水中土臭素，2-甲基异莰醇检测方案(自动进样器)

Author Anne Jurek Applications Chemist EST Analytical Cincinnati， OH Determination of 2-Methylisoborneoland Geosmin in Water Using SolidPhase Micro Extraction Application Note Environmental Abstract The compounds 2-Methylisoborneol (2-MIB) and Geosmin are theprimary source of the foul odor found in drinking water. Algalcontamination is the principal cause of the formation of thesecompounds. Geosmin and 2-MIB have such a low odor threshold，that even the slightest amount can produce an unpleasant odor andtaste in drinking water. Thus， developing a reliable sampling andanalysis platform for very low level detection is important.Standard Method 6040D describes a procedure for the detection of2-MIB and Geosmin using Solid Phase Micro Extraction (SPME)coupled with a Gas Chromatograph (GC) and Mass Spectrometer(MS). Selective lon Monitoring (SIM) is used for compounddetection down to part per trillion (ppt) levels. This examinationwill optimize the sampling and detection of 2-MIB and Geosmin. Introduction： It has been found that the presence of blue green algae in water sources produces 2-MIB andGeosmin. Both Geosmin and 2-MIB are malodorous compounds that emit a musty earthy aroma.When the algae generates an abundance of these compounds in a drinking water reservoir， there areresulting taste and odor problems. Algae blooms are influenced by their climate， as a result， theformation of Geosmin and 2-MIB is more of a problem during the summer months and in warmerclimates. Areas in the southwestern portion of the United States seem to have the most problemswith 2-MIB and Geosmin. Drinking waters are tested in order to determine water quality for prospective consumers. Two ofthe major complaints that water suppliers need to address are issues with taste and odor. Geosminand 2-methylisoborneol (2-MIB)， although non-toxic， both have very strong odors and can bedetected at levels below 10ppt. Thus， developing a reliable sampling and analysis platform isimportant. Standard Method 6040D addresses the sampling and analysis of 2-MIB and Geosmin utilizing SPMEin conjunction with GCMS in Single lon Monitoring (SIM) mode. The SPME fiber is placed in theheadspace above the sample for a period of time and then the fiber is inserted into the GC injectionport for analyte desorbtion onto the GC column. This application will develop and optimize Method6040D experimental parameters for the determination of 2-MIB and Geosmin down to 5ppt. Experimental： Headspace SPME is a non-exhaustive sampling technique so the experimental conditions requiredoptimization in order to make the extraction technique both efficient and reproducible. For theautomation of the sampling process， the EST Analytical FLEX autosampler was used. The FLEXsuite software simplified the sample method development process with the ease of its drag and dropmethod builder. The most efficient SPME fiber for this analysis was a Divinylbenzene/Carboxen/Polydimethylsiloxane(DVB/CAR/PDMS) coated fiber with a 50/30um film thickness. The Shimadzu QP2010 SE GCMSwas run in SIM mode and was fitted with a SPME liner and a Restek Rxi-5 Sil MS column. Theautosampler and GCMS experimental conditions developed for this analysis are listed in Tables 1and 2. Table 1： FLEX Autosampler Experimental Parameters GC/MS Shimadzu QP 2010 SE Inlet Split/Splitless Inlet Temp. 270°C Inlet Head Pressure 40.7kPa Mode Splitless Injection Pulse Pressure 50kPa for 2.0 min Carrier Gas Split Ratio 2 Desorption 3.0min at 270°C Column Rxi-5 Sil MS 30.0m X 0.25mm X 0.25um 60°C hold for 2.0 min.， ramp 8°C/min to 200°C， Oven Temp. Program hold for 0.5min， 20min run time Column Flow Rate 0.8ml/min Gas Helium Linear Velocity 32.6ml/min Source Temp. 220°C MS Transfer Line Temp. 300°C Acquisition Mode SIM SIM Ions 3.01 to 12.50min 95，107，108 SIM lons 12.51 to 20.00min 112， 125， 126 Event Time 0.30sec Solvent Cut Time 3.0min Table 2： GC/MS Experimental Parameters The 2-MIB and Geosmin standard was ordered from Supelco while Sodium Chloride was purchasedfrom Sigma Aldrich. A six point standard curve was prepared in water with a range of 5 to 100ppt.Ten milliliters of each curve standard was added to a prepared 20ml headspace vial and sealed. Theprepared headspace vials contained 2.5g of Sodium Chloride. A linear curve was attained for eachanalyte， see Figure 1. After the curve was established， seven replicate samples of the 5ppt and the50ppt standards were run in order to establish method detection limits and precision and accuracydata. Table 3 displays the experimental results and Figures 2 and 3 show chromatograms of boththe 5 and 50ppt standards. Figure 1： Calibration Curve Results Compound Curve MDL Precision Accuracy Precision Accuracy Curve R? (5ppt)%RSD (5ppt)%Recovery (50ppt)%RSD (50ppt)%Recovery %RSD (5ppt) 2-MIB 12.36 0.999 2.14 16.22 83.94 10.39 95.03 Geosmin 11.46 1.000 1.06 7.07 95.22 5.40 101.85 Table 3： Experimental Results Summary Figure 2： Chromatogram of 50ppt Standard Figure 3： Chromatogram of 5ppt Standard Conclusion The SPME analysis of 2-MIB and Geosmin more than met the method requirements of StandardMethod 6040D. The curve linearity from 5 to 100ppt had an R2 of 0.999 or greater and a %RSD ofbetter than 12.5. The resulting precision at 5ppt was about 16% for 2-MIB and 7% for Geosminwhile the recoveries were 84% for 2-MIB and 95% for Geosmin. At 50ppt both compoundsdisplayed improved precision and accuracy. Geosmin had 5.4% precision and 102% recovery while2-MIB had 10.4% precision and 95% recovery. Once the optimum parameters were established theFLEX autosampler proved to be an exceptional system for the SPME sampling of drinking watersamples. For More Information For more information on our products and services， visit our websitewww.estanalytical.com/products. EST analytical shall not be liable for errors contained herein or for incidental or consequential damages in connection with this publication.Information，descriptions， and specifications in this publication are subject to change without notice 该分析最有效的SPME纤维为带有50/30µm 厚度的Divinylbenzene/Carboxen/Polydimethylsiloxane (DVB/CAR/PDMS) 涂层。使用SIM模式的岛津QP2010 SE 气质连用，配合SPME专用衬管和Restek Rxi-5 Sil MS 色谱柱。实验使用EST公司的FLEX自动进样平台来完全进样的自动化。  在5～100ppt范围内制备了六点标准曲线。将10ml标液添加到20ml顶空瓶中并密封。顶空瓶含有2.5g氯化钠。每个待测物质都算出线性曲线。在建立曲线后，运行七个5ppt和50ppt标液的的重复样品，以确定方法检出限，精密度和准确度。  5-100ppt的线性曲线的R值为大于0.999，RSD高于12.5%。5ppt的2-MIB标液测得的精密度为16%，5ppt的土臭素的精密度为7%。2-MIB的回收率为84%，Geosmin的回收率为95%。50ppt的两种化合物均显示出更优秀的精密度和准确度。土臭素的精密度为5.4%，回收率为102%，2-MIB的精密度为10.4%，回收率为95%。