Atomic absorption spectrophotometry (AAS)
Atomic absorption spectrophotometry (AAS) is an analytical
technique used to measure a wide range of elements in materials
such as metals, pottery and glass. Although it is a destructive
technique (unlike ED-XRF), the sample size needed is very small
(typically about 10 milligrams - i.e. one hundredth of a gram) and
its removal causes little damage. The sample is accurately weighed
and then dissolved, often using strong acids. The resulting
solution is sprayed into the flame of the instrument and atomised
(see schematic diagram). Light of a suitable wavelength for a
particular element is shone through the flame, and some of this
light is absorbed by the atoms of the sample. The amount of light
absorbed is proportional to the concentration of the element in the
solution, and hence in the original object. Measurements are made
separately for each element of interest in turn to achieve a
complete analysis of an object, and thus the technique is
relatively slow to use. However, it is very sensitive and it can
measure trace elements down to the part per million level, as well
as being able to measure elements present in minor and major
amounts.
Further Reading
Hughes, M.J, Cowell, M.R and Craddock, P.T. 1976. Atomic
absorption techniques in Archaeology, Archaeometry, 18,
19-37.