Saxton J.M.,Nu Instruments Ltd.
Most noble gas analyses are made in static mode when instrument volume is minimized to maintain adequate sensitivity. This makes the building of large instruments to obtain high resolving power impracticable. A method is presented which makes improved use of the available resolving power to remove isobaric interferences, which may be used on multicollector instruments. By arranging that the target mass position on a minor isotope (e.g. 36Ar), from which the interference must be removed, coincides with the approximately 50% point on the side of a major isotope (e.g. 40Ar), it is possible both to set the mass accurately and to verify the mass position and stability during measurements. The peak top of the major isotope is measured in a separate mass step. Calibration measurements are necessary, using different relative amounts of target/interference, to assess residual tailing to the measurement position and also the relative efficiency at the extreme edge of the target peak. The method is demonstrated by using it to obtain 36Ar measurements free of H35Cl. With samples containing 4×10-15 to 3×10-14mol of 40Ar, 36Ar/40Ar was measured, without HCl interference, to a 1σ precision of 0.5%, only slightly worse than counting statistics. This is potentially useful for 40Ar/39Ar dating, where 36Ar is used to correct for trapped air, and may be particularly significant for smaller or younger samples. © 2015 Elsevier B.V. Source
He H.,CAS Institute of Geology and Geophysics |
Zhu R.,CAS Institute of Geology and Geophysics |
Saxton J.,Nu Instruments Ltd.
Physics of the Earth and Planetary Interiors
Noble gas isotopic ratios provide unique and important constraints for the evolution of the subcontinental mantle. We present one-step crushing noble gas isotope data from corundum and co-existing mantle xenoliths and megacrystals from the Changle volcanic fields in the middle part of the Tan-Lu Fault Zone, eastern North China Craton. The 3He/4He ratio is 7.6-8.3 times the atmospheric ratio (Ra) in corundum, indicating contributions of fluids from convective asthenosphere. The 3He/4He ratio in titanomagnetite megacrystals ranges from 5.8 to 6.5Ra, suggesting possible U-Th contamination in the crystal lattice, with the 3He/4He ratio of host magma being higher than 6.5Ra. The olivine and opx in lherzolite show high helium contents and homogeneous isotopic helium ratios (6.9-7.0Ra). The cpx in wehrlite show significantly higher helium contents and slightly higher helium ratio (7.6Ra) than co-existing olivine (7.0-7.5Ra). Combined with isotope correlation diagrams, the systematic difference in 4He abundance, the 3He/4He and 4He/40Ar* ratios of cpx, opx and olivine in pyroxenite, lherzolite and wehrlite suggest comprehensive refertilization of lithospheric mantle in the eastern North China Craton. © 2011 Elsevier B.V. Source
Nu Instruments Ltd | Date: 2010-02-03
An approach to extending the dynamic range of the detector of a mass spectrometer is described. In one embodiment, in the case of high intensity beams, means are provided to deflect the ion beam, after the collector slit (
Nu Instruments Ltd | Date: 2007-07-03
Mass spectrometers; apparatus for introducing samples into mass spectrometers; computer application software for controlling mass spectrometer apparatus and for analysing spectrometric results; and replacement parts, fittings and consumables for the aforesaid goods, namely sampler and skimmers cones, graphite gaskets, pneumatic nebulisers, spray chambers, ICP torches, quartz and glass connectors, ion counting detectors, adjustable slits, plasma shields, PVC peristaltic pump tubing, PTFE tubing, all being component parts of mass spectrometers.
Young E.D.,University of California at Los Angeles |
Rumble D.,Geophysical Laboratory |
Freedman P.,Nu Instruments Ltd. |
Mills M.,Nu Instruments Ltd.
International Journal of Mass Spectrometry
We describe a unique and novel isotope ratio mass spectrometer (IRMS), the Panorama, developed explicitly for high-mass-resolution analysis of isotopologue ratios of gas samples. The double-focussing instrument routinely operates at a mass resolving power of 40,000 with a maximum useful MRP of ∼80,000. The instrument achieves this exceptional MRP for a multi-collector using a Matsuda ion optical design with an ESA radius of 1018mm and a magnetic sector radius of 800mm. Collectors comprise 9 Faraday cups and a single channel of ion counting each with continuously variable collector slits. First results demonstrate both accuracy and precision comparable to, and in some cases, surpassing, other gas-source multi-collector IRMS instruments for singly-substituted species. For example, accurate bulk D/H and 13C/12C for methane gas measured with CH4 as the analyte are measured simultaneously with internal precision of 0.02-0.04‰ (1 std error) and ∼0.006‰ (1 se), respectively. Ion counting with continuous rebalancing of sample and standard gases permits high-precision measurements of rare, multiply-substituted isotopologues with relative abundances as small as ∼0.1ppm. In the case of methane, both 13CH3D/12CH4 and 12CH2D2/12CH4 ratios are measured with precision of ∼0.1‰ and ∼0.5‰, respectively. Accuracy of the multiply-substituted species measurements is demonstrated using isotope ratio mixing experiments. The ability to measure both δ13CH3D and δCH2D2 (‰ variations relative to the stochastic reference frame) provides heretofore unmatched capabilities to identify kinetic reaction pathways, isotope fractionation during transport, mixing, as well as temperatures of formation for methane gas. The high-resolution instrument can be used for a wide variety of applications. For example, it easily resolves 36Ar+ from 18O18O+ for oxygen bond-ordering studies. It also easily resolves 14N16O+ from 15N15N+ for measurements of the doubly-substituted N2 species. © 2016 Elsevier B.V. Source