363
spectroscopy (ICP-AES) provides high reproducibility and a quantitative linear
range greater than conventional methods with arc or spark, allowing the simultaneous determination of metals and non-metals. ICP-AES uses a very high-temperature
excitation source and molecular interferences are greatly reduced. However, analysis is more expensive and all samples have to be introduced in a dissolved form.
Furthermore, in ICP-AES, complex samples usually provide patterns that are very
difficult to interpret. ICP-AES is also a fast, multi-element technique with an
extended dynamic linear range and moderate-to-low limits of detection (LODs). Up
to 60 elements can be screened per sample run in less than 1 min. ICP-AES monitors wavelengths down to 165 nm that provide high sensitivity for phosphorous and
sulphur determinations.
ICP-MS is a powerful tool for elemental analysis, providing LODs for more than
70 elements at low concentrations, typically parts per billion or trillion (ppb or ppt).
Conventional ICP-MS systems cannot provide the lowest LODs, because of the
polyatomic interferences that can enhance the background signal or overlap the
signals of the most abundant isotopes. The use of a DRC can remove unwanted
interferences by creating specific chemical reactions with a supplementary gas,
which improves the selectivity and the sensitivity dramatically.
12.3.2 Multi-isotope Ratio
Investigations of the ratios of stable isotopes and the contents of unstable isotopes
(radioisotopes), especially heavy elements (e.g. uranium, strontium, thorium or
lead), have been used primarily in geological sciences for age determination
(Webster and Oliver 2001; Taylor et al. 2015). For heavier elements (e.g. Pb and Sr),
fractionation is insignificant compared to the original isotopic ratios because the
nuclides have high mass compared to the mass differences of the isotopes. In this
case, stable isotopic ratios depend essentially upon the origin of the ore body and
can be used for identification of the source of a material or characterization of its
transportation history (e.g.
208
Pb/
207
Pb). Strontium is the commonly used heavy
metal for isotope ratio analysis. Clearly, the present
87
Sr/
86
Sr ratio is greater for
samples that have greater ages, t, and samples with larger Rb/Sr ratios. The
87
Sr/
86
Sr
ratio therefore varies between different rock types and formations. Since Rb is an
alkali metal and Sr is an alkaline earth metal, these elements behave differently in
geological processes, creating large variations in Rb/Sr and, so, large variations in
87
Sr/
86
Sr. The
87
Sr/
86
Sr ratio has been shown to vary widely in surface rocks, so any
Sr released into soils, rivers and groundwaters has an isotopic signature that reflects
its source. Sr isotopes have also been used to trace agricultural products, which have
incorporated Sr, along with Ca, from soils incorporating the Sr isotope ratios of the
underlying rocks.
12 Characterization of Multi-element Profiles and Multi-isotope Ratio Records as…
spectroscopy (ICP-AES) provides high reproducibility and a quantitative linear
range greater than conventional methods with arc or spark, allowing the simultaneous determination of metals and non-metals. ICP-AES uses a very high-temperature
excitation source and molecular interferences are greatly reduced. However, analysis is more expensive and all samples have to be introduced in a dissolved form.
Furthermore, in ICP-AES, complex samples usually provide patterns that are very
difficult to interpret. ICP-AES is also a fast, multi-element technique with an
extended dynamic linear range and moderate-to-low limits of detection (LODs). Up
to 60 elements can be screened per sample run in less than 1 min. ICP-AES monitors wavelengths down to 165 nm that provide high sensitivity for phosphorous and
sulphur determinations.
ICP-MS is a powerful tool for elemental analysis, providing LODs for more than
70 elements at low concentrations, typically parts per billion or trillion (ppb or ppt).
Conventional ICP-MS systems cannot provide the lowest LODs, because of the
polyatomic interferences that can enhance the background signal or overlap the
signals of the most abundant isotopes. The use of a DRC can remove unwanted
interferences by creating specific chemical reactions with a supplementary gas,
which improves the selectivity and the sensitivity dramatically.
12.3.2 Multi-isotope Ratio
Investigations of the ratios of stable isotopes and the contents of unstable isotopes
(radioisotopes), especially heavy elements (e.g. uranium, strontium, thorium or
lead), have been used primarily in geological sciences for age determination
(Webster and Oliver 2001; Taylor et al. 2015). For heavier elements (e.g. Pb and Sr),
fractionation is insignificant compared to the original isotopic ratios because the
nuclides have high mass compared to the mass differences of the isotopes. In this
case, stable isotopic ratios depend essentially upon the origin of the ore body and
can be used for identification of the source of a material or characterization of its
transportation history (e.g.
208
Pb/
207
Pb). Strontium is the commonly used heavy
metal for isotope ratio analysis. Clearly, the present
87
Sr/
86
Sr ratio is greater for
samples that have greater ages, t, and samples with larger Rb/Sr ratios. The
87
Sr/
86
Sr
ratio therefore varies between different rock types and formations. Since Rb is an
alkali metal and Sr is an alkaline earth metal, these elements behave differently in
geological processes, creating large variations in Rb/Sr and, so, large variations in
87
Sr/
86
Sr. The
87
Sr/
86
Sr ratio has been shown to vary widely in surface rocks, so any
Sr released into soils, rivers and groundwaters has an isotopic signature that reflects
its source. Sr isotopes have also been used to trace agricultural products, which have
incorporated Sr, along with Ca, from soils incorporating the Sr isotope ratios of the
underlying rocks.
12 Characterization of Multi-element Profiles and Multi-isotope Ratio Records as…