Abstract: Screening methods to identify catalysts or to identify improved catalysts using mass spectrometric analysis of products of catalysis, particularly catalyst-bound intermediate products in the catalytic cycle. The methods are applicable, in particular, to screening of organometallic compounds for catalytic function. Moreover, the methods are applicable, in particular, to screening for catalysts for polymerization reactions. More specifically, the methods employ a two stage (or two step) mass spectrometric detection method in which ions formed in a first stage ionization and which are linked to catalyst performance are selected and the catalyst associated with the selected ion is identified in a second stage employing tandem mass spectrometry.