sucrose octa-acetate column at 195" C for 1 hour. The flow rate of carrier gas was checked by both the soap bubble method and "Fisher Wet Test" gas meter. Separations were also checked on a n Aerograph Model 90-P3 gas chromatograph with filament detector, a Perkin-Elmer Model 154C with thermistor and the departmental Gow-Mac 4W2 gas chromatographs. Similar curves were obtained on all three instruments. RESULTS AND DISCUSSION The theoretical plate (n) requirement of each particular separation has been calculated according t o the method of Kaiser ( 4 ) and defined as: n = 5.54
(5J
(1)
where t d r = retention time, (uncorrected), measured in mm or seconds, and blI2 = peak width a t half height, measured in m m or seconds. The minimum detectable quantity of sample ( M D Q ) is defined as the quantity required to produce 0.1-mV signal o n a I-mV recorder, when the sensitivity setting of the gas chromatograph is 1, MDQ
=
x
(mg sample) (wt sample) (0.1 mV) (2) (sensitivity of gas chromatograph) (height of peak in mV)
most efficient in the elution and separation of formaldehyde from methanol and water as compared to other substrates tested. Sucrose octa-acetate, 15 wt %, on Columpak T gave the lowest tdr/bl,2values (4.9 a t 93" c and 4.1 a t 97" C), the smallest number of theoretical plates (135 a t 93" C a n d 92 a t 97 " C), and the greatest sensitivity (MDQ-formaldehyde = 0.0020 mg at 93 " C and 0.0009 a t 97" C ) of all the columns tested. The retention time of formaldehyde was 5.2 minutes a t 93°C (Figure 1) and 4 minutes a t 97" C. The substrate for this column could be easily loaded o n its support up to 20 by weight, and still pack without difficulty. It could also be used a t operating temperatures less than 93" C , and was stable over a wide temperature range. As compared t o sucrose octa-acetate on Columpak T, the tdr/blr2 values for formaldehyde with 10 wt Ethofat 60/25 on Columpak T at 115" C , with 20 wt P E G A o n Celite a t 110" C (3), and with Porapak N a t 110" C were 5.4, 5.7, and 14.5, respectively. Similarly the smallest number of theoretical plates were, respectively, in that order 160, 179, and 1162. MDQ-formaldehyde, in mg for Ethofat 60/25, and Porapak N were 0.0525 and 0.0441, respectively. ACKNOWLEDGMENT
Sucrose octa-acetate heated a t 195" C for 1 hour proved
The authors express their appreciation to K . J. Bombaugh, Mine Safety Appliances, Pittsburgh, Pa., for helpful suggestions.
(4) R. Kaiser, "Gas Phase Chromatography," Vol. 1, Butterworth and Co., New York, 1963, p. 20.
RECEIVED for review May 12, 1967. Accepted June 23, 1967. Work supported by National Research Council of Canada, Ottawa, G r a n t A-1125.
Separation and Determination of Trinitrotoluene Isomers by Gas Chromatography D. G. Gehring and J. E. Shirk Eastern Laboratory, Explosices Department, E. I. du Pont de Nemours & Co., Gibbstown, N . J ANALYTICAL METHODS were required to monitor the individual unsymmetrical T N T isomers in symmetrical 2,4,6-TNT. An early method developed by Halfter ( I ) was based upon the selective reaction between sulfite ion and one of the nitro groups of a n unsymmetrical T N T molecule. This method determines the total amount of unsymmetrical T N T but fails to distinguish between the individual unsymmetrical isomers. Subsequently, methods utilizing infrared spectrometry ( 2 , 3), thin layer chromatography ( 4 ) , and paper chromatography ( 5 ) were reported. However, these methods generally lacked sensitivity and/or quantitative accuracy at low concentrations. In due time, gas chromatographic ( G C ) methods appeared which separated the individual dinitrotoluene (DNT) isomers (6, 7), and recently a G C method was reported which de(1) G . Halfter, 2. Anal. Chem., 128, 23 (1947). (2) F. Pristera, Appl. Spectry., 7, No. 3, 115 (1953). (3) F. Pristera, M . Halik, A. Castelli, and W. Fredericks, ANAL. CHEM., 32,495 (1960). (4) S. K. Yasuda, J . Cliromurog., 13,( I ) , 78 (1964). ( 5 ) V. Ettel, S. Pospilsil, and 2. Deyl, Cliem. Lisry, 52, 623 (1958). (6) E. Camera, D. Pravisani, and V. Ohman, Explosicsroffe, Nr 9,
237 (1965). (7) J . S. Parsons, S. M. Tsang, M. P. DiGiairno, R. Feinland, and R . A. L. Paylor, ANAL. CHEM., 33, 1858 (1961).
termines 2,4,6-TNT in castable explosives containing mixtures of T N T and other explosive additives (8). We have succeeded in separating the individual T N T isomers (except for the 2,3,6- and 2,4,6-TNT pair) by gas chromatography. Now it is possible to determine quantitatively the individual components of a n isomeric mixture and to monitor 2,4,6-TNT for low concentrations of unsymmetrical isomers. Also, D N T isomers were separated and may be individually determined together with the T N T components. EXPERIMENTAL Apparatus. All work was performed using a n F & M Scientific Corp., Division of Hewlett-Packard, Model 810 dual-column gas chromatograph equipped with a thermal conductivity filament detector and a 1-mV recorder. Two 9-fOOt X 0.25-inch stainless steel columns (one serving as reference) were loosely packed with 10 DC-LSX-3-0295 silicone copolymer (Applied Science Laboratories Inc., State College, Pa.) o n 80-90 mesh Anakrom-ABS support (Analabs Inc., Hamden, Conn.). Both columns were conditioned in the chromatograph for 2 hours a t 250" C oven ~~
~
(8) M. L. Rowe, J . Gus Chromatog.,4, 420 (1966). VOL. 39, NO. 1 1, SEPTEMBER 1967
1315
A
C
1
Programming 8°C/minute
1
4
lsolhermal
225T
15 m i n u t e s from 2 2 5 T
Figure 1. Gas chromatogram of a synthetic mixture of TNT isomers D. 2,4,5-TNT
A. 2,4-DNT B. 2,3,6- and 2,4,6-TNT C. 2,3,5-TNT
E. F.
2,3,4-TNT 3,4,5-TNT
temperature. Helium carrier gas was used a t a flow rate of 200 cc per minute during column conditioning and in all subsequent separations. Both the detector and injection port temperatures were 225" C, and the detector bridge current was maintained a t 170 mA. Reagents. The 2,4,6-TNT was D u Pont Laboratory refined material. The 2,3,4- and 2,4,5-TNT isomers were laboratory synthesized and purified by selective solvent extraction (5). Laboratory nitration of rn-nitrotoluene gave a product rich in unsymmetrical T N T and DNT isomers from which the 2,3,6-, 2,3,5-, and 3,4,5-TNT isomers and 2,3-DNT were separated and collected in pure form by gas (9) C. Conklin and F. Pristera, "Preparation and Physical Proper-
ties of Di- and Trinitrotoluene Isomers," Picatinny Arsenal Tech. Rept. No. 2525 (1958), Picatinny Arsenal, Dover, N. J.
Table I. Comparison of Calculated Dipole Moments with Relative Retention Times of TNT Isomers Dipole moments TNT isomer RRTa (Debye units) 1.22 1.22 1.35 1.41 1.51 1.60
2,4,6-TNT 2,3,6-TNT 2,3,5-TNT 2,4,5-TNT 2,3,4-TNT 3,4,5-TNT a
F
0.37 3.90 4.27 4.45 8.35 8.53
Relative to 2,4-DNT.
c
P r o g r o r n r n i n g -1 8'C / m i n u t e 225T
Isothermol
4
15 minutes from 225°C
Figure 2. Gas chromatogram of DNT and TNT isomers A . 2,6-DNT 8. 2,5-DNT C. 2,4-DNT D. 2,3-DNT (broken line)a E. 3,5-DNT
F. 3,4-DNT G. 2,4,6- and 2,3,6-TNT H. 2,3,5-TNT I. 2,4,5-TNT J . 2,3,4-TNT
Indicating peak location of 2,3-DNT if present in sample chromatography. The other five D N T isomers were purchased from K & K Laboratories Inc., Jamaica, N. Y . Identities and purities of all the isomers were established from infrared (5) and N M R spectra. N M R spectra were obtained for each T N T isomer (except for 3,4,5-TNT) and will be the subject of a separate report. Calibration and Analysis. Calibration standards were prepared by weighing into three successive 25-ml volumetric flasks 0.050, 0.100, and 0.200 gram of each component to be determined and diluting to volume with reagent grade acetone. The standard solutions were found to be stable for at least 3 months when stored in air-tight containers out of direct sunlight. G a s chromatograms were obtained by injecting 15 pl of each standard solution and programming from 100" C t o 225" C a t 8" C per minute, then maintaining 225" C (isothermal operation) until all components were eluted. The attenuator was maintained at X1 throughout the separation and the recorder chart speed was 0.5 inch per minute. Plots of peak heights cs. concentrations were linear for all components. Crude and refined TNT sample solutions were prepared by weighing 5.00 grams of sample into 25-ml volumetric flasks and diluting to volume with acetone. Fifteen p1 of each sample solution was chromatographed as above, and the concentration of each component was determined from the appropriate calibration curve.
Table 11. Laboratory Prepared Synthetic Mixtures
RESULTS AND DISCUSSION
MIXTURE 1
T h a t T N T isomers can be reproducibly gas chromatographed must be attributed to the relatively little-known fact that 2,4,6-TNT and, presumably, the other isomers, can be safely distilled at reduced pressure ( I O , I ] ) . To check for possible decomposition during GC analysis, the temperatures of the injection chamber and detector initially were set at 170" C
Component
Weight % added
Weight found
A
2,4-DNT 2,3,4-TNT 2,4,5-TNT
2.00 1 .oo 1.50
1.96 1.02 1.53
-0.04 +0.02 +0.03
2,4-DNT 2,3,4-TNT 2,4,5-TNT
MIXTURE 2 0.50 0.52 0.25 0.27 0.25 0.25
+0.02 +0.02
13 16
ANALYTICAL CHEMISTRY
...
(IO) A. F. Belayve and A. A. Yuzefovich, Dokl. Akrrd. Nmik S.S.S.R., 27, 133 (1940). ( 1 1) M. Giua, Chemica Delle Sostange Explosive, Hoelpi, hlilano, 1919.
Table 111. Percentage Concentration of Impurities in Typical Samples of Production T N T CRUDE TNT San1ple
2.5-DNT
2,4-DNT
1
0.02 0.02 %) in any production samples of TNT which were chromatographed. This observation is consistent with the theoretically expected TNT isomeric distribution as depicted in a toluene nitration chart which appears in reference (13). (13) P. de Beule, Bull. SOC.Cliim., Beiges, 42,27 (1933).
ACKNOWLEDGMENT
The authors thank D. N. Thatcher of Eastern Laboratory, Explosives Du Company, for supplying
TNT samples and for much information. Frank Pristera of Picatinny Arsenal, Dover, N. J.9 supplied Samples Of 23334-and 23435-TNT3 and we are grateful to h i m . RECEIVED for review April 14, 1967. Accepted June 14, 1967.
Quantitative Gas Chromatographic Determination of Ethanolamilnes as Trifluoroacetyl Derivatives L. E. Brydial and H. E. Persinger Union Carbide Corp., Chemicals and Plastics, South Charleston, W. Va.
COMMERCIAL ETHANOLAMINES are mixtures of mono-, di-, triethanolamine, and low concentrations of various impurities, Determination of the individual components of ethanolamine mixtures is usually made by chemical methods which are nonspecific and, for the most part, inaccurate. Monoethanolamine can be determined by the Van Slyke manometric method (1) or by the colorimetric procedure of Critchfield and Johnson (2). Diethanolamine is usually determined by a method which is based o n the reaction of mono- and diethanolamine with periodic acid (3). Triethanolamine is determined by a nonaqueous titration after the mono- and diethanolamine have been converted to less basic amides by reaction with acetic anhydride. The Van Slyke and periodate methods must be followed precisely to obtain reproducible results. Triethanolamine is also reported to react with periodate under certain conditions (3). The major limitation of the Critchfield and Johnson method is that it uses reagents which contain both di- and triethanolamine. The results of the triethanolamine determination are affected by the particular solvent and indicator employed, and show a n inverse relationship to the amount of acetic anhydride added ( 4 ) . The sum of the individual determinations for the components in ethanolamine mixtures usually totals more than 100 %. The present investigation for more reliable analytical methods for this important class of compounds was prompted by these shortcomings. In a n evaluation of direct gas chromatographic methods, the most favorable results were obtained using a column of 5 % Carbowax 20M on Haloport F. However, analysis by direct procedure is complicated by the strong hydrogen Present address, Union Carbide Corp., Chemicals and Plastics, Bound Brook, N. J. 08805 (1) E. F. Hillenbrand, Jr., and C. A. Pentz, “Organic Analysis” Vol. 111, Mitchell, Ed., Interscience, New York, 1956, p. 148. (2) F. E. Critchfield and J. B. Johnson, ANAL.CHEM.,28, 430 ( 19 56). (3) G. F. Smith, Jr., “Analytical Applications of Periodic Acid
and Iodic Acid and Their Salts”, 5th ed., G. Frederick Smith Chemical Co., Colurnbus, Ohio, 1950, p. 99. (4) L. E. Brydia and H. E. Persinger, unpublished work, Union Carbide Corp., August 1964. 131 8
ANALYTICAL CHEMISTRY
bonding character of the ethanolamines which causes excessive peak tailing. This prevents a n exact quantitative analysis. Because direct gas chromatographic procedures were not entirely satisfactory, chromatography of derivatives was investigated. Trifluoroacetic anhydride has been widely used to convert nonvolatile amino acids (5-8) and amines (9-11) to volatile N-trifluoroacetamide derivatives, but this reagent has not been used for the analysis of alcoholamines. In fact, very little quantitative analytical data o n mixtures of amines using this reagent have been reported. This paper describes a gas chromatographic procedure for the quantitative determination of ethanolamines as their trifluoroacetyl derivatives. EXPERIMENTAL
Apparatus. An F and M Model 810 gas chromatograph equipped with dual columns and thermal conductigty detector was used. The detector was equipped with w-2 filaments and was operated at a current of 185 mA. The injection port and detector were maintained at 250” C, and the column was operated isothermally at 172” C. Helium was used as carrier gas a t a flow rate of 30 ml per minute. Chromatographic Columns. The columns were aluminum, 5 feet long with 0.25-inch 0.d. The columns were packed with 5 z neopentylglycol succinate (F and M Scientific Corp., catalog L P 93) on 60- to 80-mesh Chromosorb-G (Johns-Manville Products Corp.). Chemicals. Trifluoroacetic anhydride was obtained either from Eastman Kodak (catalog 7386) or Matheson, Coleman and Bell (catalog TX 1285) and was used as received. Monoethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA) were products from the Union Carbide Corp. (5) W. M . Lamkin and C. W. Gehrke, ANAL.CHEW.,37, 383 (1 965). (6) P. A. Cruickshank and J. C. Sheehan, Zbid., 36, 1191 (1964). (7) K. Blau and A. Darbe, J . Cliromarog., 17,445 (1965). (8) S. Makisumi and H. A. Saroff, J . Gas Ckrornarog., 3, 21 (1965). (9) W. J. A. Vanden Heuvel, W. L. Gardiner, and E. C. Horning, ANAL.CHEW,36, 1550 (1964). (10) R. A. Morrissette and W. E. Link, J . Gas Chromatog., 3, 67 ( 1 965). (11) W. H. McCurdy, Jr., and R. W. Reiser, ANAL.CHEM., 38, 795 (1966).
