Detection of high molecular weight starburst dendrimers by electrospray ionization mass spectrometry

An entire series of Starburst polyamidoamine (PAMAM) dendrimers consisting of generations 1 through 10 (G1-10) have been studied by positive-ion electrospray ionization mass spectrometry (ESI-MS) using an extended mit range quadrupole mass spectrometer. Charge-state distributions were detected as high as mit 12 000 for the generation 10 dendrimer, having a theoretical molecular weight of 1 megadalton and containing approximately 93 maximum positive charges on the molecule. Accurate molecular weight determinations of the smaller generation dendrimers (G1-3, M(r) similar to 1.4 kDa to 6.9 kDa) were obtained using a commercial triple quadrupole instrument. The unit resolution ESI mass spectra provide information on the number of incomplete reactions which may occur during polymer synthesis. The extent of gas-phase charging observed by ESI-MS on the entire series of macromolecules was found to exhibit a linear relationship to M(r)(2/3), consistent with theoretical models prediciting a spherical ion structure with maximum charging controlled by Coulombic effects.