In late 1973 a slow release formulation of terbutryne (2-ethylamino-6-methylthio-4-tert.-butylamino-1,3,5triazine) was introduced commercially for the control of water weeds (CIBA-Geigy (Clarosan)). Hence it will be of increasing importance for residue analysts to be able to detect low concentrations of this compound in surface waters. In the work reported here two methods are described, one, h...