followed by gas chromatographic separation and detection. The method detection limits for methanol, l-butanol, and 2-methyl-l-propanol are much less than the current land disposal treatment standards. This microdistillation system (Wadsworth MicroVOC3) addresses many of the limitations of direct sample injection, purge-and-trap, and other azeotropic distillation systems. Small sample aliquots are required (40 mL). Analyte concentration factors are -2 orders of magnitude when a 40-mL sample aliquot is used. The total distillation time is 5 min. Typical detection limits are between 5 and 15 pg/L when the distillate is analyzed by gas chromatography with flame ionization detection. The cost of the complete system is less than $300 with glassware comprising less than $70 of the total cost.
107-02-8; acrylonitrile, 107-13-1; ethyl acetate, 141-78-6; water, 7732-18-5.
Literature Cited (1) Peters, T. Anal. Chem. 1980, 52, 211. (2) Cramer, P. H. Report to E P A Measurement of Polar, Water-Soluble, Nonpurgeable VOCs in Aqueous Matrices by Azeotropic Distillation-Gas ChromatographyfMass Spectrometry. Midwest Research Institute, September 30, 1989. (3) Cramer, P. H.; Wilner, J.; Eichelberger, J. W. Azeotropic Distillation-A Continuing Evaluation for the Determination of Polar, Water-Soluble Organics. Sixth Annual Waste Testing and Quality Assurance Symposium, July 1990. (4) Test Methods for Evaluating Solid Waste, SW-846, 3rd ed.; US.EPA, Government Printing Office: Washington, DC, 1986; Vol. 1B. (5) Fed. Regist. 1990,55126, 26986-26998. (6) Test Method Equivalency Petitions, A Guidance Manual; OSWER Policy Directive, No. 9433.00-2; EPA/530-SW87-008; U.S.Government Printing Office: Washington DC, 1987.
Acknowledgments We thank Shamrock Glass for the manufacture of all prototype and finished distillation system glassware. Registry No. Methanol, 67-56-1; l-propanol, 71-23-8; 2methyl-l-propanol, 78-83-1; l-butanol, 71-36-3; 1,4-dioxane, 123-91-1; acetonitrile, 75-05-8; propionitrile, 107-12-0; acrolein,
Received for review May 29, 1991. Accepted August 5, 1991.
A Combined Reversed-Phase and Purge and Trap Chromatographic Method To Study the Interaction of Volatile Organic Compounds with Dissolved Humic Acid in Aqueous Solutions Reyaz A. Kangot and James G. Quinn"
Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882
A combined reversed-phase and purge and trap chromatographic method was used to study the interaction of dissolved Aldrich humic acid with volatile organic compounds in aqueous solution. Humic acid bound compounds were quantified by a purge and trap gas chromatographic method after separation from unbound compounds using C18solid-phase extraction columns. Partition coefficients (Kp)were 22.7 mL/g for dichlorotoluene, 14.9 mL/g for dichlorobenzene, and 3.6 mL/g for trichloroethene. The humic-dichlorotoluene interaction was biphasic and gave a first-order rate constant of 1.8 X h-' for the slower phase, and a second-order constant of 1.01 L 8-l h-l for the faster phase. Lowering the temperature of the solutions resulted in the increased binding of dichlorotoluene to humic acid.
Introduction In the aquatic environment, interaction of organic compounds with dissolved organic matter is one of the key factors influencing their transport and fate. This interaction also indirectly influences their chemical and biological transformations. It has been well documented that humic material increases apparent water solubility of organic compounds [for examples, see Lytle and Perdue (I), Curl and Keolelan (21,and McCarthy and Zachara (3)]. In general, nonionic, low molecular weight organic compounds are solubilized mainly due to hydrophobic interactions [Karickhoff ( 4 ) ] . Development of reliable, precise, and quick methods for the study of humic-organic compound interactions has ~~
Present address: S. K. University of Agricultural Sciences and Technology, Shalimar, Kashmir, India. 0013-936X/92/0926-0163$02.50/0
been attempted over the last decade. Several references in the literature describe studies on the interaction of low molecular weight organic compounds with humic material [Chiou et al. (5), Landrum et al. (6), Garbarini and Lion (7), and Ononye et al. (S)].In the present investigation, we have used a combined reversed-phase [Landrum et al. ( S ) ] and purge and trap chromatographic method to measure the interaction of volatile organic compounds (VOCs) with dissolved humic acid (HA). The HA-bound (solubilized) fraction of VOCs was separated from the unbound fraction using reversed-phase columns, which retained the latter fraction. The solubilized VOCs were then analyzed by purge and trap gas chromatography.
Experimental Section Concentration series experiments (at room temperature, 22-24 "C) were done by adding different amounts of organic compounds in methanol to 5 mL of an Aldrich HA solution (100 mg/L) in a 5-mL glass syringe. The compounds studied included 2,6-dichlorotoluene (DCT), 1,4dichlorobenzene (DCB), and trichloroethene (TCE), and the final concentrations were in the microgram per liter range. The syringe was then capped and the solution was mixed; care was taken to avoid any air bubbles. After standing 25 min, the cap was removed and a C18Sep-Pak cartridge (Waters), having an empty 5-mL glass syringe at one end, was attached to the initial syringe. The solution in the first syringe was then passed through the Sep-Pak into the second syringe at a flow rate of -5 mL/min. The VOCs which were not bound by humic acid were trapped on the Sep-Pak column, whereas the humic-bound VOCs passed through in solution into the second syringe. This solution was then injected into a Tracor LSC-2 sample concentrator, and analysis of the compounds
0 1991 American Chemical Society
Environ. Sci. Technol., Vol. 26, No. 1, 1992 163
2 0.7 o'8 c3 Lr' 0.6 t$ 0.5 d 0.4
1
/
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5
0.3
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. . #
0
0.0
DICHLOROTOLCENE ADDED (KgiL)
Flgure 1. Effect of concentration on the interaction of dichlorotoluene with dissolved humic acid (100 mg/L).
in HA solution was done by purge and trap gas chromatography using a Tracor Model 540 gas chromatograph (photoionization and Hall detectors, in series). Purging was done for 1 2 min with helium at a flow rate of 40 mL/min. The volatile hydrocarbons were collected on a Tenaxlsilica gel trap, which was then thermally desorbed at 180 "C onto a 30-m DB-624 (J&W Scientific) fused-silica column (3-pm film, 0.53-mm i.d). The GC was programmed from 35 to 140 "C at 6 "C/min, and a Spectra Physics Model 4270 integrator was used to quantify the results. Control samples (no HA) and blanks were subtracted from the values of experimental samples. The precision of the method was &5%,and details of the procedure have been given elsewhere [Kango and Quinn (9)]. Time course experiments were also conducted in the same fashion, allowing the reaction mixture to stand for different amounts of time at room temperature. Experiments at different temperatures were also performed. The first-order rate constant for DCT was determined by plotting In (C,/C) vs time (C, is the initial concentration and C is the concentration after specified times). The second-order rate constant was determined by R,/ [DCT],[HA], [Ononye et al. (S)], where Ro is the initial rate of binding and [DCT], and [HA], are initial concentrations of DCT and HA, respectively. The equilibrium constant (K)for the DCT and HA interaction was determined by the following equation: (1) THA/[HAI = 1 + K[DCTl where Tm is the total humic acid [(HA) + (HA - DCT)], [DCT] is the unbound DCT concentration in solution after equilibration with HA, [HA] is the concentration of unbound HA in solution, and HA-DCT is the bound DCT concentration in solution [adopted from Gauthier et al. (IO)]. Free energy was calculated by AGO = -RT In K. For a mixture of two compounds, the apparent partition coefficient of one of the compounds [e.g., K*,(DCB)] with HA was related to the equilibrium concentration of the other compound (DCT) by the following equation [Curl and Keolelan (211: (2) K*B = Kp/(l + CAKA) where K*B (mL/g) is the apparent partition coefficient of DCB in the presence of DCT. KP is the true partition coefficient of DCB, CA is the equilibrium solution concentration of DCT, and K Ais the equilibrium constant for DCT (L/mg). Results and Discussion As seen in Figure 1,the amount of DCT interacting with dissolved HA increased in a linear fashion as the amount of DCT in solution increased. The R2 value for this observation is 0.996. The partition coefficient [Kp, the 164
Environ. Sci. Technol., Vol. 26, No. 1, 1992
4
20
"'YO
40
TIME (MfA)
100
120
140
Flgure 2. Effect of time on the interaction of dichlorotoluene (120 PgIL) with dissolved humic acid (100 mg/L).
-i, a
v
1 0"'"0
5
R"? =0.999 25
30
Flgure 3. Effect of temperature on the interaction of dichiorotoluene (120 hg/L) with dissolved humic acid (100 mg/L).
amount interacted per gram of HA divided by the amount present per milliliter of solution (mL/g)] were 22.7 mL/g for DCT, 14.9 mL/g for DCB, and 3.6 mL/g for TCE. Thus, with an increase in molecular weight, there was an increase in their Kp values. Garbarini and Lion (7) determined a Kd value for TCE on solid humic acid equal to 32.1 L/mg. In our study, the equilibrium constant ( K ) for the interaction of HA-DCT in solution was 0.85 L/mg and the free energy change was 0.4 kJ/mol. Time course experiments are presented in Figure 2. This figure shows that most of the DCT was bound by HA in the first few minutes of the interaction and after that a gradual leveling effect became prominent. The interaction is probably biphasic for the uptake of DCT. An attempt to plot whole time segment data for a regular first-order kinetic equation did not give a best fit to the data (R2= 0.396). We tried to analyze our data for kinetic bifactoring, as has been done by Ononye et al. (8) while studying soil humics with benzidine. Our HA-DCT study also displayed kinetic factoring; the first phase of the reaction is very rapid, achieves an apparent equilibrium within 10 min, and is best approximated by second-order kinetics. We measured the initial rate (R,) for DCT disappearance [Ononye et al. (S)] and the second-order rate constant was equal to 1.01 L g-l h-l. The second phase of the reaction gave a good fit to the first-order kinetics equation and the first-order rate constant for this phase h-l. Thus, the time course study did not was 1.8 x follow any one reaction order. Initially, the reaction rate was very rapid and the data were best approximated by a second-order kinetic equation (i.e., strongly dependent on the initial concentration of the DCT). After this period, the reaction followed first-order kinetics and the rate of reaction was very slow because most of the active sites on the HA had been covered with DCT. Effects of temperature can also be conveniently studied by the combined method, Figure 3. As seen in this figure, as the temperature is lowered, more of the DCT binds to the HA and is solubilized. It was calculated that with the
Environ. Sci. Technol. 1992, 26, 165-173
Table I. Apparent Partition Coefficient of DCB with HA as the Equilibrium Solution Concentration of DCT Increases
DCB partition coeff (KP), mL/g 14.9 14.9 14.9
DCT equilibm solution concn, Pg/L
120 180 1200
DCB apparent partition coeff (K*B), mL/g 13.5 12.9 7.4
lowering of 1 "C temperature there was approximately 0.015 pg/L more interaction between DCT and HA. These studies suggest that the temperature phenomenon can have a significant effect in terms of organic compound movement and stability during winter months, as more of it can be bound to humic substances during colder temperatures. Upon interacting a mixture of DCT (120 pg/L) and DCB (110 pg/L), we found that no marked difference from the original uptake (if separately interacted) could be observed. It was also determined that under these low concentrations, no significant difference was found between the calculated partition coefficient Kp (14.9 mL/g) and the apparent partition coefficient K*B (13.5 mL/g) of DCB (Table I). However, as is implied from eq 2 [Curl and Keolelan (2)],as the equilibrium concentration of the DCT increases, the K*Bdecreases appreciably. From the table it is shown that with increases in the equilibrium concentration of DCT in solution, the apparent partition coefficient of DCB decreases from 13.5 to 7.4 mL/g.
Conclusions (1) A method for the study of the interaction of VOCs with dissolved humic acid was developed using a combination of reversed-phase and purge and trap gas chromatography. (2) Partition coefficients for these compounds were calculated and they increased with increasing molecular weight.
(3) The humic acid-DCT interaction was found to be biphasic in nature. (4) Lowering the temperature of solutions resulted in the increased binding of DCT to humic acid.
Acknowledgments We thank Norman Farris for laboratory assistance, and James Latimar and Evelyn Dyer for assistance in the preparation of the manuscript. Registry No. Water, 7732-18-5;dichlorotoluene,29797-40-8; dichlorobenzene, 25321-22-6; trichloroethene, 79-01-6.
Literature Cited (1) Lytle, C. R.; Purdue, E. M. Environ. Sci. Technol. 1981, 15, 224-228. (2) Curl, L. R.; Keolelan, G. A. Environ. Sci. Technol. 1984, 18, 916-922. (3) McCarthy, J. F.; Zachara, J. M. Environ. Sci. Technol. 1989, 23,496-502. (4) Karickhoff, S. W. In Contaminants and Sediments; Baker, R. A., Ed.; Ann Arbor Science: Ann Arbor, MI, 1980; Vol. 2, pp 193-205. (5) Chiou, C. T.; Porter, P. E.; Schmedding, D.W. Environ. Sci. Technol. 1983, 17, 227-231. (6) Landrum, P. F.; Nilhart, J. R.; Eadie, B. J.; Gardner, W. S. Environ. Sci. Technol. 1984, 18, 187-192. (7) Garbarini, D. R.; Lion, L. W. Enuiron. Sci. Technol. 1986, 20, 1263-1269. (8) Ononye, A. I.; Graveel, J. G.; Wolt, J. D. Soil Sci. SOC. Am. J . 1989,53,981-983. (9) Kango, R. A.; Quinn, J. G. Chemosphere 1989, 19, 1269-1276. (10) Gauthier, T. D.; Shane, E. C.; Guerin, W. F.; Seitz, W. R.; Grant, C. L. Environ. Sci. Technol. 1986,20,1162-1166. Received for review March 8,1991. Revised manuscript received June 24,1991. Accepted July 27,1991. The study was supported in part by funding from the Rhode Island Department of Environmental Management and the U.S. Environmental Protection Agency (CR-815992).
Toxic Volatile Organic Compounds in Urban Air in Illinois Clyde W. Sweet* and Stephen J. Vermette
Illinois State Water Survey, 2204 Griffith Drive, Champaign, Illinois 61820 IAirborne concentrations and sources of 13 toxic volatile
organic compounds (VOCs) were evaluated in two urban areas in Illinois: southeast Chicago and East St. Louis. Concentrations and meteorological conditions were monitored between May 1986 and April 1990. Using emissions inventories and source signatures developed for the study areas, we applied wind trajectory analysis, factor analysis, and a chemical mass balance model to interpret the data. These analyses indicate that most of the toxic VOCs in the study areas come from urban area sources such as vehicle exhaust, evaporation of petroleum products, and solvent emissions by commercial and industrial sources. Emissions from large industrial point sources increase VOC concentrations within 1 km from the source, but have little effect on the overall air quality in the study areas.
Introduction During the past few years, an increased awareness of air pollutants and new potential sources of airborne toxic 0013-936X/92/0926-0165$03.00/0
chemicals have brought a concern that the release of these materials may be a health hazard. Airborne lead has been implicated as a cause of neurological problems in urban children (1). This finding resulted in the promulgation of an ambient air quality standard for lead, its removal from gasoline, and subsequent dramatic lead reductions in urban air. Recently a number of other airborne metals and volatile organic compounds (VOCs) have been identified as important cancer risk factors in the urban environment (2). These compounds are not routinely monitored in urban air, and no national ambient air quality standards have yet been established for them. Data on airborne VOCs in urban and rural areas in the United States have been reviewed ( 3 , 4 ) . Elevated levels of benzene and other aromatic hydrocarbons as well as a variety of chlorinated VOCs are found in the air of most urban areas. These air pollutants are emitted by a wide variety of area and point sources. Area sources are those involving many small sources over a wide area, such as vehicle emissions. Point sources are single large emitters
0 199 1 American Chemical Society
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