Geothermal sampling and analysis

Abstract

Sampling and analysis provide the data for all geochemical interpretation and thus it is imperative that these tasks be performed by trained personnel with insight into possible errors. Different types of containers (glass or plastic, amber or transparent) and different pre-treatment (dilution, filtering, freezing, addition of chemicals) is needed for the various constituents determined. Some constituents need analysis shortly after collection either on the spot or in a near-by laboratory which may be a field laboratory. The most common analytical techniques employed for geothermal fluid samples that are likely to be available in most laboratories are titrimetry, UVVis spectrophotometry, atomic absorption spectrophotometry (AAS), ion chromatography (IC), electrometry and gas-solid chromatography (GSC). In recent years inductively coupled plasma has become widely used both with atomic emission spectrometry (ICP/AES) and mass spectrometry (ICP/MS) but this requires expensive equipment and these instruments, particularly the latter, tend to be run by large commercial laboratories on a commercial basis and it is quite common that samples are sent there for analysis, especially for major cations and trace elements. Stable isotopes are analysed for by mass spectrometry (MS) and radioactive isotopes by radiometry. These techniques are not available to all laboratories and are frequently carried out on a commercial basis. From the returns in the inter-laboratory comparison of analytical techniques carried out by the International Atomic Energy Agency in 2002 involving 31 laboratories working with geothermal samples it is clear that AAS is the most used technique for cation analysis but titrimetry and UVVis spectrophotometry for anion analysis.