An Isotope Ratio Mass Spectrometry-Based Method for Hydrogen Isotopic Analysis in Sub-Microliter Volumes of Water: Application for Multi-Isotope Investigations of Gases Extracted from Fluid Inclusions.

RationaleThe study of multi‐isotope systematics of fluid inclusions is of great importance for understanding of the sources and evolution of fluid phases in mantle rocks and ore deposits. The most appropriate technique for such investigations is a (stepwise) crushing method that is widely used for noble gases and nitrogen. However, because of the possible influence of mechanochemical reactions and back sorption, analyses of the isotope composition of water extracted by crushing from fluid inclusions are challenging.MethodsAn isotope ratio mass spectrometry (IRMS)‐based method for hydrogen (and oxygen) isotopic analysis in sub‐microliter volumes of water extracted from fluid inclusions by crushing is presented. The verification of the possible influence of adsorption processes and mechanochemical reactions on the results of isotope analysis was performed for the first time. For that a series of parallel analyses of hydrogen isotopic ratios from water inclusions in quartz applying physically different extraction methods (crushing and thermodecrepitation) was conducted.ResultsFour series of quartz aliquots were analyzed: three series extracting water by crushing (two series for δ2H values and one for δ18O values) and one by thermodecrepitation. The mean value for the crushing results is δ2H = −85.3 ± 3.6 ‰ (1σ, n = 11), which coincides well with the thermodecrepitation data (−86.3 ± 2.0 ‰, 1σ, n = 5), suggesting that our methodological approach allows the influence of back sorption or mechanochemical reactions during the crushing experiment to be minimized. The reproducibility of the oxygen isotopic ratios is ±0.9 ‰ (1σ, n = 5).ConclusionsThe conducted experiments have shown that the influence of back sorption or mechanochemical reactions during crushing on isotopic results is not crucial for our method. The developed IRMS‐based method for hydrogen (and oxygen) isotopic analysis in sub‐microliter volumes of water is well applicable for multi‐isotope investigations of gases extracted from fluid inclusions. As an application a well‐defined 40Ar/36Ar–δ2H correlation in mantle rocks is presented for the first time.