Chemical Composition Via ICP-OES

A trace element is defined as an element that is not intentionally added. In principle, trace elements can be any element from the periodic system and are usually present in (very) small concentrations. Despite these small quantities, some trace elements have significantly impacted the properties and processes of metals and their alloys. In some cases, diffusion of these elements may cause segregation.

Monitoring and controlling the level of trace element impurities in metals and alloys is important, as impurities can affect the properties of the metal and may degrade the functionality of the finished component. ICP-OES is commonly used for the routine measurement of trace elements in metal samples because of its multi-element capability and tolerance of the high matrix level present in metal sample digests. However, developing high-purity metals and higher-performance alloys requires stricter control of a wider range of trace elements at lower concentrations, so a technique with lower detection limits than ICP-OES is required.

In ICP-OES, the sample is subjected to temperatures high enough to cause not only dissociation into atoms but to cause significant amounts of collisional excitation (and ionisation) of the sample atoms to take place. Once the atoms or ions are in their excited states, they can decay to lower states through thermal or radiative (emission) energy transitions. The intensity of the light emitted at specific wavelengths is measured and used to determine the concentrations of the elements of interest.
The sample is usually transported into the instrument as a stream of liquid. Inside the instrument, the liquid is converted into an aerosol through a process known as nebulisation. The sample aerosol is then transported to the plasma, where it is desolvated, vapourized, atomised, excited and ionized by the plasma. The excited atoms and ions emit their characteristic radiation, collected by a device that sorts the radiation by wavelength. The radiation is detected and turned into electronic signals converted into concentration information for the analyst.