Identification of 2,3-butanedione (diacetyl) as the compound causing odor events at trace levels in the Llobregat River and Barcelona’s treated water (Spain)

A study of organic compounds imparting sweet and buttery odor problems in the Llobregat River (northeast Spain) and in treated water was conducted. Solid-phase microextraction (SPME), gas chromatography–olfactometry, and flavor profile analysis (FPA) were used as analytical methodologies to identify the compound responsible for odor incidents. 2,3-Butanedione (diacetyl) with a concentration range of 0.90–26 μg/l in river water samples entering the water treatment plant was identified as the compound causing the odor events. Flavor profile analysis establishes 0.05 μg/l as its odor threshold concentration (OTC) in water, with an odor recognition concentration of 0.20 μg/l. The analyses were carried out with SPME–GC–MS and parameters affecting SPME extraction such as selection of the fiber (carboxen–polydimethylsiloxane), extraction time (30 min), temperature (60 °C), and ionic strength were evaluated. Quality parameters of the optimized method gives good linearity (r2>0.999), a limit of detection (0.08 μg/l) similar to the OTC of the compound, and good reproducibility (R.S.D.<20%). The SPME method was applied to identify the compound causing the odor.