The determination of geosmin and 2-methylisoborneol in water using isotope dilution high resolution mass spectrometry

Geosmin and 2-methylisoborneol (2-MIB) are extracted from water onto Ambersorb 572, desorbed into dichloromethane (DCM) and analyzed by gas chromatography-high resolution mass spectrometry (GC-HRMS) at a mass resolution of 7000. The use of the granular adsorbent Ambersorb 572 allows extraction by rolling the sample bottle, isolation of the adsorbent by filtration, desorption of the analytes into DCM in the autosampler vial and injection without plugging the syringe needle. Because there is no sample clean-up, HRMS is necessary to differentiate the analytes from chemical interferences when present. Isotope dilution quantitation with d3-geosmin and d3-2-MIB is required because the recoveries of geosmin and 2-MIB from water are highly variable. The Ambersorb 572/GC-HRMS method with isotope dilution quantitation was compared with the closed-loop stripping (CLS)/GC-low resolution mass spectrometry (LRMS) method with external standard quantitation. Increased productivity (up to 40 samples/day), faster turnaround times (48 h), better between-run precision (7.7% for geosmin and 5.5% for 2-MIB) and accuracy (±11% for geosmin and ±6% for 2-MIB) over the CLS/GC-LRMS method were achieved. Detection limits of 2.0 ng/L for geosmin and 2.0 ng/L for 2-MIB were obtained for the Ambersorb 572/GC-HRMS method. The method was successfully applied to 152 samples from Lake Ontario water supplies.