Inductively Coupled Plasma Atomic Emission Spectroscopy

Spectroscopic oil analysis

ICP-AES

ICP-AES stands for Inductively Coupled Plasma Atomic Emission Spectroscopy. This technique uses the inductively coupled plasma to produce excited atoms and ions that give off electromagnetic radiation of varying wavelengths. Each element of the periodic table has a corresponding wavelength. The detector within the ICP (below) detects this wavelength and also its intensity and can therefore calculate the amount of each element present within a lubricant sample.

Inductively Coupled Plasma machine :image

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A flame is generated by ionising argon gas and running it through an intense magnetic field. The temperature of the flame is about 7000K (6727°C). In comparison, our Sun's surface temperature is about 5778K (5505°C). The flame appears green but this is because it is being seen through a green filter which protects the eyes of the operator from harmful ultraviolet radiation. The true colour of the flame is pure white. The ICP reports the amount of each element present within the oil in ppm (parts per million). The data gathered from the ICP constitutes a large chunk of the overall OCLS report.

A flame generated by ionising argon gas - image

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An ICP works by using a complex system of prisms, mirrors and detectors.  The following is a brief outline of how it is able to work out element concentrations (even down to 1 ppm!) in a sample of your oil.

An overview of the entire process can be seen here.(image)

A diagram showing the full process - image

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• The plasma emissions from the torch are focused through a series of mirrors.
• The positioning mirrors self-adjust to maximise the light sensitivity.
• A collimating mirror directs the light beam onto an Echelle grating.
• This grating diffracts the monochromatic light into its constituent wavelengths.
• From here, it travels through a prism which cross-disperses the light beam into its constituent wavelength orders.
• The resultant beam from the prism forms a 2D image called an Echellogram which shows a cascade of wavelengths varying from 167 - 785 nm. (1 nm [nanometer] = 1 x 10^-9 m......one millionth of a millimetre!)
• Then, a camera mirror focuses this image onto an extremely sensitive detector chip which is cooled to -35°C to improve accuracy.
• Finally, the computer calculates the amounts of each element present in the sample based on the wavelength patterns on the detector chip.

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