Chapter 10A - Mass Spectrometry

• determines structure of molecules • destructive technique • not spectrometry (no electromanetic radiation and process destroys sample)

• determine relative molecular mass • used to help identify structure of organic molecules

• provide unique fingerprint of an unknown substance to compare w/ known substances.

• generates/detects positively charged ions from original compound • sample (g) bombarded w/ high energy electrons to form variety of +ve ions • +ve ions pass through the instrument & mass spectrum produced.

• molecular ions • fragment ions

• plots m/z ratio against relative abundance of fragments • peaks represent +ve ions only • m/z ratio = mass of +ve ion (+1)

• most abundant ion assigned 100% • all others measured against • most stable

• peak with highest m/z ratio • also called the parent ion • represents relative mass of unfragmented molecule analysed

• relative mass of unfragmented molecule (electrons = 0 weight) • bulk of fragments have single (+1) charge therefore, mass scale.

• Fragmentation • Isotopes

• breaking of covalent bonds • fragmentation of molecules into various +ve ions • only +ve molecules reach detector and show up on spectrum • uncharged particles evacuated by pump

• unpaired electron • highly reactive

• isotopes of atoms that make up the molecules • usually shown as small peaks surrounding a larger peak • relevant for haloalkanes

• requires pure samples • no structural information • not suitable for non-volatile compounds • sample destroyed

Study of how electromagnetic radiation is absorbed or emitted by matter

• form of energy that is all around us & takes many forms • interacts w/ ions, atoms & molecules • nature of interaction depends upon energy of the electromagnetic radiation