8.1 Practical Considerations
Stable isotopes of water have a major advantage over many other water analytes, in that they comprise virtually all of the sample, rather than being a minor or trace constituent, such as Cl– or 3H. This means that contamination is less of a concern during sampling and storage. However, stable isotopes are sensitive to evaporation, so ensuring the sample is well sealed is essential.
Sample bottles need not be specialized. They can be glass or plastic, but must seal completely. Sample volumes required for IRMS or CRDS are only a few milliliters, so any bottle more than 50 ml will suffice. Duplicates are useful if loss or breakage may occur. Duplicates that are labeled so it is not obvious that they are duplicates (e.g., given a fake sample number) are useful as a check of the laboratory’s precision.
Answering hydrogeological questions almost always requires knowledge of the whole water cycle, so it is usually necessary to sample precipitation and surface water, in addition to groundwater (Orlowski et al., 2016).