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Water vapor exposure chamber for constant humidity and hydrogen and oxygen stable isotope composition
Author(s) -
Oerter Erik J.,
Singleton Michael,
Thaw Melissa,
Davisson M. Lee
Publication year - 2018
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.8311
Subject(s) - chemistry , water vapor , relative humidity , humidity , gravimetric analysis , environmental chemistry , analytical chemistry (journal) , stable isotope ratio , moisture , hydrogen , thermodynamics , organic chemistry , physics , quantum mechanics
Rationale Water vapor exposure experiments have applications for studying water physisorption and chemisorption hydration and hydroxylation reactions on a wide variety of material surfaces. The stable isotopes of hydrogen and oxygen in the water molecule are useful tracers of water exchange mechanisms and/or rates in such vapor exposure experiments. Methods We designed and built a humidity chamber system that uses membrane‐mediated liquid–vapor exchange of water followed by mixing with dry air to control the relative humidity of air and its δ 2 H and δ 18 O isotopic composition. We tested the stability and precision of the humidity and its isotopic composition on hourly to 90‐day timescales. Results The humidity chamber design reported here is capable of providing relative humidity control to within ±1%, and consistent δ 2 H and δ 18 O values of the water vapor that are similar to our cavity ringdown spectroscopy (CRDS) measurement precision (δ 2 H vap ± 0.7‰ and δ 18 O vap ± 0.24‰). We quantify the isotopic enrichment effects of Rayleigh distillation in the system and provide information on water reservoir sizes large enough to buffer isotopic enrichment effects to within measurement precision. Conclusions The humidity chamber design reported here provides a means to create constant δ 2 H and δ 18 O values over the course of an exposure experiment. The design has applications to a wide range of studies of water sorption on material surfaces from foods and pharmaceuticals to geological materials.