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Pesticides/PCBs Method TO-10A <br /> [Note: Incorporating a known concentration of the solution onto the sample provides a quality assurance <br /> check to determine recovery efficiency of the extraction and analytical processes.] <br /> 11.1.8 Connect the Soxhlet extractor to the 500 mL boiling flask and condenser. Wet the glass joints with <br /> 5%diethyl ether/hexane to ensure a tight seal between the fittings. If necessary,the PUF plug can be adjusted <br /> using forceps to wedge it midway along the length of the siphon. The above procedure should be followed for <br /> all samples,with the inclusion of a blank control sample. <br /> 11.1.9 The water flow to the condenser towers of the Soxhlet extraction assembly should be checked and the <br /> heating unit turned on. As the samples boil,the Soxhlet extractors should be inspected to ensure that they are <br /> filling and siphoning properly(4 to 6 cycles/hour). Samples should cycle for a minimum of 16 hours. <br /> 11.1.10 At the end of the extracting process(minimum of 16 hours),the heating unit is turned off and the <br /> sample cooled to room temperature. <br /> 11.1.11 The extracts are then concentrated to 5 mL using a Kuderna-Danish(K-D)apparatus. The K-D is <br /> set up,assembled with concentrator tubes,and rinsed. The lower end of the filter tube is packed with glass wool <br /> and filled with sodium sulfate to a depth of 40 mm. The filter tube is then placed in the neck of the K-D. The <br /> Soxhlet extractors and boiling flasks are carefully removed from the condenser towers and the remaining solvent <br /> is drained into each boiling flask. Sample extract is carefully poured through the filter tube into the K-D. Each <br /> boiling flask is rinsed three times by swirling hexane along the sides. Once the sample has drained,the filter tube <br /> is rinsed down with hexane. Each Synder column is attached to the K-D and rinsed to wet the joint for a tight <br /> seal. The complete K-D apparatus is placed on a steam bath and the sample is evaporated to approximately 5 <br /> ML. <br /> [Note: Do not allow samples to evaporate to dryness.] <br /> Remove sample from the steam bath,rinse Synder column with minimum of hexane,and allow to cool. Adjust <br /> sample volume to 10 mL in a concentrator tube,close with glass stopper and seal with TFE fluorocarbon tape. <br /> Alternatively, the sample may be quantitatively transferred(with concentrator tube rinsing)to prescored vials <br /> and brought up to final volume. Concentrated extracts are stored at<4'C until analyzed. Analysis should occur <br /> no later than 40 days after sample extraction. <br /> 11.2 Sample Cleanup <br /> 11.2.1 If polar compounds (from example, organophosphorus and carbamate classes)that interfere with <br /> GC/ECD analysis are present,use column chromatographic cleanup or alumina. The sample cleanup will permit <br /> the analysis of most organochlorine pesticides or PCBs. <br /> 11.2.2 Before cleanup, the sample extract is carefully reduced to 1 mL using a gentle stream of clean <br /> nitrogen. <br /> 11.2.3 A glass chromatographic column(2-mm I.D.x 15-cm long)is packed with alumina,activity grade <br /> IV,and rinsed with approximately 20 mL of n-hexane. The concentrated sample extract is placed on the column <br /> and eluted with 10 mL of n-hexane at a rate of 0.5 mL/minute. The eluate volume is adjusted to exactly 10 mL <br /> and analyzed as per Section 12. <br /> 11.2.4 If both PCBs and organochlorine pesticides are sought, alternate cleanup procedures (5,6)may be <br /> required(i.e.,silicic acid). <br /> 11.2.5 Finally,class separation and improved specificity can be achieved by column clean-up and separation <br /> on Florisil(6). <br /> January 1999 Compendium of MethodsJor Toxic Organic Air Pollutants Page 10A-9 <br />