DETERMINATION OF ABSOLUTE MASS VALUES IN MALDI-TOF OF POLYMERIC MATERIALS BY A METHOD OF SELF-CALIBRATION OF THE SPECTRA

A novel calibration procedure is introduced that allows one to obtain absolute mass values in MALDI-TOF spectra of polymeric materials. The masses of the oligomers are written as the sum of two masses: mu(n) = sigma(n) + theta, where theta is the mass of the first oligomer and sigma(n) is a multiple of the polymer repeat unit and represents the distance in daltons from the first oligomer. The new calibration procedure considers theta as a variable parameter and performs a best-fit minimization. Two examples of application of the new procedure are given. Two synthetic polymers, poly(caprolactone) and poly(Bisphenol A carbonate), were analyzed by MALDI-TOF, and complex spectra showing one or more mass series up to 20 kDa were obtained. Application of this procedure allowed the interpretation of each single peak in the mass spectra and established that none of the peaks in the spectrum corresponds to fragments. It was found that the poly(caprolactone) sample consists of a series of oligomers with H and OH as terminal groups, which form sodium-cationized ions in the MALDI process. The composition of the poly(Bisphenol A carbonate) sample was more complex, since it contains a series of cyclic oligomers desorbing as sodium-cationized ions, plus two series of oligomers bearing H/phenol and phenyl/phenol as terminal groups, respectively, which form ions by capturing a proton in the MALDI process.