mixture was packed in a glass tube 8 mm in internal diameter. The packed length was about 8 cm. No attempt was made to obtain optimum column properties; the column was used only as a device for checking the operation of the titrator, Titration curves were drawn by a Varian G-14 0-10 mV recorder, with a chart speed of 4 inches per hour. The chart width on this recorder is 5 inches. Figure 4 shows the titration curves, obtained with acetic acid samples containing 100, 400, and, 800 nanomoles. The records cover the period from the beginning to the end of solvent flow through the column. Figure 5 shows curves obtained with a higher sensitivity for acetic acid samples containing 20, 60, and 100 nanomoles. The background titration is much higher at the high sensitivity. The magnitude of the background titration is controlled by the amount of methanolic NaOH added to the titration diluent. The same diluent was used for the columns of Figures 4 and 5. Variations in the background titration are also more evident in Figure 5. It is these variations that limit the sensitivity of the titrator. For quantitative determination of acids, the areas of peaks such as those of Figures 4 and 5 must be determined. Table I gives data on peak areas for
acid samples of various sizes. The areas were determined by three methods. In the first method, the peaks were cut out carefully from a Xerox copy of the recorder chart, and weighed. In the second method, the area of the peaks was measured with a polar planimeter. Because of the small size of the recorder chart used, the records were photographically enlarged (two-fold linear enlargement) before being measured ; with a recorder having a wider chart, this would not have been necessary. In the third method, an electrical integrator was used with the recorder. All three methods were used with the same set of samples. It may be seen from the table that there is no great difference in accuracy among the methods. If a 10-inch recorder chart is used, the planimetric method is most convenient. The weighing method is recommended for 5-inch chart paper. An integrator, if available, is probably the most convenient. It may be seen from the table that, as might be expected, poorer precision was obtained with small areas than with large. RECEIVED for review April 22, 1968. Accepted May 16, 1968. Work supported in part by grant No. A102967 from the National Institutes of Health, U. S . Public Health Service.
Separation and Determination of lsocyanurates by Gas Chromatography Gary W. Ruth' and Ruder Schill Marathon Oil Co., Denver Research Center, P.O. Box 269, Littleton, Colo. 80120 ISOCYANURATES, derivatives of isocyanuric acid (s-triazine2,4,6-[lH,3H,SH]trione) have been of interest even before 1885 when Hofman ( I ) discovered triphenyl isocyanurate and greatly elucidated the chemistry of these derivatives. After World War 11, the practical uses of isocyanurates and isocyanates became more fully realized, and since then many workers have been doing intensive research on the preparation and application of these compounds (2-4). The advantages of using gas chromatography for separating mixtures of these derivatives in support of their research and production are quite obvious. Very little use of gas chromatography has been made in this area. Limited separations (5) have been made, but difficulties were encountered and high molecular weight derivatives were not attempted. We have found that gas chromatography can be used for analysis of mixtures of isocyanurates which we have been unable to analyze by other means. Isocyanurates having molecular weights as high as 400 have been analyzed. We have worked primarily with the three systems reported here. Each of these systems represents the major products obtained from the basecatalyzed cotrimerization of the appropriate isocyanates. 1
To whom inquiries should be addressed.
(1) A. Hofman and 0. Olshausen, Ber., 3,269 (1870). (2) K. Shiba, Japan Chemical Quarterly, 3, 19 (1963). (3) T. C. Frazier, E. D. Little, and B. E. Lloyd, J. Org. Chem., 25,
1944 (1960). (4) E. M. Smolin and L. Rapoport, s-Triazines and Derivatives. Interscience, New York, 1959, pp 389-422. (5) E. C . Juenge and W. C. Francis, J. Org. Chem., 26, 3334 (1961) .
1582
ANALYTICAL CHEMISTRY
EXPERIMENTAL
All work was performed using an F & M Model 720.dualcolumn, programmed temperature gas chromatograph equipped with a thermal conductivity filament detector and a 1-mV, Honeywell Recorder. The columns used were 1-foot X l/4" 0.d. stainless steel columns packed with 2z Versamid 900 (General Mills, Kankakee, Ill.) on 60- to 80-mesh Chromosorb-W (Johns-ManviUe Products Corp.). Both columns were conditioned in the chromatograph for three hours at 280 "C (oven temperature). Helium carrier gas was used at a flow rate of 70 ml per minute during column conditioning and in all subsequent separations. The carrier gas pressure to instrument flow controllers was 20 psig. The injection port temperature was maintained at 285 "C while the detector was kept at 325 "C. All runs were programmed from 100 "C to 280 "C at a rate of 20 "C per minute. The detector bridge current was maintained at 150 mA, and the recorder chart speed was li2" per minute. N,N-Dimethyl-
Table I. Relative Retention Data for Isocyanurates on Versamid 900 Column
Component
RRT
1,3,5-Triallylisocyanurate 1,3,5-Tri-n-butylisocyanurate l-Allyl-3,5-diphenyl isocyanurate l-n-Butyl-3,5-diphenyl isocyanurate 1,3,5-Tribenzylisocyanurate l-Benzyl-3,5-diphenyl isocyanurate 1,3,5-Triphenyl isocyanurate
0.306 0.395 0.752 0.758 0.870
0.943 1 .GQo
formamide obtained from Matheson Coleman and Bell was used as a solvent in all of the runs. The samples consisted of approximately 250 mg of the isocyanurate mixture in 10.0 ml of solvent, and the sample size injected into the gas chromatograph was 2.0 pl. The amount of each component in the mixture was determined by peak area normalization. Because of the very close agreement between area per cent and the known weight per cent of each component in the synthetic mixtures, it was felt that thermal conductivity response factors were not necessary. RESULTS AND DISCUSSION
A complete analysis of each isocyanurate system can be accomplished in 15 minutes. Relative retentions are noted in Table I. Peak symmetry of each isocyanurate was good, and complete resolution was accomplished in all but one of the systems. However, it was found that the peaks broadened and tailed considerably after the column had been heated above 280 “C for several hours. This was probably due to loss of liquid substrate. Typical precision provided by this technique is illustrated in Table 11where results are shown for the analysis of a synthetic mixture of one of the isocyanurate systems. Nine determinations were made on the same sample over a period of three days. One determination was made on each of the other two isocyanurate systems shown in Table 11.
Table 11. Analysis of Synthetic Mixture of Isocyanurates System 1 Composition, weight Re1 std Component Known Found dev, 1,3,5-Triallyl isocyanurate 34.0 34.5. 2.26 l-Allyl-3,5-diphenyl isocyanurate 27.7 27.50 1.96 1,3,5-Triphenyl isocyanurate 38.3 38.10 1.50 System 2 1,3,5-Tri-n-butyl isocyanurate 34.8 33.7 l-n-Butyl-3,5-diphenylisocyanurate 34.5 35.4 1,3,5-Triphenyl isocyanurate 30.7 30.9 System 3 1,3,5-Tribenzyl isocyanurate 33.6 33.9 l-Benzyl-3,5-diphenyl isocyanurate 50.8 49.9 1,3,5-Triphenylisocyanurate 15.6 16.2 a Average of nine determinations. ACKNOWLEDGMENT The authors thank P. A. Argabright of the Denver Research Center, Marathon Oil Co., Littleton, Colo., for supplying the isocyanurate samples and for much helpful information.
RECEIVED for review March 6,1968.
Accepted May 10,1968
Gas Chromatographic Determination of Benzo(a)Pyrene in Cigarette Smoke Howard J. Davis Celanese Research Co., Box 1000, Summit, N. J . 07901 AN analytical method which was shorter and more versatile than the fluorometric method ( I ) for the determination of benzo(a)pyrene (BaP) in cigarette smoke was sought. Gas chromatography (GC) with an electron capture detector appeared to be the most promising because it offered sensitivity and favorable specificity of detector response in addition to the excellent separations obtainable on G C columns which would permit the analyses of other polycyclic aromatic hydrocarbons. The G C method described herein adds further to the unambiguous identification and measurement of BaP. A comprehensive review on the analyses of polycyclic aromatic hydrocarbons in tobacco smoke is contained in the recent publication of Wynder and Hoffmann (2). Another pertinent review is that by Stedman (3) on the chemical composition of tobacco and tobacco smoke. Carugno and Rossi (4) identified components of the polycyclic hydrocarbon fraction of cigarette smoke by gas chromatography with electron capture and flame ionization detectors and using glass capillary columns. Their smoke cleanup procedure included a perchloric acid treatment to eliminate, as much as possible, (1) H. J. Davis, L. A. Lee, and T. R. Davidson, ANAL.CHEM., 38,
1752(1966).
(2) E. L. Wynder and D. Hoffmann, “Tobacco and Tobacco
Smoke. Studies in Experimental Carcinogenesis,” Academic Press, New York, 1967. (3) R. L. Stedman, Chem. Rev., 68,153 (1968). (4) N. Carugno and S. Rossi, J. Gas Chromatog., 5 , 103 (1967).
interference from heterocyclic compounds eluted along with the polycyclic hydrocarbons. Because of certain limitations and deficiencies encountered with the radioactive (tritium) source in our early efforts to develop a G C method for polycyclic hydrocarbons, another type of electron capture detector was sought. One which was found to be satisfactory is basically an ionization detector utilizing a helium glow discharge as the electron source (Beckman GC-5), capable of operation at temperatures up to 400 “C. As little as 1 ng of BaP could easily be measured with satisfactory precision. EXPERIMENTAL
Reagents. Pre-equilibrated solvents and polynuclear hydrocarbons were described previously (I). Requisite standard solutions of benzo(a)pyrene, benzo(e)pyrene, and perylene were prepared with n-hexane as the solvent. Apparatus. The instrument used was a Beckman GC-5 gas chromatograph, Beckman Instruments, Inc., Fullerton, Calif., equipped with an electron capture detector and a dualflame ionization detector. A packed column was used: 9 feet, stainless steel, 0.125-inch o.d., 3z SE-30 on 60/80 mesh Chromosorb W. Procedure. The shortened smoke fractionation scheme outlined below yielded a BaP fraction suitable for gas chromatographic analysis. The internal standard, perylene, added at the beginning in order to determine the overall recovery, was measured by ultraviolet absorption spectrometry. VOL. 40, NO. 10, AUGUST 1968
0
1583
