SIM technique

SIMS techniques have occupied somewhat of a narrower niche in uranium-series analysis, but have significantly improved Th isotope analysis relative to TIMS for chemically separated samples. The major improvement relative to TIMS is an improvement by about an order of magnitude in efficiency or sample size requirements for silicates. For uranium and/or thorium rich minerals such as carbonates and zircons, both SIMS and laser-ablation MC-ICPMS have been used for the direct in situ analysis of U and Th isotopes (Reid et al. 1997 Stirling et al. 2000) on very small (pg to ng levels of total U and Th) samples, at 10-100 pm scale resolution. 

Mass spectrometric techniques for analysis of Th- U disequilibria were first developed to date corals for paleoclimate research (Edwards et al. 1987). Soon thereafter, workers at Los Alamos National Laboratory (LANE) developed methods for silicate analysis by TIMS (Goldstein et al. 1989). Typical TIMS analysis of MORE requires 0.5 to 1 gram of material in order have an analyzable load of 100 ng of Th. TIMS analyses of U and Th last 2-3 hrs and produce a precision of 0.5-2% (2a). SIMS techniques for measuring Th isotopes have also been developed (England et al. 1992 Layne and Sims 2000). Analysis of Ra and Pa isotopes by TIMS was developed in the early 1990 s significantly increasing the sensitivity over decay counting analysis (Volpe et al. 1993 Cohen and Onions 1993 Pickett et al. 1994 Chabaux et al. 1994). 

Figure 4.2 is a block diagram that illustrates the principle of the SIMS technique. The apparatus includes a primary ion source, a vacuum chamber where the objects under study are placed, a mass analyser and a secondary ion detector. 

Oxygen Diffusion Coefficient (D ), Oxygen Surface Exchange Coefficient (Ar), and Oxygen Ionic Conductivity (tr,) of LaMn03-Based Oxides Measured by SIMS Technique... 

Time of flight (TOF), 75 660-661 Time-of-flight (ToF) mass analyzers, 24 109 Time of flight diffraction (TOFD), 79 486 Time-of-flight instrumentation, in particle counting, 78 150—151 Time-of-flight-SIMS technique, 24 109 Time-resolved fluorimetry, 74 148-149 Time-resolved spectra, analysis of, 74 613 Time standards, 75 749—750 Time-temperature parameters (TTP), 73 471, 478, 479 creep properties and, 73 480 Time-temperature superposition, 27 746-747... 

Figure 7. A few examples of isotopic patterns of Ne, Ti and heavy elements in SiC and graphite grains are displayed. Absolute ratios are plotted for Ne (a) whereas abundance ratios relative to solar wind composition are plotted for Kr (c) and Xe (f). The remaining elements are plotted as %o deviations from laboratory standards. The data have been obtained on bulk SiC separates by traditional mass spectrometry for Ne (Jungck and Eberhardt 1979), Kr (Ott et al. 1988 Lewis et al. 1994), Sr, Ba (Ott and Begemann 1990 Prombo et al. 1993) and Nd (Richter 1995). SIMS techniques (caption continued on facing page)...

Charles E. Kolb, vice chair of the committee, memorandum to the committee on new technology to detect chemical agent and agent breakdown products on surfaces (with five enclosures on use of SIMS technique) dated March 22, 2000. 

Nitrogen physisorption measurements indicate large internal surface area of 402 m /g and quite narrow distribution of pore sizes with peak maximum at 3.1 nm (Fig. 7). The framework wall thickness was estimated to be 1.9 nm. The oxidation state of Ge framework as probed with X-ray photoelectron spectroscopy (XPS) and time-of-fiight secondary ion mass spectroscopy (ToF-SIMS) techniques is close to zero. 

The Mn- Cr system can be studied by TIMS, ICPMS, and SIMS techniques. For TIMS and ICPMS work, bulk samples or mineral separates are dissolved and the solutions are passed through ion-exchange columns to produce clean solutions of manganese and chromium. For minerals with high Mn/Cr ratios SIMS can obtain isotopic data while retaining the petrographic context of the measurements. The chromium isotopic compositions may have to be corrected for small additions of chromium from spallation reactions induced by cosmic rays. This is particularly important in iron-rich meteorites. 

For static SIMS, the time-of-flight SIMS (TOF-SIMS) technique is most suitable. For TOF-SIMS, a pulsed primary ion beam is used. The secondary ions emitted from the surface after one pulse, are accelerated by an electrical potential U. These ions gain the velocity v that depends on the mass m and charge Q of the ion according to ... 

Nearly all modifications that have been detected on the model level (Chap. 10) are also found in free-radical damaged DNA. Obviously the DNA-bound lesions are much more difficult to detect, and there is an ongoing discussion as to the best procedure of their excision (Chap. 13.2 for a review on the excision and repair of base lesions in vivo see Wallace, 2002). Mechanistic details concerning the formation of the base lesions have been discussed in Chapters 10 and 11, and only some additional information will be given below and in the section on clustered lesions where the phenomenon of tandem lesions, two damaged bases that are formed side by side, is dealt with. The yields of damaged bases formed upon y-irradiation in aqueous solution, as has been determined by the GC-MS/SIM technique, are compiled in Table 12.5. 

Table 12.5. Compilation of products and their G values (unit 10 9 mol J"1) in the radiolysis of ss- and dsDNA in aqueous solution as determined by the GC-MS/SIM technique (Fuci-...

The recent use of liquid matrices in SIMS has led to several significant accomplishments, particularly for the analysis of biomolecules by FAB mass spectrometry [101]. In the FAB/liquid SIMS technique, the analyte is dissolved in a liquid matrix, such as glycerol, at some optimum concentration in order to provide a surface which, during particle bombardment, is constantly replenished with sample molecules that diffuse from the bulk to the surface. The mobility of the sample molecules in the liquid matrix is an important property of this type of matrix. 

Steroids such as progesterone, testosterone, and cortisone have been derivatized and analyzed with this method. Cortisone was chosen to demonstrate the enhanced sensitivity obtained with the derivatization/SIMS technique. The SIMS results for underivatized and derivatized cortisone are presented in Figure 10. The ions that are observed from cortisone include the molecular ion [M + H]+ (m/z 361), the silver cationized ion [M + Ag]+ (m/z 467 and 469), and the fragment ion at m/z 407 and 409 corresponding to the loss of the OCHCH2OH group. 

The single most unique characteristic of the SIMS technique is its sensitivity. It can be as good as one part per billion (ppb). For example, if silicon is sputtered at a rate of 10 A/sec over an area of 100-pm x 100-/zm, then 10"u cm3/sec of material is removed. Given the density of silicon, this reduces to approximately 5 x 1011 atoms/sec. If 1% of these atoms are ionized (by charge transfer with the surface) and 10% of those ionized are collected in the mass spectrometer, then the measured ion intensity will be 5 x 10s ions/sec. If we assume we can distinguish 5 ions/sec, then a detection sensitivity of 1 part in 108 is achievable. This sensitivity is many orders of magnitude better than other techniques. 

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