NEW STANDARDS FOR THE DETERMINATION OF GEOSMIN AND METHYLISOBORNEOL IN WATER BY GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

Deuterium labelled geosmin and methylisoborneol (MIB) have been synthesized and evaluated as internal standards in the determination of geosmin and MIB in water by closed loop stripping followed by gas chromatography/mass spectrometry (GC/MS). The labelled standards were compared with chloroalkanes added as internal standards either at the time of sampling or immediately before closed loop stripping. When added at sampling time, the new standards enabled accurate determination of the geosmin and MIB present initially, even when the samples were analysed as much as 3 weeks later. The new standards gave better precision and accuracy than the chloroalkanes and overcame the underestimation of initial analyte concentration which usually results from losses of analyte through adsorption, volatilisation, biodegradation etc. during sample storage. Geosmin had a limit of detection of < 0.1 ng/l and 1 ng/l was determined with a coefficient of variation (CV) of 1.2% (n = 5). MIB was determined at 1 ng/l with a CV of 3.5% (n = 5).