EXPERIMENTAL FIGURE 3-43 Molecular mass can be determined by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. In a MALDI-TOF mass spectrometer, pulses of light from a laser ionize a protein or peptide mixture that is absorbed on a metal target (step 1). An electric field in the mass analyzer accelerates the ions in the sample toward the detector (steps 2 and 3). The time it takes an ion to reach the detector is proportional to the square root of the mass-to-charge (m/z) ratio. Among ions having the same charge, the smaller ions move faster (shorter time to the detector). The molecular weight of each ion from the sample is calculated using the time of flight of a standard.