Tungsten isotope ratio determinations by negative thermal ionization mass spectrometry (CAT#: STEM-ST-0203-LJX)

Introduction

A precise determination of the isotopic abundances of tungsten with natural isotopic composition is presented. WO−3 ions are generated by negative thermal ionization (NTI) in a double-filament ion source. La2O3 is used as a chemical substance to reduce the electron work function of the rhenium filament material. An ionization efficiency of 1% is obtained for sample loadings of 100 ng. The isotopic abundances are measured with relative standard deviations of 0.2% for the least abundant 180W isotope and 0.02–0.004% for the other tungsten isotopes. These improved isotopic data are used to recalculate the atomic weight of tungsten as 183.8417 ± 0.0001. The new NTI technique is an ideal tool for the application of isotope dilution mass spectrometry to analyse tungsten traces and for the measurement of isotopic shifts of this element in meteorites produced by the decay of 182Hf.

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Principle Applications Procedure Materials Notes Related Products

Principle

Thermal ionization mass spectrometry exploits the thermochemical reactions that occur in molecules in a sample when they are irradiated by a beam of high energy electrons. This reaction usually takes place at high temperatures, resulting in the formation of ions. The ionized species are accelerated in an electric field and then analyzed by mass spectrometry through the ion-focusing lens of a mass spectrometer. The mass spectrometer will separate and detect the ions according to their mass and charge.

Applications

For analyzing the distribution of molecules, atoms and molecular groups.
For studying the chemical structure of Earth's minerals and rocks.
For studying the structure and function of biomolecules.
For studying problems in physics.

Procedure

1. The sampling system sends the sample to be analyzed into the ion source;
2. The ion source ionizes the atoms and molecules in the sample into ions;
3. The mass analyzer separates ions according to the size of the mass-charge ratio;
4. The detector is used to measure and record the intensity of the ion current to obtain the mass spectrum.

Materials

• Sample Type:
Tungsten

Notes

Before starting the machine, check whether the water (water cooler), electricity, gas (argon/nitrogen), temperature, humidity, and exhaust air of the instrument are normal.

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