Determination of 2-MIB and Geosmin in Surface and Ground Water by Stir Bar Sorption Extraction/GC/MS in Full Scan Mode

摘要

? A method using stir bar sorptive extraction (SBSE) combined with gas chromatography (GC) /mass spectrometry (MS) in full MS scan mode has been applied for analyzing 2-methylisoborneol (2-MIB, or MIB) and trans 1,10-dimethyl-trans-9-decalol (geosmin) in ground water and surface water. Several extraction procedures and the GERSTEL instrument component parts play important roles relating to the extraction efficiencies. Parameters such as pH, ionic strength in the sample solution, sample volume, sorptive time, temperature, film thickness of the stir bar, and the diameter and inside packing materials of the Cooled Injection System (CIS 4) liner, were optimized. ? The full MS scan mode (scan range from MS m/z 40 to m/z 450) is used in this method instead of using selected ion monitoring (SIM) for determination of 2-MIB and geosmin. The advantages of full MS scan mode are to provide a molecular fingerprint of mass spectrum of 2-MIB and geosmin at lower concentrations and to identify them from the sample matrix interference. ? The analytical results generated by this method with the internal standard and surrogate compounds are highly reproducible, reliable and provide a broad calibration range. The detection limits for 2-MIB and geosmin are 3 ng/L, or 3 part per trillion (ppt) each. Based on the method detection limit (MDL) study, the detection limits can reach even lower than 3 ppt. The current calibration ranges are from 3 ppt to 80 ppt with the relative standard deviation (RSD) of relative response factor (RRF) less than 20%. The method has been in use for a year to monitor the 2-MIB and geosmin concentration levels of one San Francisco water reservoir. The results show the matrix interference can be minimized with the full mass scan mode.