The microbial metabolites geosmin and 2-methylisoborneol (2-MIB) are of significant concern for two key industries worldwide: aquaculture, currently the fastest-growing food production sector, and the drinking water industry [1,4]. These compounds elicit well-known off-flavors that pose a major hurdle for the growth of aquaculture, particularly in recirculated aquaculture systems (RAS), as they greatly hamper fish marketability and thus the economic sustainability of the fish farms [1,2,3]. Their identification and quantification in water has hitherto only been reported using chromatographic methods [5,6,7]. With odor thresholds as low as 5-10 ng/L in water and 0.25 µg/kg in fish [3], robust and highly sensitive methods are necessary for a reliable quantification. Although chromatography offers comprehensive analysis, it is oftentimes slow and tedious. Therefore, the development of more rapid analytical methods to monitor off-flavor trace levels in both drinking and aquaculture water can be of great benefit for early outbreak detection and product quality monitoring. This study proposes a novel method for quantification of these terpenoids in water based on proton-transfer-reaction mass spectrometry (PTR-MS) . First, the study investigated the fragmentation pattern of both compounds under standard proton-transfer-reaction conditions to determine specific ions suitable for quantification. Second , a static headspace (SH) method was developed after an optimization design that investigated the effect of three selected variables: temperature (°C), time (min) and NaCl content (g/L) . Finally, optimal and suboptimal PTR-MS-based methods were evaluated from an analytical standpoint (repeatability, linearity, LOD and LOQ) and their performances were compared with an established GC-MS-based method [8] . Results, on the one hand, show the typical behaviour of these two microbial metabolites in H3O+-mediated reactions , dehydration , reported for the first time in PTR-MS studies. On the other hand, a sensitive ( with LOD of 5 ng/L and 10 ng/L for 2-MIB and geosmin respectively) and fast method (10-15 min) for the quantification of these two metabolites in water samples was successfully developed. This opens the door for further developments in the quick monitoring of a wider range of contaminants and/or undesired metabolites in aquaculture and drinking water through PTR-MS.
References
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