School of Engineering and Science - Jacobs University

Figure 1. Flow-chart diagram of the two sample decomposition methods employed within the
Geochemistry Lab at JUB for silicate-bearing samples (HF-HClO 4 pressure decomposition) and
carbonate samples such as limestones and dolomites (HNO 3 carbonate decomposition). All reagents
used are super-, ultra-pure grade and dilutions are performed with deionized water (18.2 MΩ). Modified
after Dulski (2001).
decomposition provides complete dissolution of the sample powder, primarily due to
the ability of HF to dissolve silicate minerals, whereas the low-temperature HNO 3
decomposition is considered to dissolve only the carbonate mineral fraction of the
sample powder. The HNO 3 decomposition method, referred to as the ‘carbonate
decomposition’, will not dissolve refractory organic carbon and/or primary silicate
minerals. The carbonate decomposition will attack and leach secondary minerals such
as clays, though the extent of this effect will vary as a function of sample
composition. The two methods are schematically described in Figure 1, and most of
the data and discussion presented here will focus on the HF-HClO 4 decomposition
method. Regardless of the method chosen, every sample decomposition contains at
least one certified reference material (CRM) which is treated analytically as an
unknown sample, and which is considered to provide the best estimate of the accuracy
of the complete decomposition method and ICPMS analysis. The CRMs commonly
used in the Geochemistry Lab are listed in Table 1 and represent a variety of rock
types, and for any individual sample decomposition a CRM is chosen that most
closely resembles the rock type of the samples.
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