A method of making a sample plate for mass spectrometric analysis of a specimen is provided comprising applying a mask to a substrate to form at least one sample site. The sample plate comprises a substrate having an electrically conductive surface, a mask applied to the electrically conductive surface. The mask has a rougher surface than the substrate. The sample site comprises a central portion formed from the electrically conductive surface and a marginal portion formed from the mask where the marginal portion is more hydrophobic than the central portion.