normally calibrated gravimetrically; with the procedure described in this paper they can usually be calibrated in less than 7 days. For example, a mercury permeation tube with a permeation rzte of 10 nanograms per minute was calibrated in 5 days. The apparatus is ideally suited for calibration of permeation tubes for use in the field, because tubes returned to the laboratory after field use can be recalibrated in only a few hours. Also, the operator time necessary for calibration on a continuing basis is reduced; only 1.5 man-hours per day is required for calibration of two tubes per day. DISCUSSION
With the exception of the permeation tube housing, the components of this system are readily available from customary laboratory supply sources. The equipment described has been employed for a year without problems except for
background drift due to fluctuations in ambient temperatures. It is of interest that such variations would not be noted with the calibration techniques used earlier. The rapid response of this system makes possible dynamic blending of gases into a multicomponent mixture of known composition. By proper temperature programming, known synthetic atmospheres approximating those of different cities can be produced for laboratory work with this technique instead of more cumbersome dilution systems ( 4 ) . RECEIVED for review September 24, 1971. Accepted November 30, 1971. Mention of a commercial product does not constitute endorsement by the Environmental Protection Agency. (4) H. D. Axelrod et al., Amos. Emiron., 4,209 (1970).
Systematic Studies on the Breakdown of p,p’-DDT in Tobacco Smokes Investigations into the Presence of Methyl Chloride, Dichloromethane, and Chloroform in Tobacco Smokes N. M. Chopral and Larry R. Sherman Department of Chemistry, North Carolina Agricultural and Technical State University, Greensboro, N.C. 27411
IN OUR EARLIER papers ( I , 2) of the series we had reported the ,I ,I-trichloropresence of p,p’-DDT (2,2-di-(p-chlorophenyl)-l ethane), p,p’-DDE(2,2-di-(p-chlorophenyl-l,1 -dichloroethylene), p,p’-TDE (2,2-di-(p-chlorophenyl)-l,l-dichloroethane), p,p’-DDM (2,2-di-(p-chlorophenyl)-l-chloroethylene), trans-4,4’-dichlorostilbene (DCS), bis-(p-chloropheny1)methane (BCPM), and 4,4’-dichlorobenzophenone(DCBP) in p,p’DDT treated tobacco smokes. Of these compounds, the first five have the same number of carbon atoms as p,p’-DDT, and represent the products of dehydrochlorination, hydrogenation, and in the case of DCS, rearrangement reactions. The last two of these compounds, i.e., BCPM and DCBP, represent the compounds obtained from the p,p’-dichlorophenylmethyl moiety of p,p’-DDT. The other part of the p,p’-DDT molecule, i.e., the trichloromethyl moiety, on pyrolysis, could yield dichlorocarbene and trichloromethyl free radicals. In the reducing atmosphere present in the tobacco burning zone [ c j : Chopra (31 dichlorocarbene could give dichloromethane and methyl chloride, while trichloromethyl radical could give chloroform and methyl chloride. Of these three compounds, only methyl chloride has been reported to be present in tobacco smokes so far ( 4 , 5 ) . Author to whom correspondence should be addressed. ( 1 ) N. M. Chopra. J. J. Domanski, and N. B. Osborne, Beitr. Tubakforscli., 5, 167 (1970). (2) N. M. Chopra and N. B. Osborne, ANAL.CHEM.. 43,849 (1971). (3) N. M. Chopra, Proc. Second Ititerti. Cotigr. Pesticide Cliem., Tel Aviv, Israel, 1971, in press. ( 4 ) R. J. Philippe and M. E. Hobbs, ANAL.CHEM.,28, 2002 (1956). (5) J. R . Newsome, V. Norman, and C. H. Keith, Tobacco Sei., 9, 102 (1965).
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Methyl chloride is a unique chlorohydrocarbon in that it can be formed not only by the reduction of dichlorocarbene and trichloromethyl radical but also by the action of methyl free radicals in tobacco smokes on the natural organic and inorganic chlorine present in tobacco. Of the three compounds we found only methyl chloride and chloroform in tobacco smokes, and in this paper we are reporting on our investigations into the presence of methyl chloride, dichloromethane, and chloroform in tobacco smokes, and the significance of the amounts in which they are present. EXPERIMENTAL
Materials. All solvents used were of “pure” grade and were distilled before use (“Pure” grade refers to the quality of the reagent as mentioned on the reagent bottles), and p,p’-DDT used was 99.9 pure. REFERENCE COMPOUNDS.Methyl chloride (“High Purity” grade), dichloromethane (Nanograde), and chloroform (“Spectrophotometric” grade) were purchased from Matheson Co., Mallinckrodt Chemical Works, and Merck and Co., respectively. The three compounds gave only one peak each when chromatographed on three different GLC columns. Methods and Results. SMOKING OF ~ , ~ ‘ - D D T - T R E A T E D TOBACCO SAMPLES.Pesticide-free flue cured tobacco samples containing different amounts of p,p’-DDT were smoked as reported by Chopra and Domanski (6). A continuous flow of air was maintained through the apparatus throughout the smoking, and the tobacco smoke was collected in six traps containing heptane at - 80 “C. (6) N. hl. Chopra and J. J. Domanski, Beifr. Tubukforscll., 1971, in press.
Because of the great volatility of methyl chloride a different Table I. Relationship between the Amount of p,p'-DDT recovery method and a separate set of smokings had to be Incorporated into Tobacco and the Amount of Chloroform employed for it. Found in Tobacco Smoke Condensates RECOVERYOF CHLOROFORM AND DICHLOROMETHANE. After the smoking operation was over, the heptane solutions Percentage of tobacco smoke condensates in the traps were collected, conversion of pg of CHCla CC13 moiety and the residues left in the traps extracted with 5-10 ml of pg ofp,p'-DDTlg formed/g of p,p'-DDT heptane. The condensate solutions and the extracts were tobacco tobacco smoked into chloroform combined (volume, ca. 200 ml) and heated in a 250-ml threeneck flask just below the boiling point of heptane. A stream 0,on O,@ ... 2.4 0,034 4.63 of nitrogen (60 ml/min) was passed through the hot solution 7.45 38 0.96 and the vapors were collected in a trap containing heptane 102 1.60 4.59 (2 ml) at -80 "C. Chloroform and dichloromethane were 202 3.07 4.46 quantitatively distilled over with 30-40 ml of the distillate. 358 6.57 5.39 By repeating the process, it was possible to concentrate the 1527 15.80 3.04 two substances to 5-7 ml of heptane distillate, D. a Not detectable. This method was also used with tobacco smoke condensates spiked with different amounts of chloroform and dichloromethane in preparation of their recovery curves. Table 11. Relationship between the Amount of p,p'-DDT RECOVERY OF METHYL CHLORIDE.After the smoking of Incorporated into Tobacco and the Amount of Methyl Chloride tobacco samples, the traps of the original smoking apparatus Found in Tobacco Smoke Condensates were heated to just below the boiling point of heptane, and i*g of pg of methyl nitrogen was passed through the apparatus (35 ml/min) for p,p'-DDTlg chloride formed/g about five minutes. This resulted in methyl chloride being tobacco tobacco smoked distilled over. The distilled methyl chloride was passed 0.00 1931 and 1721 through sodium carbonate solution to remove any HCI, 5.0 2027 and then absorbed in a trap containing heptane, H. 100.0 2229 GAS-LIQUIDCHROMATOGRAPHY OF THE CHLOROHYDRO502.0 1885 CARBONS. A MicroTek 220 gas chromatograph equipped with a 63Nielectron capture detector and a microcoulometric detector was used in the study. The columns used were: (1) A 6-ft X 1/4-inchdiameter 3% OV-17 on Chromosorb W Estimation of Dichloromethane in p,p '-DDT Treated (mesh, 60-70) glass column; (2) A 6-ft X '/?-inch diameter Tobacco Smokes. Tobacco samples containing 2.4, 38, 20% Carbowax on Chromport XXX (mesh 80-90) glass 103, 202, 358, and 1527 ppm of p,p'-DDT were smoked and column, and (3) A 6-ft X 1/4-inchdiameter 3 % SE 30 on dichloromethane in their condensates was estimated. In all Chromport XXX (mesh, 80-90) glass column. instances, no dichloromethane was detected. Columns 1 and 2 were used for dichloromethane and ESTIMATION OF METHYLCHLORIDE IN TOBACCO SMOKE chloroform, and columns 1 and 3 were used for methyl CONDENSATES. Various p,p'-DDT-treated tobacco samples chloride. The column temperatures for dichloromethane and were smoked and methyl chloride in their condensates, as chloroform were 22 "C, and that for methyl chloride, 0 "C. absorbed in the heptane solution, H , were estimated by GLC DETECTION OF METHYLCHLORIDE,DICHLOROMETHANE, on the OV-17 column with the microcoulometric detector. AND CHLOROFORM. GLC chromatograms of heptane soluThe results obtained are shown in Table 11. As may be seen tion, H showed the presence of methyl chloride, while that of from the table, the amount of methyl chloride in all instances distillate, D showed only the presence of chloroform. No was so much that a recovery curve could not be made for it. dichloromethane was detected in distillate D. ESTIMATION OF INORGANIC AND ORGANIC CHLORINEIN The presence of chloroform in distillate D was confirmed TOBACCO. Estimation of Inorganic Chlorine. The inorganic by Fujiwara tests ( 2 ) , and by Friedel-Crafts reaction. chlorine in tobacco was estimated according to the method ESTIMATION OF CHLOROFORM IN TOBACCO SMOKE CONDENof Jones et al. (7). Tobacco (cu. 7.0 grams) was thoroughly SATES. Preparation of the Recocery Curce. six lots of 5.0extracted at room temperature with water (50 ml), and the gram samples of untreated tobacco were smoked as mentioned extract gently heated with nitric acid ( 5 ml). Silver nitrate above. The condensates obtained were combined and divided (300 mg) was then added and the solution brought to a boil into six equal parts. Five parts were then fortified with 19, and filtered. The precipitate was washed with distilled water 23,45,91, and 124 ppm of chloroform (based on 5.0 grams of followed by ethyl alcohol dried at 100 "C for 15 minutes and tobacco). The fortified and the unfortified samples were then weighed. The amount of inorganic chlorine found in tobacco processed for their respective distillates D, and the amount was 0.88% and 0.89%. of chloroform present in them was estimated on a GLC with Estimation of Organic Chlorine. The organic chlorine in the 20% Carbowax 20M column and the microcoulometric tobacco was estimated according to the method of Chopra detector. and Sherman (8). Tobacco sample (ca. 7 0 grams) was The percentage recoveries were between 88 and 97. thoroughly extracted with hexane (50 ml) at the room temEstitnation of Chloroform in p,p'-DDT Treated Tobacco perature, and the extract washed twice with equal volume of Smokes. Tobacco samples receiving various treatments of water, dried over anhydrous sodium sulfate, and heated on a p,p'-DDT were smoked and chloroform in their condensates water bath to remove the solvent. The residue was then was estimated as mentioned above. The results are given in ignited with sodium peroxide (250 mg) in a Parr bomb, Table I. In this table the percentage conversion of p,p'and the ignited product dissolved in 1N nitric acid (200 ml) DDT into chloroform is calculated on the assumption that and filtered. Silver nitrate (200 mg) was added to the only trichloromethyl moiety of p,p'-DDT is converted into filtrate and the mixture digested on a water bath for one hour, chloroform. ESTIMATION OF DICHLOROMETHANE IN TOBACCOSMOKE (7) R. M. Jones, W. F. Kuhn, and C. Varsel, ANAL.CHEM., 40, 10 CONDENSATES. Preparation OJ the Recooerj, Curce. A re(1968). covery curve for dichloromethane was prepared in the same (8) N. M. Chopra and L. R. Sherman, North Carolina Agricultural way as that for chloroform The percentage recoveries were and Technical State University, Greensboro, N.C., unpublished between 86 and 102. data, 1970. ~~
ANALYTICAL CHEMISTRY, VOL. 44, NO. 6, M A Y 1972
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filtered, washed with water and then alcohol, dried for 1 5 minutes at 100 “C, and weighed. The amount of organic chlorine in tobacco was found to be 0.022 % and 0.033 %. DISCUSSION AND CONCLUSIONS
Chloroform. Table I shows that: There is no chloroform in the smoke of tobacco samples containing no p,p’DDT; there is a linear relationship between the amount of p,p’-DDT present in tobacco and the amount of chloroform found in the tobacco smoke; and about 4 . 6 z of the trichloromethyl moiety of p,~’-DDTin tobacco is converted into chloroform. Such results would indicate that p,p’-DDT was the only source of chloroform in p,p’-DDT treated tobacco smokes. This is not surprising since under the reducing conditions prevalent in the tobacco burning zone, the presence of CClp group would be required for the production of chloroform. In pesticide-free tobacco no compound is known to be present which has this grouping. Dichloromethane. The absence of dichloromethane in tobacco smoke condensates suggests that either dichlorocarbene is not formed in tobacco smokes from tobacco treated with p,p’-DDT, or what is more likely, dichlorocarbene if formed reacts with other constituents of tobacco smoke, such as water, in preference to hydrogen. Methyl Chloride. Our value for methyl chloride (ca. 2000 pg methyl chloride/gram tobacco smoked) in tobacco smokes can be considered to be consistent with the value of 3.2 X ml of methyl chloride/puff at NTP as reported by Philippe and Hobbs (4). When calculated for 8 puffs per cigarette Philippe and Hobbs’ value comes to 580 pg of methyl chloride/cigarette smoked. The apparent difference between our values and that of Philippe and Hobbs would be expected, since our method of smoking tobacco is different from theirs, and could involve a three- or fourfold increase in the values for methyl chloride. This great amount of methyl chloride produced in tobacco smokes suggests : (a) That methyl chloride chlorine comes mainly from tobacco inorganic chlorine. Since the chlorine requirement of about 2000 pg of methyl chloride/gram of tobacco smoked (see Table 11) is about 1400 p g of chlorine, and the organic chlorine in tobacco is only about 0.026z (or 260 pg/gram of tobacco), while the inorganic chlorine is 0.89% [or 8900 pg/ gram of tobacco; cf., 0.85% as reported by Jones et al. (7)]. Further, the apparent lack of dependence of the amount of
methyl chloride on the quantity ofp,p’-DDT in tobacco would indicate that the contribution of p,p’-DDT to methyl chloride in tobacco smokes is not substantial. This conclusion is also supported by the simultaneous reporting of Johnson and Smith (9) who incorporated inorganic chlorides containing labeled chlorine and found radioactivity in methyl chloride formed in tlie smoke condensates of cigarettes made from such tobacco. (b) Jones et al. (7) report that tobacco on ashing shows a loss of chlorine from 0.85 to 0.65%. From the amount of methyl chloride formed in tobacco smokes, it appears that a substantial part of that chlorine loss is due to the formation of methyl chloride. (c) That methylation is a reaction of major importance in tobacco smokes. This is further supported by the fact that, next to CO and COz, methane, which can be formed by the action of hydrogen on methyl free radicals, is the most abundant organic compound in tobacco smokes, and that, ethane, which can be formed by the dimerization of methyl radicals, is one of the major components of the tobacco smokes ( I O , I I ) , and that most of the methylation reactions are already over by the time smoke condensates are collected. (cf., Stedman 12). ACKNOWLEDGMENT
The authors thank the School of Agriculture and Life Sciences, North Carolina State University, Raleigh, for a gift of pesticide-free tobacco. RECEIVED for review July 8, 1971. Accepted November 19, 1971. A research grant from the Council for Tobacco Research-USA made these investigations possible. This paper was presented in part before the 24th Tobacco Chemists’ Research Conference, Montreal, October 1970. It is contribution No. 5 of the Tobacco Research Project and Part IV of a study on the breakdown of p,p’-DDT in tobacco smokes. (9) R. R. Johnson and T. E. Smith, presented at the 24th Tobacco Chemists’ Research Conference, Montreal, October 1970. (10) E. L. Wynder and D. Hoffrnann, “Tobacco and Tobacco Smoke. Studies in Experimental Carcinogenesis,” Academic Press, New York, 1967. (11) J. F. Benner, Proc. Tobacco Health Confererzce, Lexington, Ky., 1970. p 31. (12) R . L. Stedman, Chem. Rec., 68, 153 (1968).
Standard Solution for Redox Potential Measurements Truman S . Light Research Center, The Foxboro Company, Foxboro, Mass. 02035
REDOXPOTENTIAL MEASUREMENTS, also known as OxidationReduction Potential (ORP), have been used to gain chemical composition information from solutions for many years. They have been used in the direct potentiometry mode and for end-point detection in potentiometric titrations. In the process industries and in effluent and water treatment systems, redox measurements are frequently linked to process controls for “closed loop” automatic process control. Two wellknown examples include chemical oxidation of cyanide waste 1038
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ANALYTICAL CHEMISTRY, VOL. 44, NO. 6, MAY 1972
with chlorine and chemical reduction of chromate wastes with sulfur dioxide (1). Redox measuring systems in theory and in practice are analogous in many ways to pH systems. In the process industries, they use the same flow-through and immersion (1) B. G. Liptak, Ed., “Instrument Engineers’ Handbook,” Vol. 11, “Process Control,” Chilton Book Co., Philadelphia, Pa., 1970, Chap. 10.14.
