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Previously there have been numerous reports of an illness commonly called "sick building syndrome" associated with a variety of offices, schools and other public access buildings. Many outbreaks of illness have been attributed to some aspect of internal building environment, the building fabric or building tightness and lack of sufficient ventilation. Building related health problems may be due to the contamination of indoor air by emissions of volatile organic compounds (VOC's) from building fabrics and furnishings, equipment, maintenance supplies (including paints, stains, adhesives, and caulks, containing petroleum-based solvents), cross contamination, bioeffluents and combustion by-products. In addition, it has been suggested that exposure to environmental tobacco smoke in occupational environments should be limited due to the potential health problems associated with these pollutants. Because many of these compounds are toxic, knowledge of the levels of such materials in the indoor environment is required in order to determine human health impacts and methodology needs to be developed in order to detect, positively identify, and quantitate the VOC's in air.
The American Chemical Society (ACS) recently participated in Congressional meeting on issues affecting indoor air pollution. This year, Congress has taken an active interest in indoor air pollution. Politicians have become aware that chemical contamination from construction and common household products may be creating health concerns. Bills in the House (H.R. 1066) and the Senate (S. 455) will involve the Environmental Protection Agency in research projects to study the sources and effects of indoor air contaminates. The society urged the congressional committee to increase funding for research in this area. (1)
The new Short Path Thermal Desorption System permits the analysis of samples by desorbing the samples directly into the gas chromatograph (GC) injection port for subsequent analysis by conventional GC detectors or via mass spectrometers. Due to its "short path" of sample flow, this new system overcomes the shortcomings of previous desorption systems by eliminating transfer lines (which are easily contaminated by samples) and providing for the optimum delivery (and therefore maximum sensitivity) of samples to the GC injector via the shortest path possible.
Figure 1 - GLT Desorption Tube packed with Adsorbent Resin for the collection of volatiles in air.
The desorption sampling tubes are constructed from Glass Lined Stainless Steel (GLT) tubes (0.25" O.D. x 4mm I.D. x 4.0" long) packed with an adsorbent porous polymer resin, 2,6-diphenyl-p-phenyleneoxide sold under the trademark Tenax®-TA and the activated graphitized carbon sold under the trademark Carbotrap (Figure 1). The adsorbent resins are held in place between two glass wool plugs. A wide variety of other adsorbent resins are commercially available which could also be utilized the selection of which will need to be determined by the operator and the nature of the pollutants being studied (2). After packing, the desorption tubes are conditioned by heating from room temperature to 320 degrees C at 4 degrees per minute and then holding at 320 degrees for four hours under constant helium gas flow of 20 to 60 ml/min. After conditioning, the tubes are immediately capped with the stainless steel caps to maintain the integrity of the resin until ready for use. When ready for sampling, the caps are removed and the desorption tube is attached to a vacuum pump via a desorption tube connector. A commercially available sample pump such as the SKC PCXR3 or other vacuum pump capable of pumping air through the packed desorption tube at a rate between 20ml/min and 200 ml/min is used to pump a known volume of air through the desorption tube, trapping the volatiles present in the adsorbent resin there in. The quantity of air sampled ranges from 1 liter to 1000 liters, depending upon the sample being analyzed and the method of analysis. After collecting, the stainless steel caps can be reinstalled on the desorption tube until ready for analysis (Figure 2).
Figure 2 - Schematic of the Technique of Short Path Thermal Desorption
When ready for analysis, the stainless steel caps are removed and the desorption tube is attached to the Short Path Thermal Desorption System and a needle cap is attached to the opposite end. The sample is then injected into the GC injection port, the desorption tube blocks are closed around the desorption tube and the desorption tube is ballistically heated to 150 degrees C with continuous gas flow through the sample for 10 minutes to drive the volatiles into the GC injection port. After desorption is complete, the GC is programmed from its initial temperature of -40 degrees C to 280 degrees C at 10 degrees per minute. Initial cryotrapping of the desorbed compounds at -40 degrees is required in order to trap the desorbed volatiles in a narrow band at the front of the GC column. The resulting compounds are identified via a mass spectrometer for positive identification of the eluted peaks.
Sample Collection Results and Discussion
Air samples from a newly constructed energy efficient house and a New York Skyscaper were analyzed with a Varian 3400 GC connected to a Finnigan MAT high resolution magnetic sector mass spectrometer to detect the presence of volatile organic compounds (VOC's) in the air. Both low and high boilers were present in the indoor air of the newly constructed energy efficient house (Figure 3). Although many low boilers were detected in the indoor air of the New York City skyscaper, very few high boilers were present (Figure 4). These samples were analyzed using a split injector with split ratios of at least 10 to 1.
Figure 3. Indoor air (100L) of a newly constructed energy efficient house
Figure 4. Indoor air (1000L) of New York skyscraper
Figure 5 shows the result of analyzing 15 liters of air from a two car garage of a residential home in which cars, lawn mowers, and gasoline are stored. The resultant compounds were identified as a variety of aromatics and hydrocarbons characteristic of gasoline. This sample was analyzed direct, with no split at the injection port.
Figure 5. Indoor Air (70L) of Household 2 Car Garage With Vehicles, Lawn Mowers, Gasoline, Etc.
In many cases, indoor air concentrations of many organic volatiles are substantially higher than outdoor levels of these same components. Figures 6 and 7 show this difference in a rural environment. A volume of 100 liters of air was required to detect any significant levels of volatile chemicals in the outside air; whereas, a 15 liter sample of indoor air was sufficient to detect volatiles in the indoor air sample. Both of these samples were analyzed on the H.P. MSD, direct with no splitting of the sample. Sources of organic chemicals are quite numerous within any indoor environment and vary depending on the type of structure, furniture, and equipment contained within. Generally, new buildings show higher levels of volatiles. This is partly due to the better sealing and energy efficiency of newer structures, which traps more volatiles and recirculated them without dilution from outdoor air. It is also due to the outgassing of compounds from building materials and furnishings.
Figure 6 - Outdoor Air In Rural Environment, 100 l. Sample
Figure 7 - Indoor Air, 151, Sample
The principal VOC's of concern are halogenated aliphatic and aromatic hydrocarbons and aromatic hydrocarbons and benzene. These can include but are not limited to the following:
4. Carbon Tetrachloride
10. Methylene Chloride
Sources of these VOC's within residences include building materials and furnishings, cleaning solvents, fuels and releases from tap water, and equipment. Figure 8 shows the volatiles emitted from the polymer coatings on printed circuit boards and other components within the equipment. They tend to be more readily emitted at the elevated temperatures at which the equipment is subjected to during normal running.
Figure 8 - Air Sample Inside PC Computer, 51. Sample
Many halogenated and benzene family VOC's are known or suspected human carcinogens. There also exist an assortment of VOC's present in homes and public buildings worldwide that have neurotoxic and/or genotoxic properties. Among these are acetone, formaldehyde, methylethylketone, hexane, benzene, toluene, and xylene used in building materials, furnishings and adhesives. Chlorinated hydrocarbons frequently found include methylene chloride (paint strippers), trichloroethane (paints), trichloroethylene (type writer correction fluid), and p-dichlorobenzene (insect repellents).
The new "Short Path Thermal Desorption" system has proven to be an effective technique for the collection of VOC's in air and their subsequent introduction into the gas chromatograph injection port for subsequent analysis via conventional detectors or mass spectrometers. The Short Path Thermal Desorption System overcomes the shortcomings of previous desorption systems to fufill the needs for enhanced sensitivity and ultimately improved air quality control.
Betz, W.R., Maroldo, S.G., Wachob, G.D., & Firth, M.C., Characterization of Carbon Molecular Sieves and Activated Charcoal for Use in Airborne Contaminant Sampling. Am. Ind. Hyg. Assoc. 50, April 1989, pg. 181.
Long, Janice. ACS on Indoor Air Pollution, Other Issues. C&E news. May 20, 1991, pg. 40.
Travis, C.C., and Hester, S.T., Global Chemical Pollution. Environmental Science and Technology., Vol. 25, No. 5, May 1991, pg. 815.
Yttria coated filament at start
Yttria coated filament after 16,000 cycles