High levels of benzene in benzoyl peroxide - A sample preparation artefact?

Benzene is a known carcinogen, that can be formed during the degradation of benzoyl peroxide (BPO). Most analytical methods for the analysis of solvents in active pharmaceutical ingredients (API's) do not account for the radical degradation of BPO when in solution, thus resulting in artefactually high amounts of benzene. In this study we proposed and demonstrated that the use of a strong inorganic base (KOH) promotes a fast BPO degradation into benzoic acid. This was confirmed by high performance liquid chromatography (HPLC). By analyzing pure benzoic acid we confirmed that it is not a source of benzene in its pure form, proving the usefulness of this degradation pathway. Using the USP methodology (based on headspace gas chromatography (HS-GC)) the levels of benzene are around 20 ppm, 100 times higher than results obtained using our proposed methodology (around 0.20 ppm). A comparable amount of benzene, around 0.20 ppm, was determined in three different BPO batches produced in different years (2019, 2021 and 2024,) and stored in controlled conditions. This suggests that the residual amounts of benzene detected derive from the radical induced pathway and not degradation over time. Validation demonstrated linearity, accuracy and precision in the range of 0.1-4.1 ppm of benzene in BPO. In this study benzene was analyzed by headspace gas chromatography mass spectrometry (HS-GC-MS). Our results show the importance of developing robust analytical methods that can generate accurate and trustworthy results when analyzing benzene in BPO.