Lecture 1 - Basic concepts, units

Question 1

What is mass spectrometry?

Answer 1

Measurement of the abundance of ions at m/z ratios

Question 2

What is required to initiate MS?

Answer 2

A loss or gain of protons (H+)

E.g
499 -> 500 (gain H+)
499 -> 498 (loss H+)

Question 3

What are the values of m and z? (m/z)

Answer 3

m = mass of the ion
z = charge of the ion
m/z = mass to charge ratio

Question 4

What is relative abundance?

Answer 4

Number of ions normalised to the highest abundant ion.

Question 5

What is an atomic mass unit?

Answer 5

A unit of mass equal to 1/12 the mass of the most abundant isotope of carbon, carbon 12, which is assigned a mass of 12, also called a Dalton (d)

Question 6

What is a unit of charge measured in?

How is it applied in m/z?

Answer 6

e (charge of electron) or thompson (th)

m/z = dalton / e
m/z = dalton / th

Question 7

What is the nitrogen rule?

Answer 7

molecular weight will be even if number of N is even or equal to 0

Question 8

What is are the most abundant BIOLOGICAL molecules?

Answer 8

Carbon (C)
Hydrogen (H)
Oxygen (O)
Nitrogen (N)
Sulphur (S)
Phosphorus (P)

Question 9

What is the relative abundance of Carbon-13?

Answer 9

1.11%

Question 10

What is the relative abundance of Hydrogen-2?

Answer 10

0.016%

Question 11

What is the relative abundance of Nitrogen-14?

Answer 11

0.38%

Question 12

What is the relative abundance of Oxygen-17 and Oxygen-18?

Answer 12

Oxygen-17 : 0.04%

Oxygen-18 : 0.20%

Question 13

What is the relative abundance of Sulfur-33 and Sulfur 34?

Answer 13

Sulfur-33 :: 0.78%

Sulfur-34 : 4.40%

Question 14

What is the relative abundance of Chlorine-37?

Answer 14

32.5%

Question 15

What is the relative abundance of Bromine-81?

Answer 15

98.0%

Question 16

what is the effect of 2 Chlorine atoms?

Answer 16

A combination of Cl-37 and Cl-35

Question 17

What happens when the monoisotopic mass is used?

Answer 17

The average mass is usually used

Question 18

What is monoisotopic mass?

Answer 18

When a compound consist only the most abundant isotope

Question 19

Under what conditions can the monoisotopic mass be defined as most accurate measurement?

Answer 19

When the monoisotopic mass is clearly resolved

Question 20

Under a mass peak graph, what does the “Average mass” correspond to?

Answer 20

The centroid of the unresolved peak cluster (The weighted average of all the isotope peaks)

This is equal to average or chemical mass of a compound

Question 21

Under what condition is the average mass used for MS?

Answer 21

If the peaks show poor resolution (cannot distinguish the monoisotopic compound)

Question 22

What is mass resolution?

Answer 22

How easily two adjacent peaks are distinguished

Question 23

What is the equation for mass resolution?

Answer 23

Mass resolution = m1 / (m2 - m1)
or.
Mass resolution = M / dM

M = height of peak
dM = Width of peak from the mid-height

Question 24

What does the accuracy of mass measurement depend on?

Answer 24

Resolution

Higher resolution = higher accuracy

Question 25

Define mass accuracy

Answer 25

How accurate the mass is measured

Question 26

Define sensitivity

Answer 26

How small an amount can be analyzed

Question 27

What does a unit of ‘e’ equal in coulombs (C)?

Answer 27

1 e = 1.602x10^-19 C

Question 28

What is ESI?

Answer 28

Electrospray ionisation

Question 29

What is the mass of a proton (H)?

Answer 29

1.007276 u

Question 30

Calculate the m/z of tyrpsinogen
mw = 23983
z = 15

Answer 30

23983 / 15 = 1598.9

Question 31

What is the equation to calculate the ‘charge state’?

Answer 31

m2 - H
_____ = Charge state (n)
m1 - m2

m1 = m/z of peak 1
m2 = m/z of peak 2
H = mass of hydrogen