Mass difference Origin
0.984016 OH ↔ NH2, e.g. de-amidiation, CHNO compounds
1.99566322 F ↔ OH, halogen exchange with hydroxy group (typically -F + OH)
2.01565 2H, opening or forming of double bond
4.955395 Na+↔ NH4+, salt adduct
7.00467078 F ↔ CN, halogen exchange with cyano group
8.96577868 Cl ↔ CN, halogen exchange with cyano group
13.979265 O ↔ 2H, e.g. Oxidation follwed by H2O elimination
14.01565 CH2, alkane chains, waxes, fatty acids, methylation
14.01565 -[C3H6ON] ↔ -[C2H4ON], acrylamide versus iodoacetamide in cysteine alkylation (gels)
15.973937 Na+↔ K+, salt adduct
15.977156 S ↔ O, sulfur compounds
15.994915 O, e.g. oxidation/reduction
17.026549 NH3, ammonium adduct/neutral ammonium loss
17.026549 NH4+ ↔ H+, salt adduct
17.96611268 Cl ↔ OH, halogen exchange with hydroxy group (typically -Cl + OH)
17.99057822 F ↔ H, halogen exchange
18.010565 H2O, water addition/loss
18.994581 CN ↔ COOH, nitrile compounds
20.929332 K+↔ NH4+, salt adduct
21.981944 Na+↔ H+, salt adduct
24.995249 CN ↔ H, nitrile compounds
27.010899 HCN, nitrile compounds
27.994915 CO
28.006148 - 2N, nitrogen loss, e.g. azido compounds (N2)
28.0313 C2H4, natural alkane chains such as fatty acids
29.97418 NO2 ↔ NH2, nitro compounds
29.997989 -NO, nitroso compounds
31.972071 S, sulfur compounds
31.98983 2O, oxygen loss
33.021464 - NH2OH, loss from hydroxamic acids
33.96102768 Cl ↔ H, halogen exchange
33.987721 H2S, sulfur compounds
37.955881 K+↔ H+, salt adduct
37.989162 2CN ↔ 2COOH, nitrile compounds
40.0313 +(C3H6O - H2O), acetone condensation after dehydration
42.010565 COCH2
42.04695 C3H6, propylation
43.005814 CONH (wrong calc. in ref.)
43.94948442 79Br ↔ Cl, halogen exchange (typically -Br +Cl)
43.98983 CO2
45.94743792 81Br ↔ Cl, halogen exchange (typically -Br +Cl)
47.966986 SO, sulfur compounds
52.9152631 79Br ↔ CN, halogen exchange with cyano group
54.9132166 81Br ↔ CN, halogen exchange with cyano group
56.0626 C4H8, butylation
58.00548 CO2CH2
58.041865 +C3H6O, acetone condensation
61.9155971 79Br ↔ OH, halogen exchange with hydroxy group (typically -Br + OH)
63.9135506 81Br ↔ OH, halogen exchange with hydroxy group (typically -Br + OH)
63.961901 SO2, sulfur compounds
63.998286 -CH3SOH, specific loss from singly oxidized methionine residues
77.9105121 79Br ↔ H, halogen exchange
79.9084656 81Br ↔ H, halogen exchange
79.956816 SO3, sulfur compounds
91.93562072 I ↔ Cl, halogen exchange (typically -I +Cl)
97.967381 H2SO4, sulfur compounds
97.976897 H3PO4, phosphorous compounds
100.9013994 I ↔ CN, halogen exchange with cyano group
109.9017334 I ↔ OH, halogen exchange with hydroxy group (typically -I + OH)
125.8966484 I ↔ H, halogen exchange
146.05791 [Deoxy-Hexose-H2O, C6O4H10], e.g. Fucose
162.052825 [Hexose-H2O, C6O5H10], e.g. Glucose, Galactose, Mannose, Fructose
164.068475 [Deoxy-Hexose-H2O, C6O5H12], e.g. Fucose
176.03209 [Glucuronic acid-H2O, C6O6H8]
180.06339 [Hexose, C6O6H12], e.g. Glucose, Galactose, Mannose, Fructose
194.042655 [Glucuronic acid, C6O7H10]
203.079374 [HexNAc-H2O, C8O5NH13], N-acetylhexoseamine
206.05791 + sinapic acid - H2O, (C11H12O5-H2O), MALDI-matrix for proteins, possible photo- or condensation adduct
221.089939 [HexNAc, C8O6NH15], N-acetylhexoseamine
289.073243 [Glutathione-H2O,C10O5N3SH15]
291.095419 [Neu5Ac-H2O, C11O8NH17], N-acetylneuraminic acid, sialic acid, NANA
305.068158 [Glutathione+O-H2O, C10O6N3SH15]
307.083808 [Glutathione, C10O6N3SH17]
309.105984 [Neu5Ac, C11O9NH19], N-acetylneuraminic acid, sialic acid, NANA
324.10565 [Sucrose-H2O, C12O10H20]
342.116215 [Sucrose, C12O11H22]
484.171011 +Tetraphenyl-tetramethyl-trisiloxane, (C28H32O2Si3), ( from silicon-based diffusion pump oil (DC7040, Dow corning)
546.186661 +Pentaphenyl-trimethyl-trisiloxane, (C33H34O2Si3), ( from silicon-based diffusion pump oil (DC7050, Dow corning)