ANALYTICAL CHEMISTRY, VOL. 50, NO. 6, MAY 1978 (26) C. D. Hodgman, R. C. Weast, R. S. Shankland, and S.M. Selby, "CRC Handbook of Chemistry and Physics", Chemical Rubber Co., Cleveland, Ohio, 1961. (27) H. Stephen and T. Stephen, "Solubilities of Inorganic and Organic Compounds", Vol. 1, Part 1, Macmillan, New York, N.Y., 1963-64. (28) J. Pollock and R. Stevens, "Dictionary of Organic Compounds", 5 vols, Oxford University Press, New York, N.Y., 1965. (29) F. K . Beilstein. "Handbuch der Organischen Chemie", J. Springer, Berlin, 1918. (30) R. L. Malcolm, E. M. Thurrnan, and G. R. Aiken, Proceedings of the 11th
779
Annual Conference on Trace Substances in Environmental Health, 1977. (31) R. L. Malcolm and W. H. Durum, U . S . Geol. Surv. Water-Supply Pap., 1817-F, 1976.
RECEIVED for review J u n e 6, 1977. Accepted February 14, 1978. T h e use of brand names in this report is for identification purposes only and does not imply endorsement by the U.S. Geological Survey.
Trapping and Determination of Labile Compounds in the Gas Phase of Cigarette Smoke Steven G. Zeldes and Arthur D. Horton" Analytical Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830
The gas phase of cigarette smoke was trapped and stored on Tenax-GC for subsequent off-site analyses. Specifically, the highly labile compounds isoprene, acetaldehyde, and acrolein were determined quantitatively in the samples which were thermally desorbed in the injector port of a gas chromatograph onto a cooled gas chromatographic column. Optimum conditions were determined for adsorption and desorption of the gas phase, and the effects of aging on the trapped gases were studied.
It is necessary to chemically characterize the cigarette smoke offered experimental animals in inhalation bioassays to define the extent and quality of the exposure. It is also of interest to determine the chemical nature of smoke-polluted environments to assess the possible impact of smoking on nonsmokers. Tenax adsorption followed by thermal desorption and gas chromatography has been evaluated as a method for characterizing the volatile organic gas phase constituents of smoke. One of the routine analyses of the gas phase of cigarette smoke is t h e determination of isoprene, acetaldehyde. and acrolein ( I ) ; the first because of its close correlation to biological activity of smoke, and the others because of their ciliatoxicity. If these highly labile compounds can he trapped and retained, then the less labile components of interest should most likely be retained also. Breakthrough volumes have been determined ( 3 . 5 , 8 )for a number of compounds, some of which appear in cigarette smoke. Double trapping experiments have shown that our results agree with those authors for compounds of common interest. Tenax-GC has been used with some success to trap labile compounds in automobile exhausts (2, 31, ambient air (3,4 ) , and stack gases ( 5 ) . T h e traps used for these samples differ only in size, each consisting of a Pyrex tube packed with Tenax held in place by glass wool plugs. T h e methodology used a t this laboratory was adapted from that of Zlatkis, Lichtenstein, and Tishbee ( 4 ) who used a Pyrex tube 11 cm long, 10-mm o.d. and 8-mm i.d. packed with 2 mL of 35 to 60 mesh Tenax. Samples were adsorbed through a condenser and desorbed in a modified injector port onto a cold precolumn, then desorbed a second time onto a n open tuhular column. At this laboratory, the traps were desorbed in the modified injector port directly onto a packed column cooled to -70 "C. This paper not subject to U S . Copyright.
EXPERIMENTAL Adsorbent. Tenax-GC (Applied Science Laboratories, Inc., State College. Pa.), a porous polymer, puly-p-2,6-diphenyIphenylene oxide was selected over other common adsorbents (Porapak, Carbosieve, or activated charcoal) for its several advantages. Its high temperature limit of 450 "C ( 6 ) and low retention volumes ( i )allow high-boiling sample components to lie desorbed more rapidly than from other adsorbents. In addition, the effect of water vapor on the efficiency of Tenax (8) is insignificant. Preparation of Traps. Traps consisted of Pyrex glass tubing (9-mm 0.d.. 5-mm i.d.) cut into 5'/,-inch lengths and fire-polished at each end. One end is ground to a taper to form a seal in the s-inch glass wool plug is placed in the tube at one end, the tube filled. while vibrating. with 60/80mesh Tenax then topped with a "!,-inch glass wool plug. Traps are conditioned by heating at 250 "C for 30 min while purging with nitrogen. Conditioned traps are stored in a desiccator. Sampling Procedure. Samples were collected from weight selected (1094 f 20 mg) Kentucky Reference (1R1) cigarettes conditioned at 75 OF and 6 0 7 ~relative humidity using an ORNL Single Port Smoking Machine. See Figure 1. Cigarettes are smoked at a rate of 1 puff per minute I 11 puffs X 35 mI,/put'f) using a small vacuum pump to draw each puff through a 0.38-mL sampling loop. An additional length of tubing is placed before the inlet to the gas sampling valve in order to collect the sample from the middle of the puff. Nitrogen carrier gas flows through '/,-inch Teflon tubing to a solenoid valve which, when activated, directs the flow through the sample loop and, when deactivated, allows the flow to bypass the loop while the puff is drawn. The carrier then travels through connecting tubing to a stainless steel three-way valve where it is either directed to the modified injector port ( 4 ) of the Perkin-Elmer 3920 gas chromatograph or to a sampling port to which a trap is attached. See Figure 1. During a standardizing run (without trapping) (Figure 2 ) , the carrier containing the sample is directed to the injector port of the gas chromatograph. A simulated trap. filled completely with glass wool, is placed in the injector port to reduce its volume. A number of such runs serves to establish the expected level of organic components in an average cigarette. For a run in which the sample will first be trapped on Tenax. then analyzed (Figure 3): a reduced carrier flow (10 mL/min) is used to purge the sample from the loop into the tapered end of the trap. Carrier gas flow was 1 2 mL/min (30 psig). Injector port temperature was 250 "C; and FID temperature 150 "C. Column. GC Column. The column used for the determination of isoprene, acetaldehyde, and acrolein was a modification of one used routinely ( 1 ) for this purpose. The stationary phase 3,3'-(trimethylenedioxy)dipropionitrile was synthesized by equilibrating a 1:2 mixture of acrylonitrile and 1,3-propanediol Published 1978 by the American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 50, NO. 6, M A Y 1978
780
Table I. Trapping Efficiency Relative to Sample Sizea Isoprene, bp 34 "C Vol. of gas
phase, mL Avfigstdrun Av crg trapped run Recovered,%
Acetaldehyde, bp 2 1 "C
Acrolein, bp 52.5 "C
4.2
6.7
4.2
6.7
4.2
6.4 6.3
10.2 8.0
10.7 8.6
17.2 10.1
1.4
2.2
1.4
1.9
78
80
59
98
100
6.7
86
a Trapping flow rate 1 0 mL/min, desorption time, 10 min.
Figure 1. ORNL
single port smoking machine and attached Tenax-GC and replacing it with the Tenax trap with its tapered end at the column inlet. Note: The sample is always back-flushed from the trap. Kith the spring and septum cap in place, the carrier gas is set at 30 psig and the trap is desorbed for 10 min at 250 "C onto the cold column. When desorption is complete, temperature programming hegins and follows that of the straight run.
traD
DISCUSSION T h e technique described in this paper requires 12 min for sampling, 10 min for desorption, and 1.5 h for analysis; a total of less than 2 h. Straight runs require 10 min less since they do not have to be desorbed. Trapping the sample provides a means for sampling a source which could not be analyzed otherwise.
-
"i-. L
Jr
2
3
L
b
L
I"
Standard chromatogram of the gas phase of a Kentucky reference ( 1 R 1 ) cigarette (not trapped) Vol of gas phase 6 7 mL, injector port, 250 O C , FID, 150 O C , flow rate, 1 2 rnL N,/min Figure 2.
-
4
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5 2~'~~;-rYLF~9"+E'HYLL 5
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7
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3 ACETSNE
1
,-,
69
5.3
'3 T
37
"n W ar
9LY
>
Y
Q
0
400
9 a
W V
75
300 65
n 4 2 m l O F G A S PHASE
55 0
5
10
15
20
N 2 F L O W R A T E DURING T R A P P I N G ( n /m n)
I
4 . 2 m l OF GAS PHASE
200 0
5
IO
(5
20
DESORPTION TIME ( m i n )
Figure 4. Trapping efficiency vs. flow rate
Figure 5. Trapping efficiency vs desorption time
adsorbent, probably because of increased total pore area. While the trap size is limited to 3l/, inches by 9-mm 0.d. by the dimensions of the injector port, variations are possible for the bore diameter and the volume of packing. The first trap was 7-mm i.d. with about 2 mL of Tenax. Trapping efficiency u a s poor and gas chromatographic elution peaks were broad and tailing. One milliliter of packing was then tried with even more disappointing results. Double plugs of 1 * / 2m L each in a single trap resulted in a significant improvement, but proved to be no better than 3 m L in a single plug. This led to the use of a smaller bore (5 mm) glass tube 5l/, inches long which was fully packed with Tenax (2.2 mL), and which resulted in a large improvement in resolution without a significant loss of capacity. A 3-mm i.d. trap was tried (0.8 mL Tenax) for which the resolution was even better. Because of the loss of capacity for the 3-mm i.d. trap, however, further work was done with the 5-mm i.d. fully packed trap. These results lead to t h e following conclusions: (1) A decrease in the bore diameter of a trap increases the resolution. (2) Greater component retention per unit volume of packing may be achieved with a decrease in bore diameter (7). Desorption. Of all the factors related to the desorption of t h e trap, the most critical is backflushing of the sample. No recognizable chromatograms were produced without using this technique. T h e time required for a t r a p t o be desorbed onto the cryothermal column refers to desorption time prior to initiating the temperature program on the chromatograph. The t r a p remains in the hot injector port during the entire run. T h e proper time is important for t h e analysis of labile compounds (see Figure 5). Likewise the temperature of the injector port must be hot enough to release all the components of interest without inducing decomposition of the more reactive ones. An injector port temperature between 250 "C and 300 "C proved to be best for isoprene, acetaldehyde, and acrolein. It became apparent after some time that part of the sample was not recovered, even though it was completely adsorbed on the trap. Four possible causes existed: (1) T h e time
elapsed between placing the trap in the injector port and replacing the septum cap on the port allowed some sample to escape. (2) The sample was retained by chemisorption on the Tenax packing. (3) T h e sample reacted with oxygen in the injector port. (4) The species of interest reacted with other constituents in the sample. An injector device for glass traps machined to attach to the injector port in place of the septum cap allowed purging of air from the injector port before injecting the trap into the hot zone and ensuring that the sample did not desorb prematurely nor react with atmospheric oxygen. Experiments performed here and by others ( 6 ) indicated that the sample did not react with the Tenax. Thus, it was concluded that the components of interest were probably reacting with other labile constituents in the smoke. T h e loss was not large and was rectified by using smaller samples and lowering the injector port temperature. Traps were assumed to be reconditioned after desorption. Repeated use of up to several dozen times resulted in no loss of efficiency, as is reported also by Pellizzari, Bunch, Berkley, and McRae ( 3 ) . Aging. Experiments on the aging of trapped samples u p to three days produced conflicting data. There was no loss of components in samples aged for 22 h and for 70 h, respectively, while samples aged only 5 h suffered high losses. Statistical analysis of aging data by the method of least squares using a linear model showed no trend in the plots of peak areas of acrolein and acetaldehyde vs. aging time u p to three days. Isoprene showed only a slight downward trend. Traps were capped with number three polyethylene end caps and placed on a shelf in the laboratory for aging. Traps were not protected from room light. It is likely that some of the caps produced a better seal than others. Future work on aging should provide a means of capping the ends of the trap tightly with Teflon seals, or possibly sealing the trap in glass capsules, and storing them in the dark. Aging of samples for over one week has been reported with the trapping of many organic compounds without a significant loss of sample ( 3 ) .
782
ANALYTICAL CHEMISTRY, VOL. 50, NO. 6, MAY 1978
CONCLUSIONS
on aging of the gas phase in Tenax
By use of the technique described herein, it is possible to trap and recover the more highly labile components in the gas phase of cigarette smoke. All of the isoprene and acrolein and 809" of the acetaldehyde was recovered. Pattern recognition of the chromatograms indicated that other major components in t h e gas phase were recovered also. T h e adsorption characteristics of many of these on Tenax have already been reported (2-8). Improvements need to be made in the storage of aged samples. Given these, this method should be applicable to remote sampling of cigarette smoke and other gases for subsequent analyses a t another site.
LITERATURE CITED A. D. Horton and M. R. Guerin, Tobacco, 176, 45 (1974) (Tob. Sci. No. 19).
W . Bertsch, R . C. Chang, and A . Ziatkis, J , Chromafogr. Sci.. 12,175 119741
E -D. Peilizzari, J. E . Bunch, R. E. Berkiey, and J. McRae, Anal. Left.. 9 (1). 45 11976). A.'Zlatkis,' H. A: Lichtenstein, and A. Tishbee, Chromafographia, 6 (2), 67 (1973). J . S. Parsons and S. Mitzner. Eviron. Sci. Techno/.,9 (12), 1053 (1975). R van Wijk, J . Chromafogr. Sci., 8, 418 (1970). L . D. Butler and M. F. Burke, J , Chromafogr. Sci.. 14, 117 (1976). J. Janak, J . Ruzickova, and J, Novak, J . Chromafogr., 99, 689 (1974). "The Chemistry of Acrylonitrile", 2nd ed.. American Cyanamid Co., 1959.
ACKNOWLEDGMENT
RELEI\ED for review November 4, 1975. Accepted February
T h e assistance of W. H. Baldwin of ORNL Chemistry Division and C.-H. H o of the ORNL Bio/Organic Analysis Section in synthesizing the 3,3'-(trimethy1enedioxy)dipropionitrile is greatly appreciated. C. K. Bayne, Computer Sciences Division, performed statistical analyses of the data
7,1978. Research sponsored by the National Cancer Institute, The Council for Tobacco Research--USA, and the Department of Energy under contract with Union Carbide Corporation. S.G.Z. from Centre College, D a n d l e , Ky. 40422, was an O R A L summer research participant.
Effects of Surface Heterogeneity on the Sensitivity of Sulfide Ion-Selective Electrodes Janis Gulens" and Brian I k e d a ' General Chemistry Branch, Atomic Energy of Canada Limited, Chalk River, Ontario. Canada KOJ IJO
non-Nernstian response of the electrode. Polishing the electrode removed this film: restored the crystal to a shiny state. and the electrode response was again rapid and mol L level). LVhen the Nernstinn (at least a t the 3 X electrode which had "failed" a t the heavy water plant was polished and tested, negative deviations from Nernstian hehavior were observed ("super-Nernstian" response) at concentrations less than 3 X 10 mol L, I . This electrode would rapidly grow films, and one of these films was examined under a scanning electron microscope (SEILI). This communication presents the study of the calibration behavior of this electrode and the results of the SEM examination of the film on its surface. The super-Nernstian response observed at low sulfide concentrations is proposed to be due to the measurement of mixed potentials that arise as a result of various surface reactions. I t is further proposed that these surface reactions primarily involve metallic silver which gradually accumulates at the electrode surface, and that the primary source of the metallic silver is the internal silver metal contact to the silver sulfide membrane.
The limit of Nernstian response of Ag,S ion-selective electrodes changes from -lo-' mol L-' to mol L-' total dissolved sulfide with increased use of these electrodes. Films or deposits appear on the surfaces of such electrodes and two of these deposits have been examined by a scanning electron microscope. The non-Nernstian response at low concentrations is attributed to the measurement of mixed potentials which, it is proposed, arise primarily as the result of the gradual accumulation of metallic silver at the membrane/solution interface. The silver metal solid contact to the inner membrane surface is proposed to be the primary source of metallic silver. Films or deposits of Ag,S or Ag,O appear on the electrode surface as a consequence of the presence of metallic silver.
'
Sulfide ion-selective electrodes. based on a sik er sulfide membrane, can be calibrated in alkaline solutions to give Nernstian response to total sulfide concentrations as low as mol L-' but only if excess reducing agent (ascorbic acid or hydrazine) is present to remove dissolved oxygen (1,2). A continuous H2S-in-water monitor, based on the sulfide ionselective electrode, was developed and used to measure the dissolved H2Sconcentration in the liquid effluent from a heacy water plant (3). During operation of the monitor a t the heavy water plant, a sulfide ion-selective electrode failed to give Nernstian response a t the mol L-' level and was replaced. Previously, some sulfide ion-selective electrodes had acquired a dull film or tarnish on their surface with use (2),and t h e appearance of this film was accompanied by slow and
EXPERIMENTAL All sulfide electrodes used were manufactured by Orion Research Inc., Model 94-16A, and have an internal solid metallic silver contact ( 4 ) . Their potentials were measured by an Orion hIodel 801 voltmeter relative t o a saturated calomel reference electrode, the latter being separated from the sample solution by a 1 mol L KC1 bridge solution. An Orion Model 605 Electrode Switch was used to simultaneously measure the potentials of several electrodes. All measurements were performed at room temperature, 300 f 3 K. Reagent grade chemicals and distilled-deionized water were used throughout. Sulfide solutions were prepared from crystals of Na2S.9H20 in 1 mol L,-' NaOH-0.1 mol L-' ascorbic acid solution ( 5 ) . Calibration curves were obtained by the standard
'Present address, Department of Chemistry,rniversitv of Guelph. Guelph, Ontario K l G 2W1. 0003-2700/78/0350-0782501 0010
C
1978 American Chemical Society
