Organic Side

Question 1

What is the first stage of Time of flight called?

Answer 1

Ionisation

Question 2

What are the two types of stage one of Time of Flight?

Answer 2

Electron Impact and Electron Spray Gun

Question 3

Describe Electron Impact (ToF) (4)

Answer 3

• Used for elements and substances with low formula mass
• The molecular ion often breaks down into smaller fragments (called fragmentation) some of these are also detected in the mass spectrum
• Sample is vaporised and then high energy electrons, from an “Electron Gun” are fired at it
• This usually knocks off one electron from each particle forming a 1+ ion.

Question 4

Describe Electron Spray Ionisation (ToF) (2)`

Answer 4

• Sample is dissolved in a volatile solvent and injected through a fine hypodermic needle to give a fine mist.
• The tip of the needle has a high voltage and is positively charged, so each particle gains a proton (H+) as it leaves the needle

Question 5

What is the name for the second stage in Time of Flight?

Answer 5

Acceleration of Ions

Question 6

Describe acceleration of ions in ToF (1)

Answer 6

The 1+ ions are accelerated using an electric field so that they all have the same kinetic energy.

Question 7

What is the equation used to find the kinetic energy of an ion?

Answer 7

KE = 1/2mv^2

KE = kinetic energy (J)
m = mass (Kg)
v = Velocity (m/s)

Rearranged: V = square root (2KE/m)

Question 8

What is the third stage of ToF?

Answer 8

Ion Drift

Question 9

Describe Ion Drift in ToF (2)

Answer 9

• The 1+ ions travel through a hole in a negatively charged plate and enter the flight tube
• Ions with different masses have a different time of flight

Question 10

What is the formula used to find Time of Flight?

Answer 10

t = d/v

t = time of flight (s)
d = distance of flight tube (m)
v = velocity of the particle (m/s)

Question 11

What is the fourth stage in ToF?

Answer 11

Ion Detection

Question 12

Describe Ion detection in ToF (3)

Answer 12

• The detector is negatively charged, so the ions are attracted to it
• A current is produced when the ions hit the detector - the more ions that hit the detector the bigger the current
• The mass of the ions hitting the detector can be calculated from the time they take to reach the detector

Question 13

What is stage five of ToF?

Answer 13

Data Analysis

Question 14

Describe Data analysis in ToF (2)

Answer 14

• The mass spectrum shows the mass to charge (m/z) ratio and abundance of each ion that hits the detector.
• As the charge of the ions are +1, the m/z ratio is effectively the mass of each ion.

Question 15

What’s the formula to find Relative Atomic Mass?

Answer 15

total relative abundance
(typically 100)