Determination of 18 Volatile Organic Compounds in Exhaust Gas from Stationary Polution Source of Rare Earth Extraction Separation Workshop by Gas Chromatography-Mass Spectrometry after Thermal Desorption

A method for determination of 18 VOCs (1,1-dichloroethane, 1,2-dichloroethylene, 1,1,2-trichloroethane, toluene, 1,2,4-trimethylbenzene, benzene, trichloroethylene, tetrachloroethylene and 10 n-alkanes such as C₇~C₁₆) in the exhaust gas from stationary polution source of rare earth extraction separation workshop was proposed by gas chromatography-mass spectrometry after thermal desorption. The sampler was combined with 2 adsorption tubes (loaded with 2 types of graphitized carbon black and 1 type of carbon molecular sieve) in series to collect 50 mL of the sample at sampling rate of 50-65 mL·min^-1 from the exhaust port of the stationary polution source. The adsorption tube was sealed and placed on the thermal desorption instrument, and the contents of 18 VOCs in the collected gas were determined according to the optimized working conditions of the instrument (the contents of benzene and tetrachloroethylene were the sum adsorption capacity of 2 adsorption tubes). The desorption temperature of the adsorption tube and the focused cold trap was set to 350 ℃, and the desorption time was set to 10 min. As shown by results, the linear range of standard curve for 10 n-alkanes was 50.0-400 ng, and the masses had linear relationships with ratios of peak areas between the other 8 VOCs and internal standards in the range of 20.0-300 ng, with detection limits (3s) in the range of 0.001 5-0.026 mg·m^-3. Test for recovery by addition standard method was made on blank samples at the 3 concentration levels, giving results of recovery in the range of 73.5%-110%, and RSDs (n=5) of the determined values ranged from 1.2% to 22%. The above method was used for analyzing blank spiked samples in 4 laboratories, and absolute values of the deviation obtained were less than the reproducibility limits calculated with referring to HJ 168-2010.