Solute species, isotopic

The concentrations of solute species are negligible compared with that of the solvent. This assumption allows us to equate the isotopic abundance in the solvent with that in the medium as a whole and to neglect the dilution of deuterium caused by the addition of an initially light substrate. 

The inclusion of activity coefficients into the simple equations was briefly considered by Purlee (1959) but his discussion fails to draw attention to the distinction between the transfer effect and the activity coefficient (y) which expresses the non-ideal concentration-dependence of the activity of solute species (defined relative to a standard state having the properties of the infinitely dilute solution in a given solvent). This solvent isotope effect on activity coefficients y is a much less important problem than the transfer effect, at least for fairly dilute solutions. For example, we have already mentioned (Section IA) that the nearequality of the dielectric constants of H20 and D20 ensures that mean activity coefficients y of electrolytes are almost the same in the two solvents over the concentration range in which the Debye-Hiickel limiting law applies. For 0-05 m solutions of HC1 the difference is within 0-1% and thus entirely negligible in the present context. Of course, more sizeable differences appear if concentrations are based on the molality scale (Gary et ah, 1964a) (see Section IA). 

Robinson, B.W., 1978. Sulphur isotope equilibria between sulphur solute species at high temperature. Proc. Int. Conf. on Stable Isotopes, Lower Hutt, N.Z., Aug. 1976, D.S.I.R. Bull., 220 203—206. 

An isotopic data input file provides EQPS with coefficients to calculate a fractionation factor (a) for each solution and mineral component (i), relative to a reference solution specie (chosen to be H2S, consistent with previous convention) using ... 

This first-order simplification occurs because in each elementary step, all but one of the concentrations is time independent and the labeled molecules enter each reaction with a molecularity of unity in elementary reaction steps. This is common for many isotopic exchange reactions occurring among solution species, but not all as will be shown below. 

III.c. Evaluation of Partition-Function Ratios for Isotopic Solute Species. The Symmetric Solvent Case. 

The principal condition for the applicability of equation (74) is that the dissolved LiBr exists in solution as undissociated diatomic molecules and not as ions. There must, of course, be a significant amount of cancellation of terms in the paxtltion-function ratio for the solute species. In particulax all purely electrostatic interactions (e.g., ion-dipole, dipole-dipole, etc.) which are isotope independent, should cancel out. Dissolution of LiBr would be ejpected to lower the stretching frequency for the LiBr bond (te). The decrease in ui,. decreases the ratio of... 

The calculated mass bias factor a is then applied to the actual measurements and used for correction of the isotope ratio value. Simultaneous methods have been developed by determination of the mass bias factor on a different element, for example thallium for the mass bias correction of lead and mercury.This principle has been adopted for species-specific isotope dilution measurements with GC-ICP-MS, with a system enabling the simultaneous aspiration of a standard solution during GC introduction. The simultaneous method was compared with mass bias correction using additionally measured standards, and showed satisfactory accuracy. Thallium was used for mass bias correction of lead and mercury species while antimony has been used for correcting tin species isotope ratios. ... 

Another approach is iterative solution of isotope effects on CS and chemical shifts at different temperatures to determine the percentage of the three species and the chemical shifts of the three species. 

The entropy of mixing of very similar substances, i.e. the ideal solution law, can be derived from the simplest of statistical considerations. It too is a limiting law, of which the most nearly perfect example is the entropy of mixing of two isotopic species. 

Zirconium [7440-67-7] is classified ia subgroup IVB of the periodic table with its sister metallic elements titanium and hafnium. Zirconium forms a very stable oxide. The principal valence state of zirconium is +4, its only stable valence in aqueous solutions. The naturally occurring isotopes are given in Table 1. Zirconium compounds commonly exhibit coordinations of 6, 7, and 8. The aqueous chemistry of zirconium is characterized by the high degree of hydrolysis, the formation of polymeric species, and the multitude of complex ions that can be formed. 

The procedure in use here involves the deposition of a radioactive isotope of the diffusing species on the surface of a rod or bar, the length of which is much longer than tire length of the metal involved in the diffusion process, the so-called semi-infinite sample solution. 

A solution of 4,4-dimethyl-5a-androst-l-en-3-one (128, 14 mg) in cyclohexane (3 ml) is stirred in a microhydrogenation apparatus in the presence of 10 % palladium-on-charcoal (15 mg) at atmospheric pressure and room temperature. The uptake of one eq of deuterium (1.15 ml) is complete in about 1 min and no more deuterium is consumed. After 5 min the catalyst is removed by filtration, and the solvent evaporated under reduced pressure. The resulting l<, 2< -d2-4,4-dimethyl-5a-androstan-3-one (129, 13 mg, 93%), mp 120-122°, exhibits 87% isotopic purity and 13% d species. ... 

The imbalance between and NMR studies in the solid state (Section VI,F) partly reflects the fact that it is easier to introduce N than into heterocyclic compounds, particularly azoles (DNMR in the solid state usually requires isotopic enrichment). Compared to solution studies, solid-state intermolecular proton transfer between tautomers has the enormous advantage that the structure of the species involved is precisely defined. 

At the same time it is recognized that the pairs of substances which, on mixing, are most likely to obey Raoult s law are those whose particles are most nearly alike and therefore interchangeable. Obviously no species of particles is likely to fulfill this condition better than the isotopes of an element. Among the isotopes of any element the only difference between the various particles is, of course, a nuclear difference among the isotopes of a heavy element the mass difference is trivial and the various species of particles are interchangeable. Whether the element is in its liquid or solid form, the isotopes of a heavy element form an ideal solution. Before discussing this problem we shall first consider the solution of a solid solute in a liquid solvent. 

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