Atomic Structure - Mass Spectrometry Flashcards
What is mass spectrometry?
A form of molecular chemical analysis
What is the principal that all mass spectrometers work on?
3
- Form ions
- Ions separated
- Ions detected
What can mass spectrometry be used for?
Provide structural information
Identify an unknown compound
Determine the relative abundance of each isotope of an element
Time of flight mass spectrometry:
Why are the apparatus kept under a vacuum?
(2)
It excludes air
It prevents ions from colliding with air
Time of flight mass spectrometry:
What are the 5 steps?
- Ionisation
- Acceleration
- Ion drift
- Detection
- Data analysis
Time of flight mass spectrometry:
What happens in step 1. Ionisation?
(5)
Sample is dissolved in volatile solvent
The vaporised solvent is forced through a hollow needle
This produces tiny positively charged droplets
Solvent then evaporates
As a result, droplets reduce in size
Time of flight mass spectrometry:
What happens in step 2. Acceleration?
(1)
The positive ions are attracted towards an electric plate
Time of flight mass spectrometry:
What happens in step 3. Ion drift?
(1)
The ions pass through a hole in the negatively charged plate
Time of flight mass spectrometry:
What happens in step 4. Detection?
(1)
The ions arrive at the detector, their flight times are recorded
Time of flight mass spectrometry:
What happens in step 5. Data analysis?
(2)
The detector passes a signal to the computer
This generates a mass spectrum
When mass spectrometry is done to 1 d.p. Called?
Low resolution mass spec
How do you calculate relative atomic mass?
(Relative abundance x isotopic mass number) + (Relative abundance x isotopic mass number)
————————————————————————————
100
Example: Cl 35 Cl 37
If the relative atomic mass was 35.5, what would this imply?
35.5 is closer to 35
Which reflects the increased relative abundance of chlorine 35
As opposed to chlorine 37
