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MALDI-TOF, Bruker Biflex III
Matrix-Assisted Laser Desorption Ionization (MALDI) with Time of Flight (TOF) mass spectrometry is an important method of measuring the mass of non-volatile ions. Time of Flight (TOF) analysis provides high precision and sensitivity. Detection of 25 femtomoles (10-15) of a peptide with a mass accuracy of 1 part in 10,000 is a common specification.

Advanced adaptations including “Delayed Extraction” show insulin (average MW=5734, spectrum not shown here) as a series of peaks for the mono-isotop-ic species (5731.6), the species containing one extra neutron (13C, 2H, or 15N), two extra neutrons, etc. Ions of 300,000 mass units can be observed.

Data interpretation is straight forward as molecular ions (MH+, or M-H-1) predominate. The matrix is a material (such as dihydroxybenzoate) that is mixed with the sample and dried on the target. A laser pulse vaporizes the matrix, releasing the entrapped peptide or other non-volatile material into the gas phase. A pulse of electrical potential sends the charged ions toward the detector, which measures the time of ion arrival and determines the mass to charge ratio.

Software is available to search databanks for short peptide sequences, patterns of peptides from protease digestions, etc. and identify unknown proteins.