The importance of propylene oxide (PPO) treatments for stored product protection has only increased in recent years, especially as the implementation of FSMA in the US puts pressure on tree nut producers to pasteurize their product. Unfortunately, analysis is complicated by the ease with which PPO will undergo nucleophilic reaction with water to form propylene glycol, or with chloride and bromide to form propylene chloro and bromo- hydrin, which can artificially lower the detected PPO residue. Avoiding the formation of these halohadrins (PXH) is of particular importance as they face regulatory scrutiny as carcinogens. The benefits and deficiencies of several methods of analysis for PPO and PXH, including the aqueous extraction used in ASTA method 23.1 and the MTBE extraction method previously reported by the authors, will be discussed. Novel methods utilizing dynamic headspace extraction and solid phase microextraction (SPME) will also be reported with particular emphasis on preventing artefactual effects. Preliminary experiments have demonstrated that while headspace sampling methods can significantly improve sensitivity for PPO, PCH and PBH (~3 orders of magnitude decrease in LOD for PBH), great care must be taken to avoid artefactually raising PCH and PBH levels.  The use of autosamplers (either dynamic headspace or L-PAL3 with SPME attachment) can greatly reduce injection to injection variability and reduce the number of person-hours required for analysis, but to fit walnuts or almonds into headspace vials they must be chopped or ground exposing further chloride or bromide to react with PPO.  Experiments using manual SPME sampling will allow the use of glassware that can accommodate whole nuts.  The use of iodide, or other nucleophiles, to compete with chloride and bromide for the reaction with PPO will also be examined.

Improved analysis of propylene oxide, propylene chlorohydrin and propylene bromohydrin

ACS Fall 2020 Virtual Meeting

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