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Interlaboratory comparison of geosmin and 2-methylisoborneol in municipal tap water.

An interlaboratory comparison ("round-robin") for geosmin and 2-methylisoborneol (MIB) was carried out between six laboratories of the Ontario Water Works Research Consortium (OWWRC). Municipal tap water was found to be a suitable medium for distribution of samples. To test stability, geosmin and MIB were added to tap water and stored at 2-4 degrees C. Under these conditions, geosmin concentrations declined by approximately 5% per month for the first 2 months. MIB concentrations were stable over a 158-day period. Three round-robins were carried out individually in 2001, 2003 and 2004. Two levels of geosmin and MIB were used: nominally 10 and 100 ng/l. In 2003 the relative standard deviation for all six participating laboratories were 34, 21, 21 and 22% for low and high level MIB, and low and high level geosmin, respectively. For all but MIB at the low level, there was a marked improvement in agreement between laboratories from 2001 to 2004. However, we recommend use of common analytical standards in order to potentially further reduce interlaboratory variability.