Automated determination of picogram-per-liter level of water taste and odor compounds using solid-phase microextraction arrow coupled with gas chromatography-mass spectrometry

Taste and odor compounds are organic chemicals produced via biochemical processes, and their presence, even at low nanogram-per-liter concentrations, can make water useless for drinking purposes. In this work, a very sensitive and completely automated analytical procedure, based on solid-phase microextraction, has been developed and optimized for determination of seven taste and odor compounds in water media, well below their odor threshold. The selected analytes were isopropyl-3-methoxypyrazine, 2-isobutyl-3-methoxypyrazine, geosmin, 2-methylisoborneol, 2,4,6-trichloroanisole, 2,4,6-bromoanisole, and beta-ionone. Compared with a conventional approach, the recently introduced PAL SPME Arrow showed a significant enhancement in sensitivity and also outstanding robustness and stability. Three commercially available fiber coatings, as well as experimental parameters of the headspace extraction procedure, such as extraction temperature, time, and ionic strength of the aqueous sample, were investigated to optimize the method. The linearity of the response was assessed over a three-orders-of-magnitude range, with R-2 values higher than 0.9914. The method was satisfactorily precise, with RSDs less than 11% at the second lowest calibration point (10-26ngL(-1)). The calculated LODs (S/N=3) were below odor thresholds of the target analytes and varied between 0.05 and 0.6ngL(-1), for just 10mL of water sample. An original and spiked river water sample was also analyzed, and relative recoveries of 75-116% were achieved. Based on these analytical performance characteristics, and compared with other published methods, the present method can be considered as the most sensitive wholly automated approach for determination of taste and odor compounds in water.