Anal. Chem. 1984, 56, 1621-1624
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Use of a Permeation Sampler for Determination of Volatile Priority Pollutants Roger D. Blanchard and James K. Hardy* Department of Chemistry, The University of Akron, Akron, Ohio 44326
A method for the sampllng and subsequent analysls of SIX volatlle organlc Prlorlty Pollutants Is described. Samples are collected by permetatlon through a slllcone polycarbonate membrane and adsorbed onto actlvated charcoal. Analysls consists of sample desorptlon and quantltatlve measurement by gas chromatography. Linearity Is obtalned between the mass of analyte collected and the product of the external concentratlon of analyte and the tlme of exposure, wlth llns arlty observed from low parts per bllllon to mld parts per mllllon. Thls method has the advantages of provldlng timewelghted-average concentratlon values, stablllzlng the collected sample, requlrlng no power, and belng simple and lnexpenslve to use. The devlce response tlme Is less than 5 mln for each compound. No slgnlflcant Interferences are observed but response Is temperature dependent. Preclslon and accuracy are comparable to presently accepted methods of collectlon and analysls.
Federal regulations which include the Federal Water Pollution Control Act of 1972 ( I ) , the Clean Water Act of 1977 (2),and a lawsuit termed the Consent Decree (3) provided the impetus for the formation of the Priority Pollutant List (4). Contained in this list is a group of 31 species classified as volatile or purgeable organics. A number of procedures have been developed for collection and determination of volatile organics (5). The present federally approved method for their determination is the purge and trap method (6, 7)in which water is collected as a grab sample or by using an evacuated container or pump and then transported from the sampling site to a laboratory where refrigerated storage may be necessary. The analysis is conducted by first purging the volatile components from a measured volume of water with an inert gas, trapping on an appropriate medium such as Chromosorb 103 or Tenax GC, and then analyzing by thermal desorption and by GC or
GC/MS. These collection procedures have a number of inadequacies. Results obtained from grab sampling are limited in that the sample only represents the conditions existing at the single point in time when the sample was taken. As concentrations can be expected to vary with time, some form of continuous sampling is often more desirable. While sampling systems that involve a pump or evacuated container can be used on a continuous basis, they are typically of limited capacity and as a result can only be used for relatively short time intervals. Once the sample has been collected, some form of on-site refrigeration must often be employed to prevent loss of the volatile components. These systems are typically bulky, expensive, and may require an external power source, all of which act to make remote or multilocation sampling difficult if not prohibitive. The following describes a method for the collection, concentration, and determination of six volatile Priority Pollutants which eliminates the inadequacies of present sampling procedures. The method is based on permeation methods 0003-2700/84/0356-1621$01.50/0
developed for ambient air sampling (8-11). A membrane is used to affect collection of compounds from the surrounding environment and the species are then trapped on the opposite surface of the membrane. The device has the advantages of low cost, simplicity, the ability to stabilize the sample, and, due to its passive nature, no power requirements. The proposed method utilizes a silicone polycarbonate membrane and a collection medium of activated charcoal. After exposure of the sampling cell to the aqueous media of interest, the charcoal is removed, the volatile components are desorbed with carbon disulfide, a proven desorption solvent (I2),and their levels are determined by gas chromatography. The species used for this study were benzene, toluene, ethylbenzene, dichloromethane, chloroform, and carbon tetrachloride. These compounds were selected due to their relative frequency of occurrence in industrial wastewaters (13).
EXPERIMENTAL SECTION Apparatus. Initial membrane evaluation was conducted by use of the exposure cell shown in Figure 1. With this cell, one side of the membrane is exposed to an aqueous solution of a single test species. The other side has a nitrogen flow across it (10 mL/min) that is directed to a flame ionization detector (Varian Aerograph, 1200 series). The cell was designed such that the volume of either side was 1mL and the exposed membrane area was 0.8 cm2. This cell was only used to evaluate the linearity and time of response of the membrane for single species. The sampling devices consisted of 17 mm i.d. glass tubing, 50 mm in length to which a silicone polycarbonate membrane (0.025 mm thick, General Electric) was affixed with silicone rubber cement. The exposure chambers were 4-L Erlenmeyer flasks in which the devices would be suspended, and magnetic stir bars were used to assure adequate circulation of the test solutions. Aluminum foil was used to cover the rubber stopper used to seal the container to prevent sample losses. The sampling device and exposure chamber are shown in Figure 2. The gas chromatograph employed for all analyses beyond the initial membrane evaluation was a Hewlett-PackardModel 5730A dual column unit equipped with twin FID detectors. Six foot by l / S in. stainless steel columns packed with 1%SP-1000on 60/80 Carbopack B (Supelco, Inc.) were used for all analyses. Temperature programming was employed with a sequence consisting of an initial temperature of 100 "C with a 4-min hold time, a temperature programming rate change of 8 "C/min, and a final temperature of 220 O C . Reagents. The sample species and carbon disulfide were all reagent grade (Fisher Scientific). Molecular sieves were used to reduce impurities in all organic liquids. The purity of each reagent was verified by gas chromatographywhere only CS2demonstrated any significant levels of contamination. It was determined that benzene was present at low levels and, as a result, blank analyses were routinely conducted and the blank value for benzene substracted from sample results. All other chemicals used were reagent grade where possible. Deionized water that had been passed through two charcoal filters (Barnstead) was used throughout and was routinely assayed for organic contaminates. The adsorbing medium used was 200 mesh activated charcoal which had been initially treated by heating to 350 "C with a nitrogen gas purge. Stock solutions were prepared by saturation of water. These solutions were kept refrigerated until used. Test solutions were then prepared by dilution of the stock solutions and were verified as to their concentration by gas chromatography. 0 1984 American Chemlcal Society
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ANALYTICAL CHEMISTRY, VOL. 56, NO. 9, AUGUST 1984
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Flgure 1. Exposure cell for inltlal membrane evaluation: (A) solution reservoir, (B) solution control valve, (C) thermostated bath, (D) membrane, (E) solution waste, (F) rotometer, (0)gas Inlet, (H) gas flow control valve, (I) exposure cell, (J) recorder, (K) electrometer. C
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Figure 2. Exposure chamber and permeation device employed in sampling. (A) 4-L flask, (B) stir bar, (C) capillary tube, (D) rubber stopper, (E) charcoal adsorbent, (F) membrane, (G) 17 mm, (H) 50 mm.
GC standards were produced by direct addition of the pure components to a known volume of CSp RESULTS AND DISCUSSION Initial Membrane Evaluation. Linearity of response and response time of the membrane were initially evaluated by use of the permeation cell. It was observed that the rate of permeation through the membrane was a function of exposure solution concentration over a range of 1-50 ppm for each species. The response time was considered to be the time required to reach 90% response at a given concentration and was found to be
