Inductively Coupled Plasma Emission Spectrometry

Inductively Coupled Plasma Emission Spectrometry

A test method of quantitative identification of the elements, Aluminium, Silicon, Sodium, Vanadium, Nickel, Iron, Calcium, Zinc and Phosphorus in residual fuel oils.

A weighted test sample is prepared first by Ashing. The residue is fused with a buffer and diluted with water. The solution is then aspirated in the plasma if the Inductively Coupled Plasma Emission Spectrometer (ICPES) and the emission radiation of the resonance lines of the elements under analysis is measured and compared to a calibration curve constructed by standard calibration solutions.

This method of elements determination can also be performed with the Atomic absorption spectroscopy AAS.

Mechanism

The ICP-OES is composed of two parts. The ICP and the optical spectrometer. The ICP torch consists of 3 concentric quartz glass tubes. A water cooled coil of a radio frequency (RF) generator surrounds part of the torch. Argon gas is typically used to create the plasma.

When the torch is turned on, an intense magnetic field from the RF generator is turned on. The argon gas flowing through is ignited with a Tesla unit (typically a copper strip on the outside of the tube). The argon gas is ionized in this field and flows in a particular rotationally symmetrically pattern towards the magnetic field of the RF coil. A stable, high temperature plasma of about 7000K is then generated as the result of the inelastic collisions created between the neutral argon atoms and the charged particles.

A peristaltic pump delivers an aqueous or organic sample into a nebulizer where atomized and introduced directly inside the plasma flame. The sample immediately collides with the electrons and other charged ions in the plasma and is broken down into charged ions. The various molecules break up into their respective atoms which then lose electrons and recombine repeatedly in the plasma, giving off the characteristic wavelengths of the elements involved.

A shear gas, typically nitrogen or dry compressed air is used to 'cut' the plasma flame at a specific spot. 1 or 2 transfer lenses are then used to focus the emitted light on a diffraction grating where it is separated into its component radiation in the optical spectrometer. The light intensity is then measured with a photomultiplier tube at the specific wavelength for each element line involved.

The intensity of each line is then compared to previous measured intensities of known concentrations of the element and its concentration is then computed by extrapolation along the calibration line.

ee also

*Atomic absorption spectroscopy
*Ashing