On-tap passive enrichment, a new way to investigate off-flavor episodes in drinking water

Because taste and odor events in drinking water are often fleeting and unpredictable phenomena, an innovative enrichment sampler has been developed to trap off-flavor compounds directly at the consumerʹs tap. The ARISTOT (Advanced Relevant Investigation Sampler for Taste & Odor at Tap) consists of a tap adapter in which seven polydimethylsiloxane (PDMS) coated stir bars are placed, allowing the stir bar sorptive extraction (SBSE) of organic compounds during each tap opening. In order to study the efficiency of ARISTOT, a private network pilot unit has been constructed in our laboratory, equipped with four faucets in parallel, solenoid valves for an automation of the system and a mixing chamber to spike drinking water with odorous compounds in order to have homogenously smelling water at each tap. After enrichment, the stir bars are taken out, in-line thermo-desorbed and analyzed by gas chromatography coupled with a mass spectrometer. The results showed the high sensitivity of ARISTOT, which was able to quickly monitor odorous compounds at the sub ng/L level. A “multishot” method was developed to analyze chemicals concentrated on the seven stir bars in only one chromatographic run, thereby increasing the sensitivity of the system. Higher enrichment factors were obtained under low water flow rates or by using longer stir bars and/or stir bars with a higher PDMS film thickness. No significant loss of extracted compounds was reported for flow rates between 2 and 4 L/min. This allowed us to spike the stir bars with an internal standard prior to sampling in order to monitor the analytical variations. It was also observed that hot water increases the loss of enriched solutes but the quantification can be corrected by internal standard addition.