A technique that separates molecules based on mass (and charge). The most commonly used method of mass spectrometry is Matrix Assisted Laser Desorption Ionization-Time of Flight (MALDI-TOF) spectrometry. The way this technique works is to immobilize your sample (can be either a mixture of various substances, or a single substance) on a solid matrix. A laser then strikes this matrix, and the energy from the laser ionizes the sample (imparting a charge to some of the molecules). An electric field is applied, and the charged molecules all fly off towards the detector, a short distance away. Molecules with higher mass, or less charge, will accelerate more slowly, and hit the detector later. Usually the same molecule will exist with several different charges, +1, +2, +3, etc. This gives good redundancy for double checking results, and provides very accurate molecular weights of compounds. With modern mass-spec systems it is possible to measure molecules up to 1,000,000 Daltons, or as small as 20 Daltons, with an error of about .01%.