A ~ I ctwm. . 1992, 64, 877-681 (5) Waiters, P. E.; Barnardt, C. A. Spectrochlm. Acta 1988. 438, 325-337. (8) Chudinov, E. 0.; Ostroukhova, I. I.; Varvanina, G. V. Freseniw 2. Anal. & e m . 1989, 335, 25-33. (7) Marlchy, M.; Mermt, M.; Mermet, J. M. Spectrochm. Acta 1990. 458, 1195-1201. (8) Can,J. W.; Horllck. G. Spectrochim. Acta 1982, 378, 1-15. (9) Azlz, A.; Brodtaert, J. A. C.; Laqua, K.; Leis, F. Spectrochlm. Acta 1984, 398, 1091-1103. (10) SChedkre, A.: Cdsmen, D. M. Anal. Chem. 1987, 59, 1185A-1198A. (11) Weber, A.; Eaitensperger, U.; (3gggeler. H. W.; Kell, R.; Tobler, L.; SchmldtQtt, A. J . AW0~olSC~.1990. 2 1 , S55-S58. (12) Schwyn, S.; Garwin. E.; Schmidt-Ott, A. J . Aerosol Scl. 1988, 19, 839-842. (13) Hinds. W. C. Aerosol Techndogy; John Wlley 8 Sons: New York, 1982; pp 184-186. (14) Ho, J.; Kownkakls, 8.; Gunning, A.; Flldes, J. J . Aerosol. Sci. 1988, 19, 1425-1428. (15) Hailer, P.: Battensperger. U. Unpublished resub, 1988, NC Laboratory, CH-3700 Splez, Switzerland. (18) Hhrds, W. C. Aerosol techndogy: John Wlley 8 Sons: New York, 1982; pp 143-148. (17) Bochert, U. K. Ph.D. Thesis, 1991, University of Hamburg (FRG), pp 86-87. (18) Bodrsrt, U. K.; Dannecker, W. J . AerosolScl. 1989, 20, 1525-1528. (19) Schmidt-Ott, A. J . AwmdScI. 1988, 19, 553-583. (20) Witten, T. A., Jr.; Sander, L. M. Phys. Rev. Lett. 1981, 4 7 , 1400- 1403. (21) Meakln, P. Computer Simulation of Growth and Aggregation Processes. In On &owth and F m , Fractal and Non-hactal Patterns In
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Physics; Stanley, H. E.. Ostrowsky, N., Eds.; Martlnus Nijhon: Dordrecht, 1986; pp 111-133. (22) Forrest, S. R.; Witten, T. A., Jr. J . Fhys. 1979, A12, L109-117. (23) Crump, J. 0.; Flagan, R. C.; Seinfeld. J. H. A d Scl. Techno/. 1983. 2, 303-309. (24) Seinfeld, J. H. Ain?ospherlc Chembby and Physhx of A t Wutbn; John Wlley 8 Sons: New York, 1986 p 397. (25) Olesik, J. W.; Den, S.J. Spectrochlm. Acta 1990, 458, 731-752. (26) Oleslk, J. W.; Fister. J. C. 111 Specfrochh. Acta 1991, 468, 851-888. (27) Flster, J. C. 111; Oieslk, J. W. Spectrochlm. Acta 1991, 468, 889-883. (28) Borowiec. J. A.; Boorn, A. W.; Diilard, J. H.; Cresssf, M. S.; Browner, R. F. A M / . Chem. 1980, 5 2 , 1054-1059. (29) Tang, Y. Q.; Trassy, C. Spectrochlm. Acta 1988, 418, 143-150. (30) Sperllng, M. Ph.D. Thesis. 1988, University of Hamburg (FRQ), pp 85-92. (31) Mermet, J. M. In Inductively coupled plesma Emission Spectroscopy, Part 2 : Applications and Fundamentab; Boumans, P. W. J. M., Ed.; John Wlley & Sons: New York, 1987; pp 358-382. (32) Bridges. J. M.; Kornblith, R. L. Astrwys. J . 1974, 192, 793-812. (33) Kornblum. 0. R.; de Galan, L. Spectrochlm. Acta 1977. 328, 71-98. (34) Kornblum, 0. R.; Smeyers-Verbeke, J. Spectrvchlm. Acta 1982, 378, 83-87. (35) Weber, A. P.; Baltensperger, U.; CJlggeler, H. W.; Tobler, L.; Keii, R.; Schmldt-Ott, A. J . Aerosol Scl., In press.
RECEIVED for review August 19, 1991. Accepted December 19, 1991.
Spray Extraction of Volatile Organic Compounds from Aqueous Systems into the Gas Phase for Gas ChromatographyIMass Spectrometry G6khan Baykut* and Annette Voigt Bruker-Franzen Analytik GmbH, Fahrenheit Str. 4, 2800 Bremen 33, Germany
A new rampling technlqw has been developed for extractlng vdatlk organk compounds from aqueous soiutlons. Uslng a m a y nozzle, very small droplets of the aqueous solutkn are generated In an extraction chamber. The clo-obtalned large total Interface area between the llquld and gas phase helps to qulckly reach the partition equilibrium of dlsrolved compounds between the liquid and the gas phase. Substances extracted Into the gas phase are preconcentrated In a sorptkn tube gas-sampUng device. A m a l deoorp#on foWowlng the preconcdratkn a b w the collected compoundr to enter the gas chromatographlc column of the GCMS. The sprayand-trap mdhod k very 8e.nrltlve and can be applied to sampilng of very low concentrations (down to 10-30 ng/L wlth 2 min of sampling). The spray extractor has the capaMilty of operating wlth aqueous systems containing surfactants.
INTRODUCTION Sampling volatile organic compounds (VOC) in aqueous solutions for gas chromatography/maas spectrometry or simply gas chromatography analyses can be done by using the headspace over the liquid The partitioning of the organic contaminant between the liquid and the gas phase
* Author to whom correspondence should be addressed. 0003-2700/92/0364-0677$03.00/0
leads to the increase of ita concentration in the gas phase obeying an exponential saturation law. The saturation concentration in the closed headspace above an aqueous sample depends on the vapor pressure of the pure compound and also on ita interaction with water molecules, while the speed of the process of saturation strongly depends on the interface area between the liquid and gas phase. Conventional dynamic headspace water-sampling devices increase the liquidlgas interface area by purging the water sample with large number of very small gas bubbles. The gas then enters the preconcentration trap4 (the “purge-and-trap” Sampling devices purging with gas bubbles have the disadvantage of getting blocked by foam, if the water sample contains surfactants Bubbling a gas through such a solution supporta the formation of foam. Nearly 30% of all industrial waste waters contains surface-active compounds causing difficulties with bubble-purging samplers. The new sampler described in this paper accelerates the formation of the partition equilibrium of chemicals between water and the gas phase by spraying the sampled liquid7+’into a chamber and extracting the compounds from the aqueous system into a carrier gas. Water samples containing surfactanta over a wide concentration range can be sampled using the spray extraction technique. EXPERIMENTAL SECTION The Spray Extractor. A method inverse to the conventional “bubble purginp” is introduced to increase the gas/liquid interface area for extraction: The aqueous sample is pumped through a 0 1992 American Chemical Society
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carrier
a
EX
aas exit
Valve Operation Event Sesuence i
I I
1 - 1
I
GI
exit lot
water level sensor
water
.
.'MU
b
carrier gas
1. (a) The spray-exiraction chamber. (b) The operation scheme of the spray-extraction chamber. The carrier gas travels against the sprayed water droplets. This countercurrent extractlon makes the transfer of VOC out of the liquid droplets more efficient.
special nozzlelointo an extraction chamber (ca. 100 cm3)forming a cone of tiny liquid droplets (Figure 1,parts a and b). By this reversal of the dispersed phase and the dispersive medium, the formation of a very large total surface area for extraction is achieved. A low-speed carrier gas passes through the droplets in the extraction chamber acting as mobile extractor phase. Following the extraction, the gas enters the sorption tube of the preconcentrator unit. The spray extractor consists of an extraction chamber (EX), where the spray process takes place (Figure 2). It further consists of a computer-controlled valve system, a carrier gas supply and transfer system, and a device to pressurize the water sample. In the version 'A" of the extractor, a closed sampling chamber is placed underneath the assembly. This version is convenient to use on sites, where large-volume water samples are available. The sampling chamber is dipped into the aqueous system, where the aqueous sample (WS)enters the chamber through the springloaded valve (Y) at the bottom. The sample is transferred into the extraction chamber (EX) by closing the inlet valves and by applying pressure. The spring-loadedinlet valve (Y)at the bottom is normally open for water entrance. The spring allows the valve only then to close, whenever the compressed gas enters the chamber, while pressure-release valve (V) is closed. Even if the container is full of water, the hydrostatic pressure alone is not enough to close the spring-loaded valve (Y) without the com-
Figure 2. The valve scheme and the valve activation event sequence of the spray extractor. P, chamber-presswizatbn valve (compressed gas entrance); R, pressure-reduction valve; C, carrier gas entrance valve; V, pressure-release valve; S, spray valve; W, waterdrain valve; Y, sprlngkaded water Inlet valve; EX, extraction chamber; WS, water carriergas exit; WD, water sample; GI,gas (compressed N2) inlet; E, drain; PR, pressure-reiease exit, LS, water-level sensor.
pressed gas. After spraying, the over-pressure in the sampling chamber is released by opening the valve, V. Since the springloaded valve (Y) opens immediately upon release of excessive pressure, a new water sample can enter the sampling chamber. In version "B", the aqueous sample is sprayed into the extraction chamber simply by using a mechanical water pump." A gear pump with a very small internal volume is used to pump the sample out of the water source and to spray it into the extraction chamber. The results presented in this paper are obtained with the version "A". The extractor operates in a computer-controlledevent sequence. Water and gas valves are opened and closed in order to fill the sampling chamber,stop the injection, purge the injection chamber, and release the excess pressure from the sampling chamber. Figure 2 shows the valve scheme and a typical event sequence of the version A. The filled lines in the event sequence show the activated periods of the corresponding valves. The extraction chamber's compressed gas and carrier gas entrances are controlled by the valves P and C, respectively. V is the pressurerelease valve, S is the water valve between sampling and extraction chamber, G is the valve which turns on and off the carrier gas flow to the preconcentration trap, W is the water-release valve, and Y is the springloaded water inlet valve of the water-sampling chamber. In the spray extractor, the spray driver (the pressure chamber or the pump) has to supply the predefined operation pressure of the spray nozzle. The elements of the spray-extraction system like the spray nozzle, a spray driver, the extraction chamber, the valves, and all connections must be able to withstand (at least) the defiied operation pressure of the spray nozzle. In the current model of the extractor, the gas pressure was 2.2 bar. The water sample enters the sampling chamber through the spring-loadedvalve. At the beginning, the pressure-releasevalve (V) closes and the compressed gas also enters the sampling chamber. The chamber gets pressurized and (simultaneously) the water-filling operation stops. The transfer valve between the sampling and the extraction chamber is still closed. By activating the transfer valve, S, the sample is sprayed into the extraction chamber. The valve at the drain tube is open at the beginning. As soon as the spray event starts, the drain valve closes. During the spray extraction, the drain valve is controlled by the water-level sensor. A "rest water", which continuously stays at the bottom of the extractor (10-15-mm high) keeps the carrier gas from escaping through the water drain (Figure lb). Organic compounds extracted from water are transferred by the carrier gas into the automatic air sampler and trapped in the sorption tube of the gas-sampling device. After the sampling period, the collected compounds are thermally desorbed and introduced into the gas chromatograph. Compounds. Commerciallyavailable compounds were used for analytical experiments. Benzene, toluene, p-xylene, tert-butylbenzene,p-dichlorobenzene,dichloromethane,trichloroethene, tetrachloroethene, naphthalene, acetone, 3-pentanone, and 4heptanone of Merck (Darmstadt, Germany) have been used to prepare the aqueous solutions.
ANALYTICAL CHEMISTRY, VOL. 64, NO. 6, MARCH 15, 1882 extraction
I
chamber
I
7
7
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naVr 9. Sd’”aUc descrlptkn of the experknental setup. The blank arrow on the lett side lndlcates the carrler gas entering the extractor and the black one shows the exlting water sample. In the drawlng, the components are not shown In their actual proportlons.
I
I 100
desorDtbn/ iniection
20
r
RESULTS AND DISCUSSION The total ion chromatogram of one of the test mixtures extracted from the aqueous solution is shown in Figure 4. The compounds in the mixture have the same concentration (10 a / L ) in water. GC peak areas show the responses of the total
400
500
(SI Flgure 4. A total Ion chromatogram. A mixture of 10 ppb of each compound In water. Peaks: (1) dlchloromethane, (2) benzene, (3) trichloroethene, (4) toluene, (5) tetrachloroethene, (6) p -xylene, (7) fert-butylbenzene, (8) p dichlorobenzene, (9) naphthalene.
25
Experimental Setup and Procedures. The analyses of spray-extracted compounds were performed using the mobile environmental mass spectrometer (MEM) of Bruker-Franzen Analytik. The MEM is a ruggedized GCMS for environmental on-site analysis. It consists of a quadrupole mass spectrometer, with a polyailoxane membrane inlet, an ion-getter vacuum pump, and a small GC oven. Solutions of compounds listed above were dissolved first in acetone, and this multicomponent mixture was then dissolved in water. The so-prepared solutions are spray-extracted. The temperature of the sample was held at 20 O C . The experimental setup is depicted in Figure 3 schematically. Carrier gas flow was kept at 2.5 mL/s. The gas chromatograph had a 20-m capillary column of 350-rm i.d. with a siloxane-based stationary phase of DB-1. The sorption tube of the automatic air sampler5was filled with 60-80-mesh Tenax TA. The experience with the automatic air sampler shows that the same sorbent tube can be used for 500-1000 sampling purging cycles. The duration of the spray-sampling period in the laboratory experiments was 2 min. All experiments were performed at 2 min of spraying time. The total volume of the water sample was 900 mL during this sampling period. The pressure of the compressed gas driving the spray process was kept at 2.2 bar. After each spray sampling, the Tenax tube was “dry-purged” with nitrogen for a period of 30 s in order to get rid of the possibly condensed water and so to prevent excessive amounts of water vapor from entering the GCMS. In the experiments, the direction of dry purging was the same as the gas-sampling direction. The breakthrough times of the sampled Compounds for the used Tenax tube (gas flow: 2.5 mL/s) were much longer than the sampling time (2 mid. Scheme I shows the directions of sampling, dry purging, and injection into the gas chromatograph after desorption.
300
time
Scheme I. Gas Flows in the Sorbent (Tenax) Tube” Tenax sampling I
‘The direction in the ’sampling” and the ‘dry purging” modes are the same. The mode called ‘desorption/injection”, where compounds are desorbed from Tenax and injected into the GC, has the opposite gas flow direction.
200
I1
a
E E
,Ez
15
m
g 10 X
!i $ 5
0 0
1
2 3 4 5 6 7 S 9 VOC concentration in water (pg/l)
10
Figure 5. The calibration diagram of the spray extractor for some compounds. The responses are obtained by the GCMS “moblle environmental ma80 spectrometer, MEM” with a Tenax tube-autmtlc gas-sampling device.
system of sampling (spray extractor), preconcentrating (sorption trap), separating (GC), and the analyzing (MS) equipment to different organic compounds dissolved in water. Extraction efficiencies of compounds from liquid into the gas phase depend on the vapor pressure of the corresponding compounds and on the extent of their interaction with water. Calibration curves (again for the complete sampling, preconcentrating, and detecting system) of some of the substances are shown in the Figure 5. Under the given conditions (2-min sampling time, 450 mL/min water flow, 150 mL/min nitrogen flow, temperature 20 “C), and by using the mobile environmental mass epectrometer, most of the compounds (benzene, toluene, xylene, trichloroethene, tetrachloroethene, p-dichlorobenzene, and tert-butylbenzene) gave at a concentration of 30 ng/L GC signals, that were about 10 times as high as the average noise level. In case of naphthalene this concentration was 300 ng/L. Compounds that are more soluble in water are more difficult to extract than the substances that are practically insoluble in water. The dipole-dipole interaction of more polar compounds with water molecules reduces their effective vapor
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Table I. Analysis Results of Spray-Extracted Compounds As Performed Using the Mobile GCMS “MEM” concn (ng/L)
average GC peak area (counts)
30 100 300 1000 3000 loo00
48 918 137 166 374 633 1041932 3 060 584 9 909 639
10 30 100 300 1000 3000
no. of experiments
re1 standard deviation, %
Benzene 4 4 4 3 3 2
18.1 11.4 2.4 3.3 8.8 2.6
loo00
36017 75 455 181785 480 034 1428 176 4 362 207 14 455 433
4 4 4 4 3 3 2
7.8 13.9 2.9 3.8 3.3 5.7 4.0
30 100 300 1000 3000 lo000
64 588 179 630 474 516 1446 742 4 450 624 15 410 551
p-Xylene 4 4 4 3 3 2
24.9 3.7 3.1 1.6 7.6 3.9
Toluene
loo00
Trichloroethene 61 398 4 163449 4 418 139 4 1179760 3 3 591 413 3 11447 022 2
12.7 4.5 1.3 5.4 11.9 0.4
30 100 300 1000 3000 10000
Tetrachloroethene 89 432 4 232 582 4 628 699 4 1817 557 3 5 685 297 3 2 18026 665
11.0 3.9 1.8 5.3 10.8 0.3
30 100 300 1000 3000 10000
tert-Butylbenzene 110813 4 309 877 4 893 539 4 2 753 503 3 8 870 709 3 28 305 855 2
19.5 7.6 4.8 1.9 10.0 3.2
30 100 300 1000 3000 10000
p-Dichlorobenzene 70 328 4 168082 4 415 449 4 1211911 3 3 827 409 3 12 920 708 2
18.6 7.2 3.7 7.4 11.3 2.4
30 100 300 1000 3000
100 300 1000 3000 10000
Naphthalene 25 926 4 84 461 4 250 786 3 710 838 3 2 518 555 2
29.3 7.0 3.7 7.6 1.5
pressure and complicates the extraction. Therefore toluene can be determined down below 30 ng/L by 2 min of sampling, while acetone cannot be determined in the nanogram/liter range in water a t this short sampling time. The limit of detection of other polar compounds like 3-pentanone and 4-heptanone are better than acetone, since the solubility of the latter ones are much less than acetone (3-pentanone has a water solubility of 4.7 parts in 100 parts and 4-heptanone 0.43 parts in 100 parts12). Figure 6 shows the data for acetone,
0
100
200
300
Concentration in Water (pg/i)
Figure 6. Examples for pdar compounds: acetone, Spentanone, and 4heptanone. Water solubility decreases with increasing number of carbon atoms. The compounds become then easier to extract from water.
3-pentanone, and 4-heptanone. The strongest response of the analysis instrument is observed for 4-heptanone among the three ketones. Water samples containing surfactants can also be sampled using the spray and trap method. The spray extractor is mechanically tested with a 5 g/L solution of the laundry detergent Persil (Henkel, Dusseldorf, Germany). Tests over several hours and overnight runs with this solution did not change the spray function. Any clogging or corrosion in the system has not been observed. However, since the spray extractor is a trace organics sampler, the usual procedure includes a wash period after each sampling, especially when solutions contain higher concentrations of some chemicals. Spraying clean water (just like sampling!) is the way to clean the extractor and the nozzle. The spray extractor has also been exposed to tests with high surfactant concentrations: Solutions of the pure soap potassium oleate in deionized water up to concentrations of 2.5 g/L could be handled by the extractor without modifications of the conditions described above.13 Above this concentration, the water flow (normally 450 mL/min) had to be reduced since the sprayed water dropping onto the “rest water” at the bottom of the extractor (Figure Ib) did cause a formation of a foam layer. At higher potassium oleate concentrations, the carrier gas slot (Figure 1)had to be elevated and adjusted. Since the method of spray extraction is capable of being applied to much higher surfactant concentrations, the current extractor design is now being improved to achieve more appropriate flow regulation. A modified operation mode will also help work in this particular application area.13 In order to observe effects of surfactants on the quantitative experimental data, a solution containing some of the volatile organic compounds has been spray extracted with and without surface active agents. The addition of the laundry detergent Persil to the sample solution has caused some (usually minor) reductions in the concentrations detected. These effecta were substance dependent and arose partly from interaction of the surfactant solution with the compounds to be detected. In
ANALYTICAL CHEMISTRY, VOL. 64, NO. 6, MARCH 15, 1992
general, any chemical environment increasing the solubility of certain compounda in the liquid phase can cause a reduction in their efficiency of extraction (by any extraction technique) into the gas phase. A thorough quantitative study about the effects of surfactants on the spray-extraction process is also currently in pr~gress.'~
CONCLUSION The results show that the spray-and-trapsampling method is very convenient for sensitive detection of ultra-low concentrations of dissolved organic matter in water. The one advantage is that one achieves very large interfacial areas between water and air. The flow rates can be more effectively controlled, since the droplets can be sprayed faster depending on the pressure applied to the spray nozzle. The flow rate of bubbles in a conventional purge-and-trap sampler cannot be increased too much After a certain limit, a fusion of gas bubbles leads to larger bubbles, which decreases the total surface area and therefore also the rate of substance transfer into the gas phase. At very small droplet radii, the transfer into the gas phase is easier not only because of the large interfacial area but also because the partition equilibrium is also shifted to the advantage of the gaseous phase.I4 The vapor pressure of liquids in the form of droplets increases with decreasing radius of curvature according to the Kelvin equation p(drop1ets) = p (bulk) exp [27 V , (1) / r R T] where p is the vapor pressure, y the surface tension of the solution, V,(1) is the molar volume of the liquid (the equation in the above form applies to pure compounds), F is the radius of the droplet, and T the temperature. The total amount of the compounds transferred into the gas phase increase when droplets are formed from the bulk liquid. However, in water this effect only becomes significant for droplets with radii less than 1 pm. For swfactantmmtainingaqueous systems, spray extraction results are good for continuous on-site monitoring. In the presence of large amounts of surfactants or other chemicals, the use of the standard-addition method leads to more accurate quantitative spray-and-trap analysis results. The efficiency of extraction for the water sampler depends on the type of compounds and on the temperature. Preliminary calculations (from comparisons with gas-sampling data) show that for most of the many tested compounds, it does not exceed 10-15% in terms of total mass extracted into gas phaseJtotal m w in aqueous system. However, this number is only true when the water sample is sprayed once and discharged afterward. Therefore, spraying the same sample more than once (circulation mode) increases the total amount of substance extracted.13 For large-volume water sources a circulated spray sampling is not necessary. However, for water samples of small volume the circulation mode is strongly recommended, where the sample passes multiple times through the extractor. The circulation mode is more con-
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venient to use with the spray extractor of version "B" (pump-spray device). The corrosion resistance (acid resistance or resistance against certain corrosive agents) properties of the spray extraction system are as good as the ones of the used material. For instance, to protect the metal parts (stainless steel) of the current model from effects of extremely low pH solutions, the samples could be neutralized before entering the extractor. Continuous applications in corrosive media may require a specially coated extracting system and special valves. The spray extractor can be used for continuous sampling and monitoring (with GCMS) of large water sources like river, lake, or sea water, industrial waste waters, and also for drinking water sources and contamination control of large water reservoirs. It can either be used together with the GCMS for on-site monitoring or it can be used as a stand-alone sampling device for collecting samples. In this version, the Tenax tube can be mounted at the exit of the extractor. Collected chemicals in the sorption tube can later be desorbed and analyzed by a GC or a GCMS.
ACKNOWLEDGMENT We wish to thank Anatoly Schiller for the steady support in construction and electromechanica and Gerhard Weiss for helpful discussions. Registry No. HzO, 7732-18-5.
REFERENCES
1
(11) (12) (13) (14)
Suffet, I . H.; Malaiyandi, M. Organic Poilutank In Water. Sampkrns Ana!~s&and Toxidty TesNng, Advances in Chemlstry Series 214; American Chemical Society: Washington. DC, 1987. Ioffe,8. V.; Vitenberg, A. 0.Headspace Analyskr and Related MU?ods in Gas Chromatography; John Wlley 8 Sons: New York, 1984. (a) Conrad, R.; Seller, W. G I T , Supplement 3, 1985, p 74. (b) Ma@za, P.; Valade, J. A.; Madigan, W. T. Int. Lab. 10 1989, 10, 7-17. Kopfler, F. C.; Ringhand, H. P.; Miller. R. 0.In Crganlc Pollutants h Water-Sampllng Analysk and Toxiclty resting; Sunet, I. H., Malaiyandi, M., Eds.; Advances in Chemlstry Series 214; Amerlcan Chemical Soclety: Washington, DC, 1987; p 425. Weiss, G. (Bruker-Franzen Analytik) Automatic Air Sampler, unpublished work. (a) Hagman, A.; Jacobsson, S. Anal. Cbem. 1989, 61, 1202. (b) Kling, H. W.; Hartkamp, H.; Buchhoiz, H. Fresenius, Z. Anal. Chem. 1985. 341, 320. (c) Clark, A. I.; McIntyre, A. E.; Lester, J. N.; Peny, R. J . Chromatogr. 1982. 252, 147. Baykut, G. (Bruker-Franzen Analytik). Spray Extractor and Spray Extraction Method; patent pending. Baykut, 0.39th ASMS Conference on Mass Spectrometry and Ailled Topics: Nashville, TN, May 19-24, 1991. Baykut. G.;Volgt, A. 12th International Mass Spectrometry Conference: Amsterdam. Netherlands. Awust 26-30. 1991. Soiii'cone spray.nozzie with inseTted static whirier. Perry, R. H.; Chliton, C. H. chemicel En@nem Mendbwk, McOrewHiII: New York. 1973; pp 18-61. The nozzle used in the experiments (Fulljet 1/8G SS1) is manufactured by Spraying Systems, Hamburg, West Qermany. The gear pump used in the spray extracting device: "Micro Pump", supplied by Cole-Parmer International, Chicago, IL. Perry. R. H.; Chilton, C. H. Chemlcal Engineers Handbook; McGrewHIII: New York, 1973; pp 3-33. Baykut, G.; Volgt, A.; Vetters, H.-P., unpublished work. For example: Atkins. P. W. Physlcel Cbemlstry, 2nd Ed.; W. H. Freeman & Company: Sen Francisco, 1982; Chapter 7.7.
RECEIVED for review August 27,1991. Accepted November 27, 1991.
