Inductively Coupled Plasma- Mass Spectrometry (ICP-MS)
In an ICP-MS, a sample is introduced to an Inductively Coupled Plasma source as an aerosol through a nebulizer. When the sample is introduced to the ICP torch, the sample is completely desolvated followed by the conversion of the elements in the sample to gaseous atoms. Towards the end of the plasma, these gaseous atoms are ionized. These ions are then transferred to the interface cones in order to be detected by the mass spectrometer. An intermediate vacuum is created by the interface cones with small diameters to allow this. These cones allow the selection of the centre portion of the ion beam that is coming from the ICP torch. The ions are then focussed by electrostatic lenses present in the system to collimate the ion beam into the mass spectrometer. Within the mass spectrometer, the ions are separated by their mass to charge ratio allowing identification of elements.
Energy Dispersive X-Ray Spectroscopy (EDX)
During an SEM analysis, X-rays are generated in two steps. The electron beam initially hits the sample and transfers part of its energy to the atoms of the sample. This energy can be used by the electrons of the atoms to “jump” to an energy shell with higher energy or be knocked-off from the atom. If such a transition occurs, the electron leaves behind a hole. Holes have a positive charge and, in the second step of the process, attract the negatively-charged electrons from higher-energy shells. When an electron from such a higher-energy shell fills the hole of the lower-energy shell, the energy difference of this transition can be released in the form of an X-ray.
This X-ray has energy which is characteristic of the energy difference between these two shells. It depends on the atomic number, which is a unique property of every element. The X-ray generated by this transition is picked up by the EDX detector unit which can identify the type of elements that exist in a sample.
X-Ray Fluorescence Spectroscopy (XRF)
During this process, the sample is irradiated with high energy X-rays from a controlled X-ray tube. When an atom that is present in the sample is struck with an X-ray with energy that is greater than the atom’s K or L shell binding energy, an electron from one of the atom’s inner orbital shells is dislodged. Following this, the atom uses an electron from one of the atom’s higher energy orbital shells to fill the vacant space left in the inner orbital due to the dislodged electron in order to regain stability. When this electron drops to the lower energy level, it releases a fluorescent X-ray with an energy value that is equal to the specific difference in energy between the two quantum states of the electron. This energy is detected by the detector present in the instrument and is recorded. Based on this energy value, the specific elements in a material could be identified as these energy values differ from element to element.
CHNS Analysis
The sample is combusted in a pure Oxygen environment. The resulting gases from the combustion of the sample are then measured automatically. The analyser can operate in 3 different mode; CHN mode, CHNS mode and the Oxygen mode. The CHN mode simultaneously detects Carbon, Hydrogen and Nitrogen content of a given material whereas the CHNS mode allows the simultaneous detection of Sulphur in addition to Carbon, Hydrogen and Nitrogen. The Oxygen mode can be used for the Oxygen content in organic materials by pyrolyzing the sample.
Atomic Absorption Spectroscopy (AAS)
Atomic absorption spectroscopy (AAS) is a technique which provides a quantitative analysis of metals in liquid samples by their absorption in light. Elemental metals absorb UV light at their unique wavelengths when excited by heat. The AAS focuses a beam of UV light which is characteristic of the analyte element, through a specific wavelength through a flame into a detector. The sample is aspirated to the flame which atomises the analytes which then in turn absorb the light, causing a decrease in the intensity of the light. This change in intensity is recorded by the detector which converts the change into intensity
