Atomic Structure

Question 1

electrospray ionisation?

Answer 1

sample is dissolved in a volatile solvent and is injected through a small nozzle under a high pressure
A high voltage is then applied to it causing each particle to gain a H+ ion. The solvent is then removed leaving a gas made up of positive ions

Question 2

electron impact ionisation?

Answer 2

sample is vapourised and an ‘electron gun’ is used to fire high energy electrons at it. This knocks off one electron from each particle in the sample so that they become +1 ions

Question 3

mass spec?

Answer 3

ionisation –> electron impact or electrospray
acceleration –> positive ions are accelerated by an electric field (it gives the same kinetic energy to all ions)
Ion drift –> ions enter a region with no electric field - they drift through at the same speed which they left the electric field, lighter ions drift at higher speeds
Detection –> lighter ions reach the detector first, it detects a current created when the ions hit it and records how long they took to pass through the spectrometer

Question 4

acceleration, lighter ions compared to heavier ions?

Answer 4

the positive ions are accelerated by an electric field/negatively charged plate. This EF/NCP gives the same kinetic energy to all of the ions. The lighter ions experience a greater acceleration, they’re given as much energy as the heavier ions but they’re lighter so they accelerate more

Question 4

how are ion detected and how is their relative abundance determined?

Answer 4

Detected –> when they reach the detector they gain an electron and produce a current
Relative abundance –> the current they produce at the detector is used to work this out as the abundance is dependent on the the size of the current. CURRENT IS PROPORTIONAL TO ABUNDANCE

Question 5

Why do particles have to be ionised in mass spec?

Answer 5

otherwise, they couldn’t be accelerated by the electric field or detected by the ion detector