A simple CO₂ equilibration method for measuring blood oxygen isotope compositions.

Area of Science:

• Stable isotope geochemistry
• Biogeochemistry
• Physiological ecology

Background:

• Blood water oxygen isotope composition (δ¹⁸O) offers insights into physiology and ecology.
• Measuring blood δ¹⁸O is typically time-consuming and costly, limiting its application.

Purpose of the Study:

• To develop a rapid, reliable, and accurate method for measuring blood water oxygen isotope compositions.
• To assess the feasibility of using a blood-CO₂ equilibration technique with GasBench and isotope ratio mass spectrometry (IRMS).

Main Methods:

• Blood samples from sheep, goats, and iguanas were fractionated into plasma, serum, and red blood cells (RBCs).
• Samples were analyzed for δ¹⁸O using CO₂ equilibration with a GasBench II system and IRMS.
• The method involved natural CO₂ outgassing or CO₂-spiked equilibration depending on the sample.

Main Results:

• The blood CO₂ equilibration method demonstrated stability over multiple days.
• Organic components in blood fractions did not significantly interfere with δ¹⁸O measurements.
• Slight, statistically significant δ¹⁸O offsets were observed between plasma, serum, and RBC fractions.

Conclusions:

• A simple blood-CO₂ equilibration method provides quick, reliable, and accurate water δ¹⁸O measurements in mammalian and reptilian blood fractions (precision ≤ 0.1‰).
• This technique enhances the application of blood stable isotope analysis in physiological and medical research.