Lapack, MA; Tou, JC; Enke, CG
Simple membranes at the inlet of a mass spectrometer were used to concentrated volatile aromatic hydrocarbons and halogenated hydrocarbons for analysis at the parts per billion level. Thinner membranes had greater throughput and shorter response times. Thicker membranes had lower throughput and longer response times. Higher temperatures also produced reduced response times, but resulted in a lowered concentration of the analytes and reduced selectivity. The geometry of the hollow fiber membrane inlet which was most effective had a configuration in which the sample flows through the inside of the hollow fiber and the analyte gases are collected on the outside of the fiber for analysis. The membranes were made from poly(dimethylsiloxane) elastomer. Membrane dimensions were 25 centimeters long with an 0.0305 centimeter inside diameter and 0.0635 centimeter outside diameter. A second membrane was 25 centimeters long with an inside diameter of 0.147 centimeters and an outside diameter of 0.196 centimeters. The mass spectrometer was a Balzers QMG 511 with a quadrupole analyzer. The analyzer pressure was 0.3 microtorr and the base pressure was 0.002 microtorr. The analytes included chloromethane, dichloromethane, chloroform, carbon tetrachloride, chloroethene, 1,1-dichloroethene, trichloroethene, tetrachloroethene, dibromomethane, bromoform, benzene, toluene, ethylbenzene, chlorobenzene, 1,3-dichlorobenzene, and 1,2,4-trichlorobenzene. (King-PTT)