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basic species was higher than with more dilute solutions, it was compensated for by adsorption of a greater amount of neutral acid from the more concentrated buffer. The fact that an increase in the concentrations of both solutions slightly reduced the effect of the column implies that the capacity of the resin to adsorb acetic and boric acids did not increase linearly with concentration. To ensure that those effects were actually due to the column packing, we ran the same gradient without the column a t different flow rates and concentrations. No effect on the size of the inflections was found. Increasing the flow rate of the mobile phase appears to be a convenient method for minimizing the influence of the column on the pH profile. The decrease in column efficiency associated with high flow rates could be compensated by using a higher efficiency column packed with smaller resin particles. Dieterle et al. (20) have shown that microparticle size ranges of XAD resins can be prepared and slurry-packed to produce high-efficiency columns. This would allow the use of higher flow rates and, thus, more nearly linear pH profiles while maintaining high chromatographic efficiency. This pH gradient method shows considerable promise both as a fingerprinting technique for humic acids and as a means for fractionating these materials prior to further characterization. The fractionations of replicate samples were quite reproducible making preparative scale analysis amenable to automation. After fractionation, the acetic acid from the buffer can be removed easily prior to characterizing the humic acid species, by readsorbing the fraction on a short column of large particle XAD resin, rinsing with dilute mineral acid to remove the buffer components, and flushing with sodium hydroxide. This procedure would have the advantage of
concentrating the humic acid fraction into a small volume of base.
LITERATURE CITED (1) Kononova, M. M. “Soil Organic Matter”, 2nd English ed.; Pergamon Press: Oxford, 1966; pp 183-228. (2) Schnitzer, M.; Khan, S. U. “Humic Substances in the Environment”; Marcel Dekker: New York, 1966; pp 281-302. (3) Gjessing, E. T. “Physical and Chemical Characteristics of Aquatic Humus”; Ann Arbor Science: Ann Arbor, MI, 1976; pp 56-73. (4) Felback, G. T. in “Soil Biochernlstry”; McLaren, A. D., Skujins, J., Eds.; Marcel Dekker: New York, 1971; Vol. 2, pp 36-59. (5) Szalay, A. Ark. Mineral. Geol. 1969, 5 , 23-36. (6) Gjessing, E. T. Chem. Environ. Apuat. Habitat, Proc. IBP-Symp. 1967, Paper No. 18, 191-201. (7) Gjessing, E. T. TMSskr. Kjemi, Bergves. Metall. 1967, 27, 8-15; Chem. Abstr. 1967, 67, 5593p. (8) Gjessing, E. T.; Lee, G. F. Environ. Sci. Techno/. 1967, 1 , 631-638. (9) Gjessing, E. T. Vatten 1970, 26, 135-141. ( I O ) Mantoura, R. F. C.; Riley, J. P. Anal. Chim. Acta 1975, 76, 97-106. (1 1) Malcolm, R. L.; Thurman,E. M.; Aiken, G. R. Proc. An. Conf. Tr. Subs. Environ. Health, 11th 1978, Paper No. 37, 307-315. (12) MacCarthy, P.; Peterson, M. J.; Malcolm, R. L.; Thurman E. M. Anal. Chem. 1979, 51, 2041-2043. (13) Thurman, E. M.; Malcolm, R. L. US. Geol. Survey, Water Resources Division, Denver, CO, 1979, Water Supply Paper No. 1817. (14) Bates, R. G. “Determination of pH: Theory and Practice“, 2nd ed.; Wiley-Interscience: New York, 1973; Chapter 5. (15) Prideaux, E. B. R. Proc. R . SOC.London, Ser. A 1916, 92, 463-468. (16) Pietrzyk, D. J.; Chu, C. H. Anal. Chem. 1977, 49, 757-763. (17) Thurman, E. M.; Malcolm, R. L.; Aiken, G. R. Anal. Chem. 1978, 50, 775-779. (18) Pietrzyk, D. J.; Chu, C. H. Anal. Chem. 1977, 49, 660-8613. (19) Flaig, W.; Beutelspacher, H.; Rietz, E. “Soil Components; Volume One: Organic Components”; Springer-Verlag: Berlin, 1975; Chapter 1. (20) Dieterle, W.; Faigle, J. W.; Mory, H. J . Chromatogr. 1979, 168, 27-34.
RECEIVED for review January 5, 1981. Accepted March 30, 1981. Supported in part by National Science Foundation Grant No. CHE 78-13269.
Multichannel, Positive Displacement Teflon and Glass Sampler for Trace Organics in Water David C. Tigweli,‘ David J. Schaeffer,” and Luther Landon Illinois Environmental Protection Agency, 2200 Churchill Road, Springfiehl, Illinois 62706
A multlchannel positlve displacement apparatus for collecting composite samples of water-borne trace organic compounds is described. A Teflon line connects each source to a separate three-way Teflon valve. Each valve is connected to a separate 50-mL syrlnge held in a machined mount which prevents lateral shear. This apparatus delivers precise volumes of 10.0-40.0 mL per channel per cycle. The all Teflon-glass construction minimizes adsorptive losses in the sample train. Multiple sources and/or multiple collection devices can be sampled simultaneously.
Numerous recent articles describe procedures for, and results obtained from, the analysis of aqueous environmental samples for organic compounds present a t trace levels (1-3). While sample storage, compound isolation, and identification procedures are documented, relatively little information is Current address: D. C. Tigwell and Associates, 2100 Tanglewilde
#71, Houston, TX 77063.
available on equipment and methods of sampling for trace levels of organic compounds. With few exceptions, most aqueous samples have been collected as “grab” samples, although some reports describe the collection of composite samples (4-6). Garrison et al. ( 5 ) described a new sampler which uses a pump with Teflon bellows, glass-ball check valves, and Teflon intake lines. Stephan et al. (6)developed a sampler employing peristaltic pumps to force sample through columns containing XAD-2 and XAD-7 resin. Several commercial manufacturers are currently advertising modified versions of their standard composite samplers (7-9) which use Teflon delivery lines and glass vacuum chambers. Three years ago the Illinois Environmental Protection Agency initiated a program to evaluate the chemical, biologic, and toxicologic significance of organic compounds being discharged to, and found in, the State’s waters (1). From the outset, we recognized that the most critical part of this project was the requirement of collecting a representative sample (10-13). In order to accomplish this, we developed an extensive list of sampling requirements (6-9,14). The sampler
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specifications were derived from these. Our work has shown that average source characteristics must be defined by as few samples as possible since analysis costs exceed $2000/sample. This is best accomplished by compositing at the time of collection (12). Thus, the sampler must be capable of taking continuous, constant volume or flow proportional samples. For theoretical reasons given by us previously (11-13), volumes delivered must be precisely controlled, especially if the data will be used to calculate loading, For the reduction of losses due to sorption and chemical reactions, all surfaces in contact with the sample must be inert, and contact time of the sample with sampler surfaces should be as brief as possible. Further, in order to reduce losses due to volatilization, samples should not be placed under negative (Le., below ambient) pressure, such as might occur with a vacuum type sampler, or any other sampler elevated above the intake point (7-9,141. The sampler must deliver the same volume of sample regardless of outlet pressure. This is very important when sorbtion columns are used with some channels and liquid collection devices are used with others. Columns also tend to load with suspended material causing a timevarying outlet pressure throughout a run. Provisions for heating and cooling (15) the collection device are also needed in order to further minimize losses due to volatilization, sorption, and chemical reactions. In many instances several process streams have to be sampled simultaneously (as before and after a waste chlorination tank) (16-18), and since no single collection method-collection in a reservoir for liquid extraction, sorption on macroreticular resins, carbon, foam plugs, etc.-is suitable for all classes of compounds, provision for multiple source sampling must be made (19). Our work provides for simultaneous collection of samples by three or more modes (19). Field equipment must possess characteristics which are not needed by laboratory apparatus. Sampling equipment must be rugged, lightweight, capable of unsupervised operation, easily repairable, and cleanable without dismantling in the field. We also required that the sampler be compatible with existing commercial flow meters, in order to facilitate its use with equipment already in place at the monitoring site. Thus, we plan to make units available on a rotating loan basis to industrial and municipal facilities in Illinois as part of a program to establish a quality State data base. This effort can only be successful if the same sampling and analytical methods are used at all sites. Differences in configuration, operation, existing hardware at the facility, etc. place requirements on sample design, since the sampler will have to interface with a number of different types of flow measuring devices.
INSTRUMENTATION
A zero headspace positive displacement device substantially meeting the requirements (4,19,20) is shown in Figure 1. All metal parts are machined brass, aluminum, and stainless steel; the case is heli-arc welded aluminum. The “pumps” are 50-mL glass syringes held in precision mounts (Figure la). In order to ensure linear movement of the syringe plungers without lateral shear, tolerances in the oscillating drive mechanism are kept a t 0.025 mm. The speed of the cycle is set by a variable-speed, gear-head dc permanent magnet motor and connecting drive (Figure Ib). The volume delivery per stroke (10-40 mL) is set by the position of the pinion (Figure IC)in the cam (Figure Id). In the model shown, one to four channels are operated simultaneously. Each channel is independent and may have its own source and collection device. The sampler has been operated by a remote computer using radiotelemetry (16-18). In order to sample volatile compounds, the sampler is interfaced to a zero headspace collection vessel consisting of a
w
/’
I
I
’
Figure 1. Mechanical arrangement of sampler.
large graduated cylinder with an inlet tube blown into the bottom. This is equipped with a tight-fitting Teflon float. As sample is forced by the pump into the cylinder, the Teflon rises. This arrangement maintains the liquid in contact with the Teflon float, eliminates contact of the sample with air, and prevents the volatilization of compounds. DeWalle et al. (18) have described the use of this arrangement for the collection of volatile compounds in sewage effluents. The reports of their studies should be consulted for further details on the use of this apparatus in sampling for volatile components. In our study, we are generally considering one source, with one channel going to a column containing 15 mL bed volume of macroreticular resin (21), the second to one containing 15 mL bed volume of activated carbon, and the third to a glass reservoir with a Teflon float for volatile organics analysis (18) and for liquid-liquid extraction of less refractory components (1,19,22). The normalized flow rate through each channel is about 15 mL/min to permit equilibration of the sample with the sorbent. Total flow through the sampler is 45 mL/min. Four to ten liters per channel are collected during 8-24 h of sampling. The sampler is triggered electronically by a quartz-controlled timer of our design for time-proportional sampling. The timer can be programmed to initiate sampler cycles at intervals ranging from 1ps to IO8s in 14 ranges over 4 decades. The current version of the sampler uses a three-way Teflon solenoid valve (Fluorocarbon Co.). Separate valves for each channel permit control of each channel, while maintaining comparability of flow through the separate channels. These valves effectively replace a single all-Teflon and glass multichannel valve developed by us previously for this work (20). No valve failures have yet occurred due to accumulation of solids, though good operating practice should include some type of rough inlet screening when large amounts of solids are present. This arrangement permits channels to be operated independently or sequentially, whereby the effluent from one channel can be the intake for the next. By the placement of a Teflon “T” in the delivery line, an accurately metered external standard can be added to any or all of the intake lines. We have done this in a study of a coking plant’s effluent which used our multichannel valve. Standards of perdeuterioanthracene and 2-ethylhexanoic acid were added by placing a “T” in the single intake line, with the stem of the “T” going to a reservoir (graduated cylinder) containing the standard
ANALYTICAL CHEMISTRY, VOL. 53, NO. 8, JULY 1981 -~
Table I. Pyrenea Fluorescence as Function of Sampler Cycle fluorescence, deviation from base line cycle trial 1 trial 2 1 10 20 30 40 50 60 70 80 100 110 120 130 140
x
std dev
-10.13 -4.25 3.63 2.50 5.38 3.25 2.13 6.00 0.76 2.63 0.50 -1.63 -0.75 -3.88 0.467 4.169
Pyrene concentration 0.0929 mg/L. 100 (arbitrary units). a
-12.06 -10.13 -2.19 -3.25 0.69 0.63 - 0.44 -1.50 2.38 -0.69 4.25 2.19 3.13 3.06 -0.767 4.720
Base line set at
dissolved in ethanol and diluted with water. At each cycle, a volume of standard was added to the sample prior to its entering the sampler. In this way one-third of the standard was delivered to each channel. EXPERIMENTAL SECTION Reproducibility of Volume Delivery. The reproducibility and bias in volume delivery were determined gravimetricallyby using distilled water equilibrated to room temperature (20-23 “C). In each series of experiments, the pump was run continuously at 45 mL/min at a delivery of 10, 20, or 30 mL. After air was removed from the sample train, 50 samples were collected “randomly” at a given delivery in 25- or 50-mL tared graduated cylinders. Three to twelve cycles lapsed between samples. The weight of each sample was corrected to the volume delivered at 20 “C. Reagents. The water used in this study was laboratory distilled-deionizedwater. Reagent grade pyrene, aniline, and phenol (Baker) were used. Preparation of Solutions, An aqueous solution of pyrene (0.0929 mg/L) was prepared according to1 May et al. (23). A synthetic water (70 mg/L NaHC03, 47 mg/L CaC12.H20,120 mg/L CaS04,anhyd) wag pumped through a column (30 X 5 cm) packed to 5 cm with 100 mesh glass beads3 coated with 1% by weight of pyrene. Solutions of phenol (7.67 mg/L, 15.52 mg/L) and aniline (3.30 mg/L, 11.00 mg/L) were prepared by directly dissolving the weighed compound in distilled water. Analysis. The sample train was flushed sequentially with 200 mL of distilled in glass methanol (Burdick and Jackson) and 200 mL of distilled water and allowed to drain,. The Teflon intake line was inserted into a solution of the teait compound, and 15 10-mL (nominal) aliquots were collected at the field pumping rate of 8.5-9 s/cycle (63 mL/min). Fifteen samples representing the first, tenth, and every tenth thereafter aliquot were collected in a clean 25-mL test tube for fluorescence spectroscopy. Fluorescence measurements were obtained by using a Perkin-Elmer Model MPF-44 spectrofluorometer. The excitation and emission wavelengths (nm) and slit widths (nm) used with pyrene, phenol, and aniline were 330,370,2.5/5.0; 270,310,5.1/5.0; and 280, 340, 5.0/5.0. RESULT13 AND DISCUSSION The current configuration of the device described here (without computer control) has been in use for 1year. Prior to that a prototype that differed primarily in the valve configuration (20) was used for 2 years. currently, eight thirdgeneration units employing solid-state circuitry are being constructed. Hall effect sensors on these units will replace the microswitches, and magnets will replace the cam dog,
1201
thereby eliminating mechanical contact. Many of the requirements we imposed on a sampler are incorporated in the design and are not individually testable. Extensive experience has shown, however, that these requirements are met under field conditions. We routinely sample using three channels each of which is connected to a different collection device. The sampler has worked well under manual and computer control a t subzero and elevated temperatures and in clean streams, primary sewage effluent, and heavily laden industrial wastes. Other potential difficulties such as bacterial growth in the sampler or carry-over have not been observed. The sampler is cleaned after each use by pumping concentrated chromic acid, distilled water, and methylene chloride. Other requirements have been verified by experiment. Laboratory studies have shown that the reproducibility of volume delivery (obtained from gravimetric measurements) was f0.16 mL (1standard deviation, 20 OC, N = 50) at each of the nominal volumes of 10,20, and 30 mL. The bias in this set of experiments was 0.5 mL at each nominal volume. All materials adsorbed some compounds. A review of the chemical and engineering literature resulted in our choice of Teflon and glass since Teflon and glass components exhibiting accepted adsorption properties are readily available. The sampler design helps reduce losses through low surface area, thereby precluding losses due to volatilization and maintenance of high flow velocities. The loss of material in the sampler was checked by using solutions of a neutral (pyrene), acidic (phenol), and basic (aniline) compound representative of those found in industrial effluents ( I , 19). Since we are concerned with relative losses through the sampling train, the emission spectra for 15 aliquots of each compound obtained from the samplers were compared with fluorescence of the stock solutions taken at the beginning and end of each experiment. The data show that the fluorescence of the first aliquot is about 10% lower than that of the stock solution, as illustrated by pyrene in Table I. While this might indicate some adsorption by the sample train, we cannot distinguish this from dilution by residual water trapped in the lines, syringes, or valves. Such losses, if real, are unimportant, since in field use the sample train is purged through several cycles with sample prior to sample collection. Further, since the average value of the aliquots is indistinguishable from the control (a< 0.05, t test), if there are small losses during the initial cycles they are insignificant during a typical 8-h (30 L) sampling run. CONCLUSION The device described here has been in use for 3 years and has worked without difficulty on clean stream, raw industrial wastes, and heavily silted samples. The selection of a computer-controlled version of this device for use in a nationwide study (16-18) acknowledges that sampling equipment which is “state of the art” relative to the analytical chemical techniques already being used is required for studies of waterborne organic compounds present a t trace levels in the environment. ACKNOWLEDGMENT We thank Ed Chian, Foppe DeWalle, William Glave, and Satu Somani. James Johnston provided laboratory facilities and guidance. Clarence Josefson donated ths pyrene solution. William Lawrence, Owen Ray, and Judy Brubaker are thanked. LITERATURE C I T E D (1) Somani, S. M.; Teece, R.; Schaeffer, D. J. J. Toxlcol. Environ. Heatth 1980, 6, 315-331. (2) Fishman, M. J.; Erdmann, D. E. Anal. Chem. 1979, 51, 317R. (3) Perry, D. L.; Chuang, C. C.; Jungclaus, G. A.; Warner, J. S. Identification of Organic Compounds in Industrial Effluent
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Anal. Chem. 1981, 5 3 , 1202-1205
Discharges"; EPA 560178-009; Environmental Protection Agency: 1978. (4) Janardan, K. G.;Tigwell, D. C.; Schaeffer, D. J. Eleventh Annual Pittsburgh Conference on Modeling and Simulation. Instrument Society of America. Research Triangle Park, N C Modeling Composite Sampling with Application to Trace Organics Monitoring, 11, Part 3, pp 985-989. (5) Garrison, A. W.; Pope, J. D.; Alford, A. L.; Doll, C. K. NBS Spec. Pub/ ( U . S . ) 1979, NO. 519, 65-78. (6) Stephan, S.F.; Smith, J. F.; Flego, U. WaterRes. 1978, 12, 447-449. (7) Lauch, R. P. "A Survey of Commercially Available Automatic Wastewater Samplers", EPA 60014-76-051; US. Environmental Protection Agency: Cincinnati, OH, 1976. (8) Huibergise, K. R.; Moser. J. H. "Handbook for Sampling and Sample Preservation of Water and Wastewater", EPA 600/4-76/049; US. Envlronmental Protection Agency: Washington, DC, 1976; National Technical Information Service, 1976, PC-259 946. (9) Shelly, P. E. "Sampling of Water and Wastewater", EPA 600/4-77/ 039; U.S. Environmental Protection Agency: Cincinnati, OH, 1977; National Technical Information Service, 1977, PB-272 664. (IO) Devera, E. R.; Simmons, B. P.; Stephens, R. D.; Storm, D. L. Samples and Procedures for Hazardous Waste Streams", EPA-BOO/ 2-80-018: US. Environmental Protection Agency: 1980. (11) Schaeffer, D. J.; Janardan, K. G. Blom. J. 1978, 20, 215-227. (12) Janardan, K. G.; Schaeffer, D. J. Anal. Chem. 1979, 57, 1024-1026. (13) Schaeffer, D. J.; Kerster, H. W.; Janardan, K. G., Environ. Manage. ( N . Y . )1980, 4 , 157-163. (14) Barkley, J. J. "Water Pollution Sampler Evaluation"; Army Medical Bloengineering Research and Development Laboratory: Fort Detrich, MD, 1975.
(15) Lin, P. C. L. "Thermal Analysis of the ISCO 1680 Portable Wastewater Sampler", EPA-600/4-80-033; U.S. Environmental Protection Agency: 1980. (16) Chian, E. S.K.; DeWalle, F. B. "Analytical Methods for Priority Pollutants in Municipal Sewage and Sludge", Water Pollution Control Federation: 1979; Abstracts 52nd Annual Conference of the Water Pollution Control Federation Oct 7-12, Session 25. (17) DeWalle, F. B.; Kalman, D. A.; Perera, C.; Chian, E. S. K. "Priority Pollutant Removal Efficiencies in POTW's as Related to their PhysicalChemical Properties", Water Pollution Control Federation: 1979; Abstracts 52nd Annual Conference of the Water Pollution Control Federation Oct 7-12, Session 8. (18) DeWalle, F.; Chian, E. "Presence of Priority Pollutants in Sewage and Their Removal in Sewage Treatment Plants First Annual Report to U S . Environmental Protection Agency", University of Washington: Seattle, WA, 1979. (19) Janardan, K. G.; Schaeffer, D. J.; Sornani, S.M. Bull. Envlron. Contamin. roxicol. 1980, 24, 145-151. (20) Tigwell, D. C.; Schaeffer, D. J. Patent Application, 1979. (21) Thurman, E. M.; Malcolm, R. L.; Aiken, G. R. Anal. Chem. 1979, 51, 1799-1803. (22) Schaeffer, D. J.; Glave, W. B.; Somani, S. M.; Janardan, K. G. Bull. Environ. Contamln. Toxlcol. 1980, 25, 569-573. (23) May, W. E.; Wasik, S. P.; Freeman, D. H. Anal. Chem. 1978, 50, 997-1000.
RECEIVED for review February 14, 1980. Resubmitted February 17, 1981. Accepted April 15, 1981.
Trace Level Determination of Selected Nitroaromatic Compounds by Gas Chromatography with Pyrolysis/Chemiluminescent Detection Arthur L. Lafleur"' and Kevin M. Mills Therm0 Electron Corporation, Analytical Instruments Department, 125 Second A venue, Waitham, Massachusetts 02254
A novel method for the trace level identification and determination of nttroaromatic compounds is described. It consists of a gas chromatograph coupled with a nitric oxide selective pyroiysis/chemilumlnescence detector (TEA Analyzer). The method gives linear response over 4 orders of magnitude and precision of 11% or better (relative standard deviation, N = 10) at the picomole level. Compounds studied include the nitrotoiuenes, five dinitrotoiuenes, and 2,4,6-trinitrotoluene. Pyrolyzer temperatures above 800 OC were required to produce optimum yields of nitric oxide from the compounds studied.
Recently, it was demonstrated that the coupling of a high-performance liquid chromatograph (HPLC) with a nitric oxide selective pyrolysis/chemiluminescence detector (TEA Analyzer) yielded a selective and sensitive method for the detection and determination of explosives and related compounds at trace levels (1-4). The types of explosive compounds studied were limited to nitrate esters and nitramines, although, in theory, any compound capable of releasing NO upon pyrolysis will produce a response. The detector is principally used for the determination of nitrosamines in a wide variety of matrices because of the property of most N-nitrosamines to liberate NO quantitatively when pyrolyzed. The advantages of the TEA Analyzer for the analysis of Present address: Massachusetts Institute of Technology, 77 Massachusetts Av., Cambridge, MA 02139.
N-nitrosamines in complex matrices have been comprehensively reviewed (5). However, when aromatic nitro compounds were investigated by using the HPLC/TEA approach, it was found that under conditions ideal for the determination of nitrosamines, nitrate esters, and nitramines, the nitroaromatics gave a relatively poor molar response (2,6). Because nitroaromatic compounds are very prominent in terms of commerce, national security, and environmental toxicology, a study was initiated to determine the feasibility of the selective determination of these compounds using some other approach that would still incorporate the advantages of highly selective NO-specific detection. The development of analytical methodology focused on the nitrotoluenes because they are among the foremost of the many nitroaromatics produced in commercial quantities. Moreover, because there is a large body of data showing the speed and simplicity of gas chromatography (GC) for their analytical separation (7), this technique was also used in the present investigation. EXPERIMENTAL SECTION Experimental Conditions and Apparatus. Identical systems were used for determining TEA Analyzer response as a function of pyrolyzer temperature and for obtaining optimum gas chromatographic separation of the nitrated toluene derivatives: The gas chromatograph used was a Model 5840A (Hewlett-Packard Corp., Palo Alto, CA). It had a glass column, 1.8 m in length, 2.0 mm inside diameter, packed with 3% OV-225 on Chromosorb W-HP 100/120 mesh. The carrier gas was argon flowing at a rate of 30 mL/min. The injection temperature was 240 "C. The column temperature was programmed from 100 to 240 O C at 8 OC/min.
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