Exam #1 Study Guide

Question 1

What types of samples are most applicable to ESI analysis?

Answer 1

• Most common method for low volatile samples

* Can be used with high mass species such as proteins

Question 2

Why is high resolution desirable in an ESI analysis?

Answer 2

• It is useful in obtaining MW information

Question 3

How are ions produced by Electron Ionization?

Answer 3

1) Sample vapor molecules go through ionization by being hit with electrons. Excess energy is absorbed and molecular ions form ( these are aka precursor ions)
2) The molecular ions then go through uni-molecular decomposition. This produces product ions.
3) Mass analysis of all product ions
4) Data Recording
5) Plot bar graph
6) Mass spectrum

Question 4

What is the most common electron energy used in EI?

Answer 4

70 eV

Question 5

What are the two chemical/ physical features that an analyte must have to be analyzed by EI.

Answer 5

• Volatile species

- Preferably positive ions

Question 6

For almost all analytes, MALDI produces many more ions than LD without a matrix. List three major reasons that the presence of a matrix enhances ion yield.

Answer 6

1) Provides H+ to form sample [M+H+]
2) The matrix molecules help separate the analyte molecules and limit cluster formation. (Provides collisions to “cool” ions.)
3) Matrixes the contain carboxylic acid group help bring sample species to gas species. Helps with ion desorption

Question 7

What pump would be used to obtain a pressure of 10^-9 Torr w/o producing a pump oil background in mass spectrometry?

Answer 7

-Cryopump

Question 8

What type of sample is most commonly analyzed in MALDI imaging?

Answer 8

-Very good for polymers such as biomolecules.