Three different quantitative methods, which rely on base-mediated reactions for the purity assessment of the hydrolytically unstable activated ester, mPEG-SC (1) are discussed. In a spectrophotometric assay, controlled base-catalyzed hydrolysis of mPEG-SC (1) affords N-hydroxysuccinimide and its concentration can be determined by UV analysis. Reaction of mPEG-SC (1) with benzylamine and a non-aqueous back titration of the remaining benzylamine can also be used for purity determination of mPEG-SC (1). HPLC analysis of derivatized forms of mPEG-SC (1) affords a potential specific assay for these polymers. The relative attributes and shortcomings of these methods are elaborated. Although the titration assay is intermediate in specificity; the greater precision of the method makes it the preferred method at this stage of development of an HPLC-ELSD or HPLC-UV assay method. The percent relative standard deviation (%R.S.D.) of the titration method was 2.9% as opposed to 8.8% for the HPLC assay. The accuracy of the titration method was shown to be 101 +/- 4.0% and was sufficient to justify a blending operation according to FDA cGMP guidelines. (C) 2008 Elsevier B.V. All rights reserved.
