Anal. Chem. 1002, 64, 2258-2262
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On-Line Membrane/Liquid Chromatographic Analyzer for Pentachlorophenol and Other Trace Phenols in Wastewater Richard G. Melcher; Dave W. Bakke, and Glen H. Hughes The Dow Chemical Company, Analytical Sciences, 1602 Building, Midland, Michigan 48667
The development and applkatlon of a unlque membrane Interface for selective extractlon and concentratlon of trace phenols In aqueous streams Is described. Selectlvlty for the extractlon of phenols Is obtalned by controlling the pH of the sample and the pH of the extractlon medla. Because the membraneused lsnonporous, the Interlacecan be useddlredy In a sample contalnlng partlculates and hlgh concentratlons of dkolved lnorganlc materlal. A mwnbraneAlquId chromatographk analyzer was developed for use on-line at a wastewater treatment plant for the determlnatlon of dlchlorophenol, trkhlorophend, tetrachlorophenol, and pentachlorophenol at low ppb levels In the plant effluents.
INTRODUCTION Silicone rubber membranes have been shown to be useful for the separation of trace organic compounds from aqueous samples. One of the first analytical applications of this type of membrane was described by Westover et al.' In this application, a tubular silicone rubber membrane was used to interface air and water samples to a mass spectrometer. The volatile compounds which permeated the membrane were drawn into the ion source for analysis. Blanchard and Hardy2 used a flat silicone polycarbonate membrane to separate volatile organic compounds from an aqueous sample. The permeated compounds were purged from the membrane cell with an inert gas stream and injected into a gas chromatograph. Zhang and Hardy used a similar system for the determination of volatile p h e n ~ l s .The ~ permeated phenols were purged from the membrane cell with helium and collected in a Tenax-TA porous polymer trap. The trap was then transferred to a thermal desorption/gas chromatographic system for analysis. These techniques are best suited for volatile and moderately volatile compounds. A membraneextraction interface has been developed which enables automatic on-line extraction, concentration, and determination of seleded trace organiccompoundsfrom aqueous streams and samples.* Since this system uses a liquid extractant for recovery, it can also be used for compounds of low volatility. This system,which uses tubular silicone rubber membranes, has been used to interface aqueous samples for flow injection analysis (FIA),596 gas chromatography (GC),T and liquid chromatography (LC).8!9 In these applications, the compounds which permeate the membrane from the ~
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To whom inquiries should be addressed. (1) Westover, L. B.; Tou,J. C.; Mark, J. H. Anal. Chem. 1974,46,567. (2) Blanchard, R.D.;Hardy, J. K. Annl. Chem. 1986,58, 1529. (3) Zhang, G.Z.;Hardy, J. K. J. Enuiron. Sci. Health 1989, A24 (8), 1011-1024. (4) Melcher, R. G.;Bakke, D. W.; Detrich, K. L. On-Line Monitor of Trace Phenols in Aqueous Streams Using a Membrane Extraction Interface. Pittaburgh Conference, 1987; paper 370. (5) Melcher, R. G. Anal. Chem. Acta 1988,214,299. (6) Melcher, R.G.;Cortes, H. J. U.S.Pat. 4775,476, Oct 4, 1988. (7) Melcher, R. G.;Morabito, P. L. Anal. Chem. 1990,62,2183. (8) Melcher, R. G.U.S.Pat. 4819,478, April 11, 1989. Bouyoucos, S. A. Process Control Qual. 1990,1,63. (9) Melcher, R.G.; 0003-2700/92/03862258$03.00/0
sample are removed at the other side of the membrane with an extracting liquid. The driving force for the extraction is related to the diffusion coefficient and the ratio of the partition coefficient of the analyte between the sample matrix and the membrane on one side of the membrane and between the membrane and the extractant on the other side of the membrane. For phenolic compounds, a strong driving force for the extraction is produced by adjusting the ample pH approximately 2 units below that of the pK, of the phenolic analyte. When the nonionized compound permeates the membraneand contacts a basic extractant, it forms a phenolic salt which is slightly soluble in the membrane and highly soluble in the aqueous extractant. The semipermeable silicone rubber membrane provides an excellent interface between "dirty" wastewater samples and the analyzer since it excludes particulates, dissolved inorganic compounds, and many watersoluble organic compounds. Two additional advantages for using an aqueous caustic extractant for phenols are (1) the extractant shows a high degree of selectivityfor phenolic compounds over neutral compounds and (2) selectivity can be obtained between phenols based on differences in their PKa values. A more detailed description of the principles of membrane selection and extraction have been discussed earlier.5g9 These works, using a liquid extractant, demonstrate the ability of membrane systems to extract and concentrate organic compounds, even phenols of low volatility such as pentachlorophenol,from the sample matrices which could not be directly injected into a chromatographic or FIA system. Phenols are an important group of compounds to be monitored in surface water, wastewater, and leachate, and an automated on-line system would give valuable data in many situations. For example, the efficiency of a biooxidation wastewater treatment plant can be monitored by observing how it handles low-level concentrations of pentachlorophenol. Pentachlorophenol is more difficult to biodegrade than most other phenols, and ita increase in the plant effluent may indicate reduced efficiency and a potential upset. Although certain selectivityis obtained from the membrane and detect.cn parameters used in an FIA system reported earlier? a complex sample, such aa wastewater, still requires further separation. Because of the nature of the basic aqueous extractant used for phenols, an LC analytical system was selected for the development of an analyzer, since it can be used directly online without a solvent exchange as required by GC analysis. The membrane/LC system developed for the determination of pentachlorophenol and other chlorinated phenols in wastewater effluent has been on-line for 6 years in various degrees of development, and its operation and performance is described in this publication.
EXPERIMENTAL SECTION Apparatus. Ertraction Panel. The steel extraction panel was wall mounted and the componentswere placed for easy access and removal (Figure 1). Valves c, d, g, n, and w were l/,-in., two-way or three-way (Whitey 4254 or 42x54) valves with air actuators. Valve c was used to switch between two samples 0 1002 American Chemical Soclety
ANALYTICAL CHEMISTRY, VOL. 64, NO. 19, OCTOBER 1, 1992
2269
e 4
FLUSH WATER
+ U Y
43 49-
t
Flgue 1. Membrane extraction panel (two-stream system): (a)sample stream 1; (b) sample stream 2; (c) stream select valve; (d) sample/ standard selectvalve;(e) standardlgrabsample transfer line; (1)sample pump 1; (g) fill valve; (h) reagent addition adapter: (I) acid pump and reservoir; (j) internal standard pump and reservoir; (k) membrane extraction cell; (I) cell overflow line; (m) magnetic stirrer; (n) drain valve; (0)extractant pump and reservoir; (p) LC Injection valve; (4)LC sample loop; (r) LC guard column; (s) LC analytical column; (t) LC detector;(u) extractantdrip Indicator;(v)LC eluent pump and reservoir; (w) eluent recycle valve; (x) silica precolumn.
streams of similar composition. This was later replaced with a dilution panel which was able to select and dilute one of four sample streams of different phenolic concentration. Valved was used to select between the sample valve c or a standardization solution (or grab sample) which was pulled up through tube e. Pump f (FMI Model No. RP-G400-1-CKC) pumped the sample through valve g to the membrane cell. Pumps i and j (FMI Lab Pump Jr., Model No. RHSYOCKC) were used to pump reagenta into the system through a machined Teflon resin block. Pump i pumped 1N HCl into the sample stream to adjust it to a pH of approximately 2. Pump j pumped the internal standard into the sample stream while the cell was filling to produce a concentration of approximately 50 ppb. These two pumps ran only for the 2 min that the cell was being filled. Pump o was used to pump the extractant, 0.02 N NaOH solution, continuously through the membrane and to the injectionvalve p. The injection valve used was a Rheodyne (Model No. 1070) fitted with an air actuator and a 100-rLsample loop. Valve n was closed after the cell was flushed with fresh sample and opened to drain the cell after the extraction was complete. Pump v (Spectroflow 400, AB1Analytical, Kratos Division)pumped the LC eluent through the injection valve and the analytical column. The eluent flow from the detector was passed through recycle valve w which directed the flow either to waste or back to the eluent bottle. Dilution Panel. The above extraction panel was used to analyzetwo different streams of similar compositionby switching valve a (Figure 1). A stream select and dilution panel, shown in Figure 2, was added so that additional streams of higher concentration could be analyzed with the same internal standard concentration. The stream selection was made during the previous cycle by opening the appropriate valve so that fresh sample was being pumped to valves ff and gg by pump hh before analysis of that stream started. Dilution was accomplished by opening valve ff for a fraction of the total cell filling time (2 min). For the remainder of the time, dilution water from reservoir ii was pumped to the cell to provide the proper dilution. Valve ee (pressurized water) was opened prior to new stream selection to back-flush the lines and clean the pump with water. The dilution systemwas tested using the sample/dilution water pumping time ratio for dilutions up to 1:lO. The dilution was checked, after setting the ratio, by manually diluting the sample and running as an undiluted stream, and agreement was found to be w i t h i the precision of the analysis. Further dilution could be obtained by letting the dilution water run for a longer period causing the flow to exit the overflow tube. In this manner it would be operating as an exponential dilution system. It would also be possible to use the volume in the line between valves ff and gg as a sample loop. Neither of these approaches was tested since most of our work used a 1:5 dilution ratio. Membrane Cell. The membrane used in this study wa Silastic brand medical grade tubing (Dow Coming, Midland, Michigan),a seamlesssiliconerubber tubing designed for clinical and laboratory applications. Silicone rubber is chemically and
4
STREAM 1
4
STREAM 2
-a-
DILUTION WATER
4
STREAM 3
d -0 4
t
STREAM 4
Flgm 2. Stream selectbn anddllutlonpanel: (aa-dd)streamselection valves; (ee)pressurized flush water valve; (ff) waterlsample to pump sample to waste valve; (hh) sample pump 2; (il) dllutbn vatve; (a) water reservoir. Extraction
Stalnless Steel
SthrBar
Flgure 3. Membrane extraction cell: cell volume, 100 mL; membrane length, 5 ft.
mechanically stable and has a high permeation rate for a large variety of organiccompounds. Dependingon the membrane size, pressures above 10-20 psi will cause the membrane to expand and possible rupture. Tubing of various sizes can be obtained from medical supply houses. The membrane size used in this work was 0.013-in. i.d. and 0.025-in. 0.d. (Dow Corning Catalog NO. 602-105). The design for a batch extraction cell is shown in Figure 3. A 5-ft length of membrane tubing was wound around a rigid support frame, and the ends were attached to a 1-in. piece of l/az-in.-o.d. stainless steel tubing. The membrane was attached by first swelliig the ends of the membrane in o-xylene and then slipping it over the tubing. When the xylene evaporated, a tight seal was formed. Connections were made to the valve using '/&16-h Valco bulkhead reducing unions inserted through the cell cap.
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ANALYTICAL CHEMISTRY, VOL. 64, NO. 19, OCTOBER 1, 1992
The cell body was made from Pyrex glass pipe with an i.d. of 1.5 in. The overflow was placed 3.5 in from the bottom to produce a cell volume of approximately 100mL. The batch cell was used instead of the smallflow-throughtype cell since it allowed mixing of the acid and internal standard with the sample, and the membrane was easy to remove for cleaning. A single membrane has been used in the continuous wastewater analyzer for periods of over 1 year with no apparent change in performance. Controller. The initial two-stream system used an eight-switch cam timer with a 45-min cycle time to operate the valves and start the integrator. The integrator was a Spectra-Physics 4270 programmed with an internal standard method. The more complex four-stream system used an Applied Automation Controller (ACC)to control the valves and pumps, integrate the chromatograms, calculate the results, and communicate to the peripherals such as the system IBM computer and the plant computer. The IBM computer provided an interface to allow program changes in the program resident in the AAC. The IBM computer also collected and stored the computed results from the AAC and the raw chromatogram. Chromatographic System. The LC column used was a Whatman Partisil 5 ODS 3, 250 mm X 4.6 mm, 5-rm particle size (Catalog No. 4238-001). A Brownlee Sphrei-5 RP-18 guard column was used (CatalogNo. OD-GU#10145A)and was preceded by a silica precolumn (Whatman Type PE WCS, Catalog No. 4391-001). The guard and analytical column were housed in an LC column oven (Jones Chromatography) and kept at 30 "C. The LC detector for the two-stream system was a Kratos Spectroflow 773 set at 290 nm and the detector for the-four stream system was an AppliedAutomation Optical AbsorbanceDetector with a fixed wavelength of 290 nm. The LC eluent, 60% acetonitrile, 10%methanol, 30% water, and 0.04 M phosphoric acid, was pumped at a flow rate of 0.8 mL/min. Reagents. The chlorophenols were obtained from Aldrich Chemical Co. Inc. A concentrated solution for preparing the calibration solution was prepared by dissolving 50-100 mg of each component in 10 mL of acetonitrile. The system was calibrated periodicallyby injecting 10pL of the concentrate into 1L of water to produce concentrations of 50-100 ppb. The extractant, 0.02 N NaOH, was prepared from 1 N NaOH (Fisher Scientific). The acid for adjusting the pH of the sample was 1 N HC1 (Fisher Scientific). The internal standard solution was prepared by weighing 36 into a small beaker and mg of 2,5-dibromo-3,4,6-trichlorophenol transferring it to 4 L of water with 40 mL of 1N NaOH solution. was prepared by bromiThe 2,5-dibromo-3,4,6-trichlorophenol nating 2,4,5-trichlorophenol(FlukaChemicalCorp.). The trichlorophenol was dissolved in dichloromethane and refluxed at 40 "C after the addition of bromine and anhydrous ferric chloride. After the reaction was complete (-48 h), a sodium metabisulfite solution was added to remove the excess bromine and dissolve the ferric chloride. The organic layer was then removed and solvent evaporated. Operation. Table I gives the timing schedule for the fourstream system set for a 30-min cycle. In summary, the sample from the stream selected in the previous cycle is pumped to the cell. Acid and internal standard solution are pumped into the stream prior to entering the cell. Ater the cell is flushed with sample, the drain valve is closed, the stirrer is turned on and the cell is filled (100 mL in 2 min). The 0.02 N NaOH extractant is pumped through the membrane and through the sample loop of the LC injection valve. After 10min, the injection valve injects the extract into the LC system for analysis. The cell is drained and filled with wash water. The on and off integration gates for each component are activated in sequence as the components elute. The timing schedule also shows other actions such as stream select and recycle commands. The system can be programmed to run only one selected stream or any combination of the four streams. The results are calculated and sent to the computers at the end of the cycle. The reagents and eluents were prepared in 4-L bottles. The LC eluent strength and flow rate were selected as a compromise. Although better resolution would be possible using a weaker eluent at a higher flow rate, this would require more eluent for the continuous operation of the analyzer. By using a stronger
Table I. Analyzer Timing Schedule for Four-Stream System time (s) operation device 0 cycle begins 1 open drain valve n 2 flow to cell valve g 2 sample stream to cell valve gg 2 acidlint std pumps on pumps i, j 2 sample 1pump ona Pump f 40 close drain valve n 40 stirrer on stirrer m 150 flow to waste valve g 150 acidlint std pumps off pumps i, j 150 water to pump valve ff 750 LC inject valve p 750 open drain valve n 780 LC load valve P 780 close drain valve n 780 flow to cell valve g 780 stream step valve aa, bb, cc, or dd 780 balance detector detector PUP0 780 extractant pump off 900 flow to waste valve g 900 eluent to waste valve w 900 pressure water on valve ee valve ff 960 sample to pump 960 sample to waste valve gg 960 pressure water off valve ee 960 sample pump 2 ona Pump hh 1070-1500 integration gates on and off 1550 recycle eluent valve w 1700 extractant pump on valve o 1800 cycle end Sample pump 1and sample pump 2 alternate in the on and off positions. eluent at a lower flow rate and a recycle of the eluent for half of the cycle time, the analyzerwas able to run for 1weekunattended. Maintenance. The membrane was cleaned weekly or earlier if a coating buildup was observed. The acid solution, the caustic extractant, and the internal standard solution were replenished once a month. The system was programmed not to calculate results if the internal standard area dropped below one-third of its calibration value. This was a signal for most malfunctions of the systemand chromatography. After severalyears of operation, a maintenance schedulewas developed. A once-a-yearshut down to replace pump seals, LC valve rotor, and LC guard columntook only4 h and, in general,prevented most malfunctions throughout the year. The seals on the acid pump had to be changed more often on a irregular basis but the seals on the LC pump lasted over 4 years. The sample pump on the dilution panel occasionally seized-up and had to be cleaned. This appeared to be more dependent on the sample than the time in service. The LC column lasted 1year or more and was changed when the chromatographic resolution became unsatisfactory. The Whatman silica precolumn lengthened the time between guard column and analytical column changes and appeared to stabilize retention times. The column heater was also found necessary to stabilize retention times.
RESULTS AND DISCUSSION The initial system developed in the laboratory was for a single sample stream for pentachlorophenol only. As the work progressed, it was modified to analyze multiple streams for trace levels of other chlorinated phenols in addition to pentachlorophenol. The results for the phenols other than pentachlorophenol in the waste stream were only estimates since other isomers were possible whose retention times and response factors were different. This occasionally resulted in split peaks or broader peaks. The isomer selected for the calibration standard for each compound had a retention time most often observed in the samples. The integration gates were set to include the peak area for most of the isomers of
ANALYTICAL CHEMISTRY, VOL. 84, NO. 19, OCTOBER 1, 1992 2261 Table 11. Membrane Extraction Enrichment Factors (Silicone Rubber Membrane, 5 ft.) compd enrichment factor0 2,4-dichlorophenol 1.9 2-bromo-4,6-dichlorophenol
2,4,6-tribromophenol 2,3,4,5-tetrachlorophenol 3-bromo-2,4,6-trichlorophenol 2,5-dibromo-4,6-dichlorophenol 2,3,4,6-tetrabromophenol
pentachlorophenol 2,5-dibromo-3,4,6-trichlorophenol 3,5-dibromo-2,4,6-trichlorophenol 2,3,5-tribromo-4,6-dichlorophenol
pentabromophenol l,6-dibromonaphthol
5.9 7.0 5.9 7.0
8.3 9.3 10.0 10.3 9.0
1.8
4-sec-butyl-2-methylphenol
10.4 5.8 1.3 1.9
Enrichment factor = concentration in extract/concentration in sample. 0
Table 111. Laboratory Precision for the Determination of Pentachlorophenol date na % RSD Standard (10 ppb) 0.56 6 day 1 6 2.5 day 2 2.0 5 day 6 Effluent (3.5 ppb) 10 4.5 day 3 5.4 8 day 4 5 5.3 day 5
day 4 day 5 0
a
5 6 7.5 4 3 3 11 11
2.9 4.0 4.2
3.2 2.7
2.8 11.7
13.1
7.4 5.2 9.8 8.5 8.4 3.2 1.8 1.8
2.4 4.0 3.8
3.4 2.9 3.0 1.9
2.0
Total data for a 4-6-h period.
8.9
2,5-di-aec-butylphenol 4-tert-butylphenol
day 6
1 2 3 6 8 9 13 14
% RSD pooledpairs
6.3
4 4 1,1,3,3-tetramethylbutyl)phenol
day 7
Table IV. Precision of On-Line Analyzer for Pentachlorophenol manual analyzer % RSDn day LC (ppb) (ppb) total
9 15
7.4
3.3
Spiked Effluent (13.5 ppb) 5 5
2.6 1.2
n is the number of consecutive runs in a group.
a compound so that a total was calculated. Since pentachlorophenol was of the most interest and had no isomers, it was used for evaluation of precision and accuracy of the system. The membrane enrichment factor for each compound and isomer is dependent on its solubility and diffusion in the membrane. Table I1lists the enrichment factor for a number of phenolic compounds based on a 5-ft. piece of tubular membrane and a 0.01 N NaOH extractant flow of 0.2 mL/ min. The permeation of unsubstituted phenol under these conditions produced an enrichment factor of less than 1and was not included in the list of analytes. Extraction tests on neutral compounds with this eluent showed that the selectivity (extraction efficiency) was approximately 250,550, and 1200 times greater for pentachlorophenol than for trichlorobenzene, tetrachlorobenzene, and pentachlorobenzene, respectively. Although neutral compounds permeate into the membrane, they are not readily extracted into the aqueous extractant. The caustic concentration was changed to 0.02 N NaOH in the final system to make sure it was not neutralized by extracted acidic compounds. This change in caustic concentration had no effect on the enrichment factors. The results of a laboratory precision study for the determination of pentachlorophenol in standard, sample, and spiked sample are shown in Table 111. Several phenomena observed in the on-line trials, however, indicated that frequent standardization or an internal standard approach would be necessary for the waste stream selected for analysis. First, a coating appeared on the membrane used in continuous
service. A standard run every day (between samples) for 7 days showed a decrease in response to 93 5% and after 14 days a decrease to 55 7%. Even though the absolute response was reduced, the recovery of a spiked sample, throughout this period, ranged from 92% to 105% when based on the calibration standard for that day. When the membrane assemblywas removed from the cell and washed under running water with a soft brush, the response was almost completely restored. A matrix effect was also observedby comparingthe response of the anaytes spiked into the sample to their response in distilled water. Even though the membrane was cleaned and calibrated, recovery of a spike in the wastewater sample varied gradually between 97 % and 80 % over a longer period of 2 months even though the response of the spiked standard water sample did not change. Temperature has been shown to have an effect on permeation on the order of 3-4 % /°C.3p5 However, the temperature of the sample stream was relatively constant during the test period and the small temperature correction did not account for the change in recovery. Any changes in the sample matrix, such as concentration of dissolvgd solids, could have some effect on the partition coefficient of the extraction. No study was conducted to elucidate the cause( 8 ) of the matrix effect, since an internal standard that had extraction parameters close to pentachlorophenolwas selected to compensate for these effects, as well as the coating effect, on a sample to sample basis. This was particularly important in the multistream system where the sample matrix and temperature could vary from point to point. After some study, 2,5-dibromo-3,4,6-trichlorophenol was selected as the internal standard because it had a chemical structure, matrix effect, and enrichment factor similar to those of pentachlorophenol. Its LC peak followed pentachlorophenol and was completely resolved. No interference peaks had been observed in this region over a 4-month period. After the internal standard system was installed, the precision of a standard solution run as a sample periodically, during continuous on-line operation, was between 3.5% and 5.5% RSD for dichlorophenol, trichlorophenol, tetrachlorophenol and pentachlorophenol even though the membrane was cleaned only weekly. In an another experiment, the results for pentachlorophenol were compared to the results obtained in the plant lab, which used a manual LC procedure, and are summarized in Table IV. The analyzer results are based on 8-10 runs over a 4-h period whereas the lab result was based on one grab sample taken during the period. The total precision calculated for the analyzer assumed that the sample stream had not changed during the sampling period. This assumption is probably not correct and the precision calculated from pooled sequential data pairs should give a better evaluation of precision. Typical chromatograms obtained with the Spectra-Physics 4270 for a calibration run and a sample are shown in Figure 4. With the Spectra-Physics integrator, chromatogramscould
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ANALYTICAL CHEMISTRY, VOL. 64, NO. 19, OCTOBER 1, 1992 STANDARD RUN
necessary to operate the more complex four-stream system. The integration program however was not able to operate on relative retention times and the integration gates had to be checked when new LC eluent was added and manually adjusted periodically. Overall, the analyzer performed well considering the difficult nature of the sample. Pentachlorophenol was determine in a range of 3-600 ppb (with dilution) in acomplex matrix containing other organic compounds, dissolved inorganic compounds, and varying amounts of particulates. Estimates were also obtained for four other chlorinated phenols in four streams on an around-the-clock basis. Charta were plotted of the analyte concentrations to follow their correlation to other parameters such as feed rate, TOC, and rainfall. An alarm level was set for pentachlorophenol on the treatment plant effluent to alert plant operators of possible upset conditions. The system also detected the presence of a noncharacteristic phenolic compound which occurred in the system, and it was able to follow the dynamics of the treatment plant and the effects of the compound on biodegradation efficiency. Less complicated sample streams may require a much simpler system. For example, a lake or stream could be monitored for a range of phenolic compounds using only sample acidification and periodic external standardization. In addition, a simple, off-line laboratory system could be assembled, using the membrane extraction principle, which would require a minimum amount of operator training.
4 5
CLPHENOLSSECONDARY FILE 1. NAME 1 2 3 4 5
DI CL TR CL TETRA CL PENTA BRCL PENA
METHOD 2.
RUN 34
PPB
RT
140.711 70.687 40.52 38.233 INTERNAL STD
5.62 7.09 8.88 12.06 13.13
SAMPLE RUN
CL PHENOLS SECONDARY FILE 1. NAME DI CL TR CL PENTA BRCL PENA
METHOD 2.
RUN 270
PPB 12.863 1.216 2.841 INTERNAL STD
RT 5.62 7.09 12.1 13.16
Flgurs 4. Typical chromatogramsof calibration standard and sample: (1) 2,edichlorophenol;(2) 2,4,6-trichbrophend;(3)2,3,4,6-tetrachlorophenol; (5) internal standard, 2,5dibromo3,4,&trlchlorophenol.
be obtained for every sample or with the plot turned off so that only the results were printed. The cam timer and Spectra-Physics integrator worked well for the one- and twostream systems. The retention times of all components were calculated relative to the internal standard so that adjustments were made automatically for slight changes in the chromatography. The Applied Automation system was
RECEIVED for review March 5, 1992. Accepted July 7, 1992. Registry No. 2,4-Dichlorophenol, 120-83-2; 2-bromo-4,6dichlorophenol,4524-77-0;2,4,&tribromophenol,118-79-6;2,3,4,5tetrachlorophenol, 4901-51-3; 3-bromo-2,4,6-trichlorophenol, 85117-86-8;2,5-dibromo-4,6-dichlorophenol, 143106-21-2;2,3,4,6tetrabromophenol,14400-94-3;pentachlorophenol, 87-86-5;2,5dibromo-3,4,6-trichlorophenol, 119916-55-1;3,5-dibromo-2,4,6trichlorophenol,40979-04-2;2,3,5-tribromo-4,6-dichlorophenol, 143106-22-3;pentabromophenol,608-71-9;1,6-dibromonaphthol, 143106-23-4;4-(1,1,3,3-tetramethylbutyl)phenol,140-66-9; 2,5di-sec-butylphenol,54932-77-3;4-tert-butylphenol,9854-4; Csecbutyl-2-methylphenol, 42413-56-9;water, 7732-18-5.
