COMPARISON OF DIFFERENT EXCITATION SOURCES AND NORMALIZATION TECHNIQUES IN LASER-ABLATION AES USING A PHOTODIODE-BASED SPECTROMETER

A new technique is evaluated for normalizing laser power fluctuations in laser-ablation atomic spectrometry. The technique involves measuring the light loss caused by scattering from the ablated material as it flows through a specially designed cell. The resulting measured optical density can be used to correct for variations in the amount of sample that has been ablated. This new approach is compared to the use of a matrix element as an internal standard. Three different excitation sources for AES(Ar-ICP, Ar-MIP, and He-MIP) were combined with laser ablation and evaluated with the new normalization approach. Although the overall performance is best for the Ar-ICP combination, the MIPs have some desirable characteristics (i.e., low background radiation) which in some cases lead to better results. The spectra were collected with a photodiode-based spectrometer that is designed for simultaneous multichannel detection and is therefore especially well suited to measurement and background correction of signals produced during transient sampling such as with laser ablation. The ability of such a spectrometer to deal with complex samples such as cast iron is discussed.