Abstract: The present invention provides an impurity measuring method comprising the steps of dropping a drop of a first solution on the surface of a substrate to be measured, moving the drop dropped on the surface of the substrate so that the drop is kept in contact with the surface and collects an impurity absorbed on the surface, recovering the drop after the movement and analyzing the recovered drop by chemical analysis to determine the type and concentration of the impurity, characterized in that the first solution is phobic to the substrate and the substrate consists substantially of Ge. The method is of particular importance for measuring metallic contamination on the surface of Ge substrates.