Mass Spectrometry

Question 1

What is the acronym used for mass spectrometry and what does it stand for?

Answer 1

VVIADD
Vaporisation in a vacuum
Ionisation
Acceleration
Deflection
Detection

Question 2

What happens in vaporisation?

Answer 2

The substance is changed from liquid or solid to gas
It is done inside of a vacuum in order to prevent other molecules from interfering with the ions that you want to examine

Question 3

What happens in ionisation?

Answer 3

Using an electron gun, the sample gets made into positive ions by being bombarded by high energy electrons, causing the sample to lose electrons resulting in positively charged ions

This process may also cause fragmentation leading to no or very small molecular ion peaks
May also knock more than one electron off the sample leading to 2+ ions which halves the m/z value

Question 5

What happens in acceleration?

Answer 5

The ions are accelerated by being attracted to a negatively charged plate, giving all the ions the same kinetic energy

Question 6

What happens in deflection?

Answer 6

The ions move through a hole in the negatively charged plate and deflected by the field from an electromagnet

Question 7

What happens in detection?

Answer 7

Ions are detected by a negatively charged plate at the end of the tube as the positive ions will induce a current when hitting the plate.
The magnitude of the current will be measured and give a relative abundance

Question 8

What is the m/z value?

Answer 8

It represents mass over charge
The charge is usually 1+ so, m/z usually just represents the mass

Question 9

What is the molecular ion peak?

Answer 9

The peak with the highest m/z value ( second right most) representing the Mr of the sample

Question 10

What is the peak next to the molecular ion peak?

Answer 10

An M+1 peak caused by the isotope in the sample
E.g. for an organic compound it maybe be carbon-13