Analysis of Air Pollutants Using Sampling Tubes and Gas Chromatography John W. Russell Analytical Laboratories, Dow Chemical Co., Midland, Mich. 48640
Sampling tubes filled with gas chromatographic packings were excellent for concentrating organic pollutants from air. The collected pollutants were thermally desorbed into a gas chromatograph and quantitated using flame ionization or flame photometric detection. Advantages of the technique are ppb sensitivity and quantitative recovery, as well as superior sample stability and sampling convenience. The suitability of various sampling tube packings for collecting specific compounds was shown by determination of breakthrough volumes and recovery values.
A frequent problem in air quality analysis involves the collection of a representative and stable sample. The collection technique must ensure that pollutants be quantitatively recoverable and sufficiently concentrated to provide the necessary sensitivity. Current sampling techniques involving gas bags, evacuated bulbs, cold-trapping, or solution trapping suffer from various drawbacks, such as surface adsorption of pollutants, water or solvent interference, inconvenience, or poor sensitivity resulting from inability to concentrate pollutants. The use of sampling tubes packed with gas chromatographic adsorbents circumvents these difficulties. A known volume of air is passed through a tube a t a controlled rate. The pollutants collected on the packing are thermally desorbed directly into a gas chromatograph for analysis. The technique has been previously used to collect 2-chloro-2bromo-l,l,l-trifluoroethane on Porapak P, Porapak Q, and Apiezon K packings ( I ) . Urine metabolites collected on Tenax-GC porous polymer (2) and bis(chloromethy1)ether collected on Chromosorb 101 porous polymer ( 3 )have been determined using gas chromatography-mass spectrometry. To extend the usefulness of this technique, different adsorbents for packing tubes and the effects of air flow rate and pollutant concentration have been systematically investigated. Gas chromatographic procedures for determination of a number of organic compounds using the tubes are also reported. Particular attention was directed toward determination of the "breakthrough volume," the sampled air volume a t which the compound being collected begins to elute from the tube. The breakthrough volume is dependent upon the gas chromatographic retention time of the compound a t ambient temperature using the adsorbent as the stationary phase. Since this volume represents the maximum volume of air that may be sampled before losses of the pollutant can occur, it was determined for each pollutant to be quantitated. In addition, recovery of the pollutant was determined by comparing the quantity of pollutant recovered from a sampling tube to the quantity introduced to the air stream that had flowed through the tube.
Experimental Breakthrough volumes were determined using two sampling tubes in series. An aliquot of a standard solution of the pollutant of interest was injected into an air stream flowing through the tubes a t a known rate, usually 100 mll min. Since the presence of water can reduce breakthrough volumes, the air stream was nearly saturated by passing the air through two water-filled bubblers to simulate the most
disadvantageous humidity conditions. The injector was heated to appropriate temperatures to ensure volatilization. After a known volume of air had passed through the sampling tubes a t ambient temperature, the second tube was analyzed to determine whether the compound had eluted from the first tube, indicating breakthrough. If none eluted (less than 1% of the quantity injected), the tube was reconnected in series, more air was passed through, and th6 second sample tube was reanalyzed. This procedure was repeated until the breakthrough volume (or an arbitrary limiting volume) was reached. Breakthrough volumes from 1-10 1. were generally determined, since
