Practice Questions for Mass Spectrometry

Question 1:

While running a new reaction, a chemist notices the evolution of a gas. A sample of this gas gave a mass spectrum in which the molecular ion (m/z = 44) was the largest ion peak. The only other significant peaks were observed at m/z = 28 & m/z = 16. What is this gas?

Enter a formula (without subscripting numbers) or a name in the answer box.     Hint: Consider the mass differences between these ions.

Question 2:

A liquid compound gave a mass spectrum showing a strong molecular ion at m/z = 156. The only fragment ions are seen at m/z = 127 & 29.
Suggest a structure for this compound.
Enter a formula (without subscripting numbers) or a name in the answer box.     Hint: Consider the mass differences between these ions.

If you don't know the entire structure but would like to propose a fragment to verify that you are on the right track, fill in the fragment or fragments below:

Fragment ion mass 29:
Fragment ion mass 127:

Question 3:

A liquid compound gave a mass spectrum in which the molecular ion appears as a pair of equal intensity peaks at m/e = 122 & m/z = 124. Small fragment ion peaks are seen at m/z = 107 & 109 (equal intensity), and at m/z = 79, 80, 81, & 82 (all roughly the same size). Large fragment ions are seen at m/z = 43 (base peak), 41 & 39.
Suggest a name for this compound.

Enter a name in the answer box.     Hints: What element is indicated by equal intensity ions differing by 2 amu?
What mass remains if the isotopic mass of this element is subtracted from the molecular ion mass?

If you don't have a final answer but would like to verify that you are on the right track, fill in the fragment or element below:

An element having equal intensity isotopic ions differing by 2 amu:
Remaining mass after subtraction of that element's mass (enter a number):



  		   
This script written by William Reusch, Dept. of Chemistry, Michigan State University. Please send comments and corrections to whreusch@pilot.msu.edu.