Comparison of two methods for the determination of geosmin and 2-methylisoborneol in algae samples by stable isotope dilution assay through purge-and-trap or headspace solid-phase microextraction combined with GC/MS

Abstract

Geosmin (1,2,7,7-tetramethyl-2-norborneol) (GSM) and 2-methylisoborneol (2-MIB), produced from the growth of blue-green algae, commonly found in lakes and reservoirs, are the major compounds responsible for the earthy and musty odours in drinking water. Two pre-extraction methods (purge-and-trap (PT) and headspace solid-phase microextraction (HS-SPME)) combined with gas chromatography/mass spectrometry (GC/MS), were introduced and compared in this study to establish simple, rapid, sensitive and selective methods for determination of GSM and 2-MIB in eutrophic water samples and algae cells. A stable isotope dilution assay (SIDA) was applied in these two methods to eliminate the matrix effect and improve the recoveries of the analytes. The deuterated compounds d₅-GSM and d₃-MIB were employed as internal standards for SIDA. SIDA-PT-GC/MS and SIDA-HS-SPME-GC/MS methods were evaluated and optimized for the extraction and detection of these two compounds. These two methods show good linearity over the concentration range of 10–500 ng L⁻¹ and give detection limits of 3.60 ng L⁻¹ of GSM and 4.12 ng L⁻¹ of 2-MIB for SIDA-PT-GC/MS, and 3.00 ng L⁻¹ of GSM and 3.10 ng L⁻¹ of 2-MIB for SIDA-HS-SPME-GC/MS. The recoveries of spiked 20, 100 and 500 ng L⁻¹ of GSM and 2-MIB from raw drinking water ranged from 81–104% for GSM and 89–111% for 2-MIB by means of SIDA-PT-GC/MS, and 83–98% for GSM and 85–121% for 2-MIB by SIDA-HS-SPME-GC/MS analysis. The SIDA-PT-GC/MS method is better used to analyze GSM and 2-MIB in clearer water samples, while SIDA-HS-SPME-GC/MS has some advantages in the determination of these two compounds in algae cells or eutrophic water samples.