Gas Chromatographic Determination of Some Hydrocarbons in Cigarette Smoke H. W. PATTON and G. P. TOUEY Tennessee € a t m a n Co., Division o f Eastman
Kodak Co., Kingsport, Tenn,
This paper concerns the results of experiments designed to study the effectiveness of gas chromatographic niethods for the separation and analysis of some components of the gaseous phase of cigarette smoke. By using a column containing silica gel and employing helium as the carrier gas, it was possible to dFtermine seven hydrocarbons in a 10-ml. sample of smoke from which the particulate matter had been removed by a special filter. The gas chromatographic method described is a simple and effective means of determining low concentrations of the compounds studied.
T
H E work described in this paper was undertaken with the general object of studying the effectiveness of gas chromatography for the separation and analysis of some components of cigarette smoke. Preliminary experiments with the method indicated that several types of components could be detected in the gaseous phase of cigarette smoke. Included among these were seven light hydrocarbon gases. Although most of these compounds had been reported present in cigarette smoke, quantitative information was not available (6). Therefore, the study was concentrated on the quantitative determination of these hydrocarbons found in cigarette smoke produced under varying smoking conditions. Quantitative results obtained by means of infrared absorption have been reported since this m-ork v a s completed ( I S ) . Considering the differences in the samples used, the results agree as well as can be expected with those rcported here. Slthough gas chromatographic methods are relatively new, their remarkable effectiveness in the separation of gases and volatile liquids has been amply demonstrated. The number of recent papers devoted to investigations in this field is evidence that the use of gas chromatography is rapidly becoming videspread. In addition to general papers on the subject (2, 6-12, 15, 16), gas chromatographic methods have been applied to the analyses of small quantities of materials produced during kinetic studies (S), fluorinated compounds (Q), hydrocarbons in automobile exhaust gases (14), and mixtures of methyl ketones ( I ) .
v a s collected in one of these, and the other served as a bypass for the carrier gas until the chromatographic system was ready for a run. The adsorbent used for packing the column was a type of silica gel having a low density and large pore size (Davison Chemical Co., Grade 70). Particles 30 to 50 mesh in size were packed into the column and held in place by glass wool. Helium was passed through the column for about 3 days before it was used for quantitative work. Columns packed with oven-dried (130' C.) silica gel required less conditioning to produce a stable background response from the thermal conductivity cell. However, it was found that a sharper separation of propylene from butane could be obtained when the silica gel column was conditioned a t room temperature. This difference is possibly related to t h e amount of moisture remaining in the adsorbent after conditioning. Calibration of Apparatus. Calibrating mixtures containing known amounts of hydrocarbons in nitrogen were prepared with the aid of the apparatus shown in Figure 2. The large spherical vessel had a volume of about 1 liter. The volumes of the smaller containers were chosen so as to produce desired concentrations of the hydrocarbons being added. The sample chamber of each of seven such vessels (only two of which are shown in the figure) mas filled with one of the seven hydrocarbons studied. These were connected in series with stopcocks turned to provide an open passage through the bypass side of each vessel. One terminal container was attached t o the spherical vessel and the other to a source of nitrogen. The system was evacuated and the stopcock between the spherical vessel and the
CONDUCTIVITY THERMAL
APPARATUS AND MATERIALS
Gas Chromatographic Apparatus. The gas chromatographic SAMPLE apparatus was essentially the same as that Dreviouslv described (15), except as noted. Helium was used as the carrier gas, with a flow rate of 50 ml. per minute. The thermal conductivity cell, used as the detector, was made by the Gow-Mac Instrument Co. to the specificaSCARITE tions submitted by the authors (15). The output of the thermal conductivity cell was recorded by a recording millivoltmeter (Leeds &. Northrup Co.) with a range of 0 to 1 mv. Figure 1. AdsorpLion colunin and sample container The column and sample container are shown in Figure 1. The portion of the column packed with silica gel was 130 cm. long and 0.55 cm. in inside diameter. The shorter portion, containing Ascarite for removal of carbon dioxide and water, was 15 em. long and 0.7 cm. in inside diameter. The two-way stopcock between the two scctions prevented air from reaching the silica gel while the sample containers were being changed. The column was used a t 25" & -BYPASS 2" C. The gas sample container was con- TO NITROGEN structed as shown in Figure 1. Each of the CYLINDER two sections of glass tubing between the two stopcocks had a volume of 10 ml The sample Figure 2. -4pparatus for preparing calibration mixtures ~
8
1685
ANALYTICAL CHEMISTRY
1686
0.12
L
1
/’ 0
0
/=
I
b
/
o
0
1i
I
006
1 0
20
40
60
8c
SAMPLING POINT, MM FROM LIGHTED END
Figure 4.
0
5
IO
15
20
TIME, M I N .
Figure 3.
Elution of smoke from silica gel by helium
vacuum pump was closed. The stopcocks on the small containers were then turned t o piovide an open path through the sample chambers. Nitrogen was allowed to sweep the hydrocarbon samples into the sphelical vessel and fill it to atmospheric pressure. The mixture was made homogeneous by adding mercury to the spherical vessel and shaking it. Apparatus for Collecting Gas Phase of Cigarette Smoke. The gas samples were obtained from cigarettes smoked in a manner that simulated normal smoking conditions. This \\as accomplished by employing a smoke collection train consisting of an automatic cigarette smoking machine, a specially designed filter for removing the liquid-solid phase of the smoke, and a gas sample container for collecting a portion of the smoke gases. The cigarette smoking machine was discussed in an earlier paper (17) I n order to vary the duration of the 35-ml. puff taken by the smoking machine, a rubber tube was inserted into the system at the bottom of the buret. Changing the degree of constriction at this point by means of a screw clamp made it possible to adjust the duration of the puff from 1.3 to 3 seconds. The filter for removing the liquid-solid phase of the smoke consisted of a disk of Cambridge filter material 1 mm. thick and 35 mm. in diameter sealed between two glass funnels directly behind the cigarette. The total volume within the two funnels was approximately 25 ml. The gas sample container previously described was connected to the smoking apparatus immediately folloRing the filter. Selection and Smoking of Cigarettes. Three brands of unfiltered, king-size cigarettes manufactured and distributed in the United States were employed in all of the smoking experiments. The cigarettes had a moisture content of 12 + 0.57’ and weighed within 312% of their average a-eight. They were stored and smoked a t a relative humidity of 55 t o 607’ and a temperature of 75’ F. The smoke collection train, consisting of cigarette, Cambridge filter, and gas sample container, was assembled and the smoking machine was standardized for a 35-ml. puff of the deaiied duration. This was one of the three puff durations studied-namely, 1.3, 2.0, or 3.0 seconds. The interval between puffs was adjusted to 1 minute. After the device waq standardized, the puff counter was adjusted to zero Except for one series of experiments, only one sample n as obtaincd from each cigarette. This material n as collected during
Relation of ethylene concentration in smoke to cigarette buLt length
the puff that caused the burning zone to move past a pencil mark initially 40 mm. from the lighted end. I n the one exception, three samples were collected corresponding to points initiall) 20, 40, and 60 mm. from the lighted end. ThP procedure for collection was as follows. Gntil the burning zone reached the point fo1 collection, the smoke mas pulled throiigh the bypass side of the gas sample container. When it \vas evident that the next puff would came the glowing coal to obliterate the pencil mark, the stopcocks on the sample container were turned to direct the gases through the sample side. A t the end of this puff the stopcocks were turned to provide an open path through the bypass side again. I n this !+-a>-a 10-ml. sample of the gaseous phase of the smoke was collected. Samples collected in this manner were analyzed by means of the gas chromatographic method. The filled sample container with the stopcocks turned to the bypass side wa3 connected into the chromatographic system (see Figure 1). hfter all connections were made and the sl stem was ready for a run, both stopcocks on the sample container \sere turned so that the carrier gas swept the sample onto the column of silica gel. The recording potentiometer automatically plotted t h e output of the therinal conductivity cell against time. RESULTS
A typical curve for the elution of a smoke sample is shown in Figure 3. Tentative identification of the compounds responsible for the peaks was based on similar curves for known substances. Confirmat,ion of the identity of ea( h conipound mas obtained by collecting t,he material correspond rig t o each peak nnd passing it through a similar gas chrom:ttograpliic system in which the column i n s packed with Celite 545 (Johns Nanville) impregnated with hexadecane. Methane was undoubtedly present, hut it was not separat,ed from nitrogen by the silica gel column. Quantitative results are based on cali1)r:ttion with known mixtures, as already descrilied. It is evident from the curve in Figure 3 that the peak for ethane partially overlaps that due t o nitrogen and other very low-boiling gases. This is also true to a lesser degree for ethylene and propane. I t was t o compensate for this “t)ackgroiind” response that the calibration mixtures xvere prepared with nitrogen :ts the major component. Individual determinations of ethane, ethFlene, propane, :md propylene are believed to be accurate t o better than i5OjO of the amount found. Because of the niinutr amounts present, acetylene, isobutane, and butane c*ouldnot 1)r determined with sufficient precision to detect changes associ:rtetl n-it,h the variables stiidied. The values report,ed for t h ( w three conipoiinda m:ty he i n crror b y a factor of 2. Samples from three l)r~~iicls of vigarettes were analyzed. They were smoked according to the procedure desc.ribed, with a puff of 2 seconds’ duration unless otherwisc Fpccified. Each value reported is the average for five run?. T h r concentrations of t~tli:mr~, c t l i ~ l e npi.oj);mt~, ~~. :xnd propylene
1687
V O L U M E 28, NO. 11, N O V E M B E R 1 9 5 6 in smoke from the bran& st.Litlicd a r c li d in Tahle I . These samples were obtained after smoking to :L rbitrary point 40 mm. from the lighted end. S o significant difference in the threr brands is indicated by these figures. Samples collected a,fter smoking brand A cigarettes a dist:tnce of 10 mm. with varying duration of puff were used to olitain the values in Table 11. blthough the 1.3-second puff seems to give lower concentrations than the standard 2.0-second puff, the differences proved to be statistically significant a t the 95% confidcnce level for propane and propylene only. None of the diflerences between corresponding vnliies for the 2.0-second piiA :md the 3.0-second pufT were statistii~dlysignificant. Results for smoke from brand A cigarrttrs :tt 20, 40, and 60 mm. itre compared in Table 111. The c-oncrntrations of each of the four hydrocarbons increased with decrrasing length of the cigarette hutt. Statistical aii:ilysi$ indicated t,hesc increases to be significant a t the 95% confidence levcl. The data for et,hylcnc are shown graphirdly in Figure 4. Corresponding graphs for t'he other components are similar. A smooth curve joining t h r averages for each of the three sampling points is someivhat ('onvex toward the abscissa in each caw. ion of the data, the deviation from linearity is not significant. tge conceiitratioii of each Table IS' contains thc c~:rlciilatecl:L of the PCVPII hydroc*:rrhorir stiitlied in :ill of the niain stremis of smoke produced h y smoking I)rand A cigtrettes a distance of 60 mm. from the lighted iJrid. Thrse v:iliic:s iwre obtained by re:tding the cwnrentration of thc 30-mni. point from graphs like the one for c~tliylrnc~ iii Figin,(,4. The :tinolint of each hj-drocarbon present) in the smoke from R standard package of cigarettes is also listed. Thrse figiirrs n-tre c::ilculatod by assuming that an iiwritgf' of 12 35-ml. piiff.< (120 nil.) is prodiiced hy smoking GO m m . of each cigarette. r2nalyscs were n i d c o n sniokc from tirand A cigarcttcs that h i d heen cut, off at the 40-mm. mark and smoked to the 60-nim. mark. The results are shown in Titble T' along with figures obtained from similar cig:tret,tcxs smoked under the sttine conditions all the n-:ty from the lighted end to the 60-mm. mark. Corresponding vitlucs in the two columns ;ire riot significantly different. These dat'a indicate that the increase in concentration of the hydrocarbon gast's i\-ith decre:tsing hiitt, length (see Table 111) is not primarily the result of pyrolysis of accumulated tars. If this Lvere the case, t,he values obtainrd for the short cigarettes should correspond to those ohtainrd for t,he full length cigarettes at t>hc20-mm. mark. The possibility that the hydroc:trbon gases are adsorlied or absorbed by the tobacco and/or tar caannot be ruled out on the basis of the experiment's perfornied. I t is also possible that the
decrease in pressure drop across the cigarette as its length decreases may increase the rate a t wl-hich air is drawn through the cigarette during a puff. However, onr would expect from the results obtained by varying the dur:ition of puff (see Table 11) that this n o d d lead to decreasing concentrations as the smoking proceeded. I t might be enlightening to bc able t o measure the temperature of the burning coal when earh sample is taken. SU>lJ.I,IlARY
A gas chromatographic method for quantit:itivc determination of ethane, ethylene, :icst,ylene, propane, propylene, isobutane, and butane in the gaseous phase of cigarette smoke was found t o be remarkably effective for t.hP separation of these components from others present in this complex mixture. It had sufficient sensitivity to enable their drtcrmination in a IO-ml. sample. Ethane, rthJ.lene, prop:tne, and prop>knc\ were present in amounts sufficient to eimble determinstiori of changes in their concentr:ttioris accompanying variations in the smoking procedure. The concentrations of these compountls increased as the lrngth of the cigarette butt ciecreased. Althongh the silica gel coliiniri dr ibcd is suit>&le for the determination of light hydroc:trboiis only, the iiw of other column p:ickings and conditions should enable analysis of some other Components of cigarette smoke. The gas chromatographic method should also be useful for separating components present in the gaseous phase of cigarette smoke for identific:at,ion by other means, p:trticularly mass spectrometry. LITERATURE CITED
(1) Berridge, S . J., T a t t s , J. D.. J . Sci. Food -4gr. 5 , 41i-31 (1954). (2) Bradford, B. W., Harvey, D., Chalkley, D. E., J . Inst. Petroleum 4 1 , 80-91 (1955). (3) ('allear, A . B., CT-etonovi6, K . J., Cali. J . Chem. 33, 1256-67 (1955).
Table 111.
Hydrocaibon Ethane Ethylene Propane Propylene
Table IV.
\-ariation of HI drocarbon Concentration with Length from Lighted End 20 mm. 0 0 0 0
Concentration, Tolrime ?& 40 mm. 0 0 0 0
15 084 051 059
6
19 OR7
?
0.25
0.117 0.065 0 076
057
069
Average Concentration of Seven H>drocarbons
in Cigarette Smoke Table I. Hydrocarbon Ethane Ethylene ProDane
Propylene
Table 11.
\'ariation of Hydrocarbon Concentration with Brand of Cigarette
~-
Brand A 0.19 0.097 0.051
Concentration, Volume % Brand E 0.17 0 093
0 057
0.064
0. Otis
Brand C 0.17 0,097 0.054 0.067
Variation of Concentration with Duration of
Puff Concentration. Volume % Hydrocarbon Ethane Ethylene Propane Propylene
1.3-sec. puff 0 16 0 084 0 051 0 057
2.0-sec.
puff 0 19
0 097 0 067 0 069
3.0-sec. puff 0.19 0,090 0,059 0.063
Voliiiiie Hydrocarbon Ethanc Ethylene Acetylene Propane Propylene Isobutane Bii t ane
n /O
02 0 1
0 01 0 06
0 07 0 001
0 006
Ml. (S.T.P.) from 20 Cigarettes 17 8
0.8 5
6 0.1 0.5
Table V. Coniparison of Concentration for Full Length and Shortened Cigarettes Smoked to Same Butt Length Concentration, Volume 7" Hydrocarbon
Full length
40 mm. shorter
0,114 0,067 0.077
ANALYTICAL CHEMISTRY
1688 Evans, D. E. M , , Tatlow, J. C., J . Chem. SOC.1955, 1184-8. (5) Fishel, J. B., Haskins, J. F., I n d . Eng. Chem. 41, 1374-6 (1949). (5) Harvey, D., Chalkley, D. E., Fuel34, 191-200 (1955). (7) James, A. T., M ~ QChemist . 26, 5-10 (1955). (8) James, A. T., Research ( L o n d o n ) 8,8-16 (1955). (9) James, 1.T., Martin, A. J . P., Brit. M e d . Bull. 10, 170-6 (4)
(1955).
S.A , , Burow, F. H., A N A L . C H E Y . 28, 1510-13 (1956). 111) Littlewood. A. B.. Phillim. C. S. G.. Price, D. T., J . Chem. SOC. 1955, 1480-9. (12) Martin, A. E.. Sinart, J., S a t w e 175, 422-3 (1955). (IO) Lichtenfels, D. H., Fleck, ~I
(13) Osborne, J. A., Adamek, S., Hobbs, IT. E . , ANAL.CHEY.28, 211-15 (1956). (14) Patton, H. W.,Lewis, J. S., Proceedings of Third National Air Pollution Symposium, Pasadena, Calif., 1955, pp. 74-9; ANAL.CHEY.27, 1034 (1955) (abstract). (15) Patton, H. W.,Lewis, J. S., Kaye, R. I , I b i d . , 27, 170-4 (1955). (16) Purnell, J. H., Spencer, 11.S., Sature 175, 988-9 (1955). (17) Touey, G. P., ANAL.CHEV.27, 1788-90 (1955). RECEIVED for review January 9, 19%. Accepted July 0, 1956. Presented a t the Tobacco Chemists' Research Conference, Korth Carolina State College, Raleigh, N C., October, 6 1955.
Titration of Copper Oxinate in Glacial Acetic Acid CHARLES H. HILL, HAN TAI, A. L. UNDERWOOD, and R. A. DAY, JR. D e p a r t m e n t o f Chemistry, €mory University, Emory University, Ga.
Organic precipitants are very useful for separating metal ions, but gravimetric determinations involving direct weighing of the precipitated metal chelates are often beset by difficulties, including not only the usual gravimetric tedium, but also errors arising from dubious weighing forms which exhibit uncertain hydration, decomposition, and volatility. It is thus of interest to investigate methods other than gravimetric for the measurement of these analytical precipitates. In the present study, it is shown t h a t copper can be determined by applying nonaqueous titrimetry to the copper oxinate precipitate. Cupric ion is precipitated from aqueous solution with oxine, the copper oxinate is dissolved in glacial acetic acid, hydrogen sulfide is bubbled through the solution to precipitate copper sulfide, and final13 the oxine solution is titrated with perchloric acid to a potentiometric end point. The method yields very satisfactory results.
600-
*5500
1500-
35 ML OF HCIO, Figure 1.
B
ECAUSE organic precipitants are, in general, weak acids and/or bases, it was reasonable to investigate the applica-
tion of nonaqueous titrimetry t o these reagents and their metal complexes. One might hope thereby t o retain the attractive features of organic precipitants in effecting separations while circumventing some of the difficulties attending their gravimetric use. Some preliminary studies along these lines with 8-quinolinol (8-hydroxyquinoline, oxine) and dimethylglyoxime have been reported b y Fritz (3). M7hen oxine is dissolved in glacial acetic acid and titrated potentiometrically with a solution of perchloric acid in glacial acetic acid, an excellent end point is obtained (Figure 1). If, on the other hand, a metal oxinate rather than oxine itself is dissolved in acetic acid and titrated, the end point is very poor (Figure 1). This has proved true in the case of iron, copper, aluminum, magnesium, and a number of other metals (4). Studies of the extents t o which the various metal oxinates dissociate in acetic acid, and the dissociation of the resultant metal acetates, would be needed t o explain the difficulty completely. Presumably the following equilibria are involved:
+ nHO.\c
+ M(OAc), HOx f HO;lc % (HpOx)+ + OAC-
M(Ox),,
%
nHOx
40
Titration curves of oxine and metal oxinates 1. Oxine 2. Aluminum oxinate 3. Copper oxinate
I
I
1
1
1
I
I-m 5 5 O L
1
"450
,
400//
5
IO 15 ML. OF HCIO,
, 20
1
Figure 2. Titration of copper oxinate solution after precipitation of copper sulfide
