Doctor of Philosophy
Department of Chemistry
Korth, Wolfgang, Determination of odour compounds in surface waters, Doctor of Philosophy thesis, Department of Chemistry, University of Wollongong, 1992. https://ro.uow.edu.au/theses/1133
Deuterated geosmin [trans-1,10-[2H3]-dimethyl-9α-decaloll and deuterated 2- methylisoborneol [2-exo-hydroxy-2-[2H3]-methylbornane] have been synthesised and evaluated as internal standards in the determination of geosmin and 2-methylisoborneol (MIB) in water by closed loop stripping analysis (CLSA) followed by gas chromatography/mass spectrometry (GC-MS) in either the full scan or multiple ion detection mode (MID).
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 three weeks later. The new standards gave better precision and accuracy than the chloroalkanes and overcame the underestimation of analyte concentration which usually results from losses of analyte through adsorption, volatilisation, biodegradation etc. during sample transport and storage. When added immediately before closed loop stripping, the labelled standards negated the need for reanalysing samples or frequent recalibration as they insensitive to changes in CLSA parameters such as, flow rate through the carbon filter, stripping time or temperature, size or shape of stripping bottle, salt concentration, sparging rate and air leaks.
Geosmin had a limit of detection of
Geosmin and MIB were stored (at room temperature and -15°C) as dilute solutions in methanol, ethanol, hexane, carbon disulphide and acetone for two years without deterioration. Dichloromethane caused substantial decomposition of MIB (but not geosmin) when stored at room temperature. However, neither compound deteriorated when stored (~ 2 years) at -15°C. The labelled compounds were effective internal standards for the determination of other volatile odorous metabolites such as the carbonyl compounds β-cyclocitral, β-ionone, geranylacetone and 6-methylhept-5-en-2- one.
An enantioselective GC technique was developed which enabled the use, for the first time, of (+)-geosmin or (+)-geosmin-d3 (from (±)-geosmin or (±)-geosmin-d3) as the internal standard for the determination of (-)-geosmin, with detection being either flame ionisation detection (FID) or MID. When (±)-geosmin-d3 is added at the time of sampling, rather than at the time of analysis, the (-)-labelled enantiomer compensated perfectly for losses of natural (-)-geosmin by biodegradation or physical and chemical processes during sample transport and storage.
Several gas chromatographic techniques were evaluated using nonchiral and chiral capillary columns combined with FID and MID detection. The order of precision and accuracy of the various methods is: enantioselective GC-MJD (labelled (t)-standard) > GC-MID (labelled (±)-standard) > enantioselective GC-FID (unlabelled (±)-standard) > enantioselective GC-FID (labelled (±)-standard).