Learning Objectives At the end of this assignment, you should be able to: Explain how the m / z values and spacing of peaks in an ESI charge envelope is used to determine molecular weight. Calculate the charge state and mass of a protein from its ESI-MS spectrum. Explain how a quadrupole ion trap mass analyzer works. Calculating the molecular weight of a protein from its electrospray ionization mass spectrum (ESI-MS) Template:HideTOC References and Resources G.L. Glish and R.W. Vachet, “The basics of mass spectrometry in the twenty-first century,” Nat. Rev. Drug Discov. , 2003 , 2 , 140-150. C. Hendrickson, “Electrospray Ionization (ESI)”, https://nationalmaglab.org/user-facilities/icr/techniques/esi C.S. Ho, et al. “Electrospray ionization mass spectrometry: principles and clinical applications,” Clin. Biochem. Rev. 2003 , 24 , 3-12. J.R. Yates, “A century of mass spectrometry: from atoms to proteomes,” Nat. Methods , 2011 , 8 , 633-637. J. Yergey, et al. “Isotopic distributions in mass spectra of large molecules,” Anal. Chem. 1983 , 55 , 353-358.