Electrospray Ionization - Mass Spectrometry
Electrospray Ionization (ESI)
Ionization technique that transforms ions of proteins and peptides from a liquid solution to a gaseous state before mass spectrometric detection. ESI Mass Spectrometry (ESI-MS) has a high sensitivity and robustness, thus making it well-suited for non-volatile molecules and complex sample solutions.
Liquid Chromatography Mass Spectrometry (LC-MS & LC-MS/MS)
A technique, where peptides and proteins in a liquid solution are physically separated in the HPLC due to their various chemical properties (hydrophobicity, hydrophilicity, size, charge). The components are released from the stationary phase into the mobile phase and subsequently detected and analyzed in the mass spectrometer (MS). If the mixture is subject to tandem mass spectrometry (MS/MS), the first MS selects precursor ions by their mass (m/z), which are then selected, fragmented and detected as product ions in the second MS.
It is also possible to combine LC-MS with UV detection, thereby achieving both UV trace chromatogram, MS ion current chromatogram and MS spectra. This method is known as UV HPLC analysis.
Variant of LC-MS/MS with flow rates in the nanoliter/min range. The system can run smaller sample amounts and has higher sensitivity than the conventional LC-MS/MS setup. NanoLC-MS/MS has very long analysis time due to low flow-rates.
SWATH mass spectrometry is a data independent acquisition (DIA) technique for detection and quantitation of all detectable compounds in a complex sample. The analysis can only be performed with a SCIEX TripleTOF instrument.
Multiple Reaction Monitoring (MRM LC-MS/MS)
Technique especially suited for quantification of specific, single proteins of particular interest (HCPs). MRM has a high sensitivity and specificity, thus making it perfect for targeted analysis of a set of low-level proteins, even if they are only ppm-level abundant.