RATIONALE The choice of containers for storage of aqueous samples
between their collection, transport and water hydrogen (2H) and oxygen
(18O) stable isotope analysis is a topic of concern for a wide range of
fields in environmental, geological, biomedical, food, and forensic
sciences. The transport and separation of water molecules during water
vapor or liquid uptake by sorption or solution and the diffusive
transport of water molecules through organic polymer material by
permeation or pervaporation may entail an isotopic fractionation. An
experiment was conducted to evaluate the extent of such fractionation.
METHODS Sixteen bottle-like containers of eleven different organic
polymers, including low and high density polyethylene (LDPE and HDPE),
polypropylene (PP), polycarbonate (PC), polyethylene terephthalate
(PET), and perfluoroalkoxy-Teflon (PFA), of different wall thickness and
size were completely filled with the same mineral water and stored for
659?days under the same conditions of temperature and humidity.
Particular care was exercised to keep the bottles tightly closed and
prevent loss of water vapor through the seals. RESULTS Changes of up to
+5 parts per thousand for d2H values and +2.0 parts per thousand for
d18O values were measured for water after more than 1?year of storage
within a plastic container, with the magnitude of change depending
mainly on the type of organic polymer, wall thickness, and container
size. The most important variations were measured for the PET and PC
bottles. Waters stored in glass bottles with Polyseal (TM) cone-lined PP
screw caps and thick-walled HDPE or PFA containers with linerless screw
caps having an integrally molded inner sealing ring preserved their
original d2H and d18O values. The carbon, hydrogen, and oxygen stable
isotope compositions of the organic polymeric materials were also
determined. CONCLUSIONS The results of this study clearly show that for
precise and accurate measurements of the water stable isotope
composition in aqueous solutions, rigorous sampling and storage
procedures are needed both for laboratory standards and for unknown
samples. Copyright (c) 2012 John Wiley & Sons, Ltd.