Chemistry 221

INSTRUMENTAL ANALYSIS
Problem Set #5:
Mass Spectrometry

Spring 2005

Problems in Skoog, Holler and Nieman

Additional Problems

  1. The exact mass of CO is 27.9949 and that of C2H4 is 28.0313. What resolution is necessary to just separate CO+ and C2H4+ found in a mixture of carbon monoxide and ethylene? Compare this requirement with that necessary to separate C20H40+ and C19H36O+ (both nominally at m/e = 280).

  2. Based on the resolution requirements calculated in #1, would a quadrupole- based mass spectrometer be suitable for the desired separations? If not, what type of mass spectrometer would be capable of resolving the species in question?

  3. Chlorine gas can be analyzed by mass spectrometry. Calculate the relative intensities for the parent, p+2, and p+4 peaks form the EI spectrum (70 eV) of chlorine (Cl2). Natural abundance info:


  4. An unknown compound gives a nominal molecular mass of 220. A mixture of the unknown and perfluorotributylamine [(C4F9)3N] is admitted to a double-focusing mass spectrometer with an accelerating voltage of 5000 volts. With C4F9+ in focus (m/e=218.9856), the accelerating and electrostatic-analyzer voltages are reduced to exactly 99.463% of the originals to bring the unknown peak to an identical focus. What is the exact mass of the unknown? Based on the following data (compound m/e), what is the elemental composition of the unknown?


  5. Calculate the time of flight for a singly-charged ion with mass 200 amu if the drift tube is 250 cm long and the acceleration potential is 2700 volts.

Created and copyright by Joel M. Goldberg. Last updated: April 13, 2003


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