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5.2 The air sample is analyzed for Cz to C2 halogenated hydrocarbons by using either the loop method or the freeze -out trap method. The freeze -out trap method is used for ppb to ppt (parts per trillion) concentrations. 5.2.1 The procedure for the loop method follows: 5.2.2 The air sample is transferred from the gas sample bag and injected into the sample loop of the GC using a clean 100 mL syringe fitted with a Luer-lok to quick - connect adapter. 5.2.3 The gas sampling valve (rotary type) is equipped with a 1 mL loop. 5.2.4 The gas sampling valve is rotated and the sample enters the GC analyzer and is separated into component com- pounds. 5.2.5 A Carbowax 1500/Carbopak C column is used to separate the halogenated hydrocarbons. Typical operating con- ditions for the gas chromatograph are: 25 mL/min helium carrier gas flow 40 mL/min 10% methane in argon make-up flow gas 80°C 10 -port valve compartment temperature 150°C injection port temperature 380'C detector temperature 6 to 1600C at 8°C/min programming column temperature Backflush: 23 min. 5.2.6 Each separated component passes through the electron capture detector and yields a response proportional to its response factor and concentration. 5.2.7 Concentrations of halogenated hydrocarbons may be cal- culated using an electronic integrator. 5.3.1 The procedure for the freeze -out method follows: 5.3.2 Immerse the sample trap in liquid nitrogen MN 2 ) and allow the temperature to stabilize while maintaining a flow of helium through the system. 5.3.3 After discarding about 50 mL of the sample, withdraw exactly 100 mL from the sample bag with a 100 mL syringe and transfer the sample into the trap. 5.3.4 Backfill the syringe with another 40 mL of helium and flush the 40 mL trrough the trap; then flush the carrier helium through the trap for three minutes. 5.3.5 Isolate the cryogenic trap by using the isolation valve which allows the carrier gas to by-pass the trap. i