Self-Calibrating Property of Matrix-Assisted Laser-Desorption Ionization Time-of-Flight Spectra of Polymeric Materials

Abstract: A calibration procedure is introduced, which allows one to obtain absolute mass values in matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) spectra of polymeric materials, thus avoiding ambiguous mass assignments, The method consists in combining the observed times of flight in a function denoted as 'modified sum of squares' (SS2) and in finding the point of minimum for SS2. The procedure takes advantage of the finding that SS2 possesses an extremum property, i.e. it takes its minimum at theta, the mass of the first oligomer appearing in the MALDI-TOF spectrum, The method was tested by recording the MALDI-TOF spectrum of an aminolyzed Nylon 6 and of a glycolized poly(butyleneadipate) (PEA) sample. Nylon 6 was found to be made of a series of oligomers bearing diaminohexamethylene (DAHM) terminal groups. PEA is made of a series of oligomers with butyleneglycol end-groups. The intense peaks seen in the mass spectra are due to sodium-cationized ions, whereas the less-intense peaks are due to potassium-cationized ions. The function SS2 was built for the two samples and a point of minimum was found at the point theta=817.6 for Nylon 6 and at the point theta=713,6 for PBA. This finding allowed the interpretation of the mass spectra.