A simple cryogenic method for efficient analysis of triple oxygen isotopes in silicates

Area of Science:

• Geochemistry
• Isotope Geochemistry
• Analytical Chemistry

Background:

• Oxygen isotope ratios (¹⁷O/¹⁶O and ¹⁸O/¹⁶O) in silicates are crucial for reconstructing paleotemperatures and fluid compositions.
• Measuring the low-abundance ¹⁷O isotope is analytically challenging, limiting its widespread application in paleoclimate studies.

Purpose of the Study:

• To develop and report a simplified, high-precision analytical technique for simultaneously measuring ¹⁷O/¹⁶O and ¹⁸O/¹⁶O ratios in silicate samples.
• To enable more accurate and accessible paleotemperature and paleofluid composition reconstructions.

Main Methods:

• Silicate samples were ablated using a CO₂ laser in a bromine pentafluoride (BrF₅) environment.
• Released oxygen (O₂) was cryogenically trapped and purified using molecular sieve zeolite (MSZ) and NaCl traps to remove contaminants like BrF₅ and nitrogen trifluoride (NF₃).
• Purified O₂ was analyzed for isotope ratios using a MAT 253 isotope ratio mass spectrometer.

Main Results:

• The developed technique achieved high analytical precisions: 0.04‰ for δ¹⁷O, 0.08‰ for δ¹⁸O, and 4 per meg for Δ'¹⁷O.
• Calibration and cross-checking with international (NBS-28, UWG-2, SCO, IMAU-O₂) and internal standards confirmed the accuracy of the measurements.
• The method effectively removes NF₃ contaminants without requiring gas chromatography (GC).

Conclusions:

• A novel, simple, quick, and cost-effective cryogenic cleaning technique was successfully developed for oxygen isotope analysis in silicates.
• This method provides highly precise and accurate δ¹⁷O, δ¹⁸O, and Δ'¹⁷O values, making it suitable for routine paleoclimate research.
• The technique overcomes previous limitations in measuring ¹⁷O/¹⁶O, enhancing the utility of oxygen isotopes in Earth science studies.