One of the most valuable tools for polymer and peptide analysis within the MC² suite of instruments is the MALDI-TOF-MS (Matrix Assisted Laser Desorption Ionisation – Time of Flight – Mass Spectrometer). The instrument is widely used for the determination of molecular weight, structure and end groups of polymer samples, and molecular weight of peptides and proteins, and can reveal structural information about a sample that may not be evident using other analytical techniques such as gel permeation chromatography.
Discovered and developed in the 1980s, MALDI-TOF-MS is used to determine the absolute molecular weight of large molecules, typically above the range detected by other types of mass spectrometry. In a typical MALDI-TOF-MS experiment, the sample (substrate) is mixed with a matrix (usually a compound containing many aromatic groups) and a salt and spotted onto a target plate. The plate is inserted into the instrument. A laser is fired at the spot and the matrix absorbs the energy – this energy is then transferred to the substrate which is ionised and “flies” to the detector. The length of time taken to fly to the detector (the time of flight) is dependent on the mass and charge of the molecule, facilitating analysis of molecular weight.
The key to obtaining a MALDI-TOF-MS spectrum is finding the correct recipe for the sample/matrix mix – a range of matrices and salts are available, and the settings on the instrument can be adjusted to optimise the data output. Interpretation of MALDI-TOF-MS spectra can identify the molecular mass of the sample and the repeat unit of macromolecular chains, aiding structure identification.
Read this application note to learn how MALDI-TOF-MS works in practice with the analysis of poly(ethylene glycol) as an example.