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Optimized Volume Determinations and Uncertainties for Accurate and Precise Manometry

Published online by Cambridge University Press:  27 May 2019

Xi Lu*
Affiliation:
School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY 11794-5000USA
Steven R Beaupré
Affiliation:
School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY 11794-5000USA
*
*Corresponding author. Email: xi.lu@stonybrook.edu.

Abstract

Precise manometric pressure, volume, and temperature (P-V-T) measurements of carbon in samples, standards, and blanks are critical for radiocarbon studies. While P and T uncertainties depend on instrument choice and environmental stability, V uncertainties depend on their method of measurement and are often overlooked. We used numerical simulations and error propagation to find optimum procedures for measuring “cold-finger” volumes equipped with capacitance diaphragm gauges (CDGs) by two common application of Boyle’s Law: cryogenic transfers and serial gas expansions with a reference flask of known volume. Minimum relative uncertainties of cold-finger volumes are comparable for these two methods (∼0.002), but the serial gas expansion method is preferred due to its convenience. Serial gas expansions can be performed to high precision by using dry air, an initial pressure ∼76% full-scale (e.g., 760 Torr), and a reference flask with an optimal volume based on preliminary estimates of cold-finger volumes and an empirical power function. The volumes of cold-fingers ≥ 12 cm3 can be determined with minimum achievable relative uncertainties of 0.0021 to 0.0023. This limit translates to minimum achievable relative uncertainties of 0.0026 to 0.0027 for P-V-T measurements of moles of gas simulated here.

Information

Type
Technical Note
Copyright
© 2019 by the Arizona Board of Regents on behalf of the University of Arizona 

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Supplementary material: PDF

Lu and Beaupré et al. supplementary material

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