124 D64. Advances in Stable Isotope Geochemistry–Applications to Earth Science Systems

Monday, 5 November 2018
1:30 PM - 5:30 PM
Room 135

A NEW METHOD OF ISOTOPIC ANALYSIS OF PERCHLORATE USING ELECTROSPRAY-ORBITRAP MASS SPECTROMETRY

Paper number: 124-12
Program: Technical Sessions
Time: 4:15 PM – 4:30 PM

Authors

Abstract

Perchlorate is a well-documented groundwater, drinking water, and food contaminant with numerous sources including industrial and military use in rocketry, airbags and explosives, import of Chilean saltpeter fertilizers, and a natural background source that appears to be pervasive across the Earth. As concerns pertaining to perchlorate contamination have grown over the past two decades, so too have attempts to conclusively identify the source(s) of perchlorate, especially via isotopic fingerprinting by tracing the perchlorate’s δ37Cl, δ18O, δ17O, and Δ17O signatures. These techniques require extensive and complex perchlorate purification to avoid interferences from other chlorine-bearing compounds, followed by pyrolysis for isotopic measurements on O2, and subsequent conversion of the resulting chloride salts to methylchloride for chlorine isotope analysis.

Here we report a new method of rapidly measuring the isotopic fingerprint of unfragmented perchlorate ion (ClO4-) at high precision using electrospray orbitrap mass spectrometry (±1‰ δ37ClSMOC is achieved in ~3 min; ±0.1‰ in ~30 min). This method allows the isotopes of perchlorate to be measured with minimal sample preparation and at high resolution, allowing assessment of the previously mentioned isotope signatures (δ37Cl, δ18O, δ17O, and Δ17O), and adds the ability to measure clumped 37Cl18O16O3. With further work, the technique would also likely be amenable to clumped 37Cl17O16O3 measurements. This technique allows measurement of perchlorate samples with minimal sample preparation and low concentrations of <0.1 ppm ClO4- (potentially lower; work is ongoing). The high resolution of the analysis permits multiple dimensions of isotope fingerprinting to be explored, while preventing any isobaric interference. This technique shows promise as a method of rapidly and conclusively demonstrating the source of any given perchlorate sample, and has the potential to yield new insights to the formation processes of perchlorate on Earth and elsewhere through analysis of its isotopic systematics.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-324166

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