ACCURATE MASS MEASUREMENTS USING MALDI-TOF WITH DELAYED EXTRACTION

Matrix-assisted laser desorption ionization time-of-fight (MALDI-TOF) mass spectrometry is now an essential tool in biopolymer analysis, Sen sitivity and mass range are unsurpassed, but mass measurement accuracy and resolution have been limited. With delayed extraction and a refle cting analyzer, mass measurements using MALDI-TOF can be made with an accuracy of a few parts per million (ppm). It is possible to distingui sh Lys from Gin in peptides, and to determine the elemental compositio n of smaller molecules (mass 100-500). In database searching strategie s, a smaller mass window, resulting from an increase in mass accuracy, greatly decreases the number of possible candidates. Mass measurement accuracy with errors less than 5 ppm is demonstrated on a mixture of 12 peptides ranging in mass from ca. 900 to 3700 Da. Mass measurements on 13 peaks in an unseparated tryptic digest of myoglobin gave result s with an overall average error less than 3.5 ppm, with a maximum erro r of 7 ppm.