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n <br />standard mixture. <br />3 Apparatus <br />3.1 A sampler with bags is required for each site. The <br />sampler and bags are prepared and operated as des- <br />cribed in the "Procedure for Atmospheric Tedlar Bag <br />Sampling". <br />4 Reagents <br />4.1 All gases used in the GC analysis shall be of the <br />highest commercial quality available. <br />4.2 Helium shall have a purity of 99.995X. <br />4.3 Halogenated hydrocarbons reference liquid standards, <br />99% purity as listed in 1.4 are used to prepare a <br />10 ppb working standard mixture which is used as a span <br />gas. <br />4.4 A mixture of 10 percent methane in argon is used as <br />make-up gas in the GC. <br />4.5 Commercial liquid nitrogen (b.p. _ -1960C) is used to <br />cool the freeze -out trap. <br />5 Procedure <br />5.1 Bags and samplers are fabricated, tested, and operated <br />as described in Appendix B, "Procedure for the Fabri- <br />cation and Testing of Sample Bags". <br />3 <br />3.2 <br />A gas chromatograph (GC) equipped with a gas inject- <br />ion valve and freeze -out trap inlet system is required. <br />An electron capture detector is used. <br />3.3 <br />One GC column is required: A glass column (6 ft x <br />1/4 in O.D.) packed with 0.2 percent Carbowax 1500 <br />on Supelco 80/100 mesh Carbopac C. <br />3.4 <br />Other GC supportive apparatus used are a strip chart <br />recorder, a remote controller, and an electronic <br />integrator. <br />3.5 <br />Ground glass syringes (50, 100, and 250 mL capacity) <br />or other suitable devices to accurately transfer air <br />samples from Tedlar bags to the sample inlet of the <br />GC are used. <br />3.6 <br />A large air -tight chamber is used to prepare standard <br />gas mixtures. <br />3.7 <br />The cryogenic traps holding the liquid nitrogen are <br />Dewar containers. <br />4 Reagents <br />4.1 All gases used in the GC analysis shall be of the <br />highest commercial quality available. <br />4.2 Helium shall have a purity of 99.995X. <br />4.3 Halogenated hydrocarbons reference liquid standards, <br />99% purity as listed in 1.4 are used to prepare a <br />10 ppb working standard mixture which is used as a span <br />gas. <br />4.4 A mixture of 10 percent methane in argon is used as <br />make-up gas in the GC. <br />4.5 Commercial liquid nitrogen (b.p. _ -1960C) is used to <br />cool the freeze -out trap. <br />5 Procedure <br />5.1 Bags and samplers are fabricated, tested, and operated <br />as described in Appendix B, "Procedure for the Fabri- <br />cation and Testing of Sample Bags". <br />3 <br />