Mass Spectrometry
An analytical technique measuring molecular mass-to-charge ratios to identify and characterise peptides. MALDI-TOF and ESI-MS are common methods. Mass spectrometry confirms peptide identity by comparing measured molecular mass to the theoretical mass calculated from the amino acid sequence.
Technical Context
MS for peptide analysis: MALDI-TOF (matrix-assisted laser desorption/ionisation time-of-flight) — sample co-crystallised with matrix, laser pulse desorbs/ionises analyte, ions separated by time-of-flight; provides molecular weight with accuracy of ±0.01% (±1 Da for a 10 kDa peptide). ESI-MS (electrospray ionisation) — sample in solution, high voltage creates charged droplets, solvent evaporation produces multiply charged ions; enables direct coupling to HPLC (LC-MS). Tandem MS (MS/MS): selected ions are fragmented by collision-induced dissociation (CID) → fragment ion analysis provides sequence information. Common fragmentation nomenclature: b-ions (N-terminal fragments), y-ions (C-terminal fragments). LC-MS/MS is the gold standard for peptide identification, de novo sequencing, post-translational modification analysis, and impurity characterisation in pharmaceutical quality control.