Evaluation of matrix-assisted laser desorption ionization-time-of-flight mass measurement accuracy by using delayed extraction.

Mass measurement accuracy of a reflectron time-of-flight mass spectrometer equipped with delayed extraction is evaluated. Mass resolution of 10,000-15,000 is achieved routinely for peptides in the mass range of 1-6 ku ionized by matrix-assisted laser desorption ionization. The mass measurement accuracy of peptides with molecular weights of 1-4 ku is 10-15 ppm by using external calibration and better than 5 ppm by using internal calibration. The mass calibration remains accurate over a broad mass-to-charge ratio range (1-4 ku), even when the calibration curve is extrapolated several thousand mass units.