Expression proteomics identifies disease-specific proteins using samples that differ by some variable. Mass spectrometry is used to measure a proteome’s fingerprint and determine the different proteins in a cell. It can also indirectly determine protein function. With mass spectrometry, cells are extracted, and the charged proteins are pushed through a vacuum tube. Scientists measure how long it takes for the particles to get from one end of the column to the other. A longer column is preferred for proteomics since scientists are measuring the mass of unknown proteomes.