Mass Spectrometry Fundamentals
Mass spectrometry tells you two crucial things: the exact atomic mass of elements or compounds, and how much of each isotope is present in a sample. Think of it as weighing atoms with incredible precision - modern instruments can measure masses to four decimal places!
High resolution mass spectrometry is where things get really clever. Even though propane (C₃H₈) and ethanal (CH₃CHO) both have a relative molecular mass of 44, high-resolution equipment can tell them apart. Propane shows up at m/z = 44.0624 whilst ethanal appears at m/z = 44.0302.
When molecules get ionised in the spectrometer, they often break apart through fragmentation. The original molecular ion (M⁺) - which is just the molecule with one electron removed - splits into smaller pieces. Each fragment creates its own peak on the spectrum, giving you clues about the molecule's structure.
The base peak represents the most abundant ion in your sample, whilst tiny M+1 peaks show up because some molecules contain carbon-13 isotopes. These fragmentation patterns work like molecular fingerprints, helping you identify unknown compounds with confidence.
Key insight: Different isotopes of halogens create distinctive patterns - chlorine's 3:1 ratio for ³⁵Cl:³⁷Cl and bromine's 1:1 ratio for ⁷⁹Br:⁸¹Br make them easy to spot in spectra.