Synthesis and odour thresholds of mixed halogenated anisoles in water A. Díaz*, C. Fabrellas*, M. T. Galceran**, F. Ventura* * AGBAR, Aigües de Barcelona, Passeig de Sant Joan, 39 08009-Barcelona, Spain (E-mail: fventura@agbar.es) ** Univ. Barcelona, Dpt Anal. Chem. Diagonal, 647. 08028-Barcelona, Spain Abstract Earthy–musty off-flavour compounds in water samples are usually associated with the presence of geosmin and 2-methylisoborneol. However, the presence of 2,3,6- and 2,4,6-trichloroanisoles or other halogenated anisoles can impart objectionable tastes and odours to the water even at very low trace levels. This paper shows the synthesis of non-commercial 2,3,6- and 2,4,6- mixed chloro/bromoanisoles which can be present in bromide rich waters and could also be suspected of imparting earthy–musty off-flavours to the water. All the synthesized compounds were subjected to the flavour profile analysis (FPA) method and their odour threshold concentrations (OTC) in water were carried out giving values in the low ng/L range. Keywords Drinking water; earthy–musty compounds; flavour profile analysis; halogenated anisoles; off- flavours; rubber descriptor Introduction Tastes and odours in drinking waters are two of the major causes of complaints. Among the descriptors associated with these events, the earthy–musty descriptor is usually the most frequently mentioned by consumers. Geosmin and MIB, with odour thresholds in water at the low ng/L level, are the two compounds of this group that account for the majority of solved cases of odour events. Recently, much attention has been paid to the presence of halogenated anisoles that can impart a musty odour to water at very low concentration levels. As examples, a wide range of reported odour thresholds for 2,3,6-trichloroanisole and 2,4,6-trichloroanisole from 0.7 and 30 pg/L, respectively (Mallevialle and Suffet, 1987), to several ng/L (UKWIR, 1996) can be found in the literature. Moreover, brominated anisoles can also be detected in bromide rich waters and, thus, 2,4,6-tribromoanisole with reported odour thresholds of 2 ng/L (UKWIR, 1996) and even 30 pg/L (Griffiths, 1977) has been related as being the compound causing odour problems in treated waters (Malleret et al., 2001) and also in packaged food (Whitfield et al., 1997). The determination of compounds that can impart odours at these trace levels and could explain some of the unsolved events analysed by classic analytical methodologies (i.e. CLSA), requires the use of compounds which often are not commercially available for fur- ther development of new methods (i.e. large volume injection, stir bar. . .). This paper focuses on the synthesis and determination of odour thresholds in water of several 2,3,6- and 2,4,6-chlorobromoanisoles. These compounds are potential candidates to produce odour events in waters containing low to median bromide levels. The OTC val- ues of several synthesized compounds as well as their descriptors using the FPA method have been determined. Methods Glassware All glassware was washed with soapy water and rinsed with tap, Milli-Q water and finally acetone. Then, it was air-dried and baked at 180ºC during 12 h. Water Science and Technology Vol 49 No 9 pp 115–119 © IWA Publishing 2004 115 Downloaded from http://iwaponline.com/wst/article-pdf/49/9/115/421208/115.pdf by guest on 25 March 2021