GEMMA and MALDI-TOF MS of reactive PEGs for pharmaceutical applications.

One of the most prominent polymer group applied for drug conjugation is poly(ethylene) glycol (PEG). Since drug production is subjected to strict restrictions on the part of the FDA and EMEA, also PEG has to be characterized accurately. Particularly its molecular mass distribution (MMD) and polydispersity can result in unrequested inhomogeneous final products. Therefore evaluation of PEG before applying it to drug conjugation is essential. In this study a new analytical method for size and molecular mass determination based on electrophoretic mobility called GEMMA is used to characterize linear PEGs with two differing terminating functional groups. To confirm the data acquired by GEMMA a second, well-established method for molecular weight determination, MALDI-TOF MS (matrix-assisted laser desorption ionization time-of-flight mass spectrometry), was applied. Utilizing these two analytical approaches four monomethoxylated PEG-succinimidyl succinate (mPEG-SS) derivatives were investigated in terms of polydispersity and MMD. Although based on differing principles, both analytical methods yield comparable results. All obtained MMD maxima for the mPEG-SS batches lie within the company stated specifications, MMD+/-10% (based on MALDI-TOF MS data). For mPEG-SS 2K a polydispersity of 1.02 and for mPEG-SS 5K, 10K and 20K a polydispersity of 1.01 were determined from GEMMA as well as from MALDI-TOF MS data and are in agreement with the company's data (based on GPC data), namely 1.05-1.10.