Sampling Gases from a Hostile Environment Andrew E. O’Keeffe Diuision of Chemistry and Physics, OfJice of Research and Monitoring, Environmental Protection Agency, National Encironmental Research Center, Research Triangle Park, N.C. 27711
ANALYSIS of gases that exist in an environment such as a flue, stack, or engine exhaust conduit can be a difficult assignment. Instrumentation is rarely available to accomplish the desired analysis under the conditions encountered, which typically include elevated temperature and the concurrent existence of high concentrations of gaseous, liquid, and solid interferences. The recent emergence ( I ) of instruments capable of measuring ambient levels of the gases with which we are presently concerned suggests very strongly that a sampling scheme should be devised that will reproducibly extract a sample from such an environment and deliver it to an appropriate ambient-level instrument for analysis. With the above end in view, and drawing upon our experience in accomplishing the quantitative transfer of minute amounts of pure gases (2-4, we have devised and demonstrated in the laboratory with equipment simulating stack conditions the following sampling scheme. Nitrogen containing 950 ppm of sulfur dioxide was passed through a 75-cm length of 1-cm i.d. quartz tubing. A flame photometric SO2 analyzer ( 5 ) (with associated pump) drew 200 rnl min-l of clean air through a 4-mm i.d. by 1-mm wall poly(tetrafluoroethy1ene) tube suspended along the axis of the quartz tube. A 10-cm segment of the assembly was maintained at 250 O C by enclosing it in a tubular combustion furnace. Under these conditions, the air sample delivered to the analyzer contained a constant and reproducible 0.9 ppm of SO2. Further, stepwise changes in the concentration of sulfur dioxide entering the quartz tube were followed, (1) R. K. Stevens and A. E. O’Keeffe, ANAL.CHEM.,42 (2), 143A (1970). (2) A. E. O’Keeffe and G. C. Ortman, ibid.,38,760 (1966). (3) A . E. O’Keeffe, ibid., 39, 1047 (1967). (4) F. P. Scaringelli, A . E. O’Keeffe, E. Rosenberg, and J. P. Bell, ibid., 42,871 (1970). ( 5 ) S. S. Brody and J. E. Chaney, J . Gas Chromatogr.,4, 42 (1966).
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FILTER 7
4 A A
STACK Figure 1. Schematic of proposed stack-sampling device
within a few seconds, by corresponding changes in the output signal. A suggested simple stack-sampling device, based on the laboratory demonstration described above, is shown in schematic form in Figure 1. Work recently completed in another laboratory and now being prepared for publication (6) will provide more detailed experimental data than I a m able to supply. (6) C. E. Rodes, Environmental Protection Agency, Technical Center, Box 12055, Research Triangle Park, N.C. 27711 (M.S.
Thesis, North Carolina State University), unpublished work.
Volume Flowmeter for Gases of Variable Viscosity or Thermal Conductivity J. F. Parcher and C. L. Hussey Department of Chemistry, The Uniuersity of Mississippi, University, Miss. 38677 IN THE COURSE of a n investigation of frontal chromatography, it was necessary to measure the volume flow rate of a series of gases with continuously varying composition, for example, a binary mixture of n-hexane and helium with the composition varying from pure helium to pure n-hexane. The thermal conductivities of hexane and helium are 46 ( 1 ) and 368 cal/ sec-cm-’C x 10-6 (2), respectively, at 100 “C., while the viscosities are 84 ( I ) and 227 (2) micropoises. Thus the (1) “Handbook of Chemistry and Physics,” R. C. Weast, Ed., The Chemical Rubber Co., Cleveland, Ohio, 51st ed., 1970. (2) R. W. Gallant, “Physical Properties of Hydrocarbons,” Gulf Publishing Co., Houston, Texas, 1968. 1102
ANALYTICAL CHEMISTRY, VOL. 44, NO. 6, MAY 1972
thermal conductivity and viscosity of the gas mixture varied dramatically, and under normal chromatographic operating conditions-Le., constant inlet pressure and with a thermal conductivity detector-the flow rate and detector response also varied with the gas phase composition. The normal soap bubble flowmeter is not applicable under these conditions because of the presence of a component, which condenses out in water. Also, any hydrocarbon will interfere with the formation of the soap bubbles. The capillary and rotameter flowmeters cannot be used because of the variable viscosity of the gas. The other common type o f flowmeter is the mass flowmeter. However, this flowmeter is useful only for gases with constant thermal conductivity.
