"Negative Ion Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Post-Source Decay Calibration Using Fibrinopeptide B," J. Jai-nhuknan and C.J. Cassady, J. Am. Soc. Mass Spectrom. 9, 540-544 (1998).

Fibrinopeptide B (Mr 1552.58) was employed as a calibration compound for matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) post-source decay (PSD) fragment ion analysis in the negative mode. Experiments were performed using both continuous and delayed extraction, with the maximum reflectron voltages being 30 kV and 21 kV, respectively. For comparison, a common positive ion PSD calibrant, ACTH(18-39) (Mr 2466.7), was also employed with cation calibration constants being applied to anion spectra. Using fibrinopeptide B as the calibrant, the anion PSD results for angiotensin II (Mr 1046.2), renin substrate tetradecapeptide (horse) (Mr 1759.0), and the custom-synthesized peptide (K₂G₄)₂ (Mr 987.1) showed a factor of 1.5-2 improvement in mass accuracy. Typical absolute m/z accuracies were within ±1 Thomson and were achieved even when the peptide being analyzed was more massive than fibrinopeptide B. In addition, both calibrants showed increased accuracy when experiments were conducted in the delayed extraction mode. Additional advantages of using fibrinopeptide B are its moderate price and the ability to perform calibration and sample analysis for anion PSD under the same instrumental conditions.