Isotopic phase separation

From the general point of view of Nemst s theorem there are tw > possibilities to make the isotopic entropy of mixing vanish at sufficiently low temperatures either isotopic phase separation or formation of some regular structure. We see that it is the first possibility which is realized. We shall give a more general derivation of this important result in the next section. 

Since spillover phenomena have been most directly sensed through the use of IR in OH-OD exchange [10] (in addition, in the case of reactions of solids, to phase modification), we used this technique to correlate with the catalytic results. One of the expected results of the action of Hjp is the enhancement of the number of Bronsted sites. FTIR analysis of adsorbed pyridine was then used to determine the relative amounts of the various kinds of acidic sites present. Isotopic exchange (OH-OD) experiments, followed by FTIR measurements, were used to obtain direct evidence of the spillover phenomena. This technique has already been successfully used for this purpose in other systems like Pt mixed or supported on silica, alumina or zeolites [10]. Conner et al. [11] and Roland et al. [12], employed FTIR to follow the deuterium spillover in systems where the source and the acceptor of Hjp were physically distinct phases, separated by a distance of several millimeters. In both cases, a gradient of deuterium concentration as a function of the distance to the source was observed and the zone where deuterium was detected extended with time. If spillover phenomena had not been involved, a gradientless exchange should have been observed. 

Figure 16.4 A more advanced ICAT design uses an acid-cleavable spacer arm to facilitate elution of labeled peptides from a (strept)avidin affinity column. The use of 14C isotopes instead of deuterium labels permits precise reverse phase separations prior to mass spec that show no elution peak time differences between isotope-labeled and normal atom-labeled peptides.

The concentrations of the two isotopes on the phase-separation branches at the saturated vapour pressure is given by [5] and [6-8] ... 

B is a powerful neutron absorber and has been employed in reactor control rods, neutron detectors, and other applications. Cascades based on exchange distillation of boron-ether complexes have usefully large a s and were used for 10B/UB isotope separation by the US DOE. Exchange distillation takes advantage of the fact that condensed phase/vapor phase separation factors can be enhanced (as compared to liquid/vapor a s) by association/dissociation equilibria in one or the other phase. At the normal boiling point (173 K) the VPIE for... 

Seawater and marine pore fluids. As discussed above, the chlorine isotopic composition of modem seawater does not vary measurably. This is not surprising in light of its long residence hme (approximately 90 million years) and its conservative behavior in the water column. In contrast, marine pore fluids have been demonstrated to vary considerably. There is also the likelihood that hydrothermal fluids may be fractionated as a result of exchange with mineral phases, as phase separation under marine hydrothermal conditions does not appear to lead to measurable fractionation (e.g., Magenheim et al. 1995). However, to date no stable-chlorine isotopic compositions of marine hydrothermal fluids have been reported in the literature. 

Vapor and brine from the Brandon vent of the East Pacific Rise have identical Fe isotope compositions, implying that phase separation does not produce an isotopic fractionation (Beard et al. 2003a). The role that sulfide precipitation plays in controlling the Fe isotope composition of the fluid remains unknown. The precision of the two sulfide analyses reported by Sharma et al. (2001) was not sufficient to resolve if sulfide precipitation would produce Fe isotope fractionation in the vent fluid. In a detailed study of sulfldes from the Lucky Strike hydrothermal field from the mid Atlantic Ridge, however, Rouxel et al. (2004) found that sulfldes span a range in 5 Fe values from -2.0 to +0.2%o, and that pyrite/marcasite has lower 5 Fe values ( l%o) as compared to chalcopyrite. The variations in mineralogy and isotope composition are inferred to represent open-system equilibrium fractionation of Fe whereby... 

Bermin J, Vance D, Archer C, Statham PJ (2006) The determination of the isotopic composition of Cu and Zn in seawater. Chem Geol 226 280-297 Berndt ME, Seal RR, Shanks WC, Seyfried WE (1996) Hydrogen isotope systematics of phase separation in submarine hydrothermal systems experimental calibration and theoretical models. 

Liebscher A, Barnes J, Sharp Z (2006) Chlorine isotope vapor-liquid fractionation during experimental fluid-phase separation at 400°C/23 Mpa to 450°C/42Mpa, Chem Geol 234 340-345 Lister GS, Kelts K, Chen KZ, Yu JQ, Niessen P (1991) Lake Qinghai, China closed-basin lake levels and the oxygen isotope record for ostracoda since the latest Pleistocene. Palaeogeogr PalaeocUmatol Palaeoecol 84 141-162... 

Figure 7.4 illustrates the phase diagram of the 4He isotope in the low-temperature condensation region. The thermodynamic properties of 4He are fundamentally distinct from those of the trace isotope 3He, and the two isotopes spontaneously phase-separate near IK. Both isotopes exhibit the spectacular phenomenon of superfluidity, the near-vanishing of viscosity and frictional resistance to flow. The strong dependence on fermionic (3He) or bosonic (4He) character and bizarre hydrodynamic properties are manifestations of the quantum fluid nature of both species. 3He is not discussed further here. 

The thermal diffusion method of isotope separation has broad application to liquid-phase as well as gaseous-phase separations. The apparatus widely used for this purpose consists of a vertical tube provided with an electrically heated central wire. The gaseous or liquid mixture containing the isotopes to be separated is placed in the tube, and heated by means of the wire. In such an apparatus two effects act to separate the isotopes. Thermal diffusion tends to concentrate the heavier isotopes in the cooler outer portions of the system, while the portions near the hot wire are enriched in die lighter isotopes. At the same time, thermal convection causes the hotter fluid near the hot wire to rise, while the cooler fluid in the outer portions of the system tends to fell. The overall result of these two effects causes die heavier isotopes to collect at the bottom of the tube and the lighter at the lop, whereby both fractions may be withdrawn... 

Figure 5 shows the EPR spectra and intensity for the x=0.06 sample. It is seen that in contrast to the x <0.06 samples at x=0.06 only a single EPR line is observed and the temperature dependence of the signal intensity recovers an usual Curie-Weiss behavior. On the other hand there is still a substantial isotope effect on the EPR line. To understand the change of the EPR spectra at x=0.06, one should first comment on the observability of the phase separation in our EPR experiments. The main difference of the EPR signals from the hole-rich and hole-poor regions is the spin relaxation rate of the Cu... 

Martens-Lobenhoffer et al. [119] used chiral HPLC-atmospheric pressure photoionization tandem mass-spectrometric method for the enantio-selective quantification of omeprazole and its main metabolites in human serum. The method features solid-phase separation, normal phase chiral HPLC separation, and atmospheric pressure photoionization tandem mass spectrometry. The internal standards serve stable isotope labeled omeprazole and 5-hydroxy omeprazole. The HPLC part consists of Agilent 1100 system comprising a binary pump, an autosampler, a thermo-stated column component, and a diode array UV-VIS detector. The enantioselective chromatographic separation took place on a ReproSil Chiral-CA 5 ym 25 cm x 2 mm column, protected by a security guard system, equipped with a 4 mm x 2-mm silica filter insert. The analytes were detected by a Thermo Scientific TSQ Discovery Max triple quadrupole mass spectrometer, equipped with an APPI ion source with a... 

Two-site immunometric or sandwich assays that made use of two or more antibodies directed at different parts of the PRL molecule were next to be developed. As with other two-site IRMA assays, the capture antibody is attached to a solid phase separation system and the second or signal antibody is labeled with a detection molecule (e.g., radio-isotope, enzyme,fluorophor, or chemiluminescence tag ). In some assays, the capture antibody is attached to the wall of test tubes, plastic beads, microtiter plates, ferromagnetic particles, or glass-fiber paper. Other assays have used the strep-avidin approach that couples biotin to the signal antibody with avidin linked to a solid phase. Most of the current immunometric assays for PRL have been adapted to fully automated immunoassay systems. Compared with the older traditional RIA methods, these automated immunometric assays for PRL generally achieve lower detection limits (0.2 to 1.0 ig/L) and improved precision (interlaboratory coefficients of variation of <8% at all concentrations), and have superior specificity (<0.05% crossreactivity with GH). 

Another strategy for stable isotope labeling of N-terminus and lysine side-chain amines is reductive animation by nondeuterated and deuterated formaldehyde. Dimethylation of peptides occurs by the formation of a Schiff base, followed by reduction with cyanoborohydride. Peptides thus labeled differ by a mass of 4 Da for each labeled pair. The labeled peak pairs show minimum isotope effects on reverse-phase separation and hence coelute (93). Dimethylation using formaldehyde with the natural isotopic abundance (hydrogen and 12C) versus a heavy form with two deuteriums and one atom of 13C... 

---