Performance assessment of proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS) for analysis of isobaric compounds in food-flavour applications

• PTR-TOF-MS offers real-time VOC profiling for food-flavour applications.
• Separation of isobaric flavour compounds in food headspace is viable by PTR-TOF-MS.
• Mass resolution and discrimination level are critical for accurate separation.
• Estimation of LOQ in solution and discrimination of isobaric compounds is presented.

Characterisation of food-flavour release using quadrupole-based on-line mass spectrometers such as proton-transfer-reaction mass spectrometry (PTR-MS, or PTR-QMS) can be complicated when nominally isobaric aroma compounds are present in complex food matrices. The recent combination of PTR-MS with time-of-flight mass spectrometry (PTR-TOF-MS) offers an analytical tool potentially capable of overcoming this problem because of its enhanced mass resolution. In this context, four pairs of isobaric compounds (cis-3-hexenol and 2,3-pentanedione, benzaldehyde and m-xylene, ethyl butanoate and 2-methylbutanol, and isobutyl isopentanoate and 1-hexanol) were investigated by PTR-TOF-MS to assess its mass-resolving power for food-flavour applications. Headspace analyses of aqueous solutions containing nominally isobaric aroma compounds that are unresolvable by PTR-QMS demonstrated that the PTR-TOF-MS mass-resolving power, which is m/z-dependent, enabled discrimination between isobaric peaks at a centre of mass separation down to at least 0.030 Da. Visual discrimination between these isobaric compound peaks in the headspace of aqueous solutions down to a concentration range of a few tens of ng mL−1 was also possible, enabling an empirical method for determining the limit of quantitation in solution for single compounds. PTR-TOF-MS offers distinct advantages over conventional PTR-MS for certain flavour release applications.