This document describes a method for the determination of the content of biocides in construction products, (either finished (dried) or in a ready-to-use state) and in eluates thereof, using liquid chromatography and tandem mass spectrometric detection (LC-MS/MS). For content analysis liquid chromatography with UV-detection can also be used, if sufficient sensitivity and selectivity is ensured (see Annex A). The method in this document is validated for the product types listed in Annex D. For eluate analysis quantification limits of 0,1 ¼g/l can be achieved.