Archaeologists who want to incorporate elemental analysis of human remains into their research designs need to carefully consider sampling criteria and requirements for various types of instrumental analysis. Samples are usually taken from mid-shaft cross sections of dense cortical bone of the femur or tibia. These bones are the thickest in the human body and the least likely to be significantly altered by the burial environment. Although most of the instrumentation now used in elemental analysis can utilize samples of 200 mg or less, collecting larger cross-sections is still desirable to allow for multiple sampling for light or scanning electron microscopy (SEM) in order to assess the preservation and suitability of that bone for dietary reconstruction. The sample also must be of sufficient size to allow for the removal of external and internal surfaces during preparation for instrumental analysis. A starting sample of approximately 2-5 g will be sufficient in most cases. Multiple soil samples from areas adjacent to the skeletons/burials and other locations at the archaeological site should also be collected to use as comparative samples to measure elemental contents of the environment.
The analysis is also enhanced by the addition of faunal and botanical samples, which can be used to measure elemental content of the trophic systems of interest to the investigator. An excellent example of this approach is seen in the 1988 Sealy and Sillen study of marine and terrestrial food pathways in South Africa.
Samples are processed for analysis using a variety of techniques designed to remove external contaminants and maximize the amount of elemental information that can be recovered. Poorly preserved samples should be discarded if they yield results for biological element levels that are out of the range of modern samples, unless there is a known explanatory model, such as in the case where numerous studies have documented high lead level toxicity in both historic and prehistoric populations of the Americas and Europe. Once the sample is cut and cleaned, it is typically ground to a powder or dissolved in solution for analysis, depending on the chosen analysis method. The most common techniques currently being utilized are inductively coupled plasma mass spectrometry (ICP-MS) and neutron activation analysis (NAA) (see Neutron Activation Analysis). Both of these methods give reliable analyses of a wide range of elements in human and animal bone, soil, and other biological and geological materials. NAA is less labor intensive, but not as widely available as ICP-MS. The elemental concentrations of the archaeological bone samples are determined by comparing their elemental signals to those of known standard samples.
New techniques involving laser ablation ICP-MS are promising since they are less destructive to the samples of interest and may be useful to analyze multiple small portions of the same sample (such as dental enamel which forms at different ages during childhood). Another innovative approach involves mapping elemental concentrations across bone tissues using scanning electronic microscopes. The combination of these techniques is a powerful way to show where contamination or postmortem change has occurred in the bone and possibly indicate areas chemically changed due to pathological conditions in bone that occurred during life.
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