A Matrix Assisted Laser Desorption Ionization (“MALDI”) ion source is disclosed comprising a first device arranged and adapted to supply a flow of liquid on to the surface of a target or a sample to be analyzed so that the liquid forms a liquid junction on the surface of the target or the sample to be analyzed and wherein analyte molecules to be ionized are extracted into the liquid junction, and a laser source emits a laser beam which causes analyte ions or an analyte plume to be released or desorbed from the liquid junction.