Oxidative degradation of polysorbate surfactants studied by liquid chromatography-mass spectrometry

Polysorbates (PSs), as acquired from manufacturing processes and chemical nature of fatty acids (FAs) used in production of biotherapeutic formulations, are heterogeneous mixtures of structurally related compounds, covering a wide range of physicochemical properties. Such complexity presents a certain challenge for analysis of these important surfactants and demands the use of methods offering sufficient resolution to monitor individual classes of species and detect changes upon stress. A liquid chromatography mass spectrometry method, benefiting from the use of low m/z marker ions, simplifies profiling of PSs by providing detailed information on FA composition even of chromatographically overlapping peaks. The ability of the method to monitor individual components and follow their changes because of oxidative stress was explored. A water-soluble azo compound was used as a model oxidizer. Major degradation products of PS 80, because of reactions involving double bond, were identified as oxo-C9:0, keto-C18:1, hydroxyl-C18:1, epoxy-C18:0, and hydroperoxy-C18:1. Stability of PS 20 components was found to depend on the carbon number of polyethoxylated (POE) sorbitan FA ester and its order. Rates of oxidative degradation increased with the length of the FA ester and, moreover, POE sorbitan diesters degraded significantly faster in comparison to the corresponding monoesters upon the oxidative stress.