Atomic emission spectroscopy with Rotrode method
Year of publication: 2001
Detection of elements – even faster and more reliable with AES
Atomic emission spectroscopy (AES) is the most commonly used method in used oil analysis for detecting wear metals, impurities and additives. It has established itself as a fast, cost-effective and, above all, reliable method for trend analysis. AES primarily detects oil-soluble additives and wear that are smaller than 5 µ in size and are therefore not visible to the naked eye.
A proven method
The elements are determined either by the ICP (Inductive Coupled Plasma) method or with a Rotrode device (RDE-Rotating Disc Electrode).
In the Rotrode method, a graphite spark wheel is used to heat part of a 2 ml oil sample to over 8,000 °C in an electric arc. The enormously high temperature excites electrons orbiting around the atomic nucleus of the element so that they leave their original path.
If the energy supply stops, the electrons fall back from the unstable circular orbit to the stable initial level. The energy potential released when the electrons fall back causes each element present to emit a light with a characteristic wavelength. Thus, the element emits light.
The light beam resulting from all elements is split or fanned out into its wavelengths by a prism or crystal lattice. Photocells are mounted in a radius behind an exit slit in such a way that they can only receive light specific to each element. The photocells can indicate the type and amount of element found by a change in current intensity excited by the intensity of the light.
An optimized analyzer
AES is a must for every OELCHECK analysis. The constantly increasing number of samples requires the use of an AES instrument of the latest generation. In the OELCHECK laboratory, an RDE spectrometer assembled in the USA is in use. A specially designed fully automatic sample changer now allows the determination of 21 elements in over 80 samples per hour. Thanks to an optimized mode of operation, the determination of some individual values is even more accurate than with the predecessor model, especially for oils with high additive concentrations. An increased energy supply excites the elements more intensively.
