Ions are separated by mass-to-charge ratio, giving molecular mass and fragmentation patterns.
Practise Analytical, Lab & Spectroscopy All Analytical, Lab & Spectroscopy topics
Mass spectrometry measures the mass-to-charge ratio, m/z, of ions formed from a sample, giving the molar mass of a compound and clues about its structure. The sample is first ionized by a method such as electron impact, electrospray ionization or matrix-assisted laser desorption, and the ions are then accelerated and separated in a mass analyser such as a quadrupole, time-of-flight or magnetic sector. A detector records the abundance of each m/z value, and the spectrum is a plot of relative abundance against m/z. The analysis is performed under high vacuum so that ions travel without collisions. High-resolution instruments measure masses precisely enough to determine elemental formulas.
Key ideas: Read the spectrum as relative abundance against m/z, with the tallest peak as base peak. For singly charged ions, m/z equals mass. Isotope patterns give clues: carbon-13 adds an M+1 peak of about 1.1 percent per carbon atom, so M+1/M x 100/1.1 estimates the carbon count. Electrospray often gives multiply charged ions for proteins, requiring deconvolution. Resolution is m divided by delta m.
Common mistakes and connections: Students read the base peak as the molecular ion, which is only sometimes true. Ionization method matters: electron impact fragments heavily while soft methods preserve the molecule. Forgetting that ions rather than neutral molecules are measured leads to a missing electron mass or adduct such as M+H or M+Na. Related to isotope abundance, fragmentation and GC-MS.
The nitrogen spectrum has its molecular ion at m/z 28 and a small N+ fragment at 14; high resolution would separate N2 (28.0061) from CO (27.9949). The interactive lesson shows this as a live animation or chart.
The exact masses of carbon monoxide (27.9949) and nitrogen (28.0061) differ enough to be distinguished at high resolution.
Ions are separated by mass-to-charge ratio, giving molecular mass and fragmentation patterns.
Mass Spectrometry Basics is a advanced topic in Analytical, Lab & Spectroscopy. It builds on beginner and intermediate topics, so review those first if needed.
Study these earlier topics in Analytical, Lab & Spectroscopy first: Gas Chromatography, HPLC, Retention Time.
The next topics in Analytical, Lab & Spectroscopy are Molecular Ion Peak and Fragmentation Patterns.
Yes. The interactive lesson includes a self-check question on Mass Spectrometry Basics, and the Analytical, Lab & Spectroscopy quiz draws on every topic in this area.
Mass Spectrometry Basics is topic 34 of 99 in Analytical, Lab & Spectroscopy.