SELF-CALIBRATING PROPERTY OF MATRIX-ASSISTED LASER-DESORPTION IONIZATION TIME-OF-FLIGHT SPECTRA OF POLYMERIC MATERIALS

A calibration procedure is introduced, which allows one to obtain abso lute mass values in matrix-assisted laser desorption/ionization time-o f-flight (MALDI-TOF) spectra of polymeric materials, thus avoiding amb iguous mass assignments, The method consists in combining the observed times of flight in a function denoted as 'modified sum of squares' (S S2) and in finding the point of minimum for SS2. The procedure takes a dvantage of the finding that SS2 possesses an extremum property, i.e. it takes its minimum at theta, the mass of the first oligomer appearin g in the MALDI-TOF spectrum, The method was tested by recording the MA LDI-TOF spectrum of an aminolyzed Nylon 6 and of a glycolized poly(but yleneadipate) (PEA) sample. Nylon 6 was found to be made of a series o f oligomers bearing diaminohexamethylene (DAHM) terminal groups. PEA i s made of a series of oligomers with butyleneglycol end-groups. The in tense 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 sp ectra.