Excessively harsh rinsing can damage a cell’s plasma membrane. NIH/3 T3 fibroblasts adhered to a silicon chip were rinsed vigorously for 30 seconds in a 150 mM ammonium acetate solution (A) Optical image from the analysis chamber of a group of NIH/3 T3 fibroblasts. (B) Ion image of m/z 86+, corresponding to C5H12N+, a characteristic phosphocholine head group fragment. Scale bar is 100 μm. (C) Higher magnification view of the area inside the box shown in (B). The lipid bilayer looks to have ruptured causing some lipid to spread into the area around the cells. Scale bar is 50 μm. (D) An image of the m/z 86+ fragment of a group of cells on a separate sample that was more gently rinsed. There is no such damage to the cells’ outer membrane. Scale bar is 50 μm.