Lanthanide concentrations

There s it is required to keep unchangeable chemical forms of material components, as well as lanthanide concentration ratio in different degree of oxidation. Therefore, the main conception of this work is to combine process of the sample decomposition and analytical reaction of the determined chemical form. 

An important method for measuring intrinsic shifts consists of measuring the shifts, S, relative to an internal standard like tetramethyl silane [Si(CH3)4] in organic solvents for two nuclei at two different lanthanide concentrations [35]. For two nuclei a and b we have... 

It is best to ran a series of spectra with increasing concentrations of the chiral shift reagent, as demonstrated by the unusual behavior of the orffio-hydrogen resonance of 2-phenyl-2-butanol with Eu(hfc)3. This resonance showed increasing enantiomeric discrimination up to a lanthanide-substrate ratio of about 0.5. At higher lanthanide-substrate ratios the nonequivalence diminished until the resonances recoalesced and then reversed their order in the spectrum. Such behavior likely reflects the dominance of a 2 1 substrate-lanthanide complex at low lanthanide concentration and a 1 1 complex at higher lanthanide concentrations. The chiral discrimination in the 2 1 and 1 1 complexes is markedly different . A similar behavior was observed for 1-phenylethylamine with Eu(dcm)3 . 

In addition to the rather astounding variation of huge lanthanide concentrations over time intervals of decades, HR 465 (RE-max) also shows [36] an enormous amount of tellurium, and, what is of interest in Sect. 4, also large abundances of palladium, osmium, platinum and mercury. The logio(Z/H)- -12 are 6.4 for Pd, above 8.0 for Te, below 3.0 for Ba, 5.3 for Os, 5.8 for Pt and 5.1 for Hg. This corresponds (with the solar values [1] given by Trimble) to overabundances D(Z) = 5.1 for Pd, probably above 6 for Te, below 1.0 for Ba, but 4.5 for Os, 3.7 for Pt and about 3 for Hg. It is perhaps even more impressive to transform the results [36] to weight concentrations in g/t, yielding 200 g palladium, more than 10 kg tellurium, less than 0.1 g barium, 30 g osmium, 90 g platinum, and 15 g mercury. These measurements were related to the r-process... 

Weltje L, Heideneeich H, Zhu W, Wolteebeek HT, Koehammee S, De Goeij JJM and Maekeet B (2002) Lanthanide concentrations in freshwater plants and mollusks, related to those in surface water, pore water and sediment. A case study in The Netherlands. Sci Total Environ 286 191-214. 

Egress of the LLBs from the cells is slow and both the emission spectra recorded in cellulo and the excited state lifetimes for Eu or Tb helicates, as well analysis of the Eu( Dq Fq) transition, prove that the LLBs are essentially undissociated in the intracellular medium. The intracellular concentration of the helicates was determined after incubation of FleLa cells 12 h with 25 /zM of LLB by measuring the lanthanide concentration with the time-resolved Delfia method. It was found to be surprisingly high under the loading conditions used, there is, on average, 8.8 x 10 mol [Eu2(L13 )3] per cell, which, taking into accoimt an estimated cell volume between 2600 and 4200 /zm, translates into 0.21-0.34 mM... 

Some authors have used precipitation techniques to concentrate the lanthanides. The most commonly used species are oxalates and fluoride. Rare-earth oxalates (R2(C204)3) have solubility products ranging from 10 to 10 M. Isolation of lanthanide cations as oxalate precipitates is often followed by ignition to the oxide, then acid dissolution of R2O3. This procedure can be expected to provide samples suitable for almost any type of detection/quantitation method. The solubility products of the fluorides (RF3) are found in the range of 10 to 10 NT. Whether precipitation techniques can be applied is partly determined by the concentration of rare-earth ions in the sample, and whether a carrier precipitation is acceptable for those samples in which the lanthanide concentration is too low. The detection method most directly impacts the viability of carrier precipitation techniques. 

By comparison with natural samples, lanthanide-bearing species from manufactured sources are typically much simpler analytical targets. The samples are often more readily dissolved and, because many of them are rare-earth-based materials, preconcentration steps can sometimes be eliminated. Recent reports have apphed analytical separation methods to determine lanthanide concentrations in metals (Kobayashi et al. 1992), alloys (Al-Shawi and Dahl 1996), and magnets (Saraswati 1993), in high-purity rare-earth oxides (Stijfhoom et al. 1993, Yin et al. 1998, W. Li et al. 1997, 1998, Wu et al. 1997, Peng et al. 1997), and in optical materials (Bruzzoniti et al. 1996). 

As to the need for development of new separation-based analytical techniques for lanthanide analysis, the present array of chromatographic methods has in some cases achieved impressive success in both resolution and sensitivity. Many chromatographic techniques can be used for a complete analysis for lanthanide content in less than 30 minutes, not including the time required for sample dissolution and preconcen-tration/preconditioning. There does not appear to be much demand for a more rapid analytical method, as the aforementioned sample dissolution/preconcentration steps will be rate limiting for analysis of most samples. For a hypodietical system in which on-line monitoring of lanthanide concentrations would be required, separation techniques of any type would ultimately not prove suitable. 

Three geometric iosmers, trans-trans, trans-cis, and cis-cis, are present in 2,4-hexadiene monomer. Only the trans-trans isomer of 2,4-hexadiene was polymerized with lanthanide catalysts as shown in Table 2. The rate of pol3nnerizatlon of 2,4-hexadiene was much slower than that of butadiene and isoprene. High levels of lanthanide concentration, with Al/Nd molar ratio around 30-40 or higher, and prolonged pol3rmerization time appeared to be necessary to have good conversion. 

Effects of external magnetic fields 346 7.2.1. Lanthanide concentration ... 

Fig. 15, The Curie temperatures of Y-T and Gd-T as a function of lanthanide concentration. In addition, the ordering temperatures of the y-Fe, hcp-Co and fcc-Ni are shown.

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