ULTRA-TRACE ANALYSES BY OPTICAL EMISSION-SPECTROSCOPY - STRAY LIGHT PROBLEM

Experimental evidence is presented to document the fact that stray light may produce substantial shifts in the background signal measured with some spectrometers when the total composition of the sample changes. The data presented were obtained with the inductively coupled plasma as an excitation source; similar effects can be expected with other excitation sources as well. Examples of various forms of stray light originating from grating defects (ghosts, near and far scatter) and defects in the design of spectrometers are presented. Various methods for the reduction, elimination or correction of stray light effects are also discussed.