PPC, but for DMBC and P M I C the final, quantitation step was not carried out. Figure 1 shows a n actual chromatogram of all four amides, obtained under the following conditions: Support Substrate Column Detector temp. Detector current Attenuation Inlet temp.
100-140 mesh glass beads 0.25% Carbowax 1500 Copper, 28 by inch 275" C. 195 ma. 1 340" C.
Internal standard was omitted from the chromatogram. The retention times and values of apparent H E T P calculated as though the chromatograms were isothermal are given in Table 111. I t is noteworthy that under these conditions, the high-boiling amides are taken off a t such low temperatures. These range from 145" C. for CBZ to 206" C. for PMIC, and appear to be the result of the choice of column packing, as pointed out initially by Hishta et al. ( I ) . Quantitative data were obtained for PPC, using the conditions described earlier for preparation of the amide, and slightly modified conditions for the subsequent chromatography. Chromatographic changes involved a lengthening of the column to 28 inches, an increase in helium flow to 45 ml. per
minute, and a change of temperature program to 11' C. per minute over an 80" to 190" C. range. Table IV lists replicate data obtained for P P C on the basis shown in Table I for CBZ. Retention times were 4.4 and 9.8 minutes Helium flow, column Helium flow, reference Sample size Initial column temp. Program rate Cutout temp.
125 ml./min. 13 ml./min. 1 pl. 125" C. 11"
c.
205" C.
for internal standard and PPC amide, respectively. The relative standard deviation for all 11 data is =!=2.4%, and F is satisfactorily constant over the range of sample levels chosen. This precision represents the combined chemical and chromatographic steps. Two commercial samples of PPC were analyzed by this technique, and the results were compared with values obtained by the chemical met,hod described by Stone (4). Table V lists the data and shows a relative error of + 2 to 3%. Based on the data presented above, we conclude that a method of general applicability has been developed for determining carboxylic acid chlorides. Although the small concentration of residual carboxylic acid usually present
initially in acid chloride samples is not determined, it is likely t h a t a modification of the procedures would accomplish this too. For example, following the formation of the amides and the extraction of excess amine, the carboxylic acid could be extracted with alkali, estefied, and subjected to gas chromatographic assay. Alternatively, the carboxylic acid could be determined by direct titration in the presence of the amide, and the same sample used for gas chromatography. ACKNOWLEDGMENT
The authors are indebted to J. P. Messerly for his original suggestion of applying gas chromatographic procedures to the determination of acid chlorides, to W. D. Cooke of Cornel1 University for reviewing this work, and t o Bristol Laboratories for permission to publish this paper. LITERATURE CITED (1) Hishta, C., Messerly, J. P., Reschke,
R. F., Fredericks, D. H., Cooke, W. D., ANAL. CHEM.32, 880 (1960). (2) Lohr, L. J., Ibid., 32, 1166 (1960). (3) Sanders, M., Murray, R. W., Tetrahedron 11, 1 (1960). (4)Stone, K. G., "Determination of Organic Compounds," pp. 97-9, McGraw-Hill, New York, 1956. RECEIVEDfor review June 6, 1962. Accepted November 14, 1962.
Determination of Tobacco Humectants by Gas Liquid Chromatography R. L. FRIEDMAN' and W. J. RAAB Technical Service I aboratory, Shell Chemical Co., Union, N.
b A technique is described for the extraction and determination of various humectant polyols added to cigarette tobaccos. Six major cigarette brands were extracted using acetone as solvent. The solution was purified and the acetone was removed under reduced pressure. The residue was then dissolved in methyl alcohol, and the presence of propylene glycol, diethylene glycol, and glycerine was determined b y chromatographic separation.
M
IXTURES
OF VARIOUS
POLYOLS,
namely propylene glycol, diethylene glycol, and glycerine, are used as humectants in the manufacture of cigarettes. A recent literature survey for a suitable technique t o determine humectant composition of cigarettes did not disclose any procedures that were relatively simple and rapid, yet
J.
capable of giving good qualitative and quantitative results. Chemical procedures involving oxidation of alpha glycols and acetylation of total hydroxyl groups gave only fragments of information, and identification of individual compounds was not totally feasible by these techniques. Also, the results from the chemical analyses can be obscured by other tobacco ingredients containing reactive hydroxyl groups. Availability of suitable equipment and successful experience with gas liquid chromatography in other fields caused us to settle on this technique as the basis of an analytical procedure for tobacco humectants. The development of an analytical technique for determination of selected components of a complex mixture usually involves two basic stepssample preparation and the actual analysis. For the analysis of tobacco humectants by GLC, it was apparent
that extraction of the humectants from the cigarette tobaccos would be a necessary first step. The crude tobacco extract would then have to be purified to rid it of gross contaminants that could interfere with or complicate subsequent analysis. Since the procedure developed may represent a step forward in the analysis of glycol-poly01 blends and, consequently, may be of practical value to some segments of the tobacco industry, a detailed description of the entire procedure will be given below. EXPERIMENTAL
Apparatus. T h e GLC equipment used in this study was a F & M Model 300 programmed gas liquid chromatograph. T h e chromatograph was fitted with a 6-foot stainless steel 1
Present addreea, Shell Chemical Co.
415 Madison Avenue, New York, N. Y. VOL. 35, NO. 1, JANUARY 1963
67
I
I
0
12.5
I
8
18
24
1
TIME (MINUTES) Figure 2. tobacco
IB
12.5
Typical chromatogram of polyols from cigarette
24
TIME ( MINUTES) Figure 1.
Typical chromatogram of polyol blend
column, ','(-inch i d . , packed with a 5:95 weight ratio of Carbowax 1500 on Haloport F. The temperature was programmed for a rise of 9" C. per minute from a n initial temperature of 50" C. to a maximum temperature of 200' C. When this point was reached, the temperature was kept constant for the duration of the run. The carrier gas, helium, was maintained at a n exhaust port flow rate of 70 ec. per minute. Both the block temperature and the injection port temperature were maintained a t 225' C. Procedure. T h e tobacco from a king-sized package of cigarettes was collected in a 43- X 123-mm. extraction thimble a n d placed in a standard 50-mm. i.d. Soxhlet extractor fitted with a standard condensor a n d a 250-ml. single neck, round-bottomed flask. T o the flask was charged 150
Table 1. Typical Analysis of PolyolTreated Tobacco Samples
Glycerine, DEG, g. P. Actual 0.32 0.20 0.32 0.20 Determined Untreated tobacco 0.0 0.0
PG, g.
0.38 0.37 0.0
Table II. Humectant Analysis of Commercial Cigarettes
Brand A B C
D E F
68
Glyc., 70 DEG, 70 PG, 2.9 3.1 2.4 1.9 3.2 2.6
1.1 ...
... ... ...
...
ANALYTICAL CHEMISTRY
...
0.9 1.6 2.1 0.8
1.4
ml. of acetone containing 0.5 gram of activated charcoal (Suchar C-1901\', manufactured by K e s t Virginia Pulp and Paper Co., Industrial Chemicals Division). The acetone n a s heated t o reflux and the tobacco sample was extracted at a rate of 10 nil. per minute for 4 hours. The extract n a s filtered and the acetone was stripped off under reduced pressure (10 to 15 mm. Hg) using a rotating el-aporometer connected to a water aspirator. The liquid concentrate was then washed with three 10-nil. portions of benzene t o remove undesirable waxes. S e a t , the mashed concentrat? was dissolved in 30 ml. of absolutp methyl alcohol. The resulting solution was slurried with 0.1 gram of activated charcoal (Kuchar C-l9OS), filtered, and stripped of methyl alcohol under reduced pressure using the ab01 e procedure. Finally, the residue was dissolved in 2.0 ml. of absolute methyl alcohol. 9 10-pl. sample of this concentrate is the feed source for the GLC unit. -4lthough less rigorously purified material can be put through the GLC and analyzed, rapid fouling of the instrument occurs without suitable feed preparation. Each of the eltraction and purification steps n a s qualitatively checked on our instrument for polyol losses, and no discernible losses mere noted. RESULTS
To test the resolution obtainable in our apparatus with the glycols and polyols in which n e were interested, propylene glycol, diethylene glycol, glycerine, and several blends were dissolved in absolute methyl alcohol and analyzed by the F 8: ?yI 300 gas liquid chromatograph (see Figure I ) . Under
the conditions used, elution times of 12.5, 18, and 24 minutes, respectively, were obtained for propylene glycol, diethylene glycol, and glycerine. From the results, a set of calibration curves relating peak area to milligrams of desired polyol were prepared. I n a study of 10 blends the presence of more than one glycol or polyol did not appear to cause any interference with the analysis of the individual desired component, and a relative error of less than 5% was obtained. Reference propylene glycol (U.S.P.) and diethylene glycol (Reagent Grade) were obtained from Fisher Scientific Co., while synthetic glycerine (99.5%) was produced by Shell Chemical Co. A sample of noncased, blended cigarette tobaccos v a s then obtained and treated with known blends of propylene glycol, diethylene glycol, and glycerine. Quintuplicate samples of the treated tobacco were extracted and analyzed. Results are given in Table I. An unexpected peak appeared (see Figure 2) which was later determined to be nicotine; however, this material did not complicate or interfere with the analysis. This technique was then put to a practical test; individual packages of popular king-sized cigarettes from six leading cigarette manufacturers were obtained locally, extracted, and analyzed in quadruplicate. Analysis of one of the sets of quadruplicate samples was repeated (Brand -4)after a known amount of ethylene glycol had been added to serve as an internal control. This permitted a further check on the quantitative estimation of the humectant level. On the basis of this run, a total humectant concentration of 4.0% wt. (based on the original cigarette tobacco weight) was calculated. I n reporting the humectant levels of the other cigarette brands (Table 11) in this particular series,
the results have purposely been equated t o a 4.0% wt. level. Between the quadruplicate samples analyzed, a total variance less than the relative error was obtained. I n additional studies a total of eight polyols, including ethylene glycol, propylene glycol, diethylene glycol, 1,3butylene glycol, dipropylene glycol, trimethylene glycol (1,3 - propylene glycol), glycerine, and 1,2,&hexanetriol, were easily separated by the described instrumental technique. However, only propylene glycol, diethylene
glycol, and glycerine were found to be present in the commercial cigarettes treated, and inasmuch as our primary coiicerii was with a technique for the analysis of cigarettes, detailed studies of the estimation of these other compounds were not made. IThile we do not feel that sugars present in the casing mixture used on coiiiniercial cigarette tobaccos would interfere with the described analytical technique, further nork by someone in the tobacco industry having an intimate knowledge of various casing
solutions should be conducted t o confirm or refute our viewpoint. ACKNOWLEDGMENT
The authors express their appreciation t o W.D. Hanus and A. C. Cocuzaa for their assistance in the above work. RECEIVED for revien- December 7, 1961. Resubmitted August 2, 1962. Accepted
October li, 1962. Presented in part a t the 15th Tobacco Chemists' Research Conference, Philadelphia, Pa., October 4-6, 1961.
Pyrolysis-Gas Chromatographic Technique Effect of Temperature on Thermal Degradation of Polymers KITTY ETTRE and P. F. VARADl The Machlett laboratories, Inc., Springdale, Conn.
p A new pyrolysis apparatus was developed, which allows exact thermal degradation studies in a wide temperature range. Three polymersnitrocellulose, poly(vitiyl alcohol), and poly(n-butyl methacrylate)-were pyrolyzed between 300" and 950" C. The composition of the breakdown products a t the different temperatures i s tabulated. The results are compared with those obtained using flash pyrolysis technique.
1
previous studies ( 2 ) , a flash filament pyrolysis unit was used to investigate polymers at a measured temperature of 650" C., and a complete qualitative and quantitative analysis of the pyrolysis products was given for each polymer at this temperature. Subsequent work proved, however, that if the breakdown has t o be studied a t different temperatures, the flash pyrolysis technique is inadequate. The pyrolysis apparatus described in the literature can be divided into two groups, those using flash filament pyrolysis and t h e others using reactor chamber techniques. The instrumentation for flash filamcnt pyrolysis consists mainly of a filament heated electrically t o the desired temperature. The sample is either dissolved in a solvent and coated on t h e filament in form of a thin layer or measured in solid form into a small cup or boat which is placed in the heating coil. Both procedures have definite disadvantages. T17ith the coating technique (1. 4, 6. 7 . 10 13. I d ) , the sample cannot be N OUR
analyzed in solid form b u t has to be dissolved and then applied to the filament. The dissolved form of the material, however, does not necessarily decompose identically to the undissolved (solid) substance; and the breakdowi products of the solvent may also appear in the chromatogram. Quantitative measurement is not possible, since the original amount cannot be weighed, nor can the amount and characteristics of the residue be determined. Finally, t h e glowing wire may act catalytically on t h e decomposition products to change their nature by secondary reactions. The second mode of operation (use of a small boat) (9, 11) eliminates most of these errors, but introduces a new major problem: The heat-up time of the sample is no longer instantaneous. The boat or cup placed in the heating coil reduces the heating rate of the filament and slows down its heat-up time. The boat itself takes over the final temperature of the filament only after a certain time, depending on its material and wall thickness; thus, the total heat-up time of the sample may vary between 20 and 40 seconds b u t can hardly be reduced belovi 20 seconds. This means t h a t the sample itself goes through t h e n-hole temperature range before reaching the desired temperature, and therefore the composition of the breakdown products reflects t h e pgrolysis not at a certain temperature but up t o a certain temperature. The products of the lower temperature pyrolysis may also react further; thus, a combination of primary and secondary
pyrolysis products may appear in the chromatogram. The fact that most flash pyrolysis setups do not allow higher carrier gas flow rates also contributes t o the possibility of secondary reactions, because the primary breakdown products stay too long in contact with the heated part- of the pyroly sis zone. A separate problem of all flash pyrolysis units ib that it is practically impossible t o measure the exact pyrolysis temperature. Therefore. in many cases the temperature of the glov-ing n-ire is evaluated only visually, by observing its color (5, 1 1 ) . Thus, although studies Kith flash pyrolysis result in reproducible data, they may be misleading in many cases. Recently, some re3earchers described the uae of reaction chambers for pyrolysis studies (3, S, 1 2 ) . These units, USUally made of a stainless steel tube, have overcome some of the difficulties of flash pyrolysis. The error of sloyer heat-up is eliminated because thi. sample is introduced (injected) directly a t the temperature of pa rolysis: the temperature is also more controllable and its nieasuremeiit is more accurate. Finally, higher flow rates can be applied, and thus the possibility of secondary reactions can be minimized There remain. however, some problems n hich are yet unsolved, such as the iiitroduction of solid samples and t h e possibility of measurements over a wide tempernture range. Further, the hot stainless steel surface of the chamber may have some catalytic effects, resulting again in secondary reactions. '
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