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Method TO-10A Pesticides/PCBs <br /> 12.4.2 Select solvent system(i.e.,mixtures of methanol or acetonitrile with water or mixtures of heptane or <br /> hexane with isopropanol). <br /> 12.4.3 Follow analytical procedures given in Sections 12.1.2 through 12.1.9. <br /> 12.4.4 If interferences are present, adjust the HPLC solvent system composition or use column <br /> chromatographic clean-up with silica gel,alumina,or Florisil(6). <br /> 12.4.5 An electrochemical detector may be used to improve sensitivity for some ureas, carbamates, and <br /> phenolics. Much more care is required in using this detector,particularly in removing dissolved oxygen from the <br /> mobile phase and sample extracts. <br /> 12.4.6 Chlorophenol(di-through penta-)may be analyzed by GC/ECD or GC/MS after derivatization with <br /> pentafluorobenzylbromide(EPA Method 604). <br /> 12.4.7 Chlorinated phenoxyacetic acid herbicides and pentachlorophenol can be analyzed by GC/ECD or <br /> GUMS after derivatization with diazomethane(EPA Method 515). DB-5 and DB-1701 columns (0.25-mm I.D. <br /> x 30-m)at 60 to 300°C/4°C per min have been found to perform well. <br /> 12.5 Analysis of Pesticides and PCBs by Gas Chromatography with Mass Spectrometry Detection <br /> (GC/MS) <br /> [Note: A mass spectrometer operating in the selected ion monitoring mode is useful for confirmation and <br /> identification ofpesticides.] <br /> 12.5.1 A mass spectrometer operating in the select ion monitoring(SIM)mode can be used as a sensitive <br /> detector for multi-residue determination of a wide variety of pesticides. Mass spectrometers are now available <br /> that provide detection limits comparable to nitrogen-phosphorus and electron capture detectors. <br /> 12.5.2 Most of the pesticides shown in Table 1 have been successfully determined by GC/MS/SIM. Typical <br /> GC operating parameters are as described in Section 12.1.1. <br /> 12.5.3 The mass spectrometer is typically operated using positive ion electron impact ionization(70 eV). <br /> Other instrumental parameters are instrument specific. <br /> 12.5.4 p-Terphenyl-d14 is commonly used as a surrogate for GUMS analysis. <br /> 12.5.5 Quantification is typically performed using an internal standard method. 1,4-Dichlorobenzene, <br /> naphthalene-d8,acenaphthene-dlo,phenanthrene-d,o,chrysene-d12 and perylene-d12 are commonly used as internal <br /> standards. Procedures given in Section 12.1.1 through 12.1.9 and Section 12.1.13 through 12.1.14 apply,except <br /> for the selection of surrogates,detector,and make up gas. <br /> 12.5.6 See ASTM Practice D 3687 for injection technique, determination of relative retention times, and <br /> other procedures pertinent to GC and HPLC analyses. <br /> 12.6 Sample Concentration <br /> 12.6.1 If concentrations are too low to detect by the analytical procedure of choice, the extract may be <br /> concentrated to 1 mL or 0.5 mL by carefully controlled evaporation under an inert atmosphere. The following <br /> procedure is appropriate. <br /> 12.6.2 Place K-D concentrator tube in a water bath and analytical evaporator (nitrogen blow-down) <br /> apparatus. The water bath temperature should be from 250C to 50°C. <br /> 12.6.3 Adjust nitrogen flow through hypodermic needle to provide a gentle stream. <br /> 12.6.4 Carefully lower hypodermic needle into the concentrator tube to a distance of about 1 cm above the <br /> liquid level. <br /> 12.6.5 Continue to adjust needle placement as liquid level decreases. <br /> 12.6.6 Reduce volume to slightly below desired level. <br /> Page 10A-12 Compendium of MethodsJor Toxic Organic Air Pollutants January 1999 <br />