Mass Spectrometry Flashcards
What is mass spectrometry?
A technique used to measure the mass of particles
What are the 5 stages?
- Ionisation - Acceleration - Ion drift - Detection - Analyse
What are the two possibilities of ionisation?
Electrospray or electronimpact
What happens in stage 1 electron impact?
You vaporise sample, then fire high energy electrons at it via an electron gun. This knocks 1 or more electrons off.
Equation for electron impact
X —-> X+ (g) + e-
What happens in stage 1 electrospray?
Sample is dissolved in volatile solvent, before being injected into a hypodermic needle, producing fine mist. Tip of needle has a high voltage and each gains a proton as it leaves the needle.
Equation for electrospray
X (g) + H+ ——-> XH+
What happens in stage 2 acceleration?
- We use charged plates that repel or attract the ion to accelerate it. -Every ion is accelerated until they all have the same kinetic energy
What happens in stage 3 ion drift?
- Ions pass through a hole in negatively charged plate forming beam and travel along flight to a detector
What happens in stage 4 detection?
- Positive ions gain electrons when they hit the negatively charged plate creating electric current. The size of the current gives number of ions hitting the plate (abundance)
What happens in stage 5 analysis for electron impact?
Fragmentation is common. Penultimate peak is mr Last peak could have carbon-13 in so its m+1
Why is electron impact usually for smaller molecules
As they’re less likely to fracture since its common
What happens in stage 5 analysis for electrospray?
Fragmentation is rare Penultimate peak gives mr as next peak has H+ attached Last peak is mr plus value of a proton ie. 1
What kind of molecules is electrospray used for?
Bigger molecules e.g. biological molecules like proteins
