Degradation Mechanisms of Polysorbate 20 Differentiated by ¹⁸O-labeling and Mass Spectrometry

To investigate the mechanisms of polysorbate (PS) degradation with the added objective of differentiating the hydrolysis and oxidation pathways.

Ultra-performance liquid chromatography mass spectrometry (UPLC-MS) was utilized to characterize all-laurate polysorbate 20 (PS20) and its degradants. ¹⁸O stable isotope labeling was implemented to produce ¹⁸O-labeled degradation products of all-laurate PS20 in H₂¹⁸O, with subsequent UPLC-MS analysis for location of the cleavage site on the fatty acid-containing side chain of PS20.

The analysis reveals that hydrolysis of all-laurate PS20 leads to a breakdown of the ester linkage to liberate free lauric acid, showing a distinct dependence on pH. Using a hydrophilic free radical initiator, 2,2-azobis(2-amidinopropane) dihydrochloride (AAPH) to study the oxidative degradation of all-laurate PS20, we demonstrate that free lauric acid and polyoxyethylene (POE) laurate are two major decomposition products. Measurement of ¹⁸O incorporation into free lauric acid indicated that hydrolysis primarily led to ¹⁸O incorporation into free lauric acid via "acyl-cleavage" of the fatty acid ester bond. In contrast, AAPH-exposure of all-laurate PS20 produced free lauric acid without ¹⁸O-incorporation.

The ¹⁸O-labeling technique and unique degradant patterns of all-laurate PS20 described here provide a direct approach to differentiate the types of PS degradation.