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Concentration and determination of trace organic pollutants in water
0039-9140~75,0101-0659 %02.@0/0
T&nro, Vol. 25,@. 659-663 @ PergamonPress,Ltd., 1978.Prmtedin Great Britain
CONCENTRATION AND DETER~INATrON OF TRACE ORGANIC POLLUTANTS IN WATER RICHARD
C. CWANG
and
JAMES S. FRITZ*
Ames Laboratory-ERDA and Department of Chemistry Iowa State University, Ames, Iowa 50011, U.S.A. (Recei& 4 July 1977. Revised 22 March 1978. Accepted 31 March 1978) Summary--Organic pollutants in water areisolated on a mini-sampler tubecontaining a macroporous resin. The sorbed pollutants are next thermally transferred to a second sorption tube and then to an analytical column where they are separated and determined by temperature-programmed gas chromatography. Excellent recoveries were obtained for tests in which model organic compounds of various classes were added to water. The water sample is much smaller than that required with previous analytical methods.
The nature and concentrations of organic pollutants in drinking water are matters of great concern. It is vital that reliable methods of water analysis be developed. Because of the extremely low concentration (usually < 1 ppM*) of those organic contaminants in drinking water that are amenable to gas-chromatographic separation an efficient concentration method is required. Gas-stripping techniques have been used successfully for volatile compounds and for highly insoluble compounds such as alkanes. ‘, 2 Solvent extraction works well for many pesticides and certain other compounds, but the degree of extraction of many classes of organic compounds is 1ow.j Other disadvantages of solvent extraction include the necessity to use very pure solvent, general inconvenience of handling large samples, and the loss of volatiles during evaporation. Activated carbon is an e&cient sorbent but desorption from it with organic solvents is often slow and incomplete. The XAD-2 resin sorption method4 is probably the most reliable and thoroughly tested method for determining trace organic pollutants in drinking water. However, the solvent evaporation step in this procedure results in a partial or complete loss of volatile compounds. In addition, the volume (2 ~1) of the ether concentrate taken for gas-chromatographic analysis is only a small fraction (l/500) of the total. To avoid these drawbacks a procedure has been developed in which organic compounds that are sorbed on a resin are the~ally desorbed directly onto a gas-chromatographic column for analysis. A thermal desorption method was proposed earlier by Mieure and Dietrich but they did not develop the method very much. They found that interstitial water often caused the FID flame to be extinguished. In the present method this difficulty is avoided by first desorbing onto a Tenax tube the sorbed organic compounds from a tube containing XAD-2. This eliminates virtually all of the water entrained in the XAD-2 tube. Then the organics are thermally desorbed from the * Parts per milliard (log).
Tenax tube directly onto column.
the gas-chromatograph
EXPERIMENTAL
Resins
XAD-2 resin from Rohm and Haas was ground and sieved in the dry state. The 60-80 mesh resin was used after purification according to the procedure of Junk et ~1.“ Tenax-GC, 60-80 mesh, was used without further purification. Apparatus nnd equipment
A Hewlett-Packard 5756 B gas chromatograph equipped with a linear temperature programmer and FID detector was used. Stainless-steel tubing was used for all columns and injection-port liners. The injection port was enlarged by drilling to accommodate the glass sorption tubes. The column for separations was either 6 ft x l/S in. o.d. packed with 5% OV-17 on Chromosorb W AW DMCS (SO--l00 mesh) or 4 ft x l/S in. packed with Tenax-GC (60-80 mesh). Sorption tubes were 2mm i.d., 1Ocm in length. They were filled with 7 cm of either XAD-2 or Tenax-GC, held in place with a plug of glass wool at either end. The XAD-2 tubes were conditioned by thermal desorption at 240” and repetitive blanks were run until a low, tolerable background was achieved. A blank run involved wetting the resin-with triplydistilled water and following steus 2 and 3 of the analvtical procedure. The Tenax-GC t&e required only a simple conditioning by heating for 1 hr at 275” to achieve a tolerable blank level. A mini-sampler for water was devised in which a 20-m] glass syringe is connected to an XAD-2 sorption tube (Fig. 1). The connection is made with the special Kel-F coupler shown in Fig. 2.
Water samples containing 3-100 ppM @g/l.) of model organic compounds were prepared by adding 2-5~1 of standard solution in methanol to a 15-ml (or larger) water sample and mixing well. Procedure 1. (Sampling). Pass a 1%ml (or larger) sample through the XAD-2 sorption tube by using the mini-sampler with hand pressure to force the water through (about l-2min). Then force as much residual water as possible from the tube, using 20ml of air. Cap the sorption tube at both ends unless the analysis is to continue without delay.
RICHAKD
660
C. CHANG
J
L
and JAMESS. FRITZ
perature.) Allow 10 min for transfer of organic solutes from the Tenax tube to the column, then separate by raising the temperature at 20”/min up to 200”, finally holding this temperature for 10min. 4: (Measurement). Inject 2-5~1 of standard organic solution in methanol through a zone heated to 220” onto a Tenax tube at room temperature (or slightly above). Des& and chromatograph the organic compounds as in step 3. Compare the heights of the sample and standard peaks to calculate the amounts of sample constituents.
-A
B
RESULTS AND DISCUSSION
J
L
-C
:‘i D
.-.r
‘:
F
/
\
E
,.. ,. ., ’ .:. :.
G
Fig. 1. Mini-sampler for small water volumes: (A) 20-ml glass hypodermic syringe; (B) water sample; (C) coupler for attachingmini-column (E) to thesyringe; (D) l/4-in. Swagelok nut; (E) 2-mm i.d. Pyrex tube; (F) glass-wool plugs ; (G) 80 mg of 60-80 mesh resin.
t 0 250”
5/16-20
Fig. 2. Kel-F coupler
Recovery
Organic compounds representing eight different classes and covering a wide volatility range were added to water (at 3-200 ppM levels) and used to test the resin extraction-thermal desorption procedure. The recovery was calculated by comparing the peak height with that for a known standard solution (in methanol) injected directly onto the Tenax tube and thermally desorbed into the GC column at 220”. The recoveries are summarized in Table 1. The average recovery was 83%. However, if the results from three polar compounds known to be incompletely retained by the XAD-2 (acetone, butanol, pentanol) are discarded, the average is 88%. The overall reproducibility is 558%. These recoveries compare well with those obtained by other procedures. However, no other single procedure will give satisfactory results for water samples containing both volatile compounds (chloroform, benzene, etc.) and less volatile substances such as naphthalene and acetophenone. The recoveries of carboxylic acids were not reproducible. This is believed to be due to the difficulty of direct determination of acids by gas chromatography. A selective method for concentration of the acids with subsequent gas chromatography of their derivatives would be more desirable. The recoveries for phenols varied from 4 to 90%. These inconsistent results are probably due to the high affinity of Tenax-GC for phenols. All attempts to improve the yield for phenols failed, and the method is not satisfactory for these compounds. Some natural water samples were analysed by the proposed method. A typical chromatogram is shown in Fig. 3, but represents only a general profile of the contaminants in the water sample, since no identification was attempted. Method
2. (7hermul &sorption). Connect the XAD-2 tube to a Tenax sorption tube. Place the XAD-2 tube in a heated zone maintained at 220” with helium flowing at 50ml/min into the XAD-2 tube and out of the Tenax tube. (The Tenax tube is held at approximately 45”.) Continue desorption from the XAD-2 onto the Tenax tube for - 15 min or until the Tenax is visibly dry. 3. (Separation). Disconnect the two tubes and place the Tenax tube in the modified GC injection port, held at 220”, and apply a helium carrier-gas flow of 20 ml/min. (The oven section of the chromatograph is at approximately room tem-
Choice
parameters
of sorbents. In our first experiments water was passed through a small column of XAD-2 and the organic compounds were thermally desorbed onto an 18 x l/4 in. GC column at room temperature and packed with Tenax-GC. A switching valve in the gas chromatograph allowed water to pass through the column to vent while organic solutes were concentrated on the Tenax. After a few minutes the valve was switched to connect the Tenax column to a second
Trace organic
pollutants
661
in water
1
60 t
170°C
3
Time,
Fig. 3. Gas chromatogram of organic compounds extracted from the drinking water of Slater, Iowa.
16 x l/8 in. Tenax column. The oven temperature programme was started and the organic substances were separated. This procedure was partly successful but had two important limitations: (1) The recovery of less volatile compounds (e.g., napthalene) was not reproducible, and (2) the stationary phase of the second GC column was limited to Tenax or some similar hydrophobic material. Several experiments were performed in which Tenax-GC was used instead of XAD-2 in the minisampler tube, but recoveries were consistently low (10-20x). The combination of both XAD-2 and Tenax-GC sorption tubes outlined in the procedure was the only method tried that gave satisfactory results for a variety of organic compounds. Table
1. Overall
recovery
Alkanes Octane Heptane Tridecane Alkylbenzenes Benzene Toluene o-Xylene Cumene Ethers Hexyl Benzyl Esters Benzyl acetate Methyl decanoate Methyl hexanoate H&forms* Chloroform Bromodichloromethane * Chlorinated
methanes
Fig. 4. Gas chromatogram of model compounds injected as a solution in methanol: (1) benzene; (2)octane; (3) toluene; (4) 2-octanone and (5) acetophenone. Desorption temperature: 170”.
Desorption temperature. The good recoveries shown in Table 1 indicate that 220” is adequate for total thermal desorption from XAD-2 onto Tenax-GC. Temperatures much above this lead to bigger blanks, apparently because of some decomposition of the XAD-2. However, whether the second desorption, from Tenax-GC onto the gas chromatographic column, is complete or not is unknown, because the peaks of the organic sample solutes (from the XAD-2 desorption) are compared with peaks of standards which are simply injected as their methanol solutions into the Tenax column. The effect of Tenax-column desorption temperature on the final chromatogram was therefore examined by injecting into the Tenax
efficiency of resin extraction and thermal desorption water at the 3- 100 ppM level
Recovery efficiency, “/,
Compounds
88 81 90 90 97 90 82 80 70 95 88 86 87 95 were tested at a concentration
mm
method
of analysis
Compounds Polynuclear aromatics Naphthalene 2-Methylnaphthalene Chlorobenzenes Chlorobenzene o-Dichlorobenzene Ketones Acetone 2-Octanone Undecanone Acetophenone Alcohols I-Butanol I-Pentanol I-Octanol I-Decanol Phenols and acids No quantitative results
of 200 ppM in water (i.e., 200 ).@I.).
on XAD-2 for organics
Recovery efficiency, %
98 97 90 82 55 83 86 92 <4Cl <40 85 84
in
662
RICHARDCCHANG
1
5
and JAMESSFRITZ
material not desorbed from the Tenax at 220” will be removed in the conditioning treatment at 275”, and will not affect subsequent performance. Deso~pti~)~ztime. The time needed for desorption of organic solutes from the Tenax tube was also studied. Figure 7 shows that benzene is desorbed much more quickly than naphthalene, which is less volatile. Wowever, desorption of naphthalene is complete in IO mm, so this desorption time was regarded as adequate, as naphthalene was the most di~cu~t (of the compounds tested) to desorb. No attempt was made to optimize the desorption times for the wide variety of compounds tested. However, desorption times in excess of 30 min may adversely affect the peak shape for compounds such as n-octane and chloroform.
1
Time,
mln
Fig. 5. Same conditions as for Fig. 4 except desorption temperature:
60-
215”.
265°C
Time,
mm
Fig. 7. Effect of the desorption A benzene,
Time,
min
Fig. 6. Sameas for Fig. 4except desorption
temperature:
265”.
tube 2 u1 of methanol solution containing 0.8 ug each of benzene, octane, toluene, 2-octanone and acetophenone. The solutes were desorbed from the Tenax tube at three different temperatures and the results compared. The chromatograms from these tests are shown in Figs. 4-6. These chromatograms show that lowering the temperature has little effect on desorption of volatile compounds such as octane, benzene and toluene, but retention of the higher-boiling compounds on the Tenax is more serious. In our procedure (step 3) it was convenient to desorb at 220” because this temperature was used for desorption of the XAD-2 tube in the other GC injection port. However, the results in Fig. 6 indicate that a higher temperature (265”, for example) would be advantageous. Any
time for the Tenax B naphthalene.
tube.
humble size und sens~ti~~~~~. The ability of the XAD-2 mini-sampler tubes to retain organic compounds from water samples larger than 15 ml was checked in two ways. In the first, injection of a standard sample of benzene and toluene (in 2 ~1 of methanol) followed by washing the tube with lOOmI of distilled water, there was no measurable loss of organic solutes. The second method was to analyse two different water samples, one of 15 ml and the other of60 ml. The recoveries were similar (Table 2). The larger XAD-2 sampler used earlier” contained 2000mg of resin and effectively removed organic impurities from at least 50 1. of water. The minisampler contains 8Omg of XAD-2 and would be expected to be effective with water samples as large as 1
Table 2. Effect of water sample size
Recovery, Compound Acetone Benzene Toluene
15-ml sample 49 90 97
“0 60-ml sample 60 90 102
Trace organic pollutants in water
litre. In one instance a I-litre sample was successfully analysed for chloroform and other halocarbons. The method is capable of detecting 0.1 ppM of organic compound in a 15ml water sampler, given a detector sensitivity (FID) of 1 ng. The sensitivity can be improved by using a larger sample size. Storage of sorbed compounds. To test the applicability of the mini-sampler for field sampling, water samples spiked with five volatile halocarbons (chloroform, carbon tetrachloride, bromodichloromethane, dibromochloromethane, and bromoform) were chosen for testing. After the synthetic water samples had been forced through the mini-samplers, these were stored in screw-capped test-tubes for a specific period of time before analysis. There was no measurable loss of the halocarbons in four days of storage. Although more results are needed, it does appear that organic compounds sorbed on the mini-sampler tubes are quantitatively retained for several days. Conclusion
The method concentrations
proposed can be used to determine low of a wide variety of organic compounds
663
in water. Since all of the organic pollutants removed from the water are used for chromatographic analysis, a much smaller water sample can be used than before. This means that field sampling with immediate sorption onto a mini-sampler is now feasible. Acknowledgements-This work was supported by the U.S. Energy Research and Development Administration, Division of Physical Research. The authors thank Dean Woods for machining special parts used in this work. They also thank H. J. Svec for his interest and for helpful discussions concerning the project. REFERENCES
1. K. Grob, K. Grob, Jr. and G. Grob, J. Chrornatog., 1975, 106.299. 2. W. Bertsch, E. Anderson and G. Holzer, ibid., 1975, 112, 701. 3. J. P. Mieure and M. W. Dietrich, J. Chromatog. Sci., 1973, 11. 559. 4. G. A. Junk, J. J. Richard, M. D. Grieser, M. D. Witiak, J. J. L. Witiak. M. D. Arauello. R. V.. H. J. Svec. J. S. Fritz and 6. V. Calder, J. Chromatog., 1974,99, 745.
T&nro, Vol. 25,@. 659-663 @ PergamonPress,Ltd., 1978.Prmtedin Great Britain
CONCENTRATION AND DETER~INATrON OF TRACE ORGANIC POLLUTANTS IN WATER RICHARD
C. CWANG
and
JAMES S. FRITZ*
Ames Laboratory-ERDA and Department of Chemistry Iowa State University, Ames, Iowa 50011, U.S.A. (Recei& 4 July 1977. Revised 22 March 1978. Accepted 31 March 1978) Summary--Organic pollutants in water areisolated on a mini-sampler tubecontaining a macroporous resin. The sorbed pollutants are next thermally transferred to a second sorption tube and then to an analytical column where they are separated and determined by temperature-programmed gas chromatography. Excellent recoveries were obtained for tests in which model organic compounds of various classes were added to water. The water sample is much smaller than that required with previous analytical methods.
The nature and concentrations of organic pollutants in drinking water are matters of great concern. It is vital that reliable methods of water analysis be developed. Because of the extremely low concentration (usually < 1 ppM*) of those organic contaminants in drinking water that are amenable to gas-chromatographic separation an efficient concentration method is required. Gas-stripping techniques have been used successfully for volatile compounds and for highly insoluble compounds such as alkanes. ‘, 2 Solvent extraction works well for many pesticides and certain other compounds, but the degree of extraction of many classes of organic compounds is 1ow.j Other disadvantages of solvent extraction include the necessity to use very pure solvent, general inconvenience of handling large samples, and the loss of volatiles during evaporation. Activated carbon is an e&cient sorbent but desorption from it with organic solvents is often slow and incomplete. The XAD-2 resin sorption method4 is probably the most reliable and thoroughly tested method for determining trace organic pollutants in drinking water. However, the solvent evaporation step in this procedure results in a partial or complete loss of volatile compounds. In addition, the volume (2 ~1) of the ether concentrate taken for gas-chromatographic analysis is only a small fraction (l/500) of the total. To avoid these drawbacks a procedure has been developed in which organic compounds that are sorbed on a resin are the~ally desorbed directly onto a gas-chromatographic column for analysis. A thermal desorption method was proposed earlier by Mieure and Dietrich but they did not develop the method very much. They found that interstitial water often caused the FID flame to be extinguished. In the present method this difficulty is avoided by first desorbing onto a Tenax tube the sorbed organic compounds from a tube containing XAD-2. This eliminates virtually all of the water entrained in the XAD-2 tube. Then the organics are thermally desorbed from the * Parts per milliard (log).
Tenax tube directly onto column.
the gas-chromatograph
EXPERIMENTAL
Resins
XAD-2 resin from Rohm and Haas was ground and sieved in the dry state. The 60-80 mesh resin was used after purification according to the procedure of Junk et ~1.“ Tenax-GC, 60-80 mesh, was used without further purification. Apparatus nnd equipment
A Hewlett-Packard 5756 B gas chromatograph equipped with a linear temperature programmer and FID detector was used. Stainless-steel tubing was used for all columns and injection-port liners. The injection port was enlarged by drilling to accommodate the glass sorption tubes. The column for separations was either 6 ft x l/S in. o.d. packed with 5% OV-17 on Chromosorb W AW DMCS (SO--l00 mesh) or 4 ft x l/S in. packed with Tenax-GC (60-80 mesh). Sorption tubes were 2mm i.d., 1Ocm in length. They were filled with 7 cm of either XAD-2 or Tenax-GC, held in place with a plug of glass wool at either end. The XAD-2 tubes were conditioned by thermal desorption at 240” and repetitive blanks were run until a low, tolerable background was achieved. A blank run involved wetting the resin-with triplydistilled water and following steus 2 and 3 of the analvtical procedure. The Tenax-GC t&e required only a simple conditioning by heating for 1 hr at 275” to achieve a tolerable blank level. A mini-sampler for water was devised in which a 20-m] glass syringe is connected to an XAD-2 sorption tube (Fig. 1). The connection is made with the special Kel-F coupler shown in Fig. 2.
Water samples containing 3-100 ppM @g/l.) of model organic compounds were prepared by adding 2-5~1 of standard solution in methanol to a 15-ml (or larger) water sample and mixing well. Procedure 1. (Sampling). Pass a 1%ml (or larger) sample through the XAD-2 sorption tube by using the mini-sampler with hand pressure to force the water through (about l-2min). Then force as much residual water as possible from the tube, using 20ml of air. Cap the sorption tube at both ends unless the analysis is to continue without delay.
RICHAKD
660
C. CHANG
J
L
and JAMESS. FRITZ
perature.) Allow 10 min for transfer of organic solutes from the Tenax tube to the column, then separate by raising the temperature at 20”/min up to 200”, finally holding this temperature for 10min. 4: (Measurement). Inject 2-5~1 of standard organic solution in methanol through a zone heated to 220” onto a Tenax tube at room temperature (or slightly above). Des& and chromatograph the organic compounds as in step 3. Compare the heights of the sample and standard peaks to calculate the amounts of sample constituents.
-A
B
RESULTS AND DISCUSSION
J
L
-C
:‘i D
.-.r
‘:
F
/
\
E
,.. ,. ., ’ .:. :.
G
Fig. 1. Mini-sampler for small water volumes: (A) 20-ml glass hypodermic syringe; (B) water sample; (C) coupler for attachingmini-column (E) to thesyringe; (D) l/4-in. Swagelok nut; (E) 2-mm i.d. Pyrex tube; (F) glass-wool plugs ; (G) 80 mg of 60-80 mesh resin.
t 0 250”
5/16-20
Fig. 2. Kel-F coupler
Recovery
Organic compounds representing eight different classes and covering a wide volatility range were added to water (at 3-200 ppM levels) and used to test the resin extraction-thermal desorption procedure. The recovery was calculated by comparing the peak height with that for a known standard solution (in methanol) injected directly onto the Tenax tube and thermally desorbed into the GC column at 220”. The recoveries are summarized in Table 1. The average recovery was 83%. However, if the results from three polar compounds known to be incompletely retained by the XAD-2 (acetone, butanol, pentanol) are discarded, the average is 88%. The overall reproducibility is 558%. These recoveries compare well with those obtained by other procedures. However, no other single procedure will give satisfactory results for water samples containing both volatile compounds (chloroform, benzene, etc.) and less volatile substances such as naphthalene and acetophenone. The recoveries of carboxylic acids were not reproducible. This is believed to be due to the difficulty of direct determination of acids by gas chromatography. A selective method for concentration of the acids with subsequent gas chromatography of their derivatives would be more desirable. The recoveries for phenols varied from 4 to 90%. These inconsistent results are probably due to the high affinity of Tenax-GC for phenols. All attempts to improve the yield for phenols failed, and the method is not satisfactory for these compounds. Some natural water samples were analysed by the proposed method. A typical chromatogram is shown in Fig. 3, but represents only a general profile of the contaminants in the water sample, since no identification was attempted. Method
2. (7hermul &sorption). Connect the XAD-2 tube to a Tenax sorption tube. Place the XAD-2 tube in a heated zone maintained at 220” with helium flowing at 50ml/min into the XAD-2 tube and out of the Tenax tube. (The Tenax tube is held at approximately 45”.) Continue desorption from the XAD-2 onto the Tenax tube for - 15 min or until the Tenax is visibly dry. 3. (Separation). Disconnect the two tubes and place the Tenax tube in the modified GC injection port, held at 220”, and apply a helium carrier-gas flow of 20 ml/min. (The oven section of the chromatograph is at approximately room tem-
Choice
parameters
of sorbents. In our first experiments water was passed through a small column of XAD-2 and the organic compounds were thermally desorbed onto an 18 x l/4 in. GC column at room temperature and packed with Tenax-GC. A switching valve in the gas chromatograph allowed water to pass through the column to vent while organic solutes were concentrated on the Tenax. After a few minutes the valve was switched to connect the Tenax column to a second
Trace organic
pollutants
661
in water
1
60 t
170°C
3
Time,
Fig. 3. Gas chromatogram of organic compounds extracted from the drinking water of Slater, Iowa.
16 x l/8 in. Tenax column. The oven temperature programme was started and the organic substances were separated. This procedure was partly successful but had two important limitations: (1) The recovery of less volatile compounds (e.g., napthalene) was not reproducible, and (2) the stationary phase of the second GC column was limited to Tenax or some similar hydrophobic material. Several experiments were performed in which Tenax-GC was used instead of XAD-2 in the minisampler tube, but recoveries were consistently low (10-20x). The combination of both XAD-2 and Tenax-GC sorption tubes outlined in the procedure was the only method tried that gave satisfactory results for a variety of organic compounds. Table
1. Overall
recovery
Alkanes Octane Heptane Tridecane Alkylbenzenes Benzene Toluene o-Xylene Cumene Ethers Hexyl Benzyl Esters Benzyl acetate Methyl decanoate Methyl hexanoate H&forms* Chloroform Bromodichloromethane * Chlorinated
methanes
Fig. 4. Gas chromatogram of model compounds injected as a solution in methanol: (1) benzene; (2)octane; (3) toluene; (4) 2-octanone and (5) acetophenone. Desorption temperature: 170”.
Desorption temperature. The good recoveries shown in Table 1 indicate that 220” is adequate for total thermal desorption from XAD-2 onto Tenax-GC. Temperatures much above this lead to bigger blanks, apparently because of some decomposition of the XAD-2. However, whether the second desorption, from Tenax-GC onto the gas chromatographic column, is complete or not is unknown, because the peaks of the organic sample solutes (from the XAD-2 desorption) are compared with peaks of standards which are simply injected as their methanol solutions into the Tenax column. The effect of Tenax-column desorption temperature on the final chromatogram was therefore examined by injecting into the Tenax
efficiency of resin extraction and thermal desorption water at the 3- 100 ppM level
Recovery efficiency, “/,
Compounds
88 81 90 90 97 90 82 80 70 95 88 86 87 95 were tested at a concentration
mm
method
of analysis
Compounds Polynuclear aromatics Naphthalene 2-Methylnaphthalene Chlorobenzenes Chlorobenzene o-Dichlorobenzene Ketones Acetone 2-Octanone Undecanone Acetophenone Alcohols I-Butanol I-Pentanol I-Octanol I-Decanol Phenols and acids No quantitative results
of 200 ppM in water (i.e., 200 ).@I.).
on XAD-2 for organics
Recovery efficiency, %
98 97 90 82 55 83 86 92 <4Cl <40 85 84
in
662
RICHARDCCHANG
1
5
and JAMESSFRITZ
material not desorbed from the Tenax at 220” will be removed in the conditioning treatment at 275”, and will not affect subsequent performance. Deso~pti~)~ztime. The time needed for desorption of organic solutes from the Tenax tube was also studied. Figure 7 shows that benzene is desorbed much more quickly than naphthalene, which is less volatile. Wowever, desorption of naphthalene is complete in IO mm, so this desorption time was regarded as adequate, as naphthalene was the most di~cu~t (of the compounds tested) to desorb. No attempt was made to optimize the desorption times for the wide variety of compounds tested. However, desorption times in excess of 30 min may adversely affect the peak shape for compounds such as n-octane and chloroform.
1
Time,
mln
Fig. 5. Same conditions as for Fig. 4 except desorption temperature:
60-
215”.
265°C
Time,
mm
Fig. 7. Effect of the desorption A benzene,
Time,
min
Fig. 6. Sameas for Fig. 4except desorption
temperature:
265”.
tube 2 u1 of methanol solution containing 0.8 ug each of benzene, octane, toluene, 2-octanone and acetophenone. The solutes were desorbed from the Tenax tube at three different temperatures and the results compared. The chromatograms from these tests are shown in Figs. 4-6. These chromatograms show that lowering the temperature has little effect on desorption of volatile compounds such as octane, benzene and toluene, but retention of the higher-boiling compounds on the Tenax is more serious. In our procedure (step 3) it was convenient to desorb at 220” because this temperature was used for desorption of the XAD-2 tube in the other GC injection port. However, the results in Fig. 6 indicate that a higher temperature (265”, for example) would be advantageous. Any
time for the Tenax B naphthalene.
tube.
humble size und sens~ti~~~~~. The ability of the XAD-2 mini-sampler tubes to retain organic compounds from water samples larger than 15 ml was checked in two ways. In the first, injection of a standard sample of benzene and toluene (in 2 ~1 of methanol) followed by washing the tube with lOOmI of distilled water, there was no measurable loss of organic solutes. The second method was to analyse two different water samples, one of 15 ml and the other of60 ml. The recoveries were similar (Table 2). The larger XAD-2 sampler used earlier” contained 2000mg of resin and effectively removed organic impurities from at least 50 1. of water. The minisampler contains 8Omg of XAD-2 and would be expected to be effective with water samples as large as 1
Table 2. Effect of water sample size
Recovery, Compound Acetone Benzene Toluene
15-ml sample 49 90 97
“0 60-ml sample 60 90 102
Trace organic pollutants in water
litre. In one instance a I-litre sample was successfully analysed for chloroform and other halocarbons. The method is capable of detecting 0.1 ppM of organic compound in a 15ml water sampler, given a detector sensitivity (FID) of 1 ng. The sensitivity can be improved by using a larger sample size. Storage of sorbed compounds. To test the applicability of the mini-sampler for field sampling, water samples spiked with five volatile halocarbons (chloroform, carbon tetrachloride, bromodichloromethane, dibromochloromethane, and bromoform) were chosen for testing. After the synthetic water samples had been forced through the mini-samplers, these were stored in screw-capped test-tubes for a specific period of time before analysis. There was no measurable loss of the halocarbons in four days of storage. Although more results are needed, it does appear that organic compounds sorbed on the mini-sampler tubes are quantitatively retained for several days. Conclusion
The method concentrations
proposed can be used to determine low of a wide variety of organic compounds
663
in water. Since all of the organic pollutants removed from the water are used for chromatographic analysis, a much smaller water sample can be used than before. This means that field sampling with immediate sorption onto a mini-sampler is now feasible. Acknowledgements-This work was supported by the U.S. Energy Research and Development Administration, Division of Physical Research. The authors thank Dean Woods for machining special parts used in this work. They also thank H. J. Svec for his interest and for helpful discussions concerning the project. REFERENCES
1. K. Grob, K. Grob, Jr. and G. Grob, J. Chrornatog., 1975, 106.299. 2. W. Bertsch, E. Anderson and G. Holzer, ibid., 1975, 112, 701. 3. J. P. Mieure and M. W. Dietrich, J. Chromatog. Sci., 1973, 11. 559. 4. G. A. Junk, J. J. Richard, M. D. Grieser, M. D. Witiak, J. J. L. Witiak. M. D. Arauello. R. V.. H. J. Svec. J. S. Fritz and 6. V. Calder, J. Chromatog., 1974,99, 745.