Principle of Optical Emission Spectrometry
Optical emission spectrometry involves applying electrical energy in the form of spark generated between an electrode and a metal sample, whereby the vaporized atoms are brought to a high energy state within a so-called "discharge plasma".
These excited atoms and ions in the discharge plasma create a unique emission spectrum specific to each element, as shown at right. Thus, a single element generates numerous characteristic emission spectral lines.
Therefore, the light generated by the discharge can be said to be a collection of the spectral lines generated by the elements in the sample. This light is split by a diffraction grating to extract the emission spectrum for the target elements. The intensity of each emission spectrum depends on the concentration of the element in the sample. Detectors (photomultiplier tubes) measure the presence or absence or presence of the spectrum extracted for each element and the intensity of the spectrum to perform qualitative and quantitative analysis of the elements.
In the broader sense, optical emission spectrometry includes ICP optical emission spectrometry, which uses an inductively coupled plasma (ICP) as the excitation source. The terms "optical emission spectrometry" and "photoelectric optical emission spectrometry," however, generally refer to optical emission spectrometry using spark discharge, direct-current arc discharge, or glow discharge for generating the excitation discharge.
Shimadzu optical emission spectrometers feature Pulse Distribution Analysis (PDA) to enhance the measurement reproducibility (accuracy). This method involves statistical processing of the spark pulse-generated emission spectra obtained from spark discharges in an argon atmosphere. The optical emission spectrometer offers rapid elemental analysis of solid metal samples, making it indispensable for quality control in steel making and aluminum metallurgy processes.