Table I

Masses and accuracies of intact proteins measured in the LTQ-Orbitrap (with and without lock mass (LM)) and amounts of proteins used for analysis

Two charge states, about 10 isotopes, and two different scans were used for mass determination. Standard deviation was calculated from these 40 values.

Molecular massMass accuracyAmount measured
TheoreticalMeasured−LM+LM
Da ppm fmol
Cytochrome c12,224.20912,224.1751.96 ± 1.332.16 ± 1.79150
α-Crystallin (A)19,820.86719,820.8386.63 ± 1.862.44 ± 1.50250
α-Crystallin (B)20,067.39320,067.4047.25 ± 1.692.78 ± 1.80250
β-Lactoglobulin18,266.39418,266.3964.72 ± 1.320.92 ± 0.79150
β-Casein23,969.22623,969.1986.50 ± 2.142.41 ± 1.84150
Ubiquitin10,026.32910,026.4844.15 ± 0.772.80 ± 1.02150