Analysis of gross differences in composition within an unlabeled cell. Endothelial cells were cultured on silicon supports, fixed on the support, dried, and analyzed with MIMS. Quantitative mass images of the surface of a whole endothelial cell were recorded in parallel at masses 12C-, 12C14N- and 31P-. An overlay of these images is shown, with 12C14N in red, 12C in green, and 31P in blue. Scale bar = 10 μm.