Rationale: The stable carbon isotope compositions of dissolved inorganic carbon (δ13CDIC) and dissolved organic carbon (δ13CDOC) are readily affected by post-sampling microbial activity if not adequately preserved. Existing preservation methods require rapid chilling, analysis, and/or toxic chemicals, all challenging to use safely in the field and during remote field seasons. Therefore, a preservation method that is safe but also effective over a range of storage times is needed when sampling waters at very remote sites. Methods: Two samples, with different dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) concentrations, were filtered with a 0.2-μm filter and preserved with six different methods, mercuric chloride, copper sulfate, phosphoric acid, benzalkonium chloride, zinc chloride, hydrochloric acid, and a filter-only control. These samples were held at 4°C, 22°C, or 35°C. Regular measurement of the DIC and DOC δ13C values were made over the following 60 days for δ13CDIC and 66 days for δ13CDOC. Results: Over the course of the experiment, mercuric chloride, copper sulfate, zinc chloride, and benzalkonium chloride resulted in δ13CDIC fractionation at both 4°C and 22°C. Only filtering to 0.2 μm at the time of collection, with or without acidification with phosphoric acid, resulted in minimal isotopic fractionation at both 4°C and 22°C and over the entirety of the experiment. For δ13CDOC values, only filtering to 0.2 μm minimized fractionation for both bulk and vial storage over 66 days at 22°C. Conclusions: Filtering to 0.2 μm at the time of collection is more effective than the use of toxic chemicals for measuring δ13CDIC and δ13CDOC values. Phosphoric acid is as effective as only filtering for δ13CDIC and may be ideal depending on sampling considerations. These results demonstrate not only that water samples can be preserved for δ13CDIC and δ13CDOC analysis for long periods, but that preservation is best accomplished with non-toxic or low-toxicity methods.
|Journal||Rapid Communications in Mass Spectrometry|
|State||Published - Nov 15 2020|
Bibliographical noteFunding Information:
The authors would like to thank Aviv Brokman at the University of Kentucky Applied Statistics Laboratory for assistance with the statistical analysis. Funding for this project was provided by the Department of Earth and Environmental Sciences and the College of Arts and Sciences to A.E. Constructive feedback from the journal editor, along with D. Doctor and two anonymous reviewers, greatly improved this manuscript.
© 2020 John Wiley & Sons, Ltd.
ASJC Scopus subject areas
- Analytical Chemistry
- Organic Chemistry