Welcome to the first edition of the Picarro Spotlight on Research that Matters—a new series showcasing important scientific work from Picarro customers around the world. Each feature will be selected by our team and will feature their thoughts on the innovative research, real-world applications, and the impact precise measurements can have on our understanding of critical environmental challenges. This month, Field Application Scientist, Russell Chedgy, PhD, summarizes a paper that showcases how the Picarro L2140-i water isotope analysis system is pivotal in improving our understanding of the roles of isotopes in animal physiology research.

In the paper, Validating a Novel Capability of Assessing Pathways of Animal Water Gain and Loss, Zachary Steele and team at Old Dominion University describe a novel approach to measure δ¹⁷O and δ¹⁸O in a single sample as a natural tracer of water flux that can be used to calculate the Δ¹⁷O of animal body water (Δ¹⁷O_BW). The Δ¹⁷O_BW values are a useful indicator of an animal's water balance and metabolic processes, providing insights into how wild animals gain and lose water.

In the study, oxygen influxes and effluxes were continuously measured in deer mice (Peromyscus maniculatus) while manipulating their water intake and metabolic rate. This oxygen flux data was then used to create a predictive model for the Δ¹⁷O_BW for the mice. These estimated values were then compared to actual Δ¹⁷O_BW values measured from blood plasma samples.

For isotopic analysis, water was cryogenically distilled from plasma (or whole blood) and Picarro’s A0340 Autosampler with the A0211 High-precision Vaporizer were then used to introduce samples into the Picarro L2140-i Analyzer. Data for the flux-based model was derived from analysis of multiple oxygen inputs and outputs that included (but not limited to) drinking water, food water, and water of excreted materials.

There was a positive correlation between the amount of water consumed by mice leading to greater Δ¹⁷O_BW values, while a negative correlation was observed for metabolic rate and Δ¹⁷O_BW values. There was a difference of <30 per meg between the predicted Δ¹⁷O_BW values based on oxygen fluxes versus actual Δ¹⁷O_BW values derived from plasma blood samples. This approach utilizing the Picarro Water Isotope Analysis solution represents a significantly more accurate method of prediction compared to other methods that report a range of 300 per meg for Δ¹⁷O_BW among other animals.

Steele hopes this type of Δ¹⁷O_BW approach, that requires only a single sample, may enable the study of water intake and metabolism of large and elusive species, mitigating the need for multiple capture events and use of costly isotope tracers.

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