Principle of surface-enhanced laser desorption ionization (SELDI)–ToF MS. This is a technique for the enrichment of proteins with specific chemical characteristics and combines chromatography with MS. ProteinChip arrays have been designed that contain chemically or biochemically treated surfaces. The sample, consisting of crude extracts or mixtures of whole proteins, is applied to the surface. After a series of washes, the targeted proteins are selectively retained. An energy-absorbing solution is added to the surface and the sample is subjected to laser desorption ionization. The formed ions are measured using a ToF mass analyzer as previously described. Characteristic features of spectra can be used for prognostic purposes (“SELDI-ToF MS and the search for disease markers”).