A method of analysing a skin-print comprising the steps of providing a porous substrate, the porous substrate extending in a substrate plane and being substantially planar and having a first end and a second end, wherein the second end tapers to a point. The method further comprises: applying to the porous substrate a skin-print to be analysed； applying a fluid to the porous substrate； applying a voltage between the first end of the porous substrate and ground to generate an electric field, by which droplets of the fluid are ionised and emitted from the point in the form of a Taylor cone； and analysing the ionised droplets using a mass spectrometer.
