Mass Spectrometry

Question 1

Mass Spectrometry is a process a sample is:

Answer 1

1. Vaporised/Atomised
2. Ionised
3. Accelerated
4. Deflected
5. Detected

Question 2

How are particles Ionised

Answer 2

Bombarded by electrons to knock off electrons and create singly charged positive ions

Question 3

How are particles accelerated

Answer 3

They are made to move rapidly

Question 4

How are particles Deflected

Answer 4

Made to follow a path by a magnetic field

Only ions with a suitable mass for mag field being applied will reach the detector

Question 5

How are particles Detected

Answer 5

Counted as ions hit an ion detector

Question 6

What determines how far an ion is deflected

Answer 6

Its mass, as all have a single positive charge

Question 7

Uses of Mass Spec

Answer 7

Detect:
•RAM of elements

•existence of isotopes and their relative abundance

•RMM of compounds

•molecular groups contained in compounds

•identity of structure of cmpnds by comparison w/ database

•mechanism of a reaction - by labelling an atom and following its path through reaction

Question 8

Fragmentation Ion

Answer 8

Positively charged ion produced when the molecular ion breaks apart

Question 9

Base Peak

Answer 9

Peak of greatest abundance in a mass spectrum

Question 10

Molecular ion peak (M+)

Answer 10

Peak produced by an ion formed by the removal of one electron from a molecule

Question 11

M+1 Peak

Answer 11

Peak produced by a molecular ion with an increased mass due to the presence of one carbon-13 atom

Question 12

Vertical and Horizontal Axis

Answer 12

Vertical: Relative Abundance
Horizontal: m/z or m/e

Question 13

Fragmentation pattern

Answer 13

Pattern of peaks with m/e values lower than M+ peak

Question 14

RAM calculated by

Answer 14

•multiplying m/z value by the relative abundace for every isotope

•adding all values together

•dividing by total of all relative abundances

Question 15

Peaks for diatomic Elements (Cl)

Answer 15

• (37Cl-37Cl)+
• (35Cl-37Cl)+
• (35Cl-35Cl)+
• 35Cl+
• 37Cl+

5 peaks

Question 16

To Find What Species Causes A Fragment

Answer 16

Break up molecule by breaking any C-C bonds and working out RMM of fragments created

Question 17

Most stable ion

Answer 17

Base peak ion

Question 18

(M-1)+ Peak

Answer 18

1 unit less than RMM compound as it loses a H

Question 19

13C

Answer 19

Occurs in 1.1% all C atoms

Measure of relative abundance (M+1)+ peak as a percentage of relative abundance of M+
Gives measure of C atoms in molecule

M+1/M+ x 100 = %

1.1= 1 C
2.2= 2 C
3.3= 3 C

Question 20

Unknown Mass Spectrum

Answer 20

Divide each % given by the atomic no. of element

Dive all by smallest to give ratio

Get empirical ratio with whole numbers

Question 21

(M+2)+ Peak

Answer 21

Halogen atom in a molecule

1/3 Height M+ = Cl atom
Same Height M+ = Br atom

35Cl:37Cl = 3:1
79Br:81Br = 1:1

Question 22

High-Resolution Mass Spec

Answer 22

Mass measured more accurately to many decimal places - enables peaks to be identified without ambiguity