N0 c(N0- -N02). Heaton (1986) has discussed the possibility of isotopically differentiating between naturally produced and anthropogenic NO. Since very little isotope fractionation is expected at... 

Albro PW, Hass JR, Peck CC, et al. 1982b. Applications of isotope differentiation for metabolic studies with di(2-cthyl hexyl) phthalate. J Environ SciHealth B 17 701-714. 

Fig. 2. Sulfur isotopes differentiation for several sulfur-rich asphaltenes during closed vessel pyrolysis. This figure is after Everlien et al. (1997). The reported as difference between values recorded for the asphaltenes and H2S produced are plotted versus temperature.

Boreham, C.J., Summons, R.E., Roksandic, Z., Dowling, L.M., Hutton, A.C. (1994) Chemical, molecular and isotopic differentiation of organic facies in the Tertiary lacustrine Duaringa oil shale deposit, Queensland, Australia. Organic Geochemistry, 21, 685-712. 

Magi, F., Facchetti, S., Garibaldi, P., Gasoline with Isotopically Differentiated Lead Added, Isotop. Ratios Pollut. Source Behav. Indie. Proc. Symp., Vienna 1974 [1975], pp. 109/19. 

A common mistake for beginners in mass spectrometry is to confuse average atomic mass and isotopic mass. For example, the average atomic mass for chlorine is close to 35.45, but this average is of the numbers and masses of Cl and Cl isotopes. This average must be used for instruments that cannot differentiate isotopes (for example, gravimetric balances). Mass spectrometers do differentiate isotopes by mass, so it is important in mass spectrometry that isotopic masses be used... 

These effects of differential vapor pressures on isotope ratios are important for gases and liquids at near-ambient temperatures. As temperature rises, the differences for volatile materials become less and less. However, diffusion processes are also important, and these increase in importance as temperature rises, particularly in rocks and similar natural materials. Minerals can exchange oxygen with the atmosphere, or rocks can affect each other by diffusion of ions from one type into another and vice versa. Such changes can be used to interpret the temperatures to which rocks have been subjected during or after their formation. 

Almost any type of analyzer could be used to separate isotopes, so their ratios of abundances can be measured. In practice, the type of analyzer employed will depend on the resolution needed to differentiate among a range of isotopes. When the isotopes are locked into multielement ions, it becomes difficult to separate all of the possible isotopes. For example, an ion of composition CgHijOj will actually consist of many compositions if all of the isotopes ( C, C, H, H, 0, O, and 0) are considered. To resolve all of these isotopic compositions before measurement of their abundances is difficult. For low-molecular-mass ions (HjO, COj) or for atomic ions (Ca, Cl), the problems are not so severe. Therefore, most accurate isotope ratio measurements are made on low-molecular-mass species, and resolution of these even with simple analyzers is not difficult. The most widely used analyzers are based on magnets, quadrupoles, ion traps, and time-of-flight instruments. 

Although isotope-dilution analysis can be very accurate, a number of precautions need to be taken. Some of these are obvious ones that any analytical procedure demands. For example, analyte preparation for both spiked and unspiked sample must be as nearly identical as possible the spike also must be intimately mixed with the sample before analysis so there is no differential effect on the subsequent isotope ration measurements. The last requirement sometimes requires special chemical treatment to ensure that the spike element and the sample element are in the same chemical state before analysis. However, once procedures have been set in place, the highly sensitive isotope-dilution analysis gives excellent precision and accuracy for the estimation of several elements at the same time or just one element. 

S. Nitz, H. Kollmannsberger, B. Weinreich and F. Drawert, Enantiomeric distr ibution and C/ C isotope ratio deter mination of -y-lactones appropriate methods for the differentiation between natural and non-natural flavours , 7. Chromatogr. 557 187-197 (1991). 

One of the possibilities is to study experimentally the coupled system as a whole, at a time when all the reactions concerned are taking place. On the basis of the data obtained it is possible to solve the system of differential equations (1) simultaneously and to determine numerical values of all the parameters unknown (constants). This approach can be refined in that the equations for the stoichiometrically simple reactions can be specified in view of the presumed mechanism and the elementary steps so that one obtains a very complex set of different reaction paths with many unidentifiable intermediates. A number of procedures have been suggested to solve such complicated systems. Some of them start from the assumption of steady-state rates of the individual steps and they were worked out also for stoichiometrically not simple reactions [see, e.g. (8, 9, 5a)]. A concise treatment of the properties of the systems of consecutive processes has been written by Noyes (10). The simplification of the treatment of some complex systems can be achieved by using isotopically labeled compounds (8, 11, 12, 12a, 12b). Even very complicated systems which involve non-... 

The route from kinetic data to reaction mechanism entails several steps. The first step is to convert the concentration-time measurements to a differential rate equation that gives the rate as a function of one or more concentrations. Chapters 2 through 4 have dealt with this aspect of the problem. Once the concentration dependences are defined, one interprets the rate law to reveal the family of reactions that constitute the reaction scheme. This is the subject of this chapter. Finally, one seeks a chemical interpretation of the steps in the scheme, to understand each contributing step in as much detail as possible. The effects of the solvent and other constituents (Chapter 9) the effects of substituents, isotopic substitution, and others (Chapter 10) and the effects of pressure and temperature (Chapter 7) all aid in the resolution. 

Low-resolution devices are those that can separate and measure m/z ratios to the nearest integer value and have a numerical resolution of up to around 1000. As such, they can separate (resolve), for example, ions at m/z 28 and 29, i.e. they allow the analyst to differentiate between CO+ and CHO, or C2H4+ and C2H5+. Using these types of instrnment, we need only consider the masses of the isotopes as integers, e.g. = 12 Da, = 1 Da, = 14 Da and = 16 Da. 

Since it is possible to differentiate well-preserved from badly preserved collagen through amino acid analysis and gel electrophoresis, it is also possible to determine which bone samples are likely to give erroneous isotopic ratios. At least for 8 C, it should be possible to estimate the in vivo isotopic signature by correcting the changed amino acid concentrations of the collagen extract. This way, a reasonable approach to the reconstruction of pale-odiet should be possible. 

These are only a few specific examples of paleodietaiy consequences of biochemical pathways. Paleodiet researchers shonld probably try to enlist the aid of metabolic biochemists in a search for other possible conseqnences of differential metabolic pathways, internal recycling of metabolites, etc. Furthermore, many of these problems will become clearer as we begin to have access to isotopic analyses of individnal amino acids or even specific carbon atoms at sites on individual AAs. 

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