Oxygen isotopes separation methods

Polymeric membranes for separation of hydrogen and oxygen isotopes were studied at INCT, Warsaw [92-95,140-141]. Both hydrophUic barriers, such as regenerated cellulose and hydrophobic PTFE membranes, were tested. The regenerated cellulose appeared to be a very good system to get high separation factors and to consider membrane permeation as possible and competitive method for enrichment deuterium and 0 in natural water. 

Zakrzewska-Trznadel, G. et al.. Separation of hydrogen and oxygen isotopes by membrane method, Sudia Universitaties Babes-Bolyai, Physica, Special Issue 1, XLVIII, 39, 2003. 

The occurrence of isotopes among the 83 most abun-dantelements is widespread, but separation methods are complicated and costly. Twenty-one elements have no isotopes, each consisting of only one kind of atom (see note below). The remaining 62 natural elements have from 2 to 10 isotopes each. There are 287 different isotopic species in nature noteworthy among them are oxygen-17, carbon-14, uranium-235, cobalt-60, and strontium-90, all but the first being radioactive. 

Figure 5. Oxygen isotopic compositions of minerals in CAIs from CV chondrites, (a) Data obtained by the BrFs method on mg quantities of mineral separates from coarse-grained type B inclusions from Allende (Clayton et al. 1977 Mayeda et al.

The most impressive use of the substoicheiometric displacement technique is the automated isotope dilution method of Ruzicka and Lamm for the determination of Hg in biological materials. After oxygen flask destruction of the samples and preliminary manual separation, the Hg is automatically extracted from an aqueous solution by a substoicheiometric amount of zinc dithizonate and the activity of the extract measured. The method has been used in the 0.4—0.004 pg of Hg range. At the present time, when there is concern about the concentration of toxic elements in foodstuffs and the environment, an automated analysis system of this type could be of great value for large-scale routine monitoring of trace element levels. 

The use of larger particles in the cyclotron, for example carbon, nitrogen or oxygen ions, enabled elements of several units of atomic number beyond uranium to be synthesised. Einsteinium and fermium were obtained by this method and separated by ion-exchange. and indeed first identified by the appearance of their concentration peaks on the elution graph at the places expected for atomic numbers 99 and 100. The concentrations available when this was done were measured not in gcm but in atoms cm. The same elements became available in greater quantity when the first hydrogen bomb was exploded, when they were found in the fission products. Element 101, mendelevium, was made by a-particle bombardment of einsteinium, and nobelium (102) by fusion of curium and the carbon-13 isotope. 

In principle, the three isotope method may be widely applied to new isotope systems such as Mg, Ca, Cr, Fe, Zn, Se, and Mo. Unlike isotopic analysis of purified oxygen, however, isotopic analysis of metals that have been separated from complex matrices commonly involves measurement of several isotopic ratios to monitor potential isobars, evaluate the internal consistency of the data through comparison with mass-dependent fractionation relations (e.g., Eqn. 8 above), or use in double-spike corrections for instrumental mass bias (Chapter 4 Albarede and Beard 2004). For experimental data that reflect partial isotopic exchange, their isotopic compositions will not lie along a mass-dependent fractionation line, but will instead lie along a line at high angle to a mass-dependent relation (Fig. 10), which will limit the use of multiple isotopic ratios for isobar corrections, data quality checks, and double-spike corrections. 

DIP. As with the previously described difference methods, a pellet from a separate split is subjected to oxidation/hydrolysis for determination of TDP, and DOP is derived by difference. This method has also been adapted for use in concentrating DOP for isotopic studies of phosphate oxygen in seawater (see Section 8.13.3.3.3 Cohnan, 2002). 

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