Isotope online separations

Some isotopes of element 111 should have half-lives of seconds or more. Promising production reactions need to be investigated first using an online separator and detection system to measure half-lives and production cross sections before chemical studies can be contemplated. 

Isobaric interferences (especially those arising from the plasma itself, e.g., ArO+ on Fe) can be eliminated using cool-plasma conditions, sometimes in combination with a shield torch. This option is not suitable for seawater samples because a cool plasma, in the presence of a heavy matrix, cannot fully ionize elements with high first ionization potentials, notably Zn, Cd, and Hg. Protocols have thus been established for analysis of 10-fold diluted seawater on instalments with sufficiently high resolution to separate most of the affected isotopes from their isobaric interferences [1], To circumvent the issue entirely, others have used online chemical extraction to separate analytes of interest... 

For reproducible expression analysis and protein quantification MS methods based on isotopic labeling are available. They were designed in conjunction with two or more dimensional chromatographic peptide separation coupled online to MS and require advanced bioinformatics input to analyze the complex data sets in a reasonable time frame. This is also true for the alternative fluorescence-based technology of differential gel electrophoresis (DIGE Fig. 10.6) with tailor-made software which allows statistical validation of multiple data sets. 

Prior to about 1955 much of the nuclear information was obtained from application of atomic physics. The nuclear spin, nuclear magnetic and electric moments and changes in mean-squared charge radii are derived from measurement of the atomic hyperfine structure (hfs) and Isotope Shift (IS) and are obtained in a nuclear model independent way. With the development of the tunable dye laser and its use with the online isotope separator this field has been rejuvenated. The scheme of collinear laser/fast-beam spectroscopy [KAU76] promised to be useful for a wide variety of elements, thus UNISOR began in 1980 to develop this type of facility. The present paper describes some of the first results from the UNISOR laser facility. 

Fig. 1. Schematic of the laser system online to UNISOR isotope separator.

The data recorded as the laser frequency is scanned consists of the fluorscence signal from the PMT, a Doppler-free I2 spectrum and frequency markers from the etalon. The etalon provides a calibration of the frequency scan. The Doppler-free I2 spectra provides an absolute frequency reference used to correct for small laser frequency drifts, separator voltage drifts and to determine the absolute acceleration voltage of the separator for the Doppler shift corrections. We are thus able to record data over long periods of time, e.g. 3 hours, and maintain a reasonable resolution of 100 MHz. Some of the first online data recorded with this system is shown in Figure 2. The overall detection efficiency has been measured to be 1/1000, i.e. one detected photon per 1000 atoms, for the largest transition in the nuclear spin 1/2 isotopes. 

Studies of 0/ 0 isotope variations in several vascular plant species, mosses and environmental surface bog water from temperate peat bogs (Switzerland) used as climatic archives for paleoclimatic reconstruction were reported by Menot-Combes et 8 0-values in organic material were determined by the online continuous flow method after sample pyrolysis at 1080 °C in the presence of glassy carbon in a Carlo-Erba elemental analyzer. The gases obtained (CO, N2 and H2O) were separated by passing them through a water trap and a GC column in a helium carrier gas. The isotope composition of CO was measured with a VG Prism II isotope ratio mass spectrometer relative to the VSMOW isotope standard. The overall analytical uncertainty is 0.08%o for water 8 0-values." ... 

Furthermore, online chromatographic coupling techniques such as HPLC and CE coupled to ICP-MS with the isotope dilution technique have been used for element quantification in specia-tion analysis. Species analysis by ICP-SFMS in medical research has been performed by Prange et a/. on separated isoforms of metallothionein (e.g., of rabbit liver) by capillary electrophoresis (CE). For quantitative determination of S, Cd, Cu and Zn in isoforms, highly enriched " S, Cu, Zn and Cd spikes are added to the analyte solution in the interface region of CE. 

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. ... 

Recent advances in isotope analysis include the ability to analyse isotopically smaller proportions of individual compounds by the use of more sensitive online isotope ratio mass spectrometers (cf. Merritt Hayes 1994 Merritt et al. 1994) and stable carbon isotope determination of individual n-alkanes, isoprenoids and biomarkers in petroleums is now a standard tool. Despite early work on collection of chromato-graphically separated individual n-alkanes followed by combustion and isotope determination (Welte 1969) it was for a number of years impossible to analyse isotopically long chained alkanes with the same comfort and ease as the... 

Both on-column and post-column detection schemes have been developed for radionuclide detection for CE. The most common type used is an on-column configuration, which yields detection limits in the 10 M range for isotopes such as P. Isotachophoretic separations of C were among the first examples of online capillary radionuclide detection, performed by Kaniansky et al. The associated instmment uses 300-p,m ID fluorinated ethylene-propylene copolymer capillary tubing, and the separation eluent flows directly into a plastic scintillator cell between two PMTs. The scintillation events are detected coincidentally between the two PMTs, such that only if both PMTs receive an input within a short time will they register the count as signal. This kind of coincidence detection ensures that nonscintillation photons that come from outside the detection cell and only hit one PMT are not counted. This system exhibits a detection limit of 16 Bq for analytes, with a detector efficiency of 13-15%. 

The isotopic richness of elements present in most coordination complexes means that the use of a simulation program (if not included with the mass spectrometry software, available separately or online (e.g., the Chemputer at http //www.shef.ac.uk/chemistry/chemputer/ isotopes.html)) is important in ion assignment. Accurate mass determination ( 0.0001 mjz) is less commonly employed due to the high likelihood of ambiguity in the ion composition at high mass. 

To search for new transuranium nuclides and to study decay properties of these nuclei, a composite system consisting of the gas-jet transport apparatus and an online isotope separator (JAEA-ISOL) has been developed by Ichikawa et al. (2002). This system enables one to simultaneously determine the mass number via the isotope separator and the atomic number by the measurement of X-rays associated with the EC/P" decay of a nucleus. The experimental setup is schematically drawn in O Fig. 18.9. 

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