Electron impact is a process where high-energy electrons collide with atoms or molecules, causing ionization or excitation. This technique is commonly used in mass spectrometry to analyze the composition of substances. When an electron strikes an atom, it can knock out one of the atom's electrons, creating a positively charged ion. The resulting ions can then be detected and measured, providing valuable information about the sample's molecular structure. Electron impact is particularly effective for small, volatile molecules, making it a popular choice in chemical analysis and research.