Mass Spectrometric Analysis
The digested protein can be analyzed with different types of mass spectrometers such as ESI-TOF or MALDI-TOF. MALDI-TOF is often the preferred instrument because it allows a high sample throughput and several proteins can be analyzed in a single experiment, if complemented by MS/MS analysis.
A small fraction of the peptide (usually 1 microliter or less) is pipetted onto a MALDI target and a chemical called a matrix is added to the peptide mix. The matrix molecules are required for the desorption of the peptide molecules. Matrix and peptide molecules co-crystallize on the MALDI target and are ready to be analyzed.
The target is inserted into the vacuum chamber of the mass spectrometer and the desorption and ionisation of the polypeptide fragments is initiated by a pulsed laser beam which transfers high amounts of energy into the matrix molecules. The energy transfer is sufficient to promote the transition of matrix molecules and peptides from the solid phase into the gas phase. The ions are accelerated in the electric field of the mass spectrometer and fly towards an ion detector where their arrival is detected as an electric signal. Their mass-to-charge ratio is proportional to their time of flight (TOF) in the drift tube and can be calculated accordingly.
Read more about this topic: Peptide Mass Fingerprinting
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