A laser-based microanalytical method for the in situ determination of oxygen isotope ratios of silicates and oxides

Journal Article · Tue May 01 04:00:00 EDT 1990 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(90)90160-M· OSTI ID:6206960

Sharp, Z D ^[1]

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1. Geophysical Laboratory, Washington, DC (USA)

A new laser-based microanalytical method for oxygen isotope determinations of silicates and oxides has been developed whereby analyses are made on <100 {mu}g samples or of in situ spot determinations of <300 {mu}m in diameter. This new method differs from the conventional fluorination technique in that samples are heated directly by a laser, much lower blanks are achieved, and far smaller amounts of material can be analyzed. The intense and focused heat source allows for in situ analyses to be made on even the most refractory minerals. Sample separates are placed on a nickel sample holder in a 304-stainless steel sample chamber and are heated with a 20W CO{sub 2} laser. The infrared laser radiation is admitted through a BaF{sub 2} window, a material that is transparent to both infrared and visible radiation, and does not react with fluorine. Either BrF{sub 5} or ClF{sub 3} is used as the fluorinating agent. The released oxygen is passed successively over a cold trap and through a hot mercury fluorine-getter, and is converted to CO{sub 2} by reaction with hot carbon in the presence of a Pt-catalyst. Up to 19 samples can be loaded and degassed simultaneously with the current design, and reaction times for each sample are generally less than 2 min. The precision and accuracy ({plus minus}0.1{per thousand}) is equal to the conventional fluorination method. Replicate in situ spot-analyses were made of quartz and magnetite on a polished thick section and of olivine on a single large olivine crystal. Analyses yielding from <1-4 {mu}moles of CO{sub 2} gave the expected {delta}{sup 18}O value within 0.5{per thousand}.

• OSTI ID: 6206960
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 54:5; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ACCURACY
ALKALINE EARTH METAL COMPOUNDS
CHALCOGENIDES
CHEMICAL ANALYSIS
CHEMISTRY
EMISSION SPECTROSCOPY
FLUORESCENCE SPECTROSCOPY
GEOCHEMISTRY
IRON COMPOUNDS
IRON ORES
IRON OXIDES
IRON SILICATES
ISOTOPE RATIO
ISOTOPES
LASERS
MAGNESIUM COMPOUNDS
MAGNESIUM SILICATES
MAGNETITE
MICROANALYSIS
MINERALS
OLIVINE
ORES
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
PERFORMANCE TESTING
QUANTITATIVE CHEMICAL ANALYSIS
QUARTZ
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SILICON OXIDES
SPECTROSCOPY
TESTING
TRANSITION ELEMENT COMPOUNDS