Table 12.3 Characteristics of some trace metal techniques
Technique Approximate
operating rangeRelative precision RemarksICP-AES ppb – major 0.2–4% sensitive, precise, qualitative and quantitative
technique with a wide linear response
ICP-MS sub ppb–ppm 1 – 5% ultrasensitive and selective, excellent qualitative
potential, can distinguish isotopic ratios
AAS 0.1–100 ppm 0.5–2% excellent quantitative technique but not suitable for
qualitative analysis
FES 1 – 100 ppm 1 – 4% limited in scope because of susceptibility to
interference
AFS sub ppb–ppm 0.2–4% limited applicability but valuable for low
concentrations of Hg and elements with volatile
hydrides
electron probe 50 – 500 ppm 5 – 10% useful for localized analysis on parts of samples;
analyses surface layer only; costly equipment;
qualitative and quantitative applications
X-ray fluorescence 20 ppm–0.1% 5 – 10% best suited to heavy elements in light matrices, very
simple to operate; costly equipment; qualitative and
quantitative applications
neutron activation
(gamma-ray
spectrometry)sub ppb–10 ppm 1 – 5% expensive and specialized; qualitative and quantitative
information at ultra-trace levelsvegetation and sediments. The former give additional indications of incorporation of metals into the
food chain. The latter, by virtue of the presence of hydrous oxides of Al, Mn and Fe, concentrate metals
by sorption. Samples of these indicators were also collected. In investigations such as this it is often
needed to obtain information on the exact chemical species of the metal, especially for metals such as
Hg and Cd. In this particular example such investigations were not required.
The actual analysis of the samples started with a qualitative survey to identify the principal metals
present. ICP-AES was selected as being most suitable for this because it provided a permanent record, a
multi-element analysis, and good sensitivity. Solutions of the shellfish tissue were prepared for analysis
by wet oxidation, and the sediments were digested with 40% v/v