The contamination of the surface of 316L stainless steel in the electrospray ionization source of a mass spectrometer is investigated using an accelerated method of contamination from a mixture of human blood plasma, diluted in methanol, and a water/acetonitrile mobile phase. Solid contaminants containing organic and inorganic components are identified. The morphology and composition of the contamination are shown to depend upon the orientation and temperature of the stainless steel, with the morphology showing self-organizing features as the contamination builds. A model is proposed to explain the morphology, involving rapid evaporation of the droplets that impinge on the stainless steel surface. (c) 2012 Elsevier B.V. All rights reserved.