Atomic spectroscopy is an analytical technique which uses light either absorbed or emitted from an analyte, to determine the elements present in a sample. CREST has access to a number of instruments.
In each method, the analyte is atomised. The free atoms in the sample chamber are in an excited state, and can absorb or emit photons of specific wavelengths, characteristic of the atoms present. Samples are either in liquid form, or extracted into a liquid form by a method of “digestion”. Samples are analysed and compared to a standard reference material. The different approaches are outlined below:
Flame atomic absorption spectroscopy (F-AAS): This method of atomic spectroscopy relies on a flame mixed with acetylene, air, or nitrous oxide, in order to atomise the sample. The gases incorporated result in different temperatures which can be critical depending on the sample to be analysed. Using characteristic wavelengths of elements, the amount of light absorbed by the free atoms is measured. This is correlated to the concentration of those atoms in the solution. The method can be prone to interferences form alkali metals, and such is limited to samples not containing excess quantities of sodium, lithium, potassium, or caesium salts. This approach is useful for single element analysis, as it is reliant on lamps of the element of analysis, and can only detect one element per analysis. Detection limits generally considered to be in the 10–1000 ng/g range.
Inductively coupled plasma optical/atomic emission spectroscopy (ICP-OES/AES): The plasma of an ICP is twice as hot as the flames used in F-AAS. The plasma consists of ignited argon (via tesla coil) and can reach temperatures of up to 10, 000 K. The sample atoms are in the excited state, and emit photons, characteristic to the elements present, when returning to the ground state. Emitted photons are collimated, dispersed both horizontally and vertically, before reaching the charged injector device (CID) detector. The amount of sample required is reduced in comparison to F-AAS, and the detection limits are also lowered. Excess concentrations of alkali metals should also be avoided in this approach. Detection limits generally considered to be in the 0.1–10 ng/g range.