The exact modification of calcium aluminates is essential for the production and quality of aluminium killed high quality steel grades. By the use of a new analytical method called OES-PDA it is possible to get information about the chemical composition and number of non me-tallic inclusions before the casting process. The optical spark emission spectrometry (OES) is well known since decades, but through further development the number and composition of non metallic inclusions can be predicted in a few seconds. Up to now the analysis of non metallic inclusions is done by SEM-EDX, a time and money consuming method. The present work deals with the development of the right analytical adjustments for OES-PDA, further-more with the improvement of the sample preparation and with reference analysis of the new method with SEM-EDX. A clogging figure is generated to describe the modification of calci-um aluminates through experiments and statistical evaluation of steels for cold upsetting and extrusion produced by voestalpine Stahl Donawitz GmbH & Co KG.