t o polar materials, the latter is a valuable confirmatory accessory. Unlabeled peaks observed in many of the chromatograms are caused b y the presence of high boiling solvents, fatty acids, or polyol impurities. Solvent peaks, as in Figures 3 and 4, appear in the early part of the chromatograms and do not interfere with the analysis, but if desired, they can be removed by drying the resin sample prior to treatment with the amine. By establishing relative retention times on the polar and nonpolar columns described, the method can be ex%endedto include other polyols. Dipentaerythritol was investigated but did not separate under the conditions of test. One pes cent concentrations of most
of the polyols could be detected in alkyd resins, but the detectability decreases with increasing boiling point of the poly01 acetate. When small amounts of a poly01 are present, the peak heights can be enlarged by increasing the sample volume or decreasing the recorder range. ACKNOWLEDGMENT
The advisory assistance of C. F. Piekett, director of the laboratory, is acknowledged and appreciated. LITERATURE CITED
(1) Clifford, J., Analyst 85, 475 (1960). (2) Ginsburg, L., ANAL.CHEM.31, 1822 (1959). (3) Kappelmeier, C. P. A., ed., “Chemical
P.
(1959). (10) Wisniewski, D. F., Stalker, G. C., Petrol. Refiner 40, 117 (1961).
RECEIVETI for review May 4, 1961. Accepted Augupt 7, 1961. *
hromatograp
rs JAMES S. PARSONS, S. M. TSANG, and M.
halysis of Resin-Based Coating Materials,” p . 121-4, Interscience, New York-LondPon, 1959. (4) Kappelmeier, C. B. A., Moiostert, J., Boon, J. I?., Verjkruniek 27, 291 (1954). (5) Kline, G. M., ed., “Analytical Chemistry of Polymers,” Vol. XU, of “Nigh Polymers,” pp. 25-31, Interscience, New York-London, 1959. (6) Link, W. E., Hickman, H. M., Morreasette, R. A., J. Am. Oil Chemists’ Soc. 36,300 (1959). (7) Nadeau, H. G., Oaks; D. M., ANAL. CHEM.32,1760 (1960). (8) Sargent, R., Rieman, W., Anat. Chim. Acta 16,144 (1957). (9) Smullin, C., Hertmann L., Stetzler, R.,J. Am. Oil Chemists’ SOC.36, 179
DiGlAlMO
Research laboratories, American Cyanamid Co., Bound Brook,
N. .!.
RAYMOND FEINLAND and R. A. b. PAYLOR Cenfral Research laboratories, American Cyanamid Co., Stamford, Conn.
The separation and analysis of the three mononitrotoluene and the six dinitrotoluene isomers was accomplished by gas-liquid partition chromatography employing an efficient Apiezon L column. HE separation and analysis o’f nitrotoluene isomers has been important in nitration studies of toluene for a number of years. Current interest in dinitrotoluenes has increased since they are precursors to toluene diisocyanates and urethane foams (I). Previous methods (1,4-6) have been tedious, lengthy, and leave questions about complete separation of all isomers. Recently, Kolbe et al. (IO) employed the isotope dilution methods for isomer determinatione. Gas chromatography offered the greatest potential for separation of all isomers and a fast analysis. The mononitrotoluene isomers were completely separated by gas chromatography with 2,4,7-trinitrofluorcnone (8) as the liquid phase, but our attempts to separate the dinitrotoluene isomers with the latter column were not successful. The mononitrotoluene isomers with small amounts of 2,4- and 2,6-dinitrotoluene can also be determined by infrared (9) ; however, the complete analysis of all mono- and dinitrotoluene
isomers was not possible by infrared. The mononitrotoluenes were separated from the dinitrotoluenes by liquidliquid partition column chromatography using heptane (mobile)-2-methoxyethanol (stationary) solvents, but this separation procedure and an infrared finish were too time consuming to compete with a gas chromatography method. An efficient Apiezon L grease column was found best for separation of the nine-component mono- and dinitrotoluene mixture. Recently, Knowles, Norman, and Radda (7) used Apiezon L for separation of the mononitrotoluene isomers, but they did not mention the separation of dinitrotoluene isomers. EXPERIMENTAL
Column Preparation. Chromosorb W (acid washed, flux calcined diatomaceous silica) was screened to 60- to 80mesh. Five grams of Apiezon L grease (J. J. Biddle & Co.) was dissolved in 150 ml. of benzene and then mixed with 45 grams of Chromosorb W. This mixture was added t o a 12 x 18 inch pan and rocked on a steam bath until the material became sticky. Then the mixture was stirred with a wire gauze until dry. Finally the free-flowing powder was dried under vacuum for 2 hours at 60” 6. A 12-foot
stainless steel column was packed while continuously vibrating the column. Helium mas used a t a flow rate of 112 cc. per minute (soap bubble method a t exit) with an inlet heater temperature of 260” C. The sample size was 2 pl. or less and the chart speed was 2 inches per minute. The column temperature was 213” C. Instrument. T h e Podbielniak Chromacon KO-9580 was used. This instrument was equipped with a hot wire detector and a 1-mv. recorder. Staridards. T h e mononitrotoluene isomers and 2-nitro-p-xylene (internal standard) were purified b y fractional distillation. T h e 2,6- and 2,4-dinitrotoluene isomers were purified by crystallization. Purity was determined by cryoscopy. These purified standards and the other dinitro isomers, exoept for 2,3-dinitrotoluene, were free of impurities when examined b y the gas chromatography method a t high sensitivity. The chromatogram of the 2,3-isomer was established from a reaction mixture known to contain this isomer by synthesis (3). Calculations area of isomerX Per cent isomer = area of standard weight standard 1 weight sample x -jjx 100
.
area of isomer F = area of standard
X
weight of standard
weight of isomer
Table 1.
Isomer
2-Nitrotoluene 3-Nitrotoluene 4-Kitrotoluene 2-Nitro-p-xylene 2,6-Dinitrotoluene 2,3-Dinitrotoluene 2,5-Dinitrotoluene 2,4-Dinitrotoluene 3,4-Dinitrotoluene 3,5-Dinitrotoluene
Retention Times Relative to 2,6-DNT 196' C. 213' c. 0.34 0.42 0.45 ...
0.34 0.42 0.45 0.57
1.29 1.33 1.59
1.25 1.32 1.53 1.62 1.69
1.OO
1.76 1.76
II.
Table
Retention Times
2-Nitrotoluene 3-Nitrotoluene 4-Nitrotoluene 2,6-Dinitrotoluene 2,3-Dinitrotoluene" 2,5-Dinitrotoluene 2,4-Dinitrotoluene 3,PDinitrotoluene 3,5-Dinitrotoluene
1 .OO
0
Calibration Factors
F
Standard Deviation of F
Number of Runs
Composition Range, %
0.991 0.959 1.005 0.844
0.0076 0.0218 0.0103 0.0085
13 13 13
9-24 2-6 10-40 5-20
:
13 . . e
0 i67
0.0350
0.0110 0.0750 0.0890
0.849 0.430 0.390
(retention time)a (base line width of chromatogram tangents)2 were 4300 plates for a 12-foot column at 213' C., based on the chromatogram of the 2,6-dinitrotoluene isomer. It was necessary to have a t least this efficiency for the desired separation. Special care was taken to avoid fines. Calibration factors were determined for each of the isomers us. the internal standard, 2-nitro-p-xylene, using peak height x width a t half peak height method of area computation. The factors, F , with reproducibility data are presented in Table 11. All the isomers except 2,3dinitrotoluene were included in the runs over the composition range shown in column 5. Small variations (5 to 10%) in these factors have been observed with a newly packed column and a replacement thermal conductivity cell. Values found for a synthetic blend of the isomers (in a concentration range, see Table 11, of interest for nitration studies) except 2,3dinitrotoluene using the factors in Table 11 were within =k0.4%.
The chromatograms in Figure 1 show some overlap in several cmes. However, the separation was adequate for obtaining quantitative results in the composition range of interest for nitration studies. During the development of the method, silicone grease gave a
0 .&3
9 9
0.3-1
5-30
13
1-3
Pure isomer not available.
DEVELOPMENT AND METHOD
The separation of mononitrotoluene and dinitrotoluene isomers is shown by the chromatograph in Figure 1. Data in Table I for re tention times of various isomers relative to 2,6-dinitrotoluene a t two column temperature levels indicate that the higher temperature gives the better separation. This better overall resolution a t higher column temperature is different from the usual gas chromatographic behavior. Theoretical plates calculated according to the formula,
13
I
A
8
16
~
0
TIME (MINI
Figure 1. Chromatograph uene isomers
of mono- and dinitrotol-
A.
2-Nitrotoluene 3-Nitrotoluene 4-Nitrotoluene D. 2,6-Dinitrotoluene E. 2,3-Dinitrotoluene F. 2,5-Dinitrotoluene G. 2,4-Dinitrotoluene H. 3,4-Dinitrotoluene 1. 3,S-Dinitrotoluene S. 2-Nitro-p-xylene (internal standard) Chart speed 0.5 inch per mln. B. C.
better separation of 2,4- and 3,4dinitrotoluene, but 3-nitrotoluene and 4-nitrotoluene were poorer. Improvements might be achieved by varying the amount of stationary liquid. The 10% by weight Apieeon L column packing recommended in this paper gave the separation of all isomers; whereas, the higher amounts of Apiezon L (20%) for commercial packings gave a poorer separation. Polar liquids or a selective liquid like 2,4,7-trinitrofluorenone (8) at low stationary liquid levels might give a more complete separation of all the isomers and still keep the elution times minimal. ACKNOWLEDGMENT
The authors thank S. RIP. Davis, Charles Maresh, and A. P. Paul for their interest and encouragement. Also, the authors thank Charles Pidacks for liquid partition chromatography studies.
LITERATURE CITED
(1) de E Beule, P., Bull. SOC. chim. Belg. (1) 42,27 (1933). (2) Chem. Eng. News 38, 29 (May 16, 1960). 19tiU). (3) Gibson, W. H., Duckham, R., Fairbairn, R., J. Chem. SOC.1922 121,270. J., (4) Holleman, A. F., Vermeulen, J. de Mc Moov, W. J., Rec. trav. chim. 33, I! (1914). (5) Ingold C. K., Lapworth, A,, Rothstein, E!., Ward, D., J . Chem. SOC. 1931 130, 1959. (6LAOne6, W. W., Russell, M., Zbid., 1947 YL.1.
(7) Knowles, J. R., Norman, R. 0. C., Rrtdda, 6. K., Ibid. 1980 4885. (8) Norman, R. 0. d., Proc. Chem. Soe. 1958, 151. (9) Pristera, F., Halik, M., ANAL.CHEM. 27, 217 (1955). (10) Roberts, R. M., Heiberger, P., Wathns, J. D., Browder, H. R., Kolbe, K. A., J . Am. Chem. SOC.80, 4285
(1968).
RECEIVED for review May 4, 1961. Accepted September 26, 1961. YOL. 33,
NO. 13,
DECEMBER 1961
@
1859
