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Anal. Chem. 1986, 58, 1529-1532
/
The current method complies with the requirements for sampling and analyzing airborne compounds in the industrial hygiene sector. The high separation efficiency of the capillary column, in combinatioawith selective detection of nitrogen compounds, permits this method to be used in various kinds of industrial environments. Registry No. Amberlite XAD-7, 37380-43-1; N-methylmorpholine, 109-02-4.
LITERATURE CITED
+L-/
IF1
+'I-
*
(1) Balin, L.; Wass, U.; Aundunsson, G.; Mathiasson, L. Br. J. Ind. Med. 1983, 40, 251. (2) Candura, F.; Moscato, G. Br. J. Ind. Med. 1984, 4 7 , 552. (3) NIOSH Manual of Analytical Methods, 2nd ed.; National Institute for Occupational Safety and Health: Clncinnati, OH, 1977; Vol. 3, method S 146. (4) Ferrari, P.; Guenier, J. P.; Muller, J. Chromafographia 1985, 20, 5. (5) Lovkvist, P.; Jonsson, J. A. J. Chromatogr. 1984, 266,279. ( 6 ) Fltzpatrick, M. R.; Warner, P. 0.; Thiel, D. P.; Lubs, P. L.; Kerfoot, E. J. Am. Ind. Hyg. Assoc. J . 1983, 4 4 , 425. (7) Dalene, M.; Mathiasson, L.; Jonsson, P. A. J. Chromatogr. 1981, 207, 37. (8) Audunsson, G.; Mathiasson, L. J. Chromatogr. 1983, 267, 253. (9) Audunsson, G.;Mathiasson, L. J. Chromatogr. 1984, 375, 299. (10) Hans&, L.; Sollenberg, J.; Uggla, C. Scand. J. Work. Environ. Heaffh 1985, 7 1 , 307. (11) Ahnfelt, N. 0.; Hartvig, P.; Karisson, K. E. Chromatographia1982, 76, 60.
(12) Gubitz, G.;Wlntersteiger, R.; Hartinger, A. J. Chromatogr. 1981, 278,
51.
No interfering compounds from the factory were detected in the analysis of methylmorpholine, neither by GC/FID nor by GC/NPD. The identity of methylmorpholine in the workplace samples was confirmed by GC-MS, and the air level range was 8-20 mg/m3.
(13) Kudoh, M.; Matoh, I.; Fudano, S. J. Chromatogr. 1983, 267, 293. (14) Andersson, K.; Levin, J.-0.; Lindahl, R.; Nilsson, C.-A. Chemosphere 1984, 73, 437. (15) Andersson, E.; Andersson, K.; Nilsson, C.-A. J. Chromatogr. 1984, 297, 257.
RECEIVED for review November 7,1985. Accepted February 3, 1986.
Continuous Monitoring Device for the Collection of 23 Volatile Organic Priority Pollutants Roger D. Blanchard and James K. Hardy*
Department of Chemistry, University of Akron, Akron, Ohio 44325
A method that allows for continuous monltorlng or single-point analysis of volatlle organic prlorlty pollutants has been developed. The method Is based on permeation of volatlle organlc compounds through a slllcone polycarbonate membrane, from a sample water matrix, Into an Inert gas stream. The volatlle organlc compounds are collected In a sampling loop connected to a six-port valve and then directed Into a caplllary column of a gas chromatograph. The procedure has the advantages of being simple and not requiring tlme-consumlng preconcentratlon steps and It can be used either In the field or In the laboratory. Detection llmlts are in the low parts-per-bllllon range. Llnear results of response vs. concentratlon are obtained from the low parts-per-billion to the low parts-per-mllllon range. Permeation rates increase In a nearly llnear manner with temperature. Preclslon Is comparable to present methods of analysis.
Federal regulations, which include the Federal Water Pollution Control Act of 1972 (1)and the Clean Water Act
of 1977 ( 2 ) ,require monitoring of effluent streams for hazardous pollutants. A list classified as the Priority Pollutant List contains 129 compounds that are to be regulated. Contained within the list are a group of compounds designated as volatile or purgeable organics consisting of 31 compounds. The present Federal Environmental Protection Agency (EPA) approved method of collection and analysis of volatile organic priority pollutants involves obtaining a grab water sample from an effluent stream, transporting the sample to a laboratory, and analyzing the sample by a procedure called the purge and trap technique ( 3 , 4 ) . In this procedure, the water sample is placed in a purge vessel, and an inert gas is bubbled through the sample to remove the volatile components contained in the water. The volatile components are trapped on an adsorbing matrix and thermally desorbed for analysis by gas chromatography or GC/MS. This procedure is limited in that it only provides concentration values for a certain point in time at a specified location, it does not provide for a long-term stabilized sample prior to analysis, and the procedure contains difficulties inherent in the purge and trap technique such as incomplete desorption of volatile components from the ad-
0003-2700/86/0358-1529$01.50/0 0 1986 American Chemlcal Society
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ANALYTICAL CHEMISTRY, VOL. 58, NO. 7, JUNE 1986
Side View E
F
Nltrogen Gas Half
Water Half
of Permeation Cell
o l Permeation Cell
.-rl S
I
J
P' A
B
K
I
0
Figure 1. Permeation cell: (A) water inlet, (B) helium gas inlet, (C) 12.7 cm, (D) 2.1 cm, (E) water outlet, (F) helium gas outlet, (G) 4'/.,-in. wingnut screws, (H) 7.2 cm, (I) 2.4 cm, (J) 0.35 cm wide recessed 7 mm for screen, (K) 0.5 cm deep, (L) 7.9 cm, (M) 1.9 cm, (N) 30-mmdeep groove for 35-mm 0-rlng, (0) 15 mm wide, flush with outer surface, (P) 0.5 cm deep.
sorbing matrix, memory effects, and degradation of the adsorbing matrix (5) that can lower the precision and accuracy of the technique. This paper describes an alternative approach that allows for continuous monitoring of an effluent stream or, alternatively, a single-point analysis of a grab-collected sample. The technique utilizes permeation of volatile organic priority pollutants through a semipermeable membrane that is contained in a permeation cell. Collection of volatile organic priority pollutants by permeation through a semipermeable membrane has previously been demonstrated as a viable alternative to grab sampling or collection by pumping or evacuated flask systems (6,r). The permeation cell approach is simple; it can provide a continuous measure of volatile component concentrations over an extended period of time: it does not require time-consuming preconcentration steps: and it eliminates the problems associated with the purge and trap technique mentioned previously.
EXPERIMENTAL SECTION Apparatus. The fundamental component of the permeation technique described in this paper is a permeation cell consisting of a stainless-steel casing containing a semipermeable membrane of silicone polycarbonate (0.025 mm thick, General Electric) situated between two chambers. Figure 1 is a diagram of the permeation cell used in this study. One surface of the membrane has an aqueous sample flowing across it, and the other surface has helium gas flowing across it. Volatile components contained in the aqueous sample permeate through the membrane and are carried by the helium carrier gas to a sampling loop connected to a six-port valve. Once a sample containing volatile organics is collected in the sampling loop, the position of the six-port valve is changed to direct the contents of the sampling loop into the capillary column of a gas chromatograph. The components from the sampling loop are separated on the capillary column and then detected by flame ionization. Figure 2 is a diagram of the complete system used in this permeation technique. The silicone polycarbonate membrane used in the permeation cell was 0.025 mm thick and 7.2 cm in diameter. Two screens, composed of nickel, were placed on either side of the membrane, and four metal spacers, 0.20 in. X 0.40 in. were welded to each screen. The spacers abutted the back wall of the permeation cell and prevented displacement of the membrane from the center of the permeation cell. Stainless-steel tubing,l/, in. i.d., was used to connect the permeation cell to the six-port valve. The six-port valve was a Rheodyne Model 7001. The sampling loop consisted of stainless-steel tubing 0.508 mm in diameter and 49.3 cm in length with a volume of 100 pL. The gas chromatograph used was a Hewlett-Packard Model 5730A, and the capillary column was an SPB-1 fused silica column 60 X 0.32 mm i.d. with a bonded stationary phase 1.00 p m in thickness. A Hewlett-Packard Model 3390A integrating recorder was used for recording chromatograms. Reagents. All organic reagents used were reagent grade. Distilled water, which was filtered through carbon (Barnstead) to remove organic contaminants, was used to make all aqueous
I
P 1
H
R
lo
Flgure 2. Complete system for continuous collection of volatile organic priority pollutants: (A) solution reservoir, (B) solution control valve, (C) thermostated bath, (D) permeation cell, (E) solution waste, (F) rotometer, (G) helium gas inlet, (H) inlet gas control valve, (I) rotometer, (J) helium gas inlet to permeation cell, (K) inlet gas control valve, (L) silicone polycarbonate membrane, (M) SIX-portvalve, (N) sampling loop, (0) waste helium gas, (P)gas chromatography column, (Q) flame ionization detector, (R) electrometer, (S) recorder.
v)
Figure 3. Chromatogram of five components used in initial method evaluatlon: (1) water vapor, (2) dichloromethane, (3) chloroform, (4) benzene, (5) toluene, (6) ethylbenzene. Chromatographic conditions are as follows: column temperature, 100 OC, isothermal; detector temperature, 250 OC; flow rate, 1.5 mL/min.
solutions. Carbon disulfide (Fisher Scientific) was used to make standards containing volatile organic priority pollutants for determination of volatile organic concentrations in aqueous stock solutions. The carbon disulfide was found to contain benzene in low concentrations, so the response obtained for benzene in carbon disulfide was subtracted from benzene in standards to obtain the response from the added benzene itself in the standards. Lower concentration aqueous solutions containing volatile organic components were made by dilution of stock solutions.
RESULTS AND DISCUSSION Evaluation of Method. To make a rapid determination of the feasibility of this method, five compounds (dichloromethane, chloroform, benzene, toluene, and ethylbenzene) were dissolved in water for analysis. With five compounds, conditions could be established on the gas chromatograph for rapid analysis. The five compounds represent both aromatic and halogenated compounds, which make up a majority of the volatile organics, and they also represent the most frequently occurring volatile organics in effluent streams (8). Figure 3 is a chromatogram of the five components analyzed using this permeation technique. In Figure 3, the first peak is due to water vapor, which permeates through the membrane
ANALYTICAL CHEMISTRY, VOL. 58, NO. 7, JUNE 1986
Table 111. Precision Results for Permeation and Purge and Trap Techniques Including Single-Operator ASTM Purge and Trap
Table I. Percent Change per Degree and Correlation Coefficient Data for Temperature Effect Results compd
% changeldegree'
corr coeff
dichloromethane chloroform benzene toluene ethylbenzene
5.82
0.971
7.63 4.96
0.979 0.975
compd
concn, ppb
permeation
7.23 8.80
0.984 0.996
dichloromethane
201
chloroform
369 250
5.91 3.14 4.67
273
7.84 9.20
OResults relative to 22.0 "C. Table 11. Concentration Range and Correlation Coefficient Data for Five Volatile Organic Priority Pollutants compd
dichloromethane chloroform benzene toluene ethvlbenzene
concn range, ppm 0.045-1.44 0.074-1.18 0.0072-0.464
0.0078-0.500 0.006-0.424
1531
coir coeff
0.9999 0.9993 0.9995 0.9995 0.9996
and causes a disturbance of the flame which is noticeable at sensitive electrometer settings. The chromatogram demonstrates that the components come out as sharp, highly resolved peaks. The helium flow rate through the permeation cell was 10 mL/min; the solution flow rate through the permeation cell was 20 mL/min; and the permeation cell was maintained at a temperature of 22 "C. These values were used throughout the experimentation unless otherwise stated. The helium and solution flow rates through the cell were optimum values for sample collection in the sampling loop. Response vs. Temperature. Previous work (6, 7) has shown that the permeation rate is nearly linearly dependent on temperature at temperatures below 30 "C. To determine the effect of elevated temperatures on permeation rates, the permeation cell was placed in a water bath in which incremental changes in temperature from 22 to 95 "C were used. The response vs. temperature increased in an approximately linear manner over this range. Table I contains the percent change per degree relative to 22 "C and correlation coefficients for each of the five compounds studied. All subsequent studies performed a t constant temperature after the initial method evaluation were done at 50 "C. This temperature was used to effect a higher rate of collection of the volatile organic components while minimizing the amount of water vapor that permeates through the membrane. Also, elevated temperatures beyond 80 "C result in deformation of the silicone polycarbonate membrane (9). Response vs. Concentration. A study of response vs. concentration was performed over concentrations ranging from the low parts-per-billion to low parts-per-million range to determine linearity. Table I1 contains concentrations ranges and correlation coefficient data for the five organic components studied. All compounds demonstrated a high degree of linearity over this range and previous work (6, 7) indicates that linearity would be maintained at higher concentrations than those studied. Statistical Evaluation of Method. To determine the precision of the permeation technique, and to compare the precision of the permeation technique with the purge and trap technique, a series of eight analyses were performed for both techniques with the same concentrations of the five organic compounds mentioned previously. Conditions for the purge and trap technique were those specified by Bellar and Lichtenberg (41,and conditions for the permeation technique included a permeation cell temperature of 50 "C, helium flow rate of 10 mL/min, and solution flow rate of 20 mL/min. Results of the precision study are given in Table 111. Also included in the table are concentration values for each com-
% re1 std dev
benzene toluene ethylbenzene
243
purge and trap 4.17 4.96 4.07 3.46 3.87
ASTM Results chloroform benzene
ethvlbenzene
370 196 168
6.41 7.76 10.7
Figure 4. Chromatogram of 23 volatile organic priority pollutants. Table IV contains peak designations. Chromatographic conditions are as follows: column temperature, 30 "C for 16 min and then 4 "Clmin to 100 "C; flow rate, 0.5 mL/min; detector temperature, 250 "C.
pound studied and single-operator precision data for three compounds found in the ASTM methods (IO)using the purge and trap technique. Concentration values of the three volatile organic compounds used in the ASTM study are comparable to those used in this study, and the concentration are included in the table. In a direct comparison of the techniques in this laboratory, the purge and trap technique provided slightly more precise data. When the permeation technique is compared with ASTM precision results, the permeation results are slightly more precise. The results indicate that comparable results can be obtained by both techniques. Separation of 23 Volatile Organic Priority Pollutants. A water solution containing 23 volatile organic priority pollutants was analyzed by the permeation technique to determine the feasibility of this method for separating a majority of the volatile organic priority pollutants. The solution was made by dissolving the 23 volatile organic compounds in water. Concentrations of the components varied from approximately 0.5 to 5 ppm. Concentrations were made relatively high to ensure the all components could be easily detected. The list was limited to 23 components because the majority of the remaining compounds have half-lives in water of less than a day (11) or were not commercially available. The solution contained the following volatile organic priority pollutants: dichloromethane, chloroform, benzene, toluene, ethylbenzene, carbon tetrachloride, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, 1,l-dichloroethylene, 1,l-dichloroethane, 1,1,2-trichloroethane, trichlorofluoromethane, acrylonitrile, bromoform, trichloroethylene, 1,3-dichloropropane, chlorobenzene, 1,2-dichloropropane, trans-1,2-dichloroethylene,bromodichloromethane, l,l,l-trichloroethane, and tetrachloroethylene. Analysis involved allowing the solution containing the 23 volatile components to flow through the permeation cell,
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ANALYTICAL CHEMISTRY, VOL. 58, NO. 7, JUNE 1986
Table IV. Elution Order and Retention Times of 23 Species in the Chromatogram of Figure 4 peak no. 1 2
3 4 5
6 7
8 9 10 11 12
13 14 15 16 17 18 19 20
retention time, min
compd acrylonitrile 1,l-dichloroethylene dichloromethane
8.43 9.04 9.27
trans-1,2-dichloroethylene
11.24
1,l-dichloroethane chloroform 1,2-dichloroethane l,l,l-trichloroethane benzene carbon tetrachloride 1,2-dichloropropane bromodichloromethane trichloroethylene 2-chloroethyl vinyl ether cis-1,3-dichloropropene
11.72 14.98 17.44 18.24 19.63 20.09 22.11
22.66 22.78 24.33 24.88 26.04 26.33 26.86 29.12 30.49 31.33 31.74 32.73
trans-1,3-dichloropropene
21 22
1,1,2-trichloroethane toluene tetrachloroethylene chlorobenzene ethylbenzene bromoform
23
1,1,2,2-tetrachloroethane
Table V. Detection Limits for Selected Volatile Organic Priority Pollutants compd
detection limit, ppb
dichloromethane chloroform benzene toluene ethylbenzene
45.0 74.0 7.2
7.8 6.6
collecting the volatile components in the sampling loop, and then separating and detecting the components with the gas chromatograph. Table IV contains a list of the compounds analyzed, the order of elution, and the uncorrected retention times corresponding to the chromatogram in Figure 4. The results demonstrate that this method can be used for large numbers of volatile organic compounds in a single analysis. Time of Analysis. Analysis time is dependent on how many components are to be separated. T o separate the five compounds initially studied required an analysis time of under 10 min and did not require temperature programming. T o separate 23 compounds required an analysis time of approximately 30 min and required the temperature programming sequence specified in Figure 4. The sampling loop can be refilled during the oven cooling cycle used in temperature programming. A solution flow of 20 mL/min for approxi-
mately 30 min is required for flushing when sequential analyses at low parts-per-billion and high parts-per-billion concentrations are performed. Modifications of the permeation device that allows for more rapid change of solution concentrations at the membrane surface and minimizes mixing of previous solution with new solution could lower this time period to a more reasonable value. Detection Limits. Table V contains a list of detection limits for the five compounds used in the initial method evaluation. Benzene, toluene, and ethylbenzene were detectable at concentrations below 10 ppb and the chlorinated methanes at higher concentration values. A number of modifications of the equipment and procedure could be used to lower the detection limit, which include increasing the surface area of the membrane, increasing the volume of the sampling loop, and increasing the permeation cell temperature. An increase in each parameter has the effect of increasing the amount of volatile organic component collected, although increasing temperature can cause problems that were mentioned previously. Registry No. Acrylonitrile, 107-13-1; 1,l-dichloroethylene, 75-35-4; dichloromethane, 75-09-2; trans-1,2-dichloroethylene, 156-60-5; 1,l-dichloroethane, 75-34-3; chloroform, 67-66-3; 1,2dichloroethane, 107-06-2;l,l,l-trichloroethane, 71-55-6; benzene, 71-43-2; carbon tetrachloride, 56-23-5; 1,2-dichloropropane,78-87-5; bromodichloromethane, 75-27-4; trichloroethylene, 79-01-6; 2chloroethyl vinyl ether, 110-75-8; cis-1,3-dichloropropene, 10061-01-5; trans-1,3-dichloropropene,10061-02-6; 1,1,2-trichloroethane, 79-00-5; toluene, 108-88-3; tetrachloroethylene, 127-18-4;chlorobenzene, 108-90-7;ethylbenzene, 100-41-4;bromoform, 75-25-2; 1,1,2,2-tetrachloroethane, 79-34-5; water, 7732-18-5. LITERATURE CITED federal Water Pollution Control Act Amendments of 1972, Statutues atLarge, 1972; GS4.111:66, p 816. Clean Water Act of 1977, Statutes at Large, 1977; GS4.111:91, p 1509. “Guidelines Establishing Test Procedures for the Analysis of Pollutants”,f e d . Req. 1979, 44 (Dec 3), 69464. Bellar, T. A.; Llchtenberg, J. J. J . Am. Water Works Assoc. 1974, 66,739-744. Pierce, C. L.; Kongovi, R. R.; Narangajavana, K.; Brock, G. L.; Grochowskl, R. J. Am. Lab. (fairfield, Conn.) 1981, 13, 34-42. Hardy, J. K.; Blanchard, R. D. Anal. Chem. 1984, 5 6 , 1621-1624. Hardy, J. K.; Blanchard, I?. D. Anal. Chem. 1985, 5 7 , 2349-2351. Keith, L. H.; Telliard, W. A. Environ. Sci. Techno/. 1979, 1 3 , 416-423. General Electric Corp., personal correspondence, 1985. 1983 Annual Book of ASTM Standards; ASTM: Philadelphia, PA, 1983; 11.02, pp 39-44. Water-Related Environmental Fate of 129 Priority Po//utants 1979; E l .28:FE-2445-1/~.2. ‘I,
RECEIVED for review September 26, 1985. Accepted January 31, 1986. This work was supported by the donors of the Petroleum Research Fund, administered by the American Chemical Society (Grant 14080-G5).
