THE ANALYSIS OF TRIHALOMETHANES IN FINISHED WATERS BY THE PURGE AND TRAP METHOD ^ PRO^ U. S. ENVIRONMENTAL PROTECTION AGENCY ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY CINCINNATI, OHIO 4526S ------- Foreword This method has been prepared by the staff of the Environmental Monitoring and Support Laboratory-Cincinnati at the request of the Office of Water Supply. Comments and suggestions offered by the Municipal Environmental Research Laboratory and the Division of Technical Support on the August 1, 1977 draft are gratefully acknowledged. The procedure represents the current state-of-the-art, but as time progresses improvements are anticipated. Users are encouraged to identify problems and assist in updating the method by contacting the Environmental Protection Agency, Environmental Monitoring and Support Laboratory, Cincinnati, Ohio 45268. ------- The Analysis of Trihalomethanes in Drinking Water by the Purge and Trap Method Scope 1.1 This method is applicable in the determination of chloroform, dichlorobromomethane, dibromochlororaethane, and bromoform in drinking water or raw source water. The concentration of these four compounds may be totaled to determine total trihalomethanes (TTHM). 1.2 Though the actual detection limits are highly dependent upon the gas chromatographic column and detector employed, the method can be used over a concentration range of approximately 0.1 to 1500 micrograms per liter. 1.3 Well in excess of 100 different water supplies have been analyzed using this method. Supplementary analyses using gas chromatog- raphy mass spectrometry (GC/MS) have shown that there is no evidence of interference in the determination of trihalomethanes. For this reason it is not necessary to analyze the raw source water as is required with the interim Liquid/Liquid Extraction Method. Summary 2.1 An extraction/concentration technique is incorporated within the method which enhances the amounts of trihalomethanes injected into the gas chromatograph by a factor of 1000 over direct injec- tion gas chromatography and by a factor of 200 over the interim Liquid/Liquid Extraction Method. ------- 2.2 Trihaloraethanes are extracted by an inert gas which is bubbled through the aqueous sample. The trihaloraethanes, along with other organic constituents which exhibit low water solubility and a vapor pressure significantly greater than water, are efficiently transferred from the aqueous phase to the gaseous phase. These compounds are swept from the purging device and are trapped in a short column containing a suitable sorbent. After a predetermined period of time, the trapped components are thermally desorbed and backflushed onto the head of a gas chromatographic column and separated under programmed conditions. Measurement is accomplished with a halogen specific detector such as electrolytic conductivity or microcoulometric titration. 2.3 Confirmatory analyses are performed using dissimilar columns, or by mass spectrometry.'. 2.4 Aqueous standards and unknowns are extracted and analyzed under identical conditions in order to compensate for extraction losses. 2.5 The total analysis time is approximately 35 minutes per sample. Interferences 3.1 Impurities contained in the purge gas and organic compounds out-gasing from the plumbing ahead of the trap usually account for the majority of contamination problems. The presence of such interferences are easily monitored as a part of the quality control program. Sample blanks are normally run between each -set of samples. When a positive trihalomethane response is noted in the sample blank, the analyst should analyze a method ------- blank. Method blanks are run by charging the purging device with organic-free water and analyzing in the normal manner. Whenever trihalomethanes are noted in the method blank, the analyst should change the purge gas source and regenerate the molecular sieve purge gas filter. Subtracting the blank values is not recommended. The use of non-TFE plastic tubing, non-TFE thread sealants, or flow controllers with rubber com- ponents should be avoided since such materials generally out-gas organic compounds which will be concentrated in the trap during the purge operation. Such out-gasing problems are common when- ever new equipment is put into service; as time progresses minor out-gasing problems generally cure themselves. 3.2 Several instances of accidental sample contamination have been noted and attributed to diffusion of volatile organics through the septum seal and into the sample during shipment and storage. The sample blank is used as a monitor for this problem. 3.3 . For compounds that are not efficiently purged, such as broraoform, small variations in sample volume, purge time, purge flow rate, or purge temperature can affect the analytical result. Therefore, samples and standards must be analyzed under identical conditions. 3.4 Cross contamination can occur whenever high level and low level samples are sequentially analyzed. To reduce the likelihood of this, the purging device and sample syTinge should be rinsed out twice between samples with organic free water. Whenever an unusually concentrated sample is encountered, it is highly ------- - 4 - recommended that it be followed by a sample blank analysis to insure that sample cross contamination does not occur. For samples containing large amounts of water soluble materials, it may be necessary to wash out the purging device with a soap solution, rinse with distilled water, and then dry in a 105°C oven between analyses. 3.S Qualitative misidentifications are a problem in using gas chromatographic analysis. Whenever samples whose qualitative nature is unknown are analyzed, the following precautionary measures should be incorporated into the analysis. 3.5.1 Perform duplicate analyses using the two recommended columns (4.2.1 and 4.2.2) which provide different retention order and retention times for the tri- halomethanes and other organohalides. 3.5.2 Use element specific detectors. 3.5.3 Whenever possible use GC/MS techniques which provide unequivocal qualitative identification^. 4. Apparatus 4.1 The purge and trap equipment consists of three separate pieces of apparatus: the purging device, trap, and desorber. Con- struction details for a purging device and an easily automated trap-desorber hybrid which has proven to be exceptionally efficient and reproducible are shown in Figures 1 through 4 and described in 4.1.1 through 4.1.3. An earlier acceptable version of the above mentioned equipment is described in Ref. 1. ------- - 5 - 4.1.1 Purging Device Construction details are given in Figure 1 for an all-glass 5 ml purging device. The glass frit installed at the base of the sample changer allows finely divided gas bubbles to pass through the sample while the sample is restrained above the frit. Gaseous volumes above the sample are kept to a minimum to eliminate dead volume effects, yet allowing sufficient space for most foams to disperse. The inlet and exit ports are constructed from heavy walled 1/4 inch glass tubing so that leak-free removable connections can be made using "finger-tight" compression fittings containing Teflon ferrules. The removable foam trap is used to control samples that foam. ' 4.1.2 Trapping Device The trap (Figure 2) is a short gas chromatographic column which at 22°C retards the flow of the compounds of interest while venting the purge gas and, depending on which sorbent is used, much of the water vapor. The tTap should be constructed with a low thermal mass so that it can be rapidly heated for efficient desorption, then rapidly cooled to room temperature for recycling. Variations in the trap ID, wall thickness, sorbents, soTbent packing order, and sorbent mass could adversely ------- - 6 - affect the trapping and desorption efficiencies for compounds discussed in this text. For this reason, it is important to faithfully reproduce the trap configurations recommended in Figure 2. The general purpose trap con- taining only Tenax is used for the trihalomethanes and compounds that boil above 30 °C. Compounds that boil below 30°C are not strongly sorbed by Tenax; therefore, such compounds pass through Tenax traps and are vented under normal purging conditions. If such compounds are to be determined, in addition to the trihalomethanes, the multi-purpose trap should be used. Grade-15 silica gel effectively retards the flow of most gaseous substituted organics at 22°C while allowing efficient desorption at 180"C. Higher boiling compounds do not efficiently desorb from the silica gel. The Tenax-silica gel multi-purpose trap utilizes the sorptive properties of the two sorbents providing a trap which effectively sorbs and desorbs a wide variety of organic compounds. 4.1.3 Desorber assembly - Details for the desorber are shown in Figures 2, 3, and 4. With the 6-port valve in the Purge- Sorb position (Figure 3), the effluent from the purging device passes through the trap where the flow rate of the organics is retarded. The GG carrier gas also passes through the 6-port valve and is returned to the GC. With ------- - 7 - the 6-port valve in the Purge-Sorb position, the operation of the GC is in no way impaired; therefore, routine liquid injection analyses can be performed using the gas chromatograph. After the sample has been purged, the 6-port valve is turned to the desorb position (Figure 4). In this configuration, the trap is coupled in series with the gas chromatographic column allowing the carrier gas to back-flush the trapped materials into the analytical column. Just as the valve is actuated the power is turned on to resistance wire wrapped around the trap. The power is supplied by an electronic temperature controller. Using this device, the trap is rapidly heated to 180*0 and then maintained at 180°C with minimal temper- ature overshoot. The trapped compounds are released as a "plug" to the gas chromatograph by this heat and backflush step. Normally, packed columns with theoretical efficiencies near 500 plates/foot under programmed temperature conditions can accept such desorb injections without altering peak geometry. Substituting a non-controlled power supply, .such as a manually-operated variable transformer, will provide non-reproducible retention times and poor quanti- tative data unless Injection Procedure (8.9.2) is used. -4.1.4 A commercial device manufactured by Tekmar has been tested and shown to be equivalent: Tekmar, P.O. Box 37202, Cincinnati, Ohio 45202. This device or its equivalent may be used. ------- - 8 - 4.2. Gas chromatograph - The chromatograph must be temperature programmable and equipped with a halide specific detector. 4.2.1 Column 1 is an unusually efficient column which provides outstanding separations for a wide variety of organic compounds. Because of its ability to resolve tri- halomethanes from other organochlorine compounds, column I should be used as the primary analytical column (see Figure 5). 4.2.1.1 Column I parameters: Dimensions - eight feet long x 0.1 inch ID stainless steel or glass tubing. Packing - 0.2% Carbowax 1500 on Carbopack-C (80/100) mesh. Carrier Gas - helium at 40 ml/minute. Temperature program sequence - 60°C isothermal for 3 minutes, pro- gram at 8°C/minute to 160°C, then hold for 2 minutes or until all compounds have eluted. NOTE: It has been found that during handling, packing, and programming, active sites are exposed on the.Carbopack-C packing. This results in poor resolution of constituents and poor peak geometry. To correct this, place a 1 ft. 0.125 in. 00 x 0.1 in. ID stainless steel column packed with 3% Carbowax 1500 on ChromosoTb-W 60/80 mesh in series before the CaTbopack-C column. Condition the precolumn ------- - 9 - and the Carbopack columns with carrier gas flow at 190°C overnight. The two columns may be retained in series for routine analyses. Trihalomethane retention times are listed in Table 1. 4.2.2 Column II provides unique organohalide-trihalomethane separations when compared to those obtained from Column I (see Figure 6). However, since the resolution between various compounds is generally not as good as those with Column I, it is recommended that column II be used as a qualitative confirmatory column for unknown samples when GC/MS confirmation is not possible. 4.2.2.1 Column II parameters: Dimensions - six feet long x 0.1 inch ID stainless steel or glass. Packing - n-octane on Porisil-C (100/120 mesh). Carrier Gas - helium at 40 cc/minute. Tempera- ture program sequence - S0°C isothermal for 3 minutes, program at 6'/minutes to 170°C, then hold for 4 minutes or until all compounds have eluted. Trihalomethane retention times are listed in Table 1. 4.3 Sampling containers - 40 ml scTew cap vials sealed with Teflon faced silicone septa. Vials and caps - Pierce #13075 or equivalent Septa - Pierce #12722 or equivalent ------- - 10 - 4.4 Syringes - 5-ral hypodermic with luerlok tip.(2 each). 4.5 Micro syringes - 10, 25, 100 yl. 4.6 2-way syringe valve with luer ends (3 each). 5. Reagents and Materials 5.1 Porous polymer packing 60/80 mesh chromatographic grade Tenax GC (2,6-diphenylene oxide). 5.2 Three percent OV-1 Chromosorb-W 60/80 mesh. 5.3 0.2% Carbowax 1500 on Carbopack-C (80/100 mesh) available from Supelco; request Batch #R-1579. 5.4 N-octane on Porasil-C (100/120 mesh) available from Waters Associates. 5.5 Three percent Carbowax 1500 on Chromosorb-W (60/80 mesh). 5.6 Dechlorinating compound-crystalline sodium thiosulfate, A.C.S. Reagent Grade. 5.7 Activated carbon - Filtrasorb-200, available from Calgon Corp., Pittsburgh, PA, or equivalent. 5.8 Organic-free water 5.8.1 OTganic-free water is generated by passing tap water through a carbon filter bed containing about 1 lb. of activated carbon. 5.8.2 A Millipore Super-Q Water System or its equivalent may be used to generate organic free deionized water. NOTE: Test organic free water daily by analyzing according to this method. See (8). ------- - 11 - 5.9 Standards 5.9.1 Bromoform - A.C.S. Reagent Grade 5.9.2 Bromodichloromethane 97% - available from Aldrich Chemical Company. 5.9.3 Chiorodibromomethane - available from Columbia Chemical Inc., Columbia, SC. 5.9.4 Chloroform - A.C.S. Reagent Grade. 5.10 Standard Stock Solutions 5.10.1 Place about 9.8 ml of methyl alcohol into a ground glass stoppered 10 ml volumetric flask. 5.10.2 Allow the flask to stand unstoppered about 10 minutes or until all alcohol wetted surfaces have dried. 5.10.3 Weigh the flask to the nearest 0.1 rag. 5.10.4 Using a 100 yl syringe, immediately add 2 drops of the reference standard to the flask, then reweigh. Be sure that the 2 drops fall directly into the alcohol without contacting the neck of the flask. 5.10.5 Dilute to volume, stopper, then mix by inverting the flask several times. NOTE: Because of the toxicity of trihalomethanes, it is necessary to prepare primary dilutions in a hood. It is further recommended that a NI0SH/MESA approved toxic gas respirator be used when the analyst handles high concentrations of such materials: ------- - 12 - 5.10.6 Calculate the concentration in micrograms per microliter from the net gain in weight. 5.10.7 Store the solution at 4°C. NOTE: , All standard solutions prepared in methyl alcohol are stable up to 4 weeks when stored under these conditions. They should be discarded after that time has elapsed. 5.11 Calibration Standards 5.11.1 Prepare, from the standard stock solutions, secondary dilution mixtures in methyl alcohol so that a 20 pi injection into, 100 ml of organic-free water will generate a calibration standard which produces a response close (±10%) to that of the unknowns. NOTE: Aqueous standards are not stable and should be discarded after one hour. 5.11.2 Purge and analyze the aqueous calibration standards in the same manner as the unknowns. 5.12 Quality Check Standard (2.0 ug/1) 5.12.1 From the standard stock solutions, prepare a secondary dilution in methyl alcohol containing 10 ng/yl of each trihalomethane. 5.12.2 Daily, inject 20.0 ul of this mixture into 100.0 ml of organic-free water and analyze according to the Procedure (8). (See 5.11.1 note.) 6. Sample Collection and Handling 6.1 The sample containers should have a total volume in excess of 50 ml. ------- - 13 - 6.1.1 Narrow mouth screw cap bottles with the TFE fluorocarbon face silicone septa cap lineTS are strongly recommended. Crimp-seal serum vials with TFE fluorocarbon faced septa are acceptable if the seal is properly made and maintained during shipment. 6.2 Sample Bottle Preparation 6.2.1 Wash all sample bottles and TFE seals in detergent. Rinse with tap water and finally with distilled water. 6.2.2 Allow the bottles and seals to air dry at room temperature, then place in a 105°C oven for one hour, then allow to cool in an area known to be free of organics. NOTE: Do not heat the TFE seals for extended periods of time (>1 hour) because the silicone layer slowly degrades at 105°C. 6.2.3 When cool, seal the bottles using the TFE seals that will be used for sealing the samples. 6.3 Sample Preservation - Sodium thiosulfate, a chemical dechlorinating agent, is added to the sample in order to arTest the formation of trihalomethanes after sample collection (Ref. 2). If chemical preservation is employed, the preservative is also added to the blanks. The chemical preservative (2.5 to 3 rag/40 ml) is. added to the empty sample bottles just prior to shipping to the sampling site. Do not add sodium thiosulfate to samples when data on maximum trihalomethane formation is desired. ------- - 14 - Sample Collection 6.4.1 Collect all samples in duplicate. 6.4.2 Fill the sample bottles in such a manner that no air bubbles pass through the sample as the bottle is filled. 6.4.3 Seal the bottles so that no air bubbles are entrapped in it. 6.4.4 Maintain the hermetic seal on the sample bottle until analysis. 6.4.5 Sampling from a water tap. 6.4.5.1 Turn on water and allow the system to flush. When the temperature of the water has stabilized, adjust the flow to about 500 ml/minute and collect duplicate samples from the flowing stream. 6.4.6 Sampling from an open body of water. 6.4.6.1 Fill a 1-quart wide-mouth bottle with sample from a representative area. Carefully fill duplicate sample bottles from the 1-quart bottle as noted in 6.4.2. 6.4.7 ' If preservative has been added to the sample bottles, fill with sample just to overflowing, seal the bottle, and shake vigorously for 1 minute. 6.4.8 Sealing practice for septum seal screw cap bottles. 6.4.8.1 Open the bottle and fill to overflowing, place on a level surface, position the TFE side of ------- - IS - the septum seal upon the convex sample meniscus and seal the bottle by screwing the cap on tightly. 6.4.8.2 Invert the sample and lightly tap the cap on a solid surface. The absence of entrapped air indicates a successful seal. If bubbles are present, open the bottle, add a few additional drops of sample and reseal bottle as above. 6.4.9 Blanks 6.4.9.1 Prepare blanks in duplicate at the laboratory by filling and sealing sample bottles with organic-free water just prior to shipping the sample bottles to the sampling site. 6.4.9.2 If the sample is to be preserved, add an identical amount of preservative to the blanks. 6.4.9.3 Ship the blanks to and from the sampling site along with the sample bottles. 6.4.9.4 Store the blanks and the samples collected at a given site (sample set), together. A sample set is defined as all the samples collected at a given site (i.e., at a water treatment plant, the duplicate raw source waters, the duplicate finished waters and the duplicate blank samples comprise the sample set). ------- - 16 - Conditioning Traps' 7.1 Condition newly packed traps overnight at 200°C with an inert gas flow of at least 20 ml/min. 7.1.1 Vent the trap effluent to the room, not to the analytical column. 7.2 Prior to daily use, condition traps 10 minutes while backflushing at 180°C. 7.2.1 The trap may be vented to the analytical column; however, after conditioning the column must be programmed prior to use. Extraction and Analysis 8.1 Adjust the purge gas (nitrogen or helium) flow rate to 50 ml/min. 8.2 Attach the trap inlet to the purging device. Turn the valve to the purge-sorb position (Figure 3). 8.3 Open the syringe valve located on the purging device sample introduction needle. 8.4 Remove the plungers from two 5 ml syringes and attach a closed syringe valve to each. 8.5 Open the sample bottle and carefully pour the sample into one of the syTinge barrels until it overflows. Replace the syringe plunger and compress the sample. Open the syringe valve and vent any residual air while adjusting the sample volume to 5.0 ml. Close the valve. ------- - 17 - 8.6 Fill the second syringe in an identical manner from the same sample bottle. This second syringe is reserved for a duplicate analysis, if necessary. 8.7 Attach the syringe-valve assembly to the syringe valve on the purging device. 8.8 Open the syringe valve and inject the sample into the purging chamber. Close both valves. Purge the sample for 11.0 ± .05 minutes. 8.9 After the 11 minute purge time, attach the trap to the chromato- graph (turn the valve to the desorb position) and introduce the trapped materials to the GC column by rapidly heating the trap to 180°C while backflushing the trap with an inert gas between 20 and 60 ml/min for 4 minutes. 8.9.1 If the trap can be rapidly heated to 180°C and maintained at this temperature, the GC analysis can begin as the sample is desorbed, i.e., the column is at the initial 60®C operating temperature. The equipment described in Figure 4 will perform accordingly. 8.9.2 With other types of equipment (see 4.1.4 and Reference 1) where the trap is not rapidly heated or is not heated in a reproducible manner, it is necessary to transfer the contents of the trap into the analytical column at 30°C where it is once again trapped. Once the transfer is complete (4 minutes), the column is rapidly heated to the initial operating temperature for analysis. ------- - 18 - 8.9.3 If injection procedure 8.9.1 is used and the early eluting peaks in the resulting chromatogram have poor geometry or variable retention times, then method 8.9.2 should be used. 8.10 After the extracted sample is introduced into the gas chromatograph, empty the gas purging device using the sample introduction syTinge, follow by two 5 ml flushes of organic-free water. When the purging device is emptied, leave the syTinge valve open allowing the purge gas to vent through the sample introduction needle. 8.11 Analyze each sample and sample blank from the sample set in an identical manner (see 6.4.9.4) on the same day. 8.12 Prepare calibration standards from the standard stock solutions (5.10) in organic-free water that are close to the unknown in trihalomethane composition and concentration (9.1). The concen- trations should be such that only 20 yl or less of the secondary dilution need be added to 100 ml of organic-free water to produce a standard at the same level as the unknown. 9. Analytical Quality Control 9.1 Analyze the 2 yg/1 quality check sample daily before any samples are analyzed. Instrument status checks and lower limit of detection estimations based upon response factor calculations at two times the signal to noise ratio are obtained from these data. In addition, response factor data obtained from the 2 yg/1 quality check standard can be used to estimate the concentration ------- - 19 - of the unknowns. From this information the appropriate standard dilutions can be determined. 9.2 Analyze the EMSL-Cincinnati volatile oTganics quality control samples or their equivalent on a quarterly basis. 9.3 Analyze the sample blank to monitor for potential interferences as described in section 3.1, 3.2 and 3.4. Calculations 10.1 Quantify the unknowns by comparing the peak height of the unknowns to the standard peak height (8.12). Round off the data to the nearest yg/1. * (cone. std. Mg/1) 10.2 Report the results obtained from the EMSL Quality Control Sample and the lower limit of detection estimates along with the data for the unknown samples. 10.3 Calculate the total trihalomethane concentration (TTHM) by summing the 4 individual trihalomethane concentrations in yg/1. TTHM (yg/1) = (Cone. CHCU) + (Cone. CHBrCl2) + (Cone. CHBr2Cl) + Cone. CHBr^)• 10.4 TTHM (ffig/1) = 10.5 Calculate the limit of detection (L0D) for each trihalomethane not detected vising the following criteria: -2 fHHeffJ where B = peak height (mm) of 2 yg/1 quality check standard A = 2 times the noise level in (mm) at the exact retention ------- - 20 - time of the trihalomethane or the baseline displace- ment in (mm) from the theoretical zero at the exact retention time of the trihalomethane. ATT = Attenuation factor Accuracy and Precision 11.1 One liter of organic-free water was dosed with the trihalomethanes; The dosed water was used to fill septum seal vials which were stored under ambient conditions. The dosed samples were randomly- analyzed over a 2-week period of time. The data listed in Table II reflect the errors due to the analytical procedure and storage. ------- - 21 - Table 1 Retention Data (minutes) Column I Column II Chloroform 8.2 12.2 Bromodichlororaethane 10.8 14.7 Dichlorobromomethane 13.2 16.6 Bromoform 15.7 19.2 ------- - 22 - Table II Accuracy and Precision for Trihalomethanes Chloroform Dose Number* Mean Standard yg/1 samples yg/1 deviation 1.19 12 1.21 0.14 11.9 8 11.3 0.16 119 11 105 7.9 Bromodichloromethane Dose Number* Mean Standard yg/1 samples yg/1 deviation 1.60 12 1.52 0.05 16.0 8 15.1 0.39 160 11 145 10.2 Chlorodibromomethane Dose Number* Mean Standard yg/1 samples yg/1 deviation 1.96 12 1.91 0.09 19.6 8 19.1 0.70 196 11 185 10.6 Bromoform Dose Number* Mean Standard yg/1 samples yg/1 deviation 2.31 12 2.33 0.16 23.1 8 22.5 1.38 231 11 223 16.3 •Single laboratory data ------- - 23 - References Bellar, T. A., Lichtenberg, J. J., Determining Volatile Organics at the Microgram per Litre Levels by Gas Chromatography, Journal AWWA., 66, 739 (December, 1974). Identification and Analysis of Organic Pollutants in Water, Keith, L. H., Ann Arbor Science, p. 87 (1976). ------- COLUMN: n-OCTANE ON PORASIl-C PROGRAM: 50°C-3 MINUTES 6°/MINUTE TO I70"C DETECTOR: ELECTROLYTIC CONDUCTIVITY 12 14 16 RETENTION TIME MINUTES FIGURE 6 CHROMATOGRAM OF ORGANO HALIDES ------- OPTIONAL FOAM TRAP - EXIT 1/ IN. O.D. JI4MM. O.D. INLET 1/4 IN. O.D. 1A IN. O.D. EXIT 10MM. GLASS FRIT MEDIUM POROSITY SAMPLE INLET 2-VMY SYRINGE VALVE 17CM. 20 GAUGE SYRINGE NEEDLE 6MM.O.D. RUBBER SEPTUM 10MM. O.D. INLET 1/4 IN. O.D. / ¦J 1/16 IN. O.D. STAINLESS STEEL / 13X MOLECULAR SIEVE PURGE GAS FILTER * PURGE GAS FLOW CONTROL • » • isrwi^r ------- PACKING PROCEDURE MULTIPURPOSE TRAP OENERAL PURPOSETRAP OLASS WOOL 5MM GRADE IS SILICA GEL 8CM IENAX 15CM 3% OV-I »CM GLASS WOOL 5MM I M m m ;f/ 'd? i® 4v ¦$; 'Wi tw Is m it %. m GLASS WOOL 5MM y3 TRAP INLET TEN AX 23CM 3JS OV-1 GLASS WOOL 1CM S MM Ufl M tU $ M $ §t 'l.fy 4 M A', u :S| / i.v* $V; 'fe-i :iix. M TRAP IN1ET FIGURE 2 TRAP CONSTRUCTION ------- CARRIER OAS FLOW CONTROL PRESSURE REGULATOR UQUID INJECTION PORTS PURGE GAS FLOW CONTROL \ 13X MOLECULAR SIEVE FILTER COLUMN OVEN —CONFIRMATORY COLUMN TO DETECTOR ANALYTICAL COLUMN HEATER CONTROL PURGING DEVICE NOTE: ALL LINES BETWEEN TRAP AND GC SHOULD BE HEATED TO 80°C FIGURE 3 PURGE-TRAP SYSTEM (PURGE-SORB MODE) ------- CARRIER GAS FLOW CONTROL PRESSURE REGULATOR LIQUID INJECTION PORTS PURGE GAS v FLOW CONTROL X 13X MOLECULAR SIEVE FILTER COLUMN OVEN CONFIRMATORY COLUMN TO DETECTOR ANALYTICAL COLUMN HEATER CONTROL NOTE: ALL LINES BETWEEN TRAP AND GC SHOULD BE HEATED TO 80°C PURGING DEVICE FIGURE 4 PURGE-TRAP SYSTEM (DESORB MODE) ------- COLUMN: 0.2% CARBOWAX 1S00 ON CARBOPACK-C PROGRAM: 60°C-3 MINUTES 8°/MINUTE TO 160°C DETECTOR: ELECTROLYTIC CONDUCTIVITY S ec O 8 10 12 14 RETENTION TIME MINUTES riounr c ri inrvn A HA AC AD/^AKIAUAI IHPC ------- |