A colorimetric method to quantify methylisoborneol and geosmin in water and fish flesh based on a spot test by Wood and Snoeyink was developed. To test water samples, one liter of filtered water is pumped through a solid phase extraction device and the off-flavor eluted from the device with toluene. The toluene is combined with a 1 percent vanillin in concentrated sulfuric acid and agitated for 30 min to produce the color change. The standard solution is yellow and at increasing concentrations of 2-methylisoborneol or geosmin the color changes from light orange to blood red. Extraction from 1 liter of water results in a sensitivity of 1 ppb. This is suitable for quality control of seafood. For use in measuring action levels (high and low ppt levels for aquaculture and drinking water, respectively), extraction from greater volumes will be required.

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