Identification of leachables observed in the size exclusion chromatograms of a low concentration product stored in prefilled syringes
Requisite leachables testing of pharmaceutical products is commonly conducted with pre-defined analytical methods on a subset of materials intended to be representative of the marketed product. Throughout product development, leachables may occasionally be detected in other methods not specifically intended for monitoring such impurities. We have identified two leachables, ethyl 4-ethoxybenzoate (E4E) and 2,6-di(t-butyl)-4-hydroxy-4-methyl-2,5-cyclohexadien-1-one (BHT-OH) in a low concentration product stored in prefilled syringes (PFS). The leachables were initially detected by size exclusion chromatography (SEC) as late-eluting impurity peaks. Syringe component extraction studies indicated that the impurities were related to the syringe stoppers. Positive identification of E4E was accomplished by reversed phase liquid chromatography- tandem mass spectrometry (RPLC-MS/MS). Positive identification of BHT-OH required RPLC-solid phase extraction-cryoflow NMR (RPLC-SPE-NMR), as initial RPLC-MS/MS investigations were unsuccessful in elucidating the structure. We focus specifically on the efforts required to identify the leachables, and the fortuitous mixed mode separation mechanism and low concentration nature of the product, which were the main factors contributing to the unlikely detection of the leachables by SEC. We note that our investigations were conducted independently of formal leachables and extractables (L&E) studies and we discuss challenges with designing and conducting such studies in a manner that captures the comprehensive L&E profile of a product.