Isotope dilution analysis Isotopic exchange

A more detailed study of the nitration of quinolinium (l) in 80-05 % sulphuric acid at 25 °C, using isotopic dilution analysis, has shown that 3-) 5-) 6-, 7- and 8-nitroquinoline are formed (table 10.3). Combining these results with the kinetic ones, and assuming that no 2- and 4-nitration occurs, gives the partial rate factors listed in table 10.4. Isoquinolinium is 14 times more reactive than quinolinium. The strong deactivation of the 3-position is in accord with an estimated partial rate factor of io for hydrogen isotope exchange at the 3-position in the pyridinium ion. It has been estimated that the reactivity of this ion is at least 10 less than that of the quinolinium ion. Based on this estimate, the partial rate factor for 3-nitration of the pyridinium ion would be less than 5 x io . 

This study presents kinetic data obtained with a microreactor set-up both at atmospheric pressure and at high pressures up to 50 bar as a function of temperature and of the partial pressures from which power-law expressions and apparent activation energies are derived. An additional microreactor set-up equipped with a calibrated mass spectrometer was used for the isotopic exchange reaction (DER) N2 + N2 = 2 N2 and the transient kinetic experiments. The transient experiments comprised the temperature-programmed desorption (TPD) of N2 and H2. Furthermore, the interaction of N2 with Ru surfaces was monitored by means of temperature-programmed adsorption (TPA) using a dilute mixture of N2 in He. The kinetic data set is intended to serve as basis for a detailed microkinetic analysis of NH3 synthesis kinetics [10] following the concepts by Dumesic et al. [11]. 

Elderfield and Greaves [629] have described a method for the mass spectromet-ric isotope dilution analysis of rare earth elements in seawater. In this method, the rare earth elements are concentrated from seawater by coprecipitation with ferric hydroxide and separated from other elements and into groups for analysis by anion exchange [630-635] using mixed solvents. Results for synthetic mixtures and standards show that the method is accurate and precise to 1% and blanks are low (e.g., 1() 12 moles La and 10 14 moles Eu). The method has been applied to the determination of nine rare earth elements in a variety of oceanographic samples. Results for North Atlantic Ocean water below the mixed layer are (in 10 12 mol/kg) 13.0 La, 16.8 Ce, 12.8 Nd, 2.67 Sm, 0.644 Eu, 3.41 Gd, 4.78 Dy, 407 Er, and 3.55 Yb, with enrichment of rare earth elements in deep ocean water by a factor of 2 for the light rare earth elements, and a factor of 1.3 for the heavy rare earth elements. 

NATURAL ABUNDANCE ISOTOPE EXCHANGE KINETICS COMPARTMENTAL ANALYSIS ISOTOPE DILUTION Isotope effects,... 

One must be aware of the possible occurrence of certain problems in isotope dilution analysis. One of these is incomplete isotopic exchange, in which the active and inactive atoms do not mix. This lack of exchange can be due to differing physical and chemical states of tracer and inactive materials. Steps must be taken to ensure complete exchange. One must also be sure that the labeled position in any compound is relatively inert. If the atom in question is very labile, one can get a reduction in specific activity without any dilution having taken place. To compare specific activities, all samples must be counted under identical conditions with proper corrections for self-absorption in samples of varying mass. 

Because interference-free isotopes are most effective for isotope dilution analysis, potential sources of interference may need to be removed before analysis. Separation procedures based on anion exchange [194-197], cation exchange [198], solvent extraction [199], and anodic stripping [200] prior to isotope dilution analysis have been described. 

A method for the accurate online ultratrace analysis of palladium in environmental samples (road dust and contaminated soil samples) by ICP-MS after separation of interferent cations by cation exchange chromatography was introduced by Hann and co-workers. ° Palladium was selectively adsorbed online onto a Cjg microcolumn which had been reversibly loaded with a complexing agent A,Al-diethyl-Al -benzoylthiourea (DEBT). The palladium complex formed was eluted with methanol and introduced into an ICP-SFMS via microconcentric nebulization with membrane desolvation. Isotope dilution analysis was employed for quantification purposes. ... 

Speciation Overview Waters, Sediments, and Soils. Environmental Analysis. Extraction Solid-Phase Extraction. Food and Nutritional Analysis Overview. Geochemistry Soil, Minor Inorganic Components. Ion Exchange Overview. Isotope Dilution Analysis. Liquid Chromatography Overview. Polarography Overview. Sample Handling Sample Preservation. Voltammetry Overview. Water Analysis Industrial Effluents. X-Ray Absorption and Diffraction X-Ray Absorption. 

See also Activation Anaiysis Neutron Activation. Atomic Emission Spectrometry Principies and Instrumentation. Bleaches and Sterilants. Chiroptical Analysis. Chromatography Principles. Conductimetry and Oscillometry. Coulometry. Fire Assay. Food and Nutritional Analysis Overview. Gas Chromatography Principles. Gravimetry. Indicators Redox. Infrared Spectroscopy Overview. Ion Exchange Oven/iew. Isotope Dilution Analysis. Lipids Fatty Acids. Liquid Chromatography Size-Exclusion. Radiochemical... 

Later, Busto et al. used synthesized Fe-labeled transferrin to determine individual transferrin isoforms in human serum samples for the species-specific mode. The stability of the prepared proteins was tested for 1 week and no iron exchange had occurred. They concluded that the results are in good agreement with other calibration methods, e.g. the species-unspecific method however, the species-spedfic mode can offer better precision. Hoppler et al. also synthesized and characterized Fe-labeled Phaseolus vulgaris ferritin for isotope dilution analysis. " ... 

Muniz et al. quantitatively analyzed the metal containing proteins in human serum by anion-exchange chromatography coupled to post-column isotope dilution analysis with double focusing ICP-MS. Parallel analysis of human serum from healthy volunteers and patients on hemodialysis was also undertaken. They found different amounts of iron-containing proteins between healthy and renal disease individuals and indicated that Fe bound to albumin decreased in patients with renal disease. ... 

A logical approach which serves to minimise such uncertainties is the use of a number of distinctly different analytical methods for the determination of each analyte wherein none of the methods would be expected to suffer identical interferences. In this manner, any correspondence observed between the results of different methods implies that a reliable estimate of the true value for the analyte concentration in the sample has been obtained. To this end Sturgeon et al. [21] carried out the analysis of coastal seawater for the above elements using isotope dilution spark source mass spectrometry. GFA-AS, and ICP-ES following trace metal separation-preconcentration (using ion exchange and chelation-solvent extraction), and direct analysis by GFA-AS. These workers discuss analytical advantages inherent in such an approach. 

An isotope dilution mass spectrometric method involves the addition of a known quantity of Tc followed by chemical separation, purification, and measurement of the Tc/ Tc isotopic ratio . An improved technique has been developed for the analysis of Tc in environmental samples. After spiking with Tc the isolated technetium is concentrated onto anion exchange beads. Determination of as little as 1 pg has been achieved through the enhanced ionization efficiency afforded by the resin bead source ... 

Off-line dicarbamate solvent extraction and ICP-MS analysis [317] provided part-per-trillion detection limits Cd (0.2 ppt), Co (0.3 ppt), Cu (3 ppt), Fe (21 ppt), Ni (2 ppt), Pb (0.5 ppt), and Zn (2 ppt). Off-line matrix removal and preconcentration using cellulose-immobilized ethylenediaminetetraacetic acid (EDTA) have also been reported [318]. Transition metals and rare earth elements were preconcentrated and separated from the matrix using on-line ion chromatography with a NTA chelating resin [319]. Isotope-dilution-based concentration measurement has also been used after matrix separation with a Chelex ion-exchange resin [320]. The pH, flow rate, resin volume, elution volume, and time required for isotope equilibration were optimized. A controlled-pore glass immobilized iminodiacetate based automated on-line matrix separation system has also been described [321]. Recoveries for most metals were between 62% and 113%. 

Despite these difficulties the use of the silica gel technique for the solid probe/quadrupole mass spectrometer system holds promise for the analysis of some nutritionally important metals Both zinc and copper have been extracted successfully from serurn and zinc has also been extracted from urine and feces by using an anion exchange purification Biorad A61X8 (100-200 mesh) chloride form) anion exchange resin has been used to separate copper and zinc from acidic solutions (6) We have adapted this method to the separation of these two metals from acidic solutions of AAS standards urine serum and deproteinated fecal homogenate by elution with sucessively dilute acid solutions Recovery of an isotopic spike ai subsequent mass spectral analysis has been demonstrated with a Zn spike added to 1ml aliquots of a Fisher Certified AA Standard (zinc concentration Img/ml) Results of this experiment are shown in Table III ... 

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