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.