Analytical Experience

final-fig-3a

Laser Fluorination line  attached to a MAT 253 Isotope Ratio Mass Spectrometer. Oxygen Isotope Laboratory at the Open University.

As a Research Fellow at the Open University I undertake high precision oxygen isotope analysis by laser-assisted fluorination.  This work involves both routine instrument maintenance and calibration, as well as longer term development responsibilities. In particular, we are currently modifying our fluorination line to significantly reduce the amount of sample required for each analysis, i.e. down to about 0.1 mg compared to the current norm of 1 to 2 mg.

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Open University laser fluorination system. The sample chamber and infrared laser are housed within the laser safety box. Inset: Two-part chamber with the upper half incorporating a BaF2 window for simultaneous viewing and laser-heating of samples. The two halves of the chamber (lower half not visible) are kept vacuum tight by a compression seal involving an internal copper gasket and external quick-release KFX clamp. Samples are loaded in a removable Ni block with drilled wells (14 are present in the example shown above).

Laser fluorination relies on the safe handling and disposal of BrF5. In order to undertake these procedures we designed and built a new preparation and waste disposal line. BrF5 is potentially the most dangerous reagent used in geochemical analysis. I am currently the person responsible for the preparation and disposal of this substance.

new-brf5-disposal

BrF5 preparation and disposal line. This line is used to prepare small batches of BrF5 before they are put on the main fluorination line. It is also used to safely dispose of the waste reactants following analysis.

All trouble-shooting, maintenance and cleaning of the isotope ratio mass spectrometers used for oxygen isotope analysis (MAT 253) are done in-house. As a result of the experienced gained over the last fifteen years I have gained an excellent practical understanding of isotope-ratio mass spectrometry.

A major issue with the analysis of meteoritic finds is the often high level of terrestrial contamination. To mitigate this problem we use a technique involving leaching in ethanolamine thioglycollate (EATG). Tests have demonstrated that this procedure is efficient at removing Fe-rich alteration products, without significantly shifting the primary oxygen isotope composition of the samples. We have been able to demonstrate that EATG treatment is preferable to conventional leaching in dilute HCl, as this latter method can partially remove indigenous glass and feldspathic-rich material. This technique has been used to determine the levels of primary heterogeneity in weathered primitive achondrites (Greenwood et al., 2012. GCA 94, 146-163).

As a Project Officer in the Department of Earth Sciences, University of Cambridge, I was responsible for the day-to-day operation and calibration of both wavelength dispersive and energy dispersive electron microprobes. I also had responsibility for the training and supervision of both external and internal users. As a Research Fellow at the Natural History Museum in London I undertook detailed studies of extraterrestrial materials using a wide range of analytical SEMs and electron microprobes. I also carried out Mg isotope studies of CAIs in various meteorites using the Edinburgh and Cambridge secondary ion microprobes.

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