(8) Harms, D. L., AKAL.CHEhf. 25, 1140 (1953). (9) Haworth, J. E., Grant, W. J., “Introduction t o Petroleum Chemicals,” H. Steiner, ed. pp. 135, 140, Pergamon, London, 1961. (10) Hewitt, G. C., Whitham, B. T., Analyst 86,643 (1961). (11) Holland, P. D., A. E. T. Research Laboratory, Rugby, private communication, August 1962. (12) Houwink, R., ed., “Elastomers and Plastomers, Vol. 111, Testing and Analysis: Tabulation of Properties,” Elsevier, .imsterdam, 1948.
(13) Keulemans, A. I. AI., Verver, C. G., “Gas Chromatography,” 2nd ed., Reinhold, New York, 1959. (14) Kline, G. M., ed., “Analytical Chemistrv of Polvmers.” Hinh Polvmers, V O ~12, . Interscience, -NEW YO&, Pt. I, 1959, Pts. I1 and 111, 1962. (15) Kruse, P. F., Wallace, W. B., ANAL. CHEM.25,1156 (1953). (16) .Lehmann, F. A., Brauer, G. M., Ibzd., 33,673 (1961). (17) Nelson, D. F., Kirk, P. L., ANAL. CHEM.34,899 (1962). (18) Nelson, D. F., Yee, J. L., Kirk, P. L., Microchem. J . 6 , 225 (1962).
(19) Pariss, W. H., Holland, P. D,, Brit. Plastics 33, 372 (1960). (20) Porter, R. S., Hoffman, A. S., Johnson, J. F., ANAL. CHEM.34, 1179 IIFl62\. \ - - - - I .
(21) Tyron, M., Horowitz, E., Mandel, J., J . Res. Natl. Bur. Std 55, 219 (1955). (22) Wake, W. C., “The Analvsis of Rubber ’ & Rubber-like Po1;mers.” Rlaclaren, London, 1958. (23) Zemany, P. D., ANAL.CHEM. 24, 1709 (1952). RECEIVEDfor review December 10, 1962. Accepted October 1, 1963.
Gas Chromatographic Determination of Alkyl Substituted Ureas R. W. REISER lndusfrial and Biochemicals Department,
E.
1. du Ponf de Nemours & Co., Wilmington, Del. R
This paper presents a new technique, direct gas chromatography, for the analysis of the subject compounds. Although these compounds are thermally unstable, they can b e chromatographed if the proper column packing and chromatographic conditions are used. The alkyl ureas can b e eluted from low loaded columns and glass beads are the most satisfactory solid support of those tested. Even supports made of silanized diatomaceous earth and fluorocarbon resins caused a fair amount of irreversible adsorption and/ or decomposition of the alkyl ureas. Carbowax 2 0 4 proved to b e the most satisfactory liquid phase of those tested. A 2-foot long column containing 0.5% Carbowax 2 0 4 on 60- to 80-mesh glass beads was used to separate and analyze isomeric mixtures of these compounds.
T
HE
STRUCTURE of the alkyl sub-
stituted ureas t o be discussed in this paper are’ Table I.
O
\
/ R
R
R
I1
/
s-c-s
R‘
O
‘I
\
H/N-c-x R
R / \€I
0
\
I/
lT-C--T\“?
/ R R \
0
I’
S-C-XH?
/
H‘ where R is methyl, ethyl, n-propyl, or iso-, sec-, or tert-butyl. The only published methods available for determining these compounds in-
?t-,
volve the color reaction with p-dimethylaminobenzaldehyde ( 2 ) . The direct colorimetric method is not selective and the method based on paper chromatographic separation and color development is time-consuming and difficult to reproduce. .k further limitation is that the urea must contain at least one primary amide group to react nith this reagent. Gas chromatography offers a rapid, selective, and reproducible method for determining the subject alkyl ureas. At the outset of this study i t via? recognized that these compounds might be too unstable thermally to be subjected to gas chromatographic analysis. The mode of dissociation of alkyl ureas at elevated temperatures has been described in the literature (6), and sereral are known to decompose a t their melting points. Furthermore, there was no information available in the literature regarding boiling points or sublimation temperatures for most of these compounds. However, it has now been shown that, by the proper choice of
Results of Tests Using Various Liquids and Solid Supports
2OYc SE-30 (?ilicone gum
Qualitative Result Compounds did not elute (column held at upper temperature for 20 minutes) Silanized Chromosorb W, 60- t o 80-mesh Compounds did not elute (column held at upper temperature for 20 minutes) Silanized Chromosorb W. 60- to 80-mesh Peak tailing and relatively low peak areas
15y0Apiezon L grease 2 0 7 ~S E - ~ O 20‘30 SE-30 0 2% SE-30 0.270 Polyphenyl ether OS-138 3 5 Uiethrlene glycol succinate ?% Epon IO01 resin 2 5 Carbon ax 20-hl 2% CarboTT-au 20-hI 0 j r c Carbon ax 20-hI
Fluorocarbon resin, 40- to 60-mesh Chromosorb W, 60- to 80-mesh Chromosorb P, 60- to 80-mesh Glass beads, 60- to SO-mesh Glass beads, 60- t o 80-mesh Chromosorb W, 80- to 100-mesh Silanized Chromosorb W, 80- t o 100-mesh Fluorocarbon resin, 40- to 60-mesh Hilnnized Chromosorb W, 80- to 100-mesh Glass beads, 60- to 80-mesh
Liquid Phase lornQCarboys.; 20-1cI 20y0 Carbon a\ ‘20-11
: rubber)
96
ANALYTICAL CHEMISTRY
Support Fluorocarbon resin, 30- to 60-mesh
Peak tailing and relatively low peak areas peaks obtained S o peaks obtained S o peaks obtained No peaks obtained No peaks obtained Compounds eluted but relatively low peak areas obtained Compounds eluted but relatively low peak areas obtained Compounds eluted; peak areas somewhat low Compounds eluted : no evidence of irreversible adsorption or decomposition So
n
Ti
Column 1
1 1
2 % 'CARBOWAX' 20M CIN 80-100 MESH DIATOPORT S
A u / L A
minimize residence time in the column and long enough t o give sufficient resolution. A relatively high flow rate of 100 cc. per minute was used to minimize residence time both in the vaporizer and the column. The vaporizer temperature was maintained at 290" C. and the detector block at 230" C. When columns were tested for the first time. the temperature was programmed from 100" to 220" C. at 10" per minute.
Column 3
2 % 'CARBOWAX' 20M ON 4 0 - 6 0 M E S H COLUMPAK T
z
a 0
0
v) W
1
2
a
3
4
5
6
7
3
8
0 1 2 3 P 4 5 6 7 8 9 J 1 0 1 1 1 2 L
TIME (minuter)
TIME (minuter)
RESULTS AND DISCUSSION Column 4 Column 2
2% 'EPON 001' RESIN ON 60-80 M E S H
3
Preliminary studies indicated that the optimum column would be one containing a polar liquid on an inert support a t a relatively low loading. Carbowax 20-M was the most satisfactory liquid of those tested and glass beads appeared to be the most inert support of those tested. Each of the columns listed in Table I was tested by injecting 3 pl. of the butyl urea test mixture. Figure 1shows several chromatograms of the butyl urea test mixture using various types of supports and liquid phases. The order of elution in all cases was terlbutyl, sec-butyl; isobutyl, and n-butyl. Each column was maintained a t 175" C. Column 1 contained 2Y0Carbowax 20-1vI on 80- to 100-mesh Diaport S (F&M Scientific Corp.) which is a silanized diatomaceous earth support. Column 2 was packed with 2y0 Epon 1001 resin on 60- to 80-mesh Diatoport S. Epon 1001 is a polar epoxy resin which has been recommended for covering active site. on the support (3). Column 3 contained 2% Carbowax 20-Mon 40- to 60-mesh Columpak T (Fisher Scientific Co.) which is a support made of Teflon 6 (registered trademarkof E. I. du Pont de Nemours & Co. for its fluorocarbon resins). Column 4contained 0.57, Carbowax 20-M on 60- to 80-mesh glass bead.. Because of differences in the bulk density of the supports, 0.5% liquid on
0.5% 'CARBOWAX' 20M ON 60-80 MESH GLASS BEADS
lh
hz
2 . 6 d0 1 2 3 4 5 6
40 1 2 3 4 5 6 TIME (minJtes)
TIME (minuter)
Comparison of several types of supports and liquid phases
Figure 1 .
Each column was 2 feet long and maintained a t 175' C. with CI 100 cc./minute flow raie. A test mixture consisting of equal amounts of each of the four monosubstituted butyl urea isomers was used
column packing and chromatographic conditions, these alkyl ureas can be chromatographed and isomeric mixtures can be separated and malyzed. I t was established that these compounds chromatograph unchanged by trapping several fractions and el- aracteriaing them by infrared spectrometry and melting point. Unsubstituted urea and the phenyl-substituted ureas were found to be too unstable thermally to be analyzed by this method. EXPERIMENTAL
Apparatus. An F&hI Model 720 gas chromatograph equipped with a 1-mv. Brown recorder and thermal conductivity detector was used in this work. Helium, dried with type 5A Molecular Sieve, was used as carrier gas. The columns vere constructed from Iir-inch o.d., llrinch i.d. stainless steel tubing. The volumn packings were made by dissolving the liquid phase in an appropriate low-boiling solvent and evaporating the solvent
,not 240
,
,
,
,
,
,
260
280
300
320
340
360
TEMP
PC)
VAPORIZER
,
,
with constant stirring while it was in contact with the support. The columns were packed using mechanical vibration The glass beads (Microbeads, Inc., Toledo 6, Ohio) contained iron particles which were removed with a magnet. Procedure. Several test mixtures were prepared to show the utility of this technique for qualitative and quantitative analysis. A mixture containing 20 mg. per ml. of tert-, sec-, iso-, and n-butyl ureas was used to evaluate several columns. In all cases, 60 to 80 pg. (3 to 4 pl.) of each component was injected from a methanol solution using full instrument sensitivity. The columns tested were 2 feet in length. This was short enough to
2,
380 400
Figure 2. Determination of the optimum vaporizer temperature for n-butyl urea
I
0
1
l
2
I
l
3 4 5 TIME (minuleo)
l
l
6
~
7
i
8
Figure 3. Chromatogram of methyl, ethyl, n-propyl, and n-butyl ureas Carbowox 2 0 4 glass bead column a t 175' C.
VOL. 36, NO. 1, JANUARY 1964
97
Table II. Quantitative Comparison of Peak Area Response Obtained on Chromatograms Shown in Figure 1
Column DO.
Table
111.
Sample size, MI.
Relative
tertButy1
Peak area integrator counts sec-Butyl Isobutyl n-Butyl
Retention Times
(0.5% Carbowax 20-M-glass bead column at 175" C., 100 cc. per minute flow rate) Relative Alkyl substituted urea retention time n-Butyl 1 .00 Isobutyl 0.75 n-Prop 0.70 Methy? 0.53 Ethvl 0.53 sec-Bu tyl 0.55 1.3-Dimethvl 0.30 te&Butyl " 0.2s 1,l-Dimethyl 0.16 Trimethyl 0.091
glass beads gives approximately the same amount of column liquid as 2% on the other supports ( 1 ) . Table I1 lists the areas of the four butyl ureas obtained from the chromatograms shown in Figure 1. It can be seen t h a t column 4 gave the highest response for alkyl ureas. The low areas obtained with column 3 us. column 4 indicate that Columpak T causes a fair amount of irreversible adsorption and/or decomposition of these compounds. Likewise the low areas obtained with Column 2 relative to Column 1 indicate that Epon 1001 is less efficient than Carbowax 20-M in covering active sites on the support. Peak area %
Total
was very close to weight % for several test mixtures analyzed on column 4, whereas erratic results were obtained on the other columns This type of column has been used for the analysis of high molecular weight alcohols and hydrocarbons (4) and should be generally useful for highboiling polar compounds. Figure 2 shows the curve obtained m-hen vaporizer temperature is plotted against peak area. These data were obtained by carefully injecting 5 11. of a 20 mg. per ml. solution of n-butyl urea at the various vaporizer temperatures, and measuring the peak area n i t h a Disc Integrator. Each point on the curve represents the average of three runs. .4t the lower vaporizer temperatures volatilization was not complete, and at higher temperatures decomposition became excessive. The optimum vaporizer temperature appears to be 270" t o 290" C. Since n-butyl urea appeared to be the least volatile (highest retention time) of the compounds studied, its optimum vaporizer temperature was used to assure complete vaporization of the mixtures. Figure 3 shows a chromatogram of a mixture of methyl, ethyl, n-propyl, and n-butyl ureas. Methyl and ethyl are not separated and together produce the first peak. This chromatogram was
CH;
Table IV. Correlation of Area Per Cent With Weight Per Cent
Isomer tert-Butyl urea sec-Butyl urea Isobutyl urea n-Butyl urea Tetramethyl urea Trimethyl urea 1,l-Dimethyl urea 1,3-Dimethyl urea Methyl urea
m7t. 7, added
Area %
19.9
found 24.6, 25.0 27.3, 26.7 25.5, 2 5 . 4 22.6, 2 2 , s 19.3, 19.2 20.9, 20.4 20.0, 20.4 20.3, 2 0 , 3
20.1
19.5) 19.5
25.4 25 .O
24.8
24.8
19.8 20.2 19.9
obtained on the Carbowax 20-11 glass bead column at 175" C. Figure 4 shows separation of five methyl-substituted ureas. I n this case the column temperature was held a t 80" C.for 4 minutes for the elution of tetramethylurea, and then programmed to 180" C. a t 10" per minute. The retention temperatures were 140" C. for trimethylurea, 160" C. for unsymmetrical dimethylurea, and 180" C. for symmetrical dimethylurea. Methylurea eluted after the upper temperature had been reached. Table TI1 gives the relative retention times obtained from separations on t h e Carbomax 20-M glass bead column. The absolute retention times were not reproducible because of the high flow rate and difficulties in reproducing t h e column packing. The reproducibility of the relative retention times was about 15%. The analytical utility of this gas chromatographic method is demonstrated by the data in Table IV which shorn the relationship between weight % ' added and area % found for the butyl- and methyl-substituted ureas. These data were obtained from chromatographic separations on the Carbowax-glass bead column. Areas were measured with a Disc Integrator. ACKNOWLEDGMENT
1
0
II CH N-C-NHz 3-H
Figure 4.
Separation
of the methyl substituted ureas
Carbowax 20-M glass bead column; temperature programmed from 80' to 180" C. at 1 Oo/minule VU
0
ANALYIILAL L n C M I D I K l
The author thanks R. L. Dalton and J. J. Kirkland for their encouragement and helpful suggestions. LITERATURE CITED
(1) Ashley, J. W., Reilley, C. S . , Hur-
witz, P., Rogers, L. B., ANAL.CHEM. 34, 1539 (1962). ( 2 ) Cline, R. E., Fink, R. hl., Ihid., 28, 47 (1956). (3) Coulson, D. 31. e t al., Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Paper No. 12, 1962. (4) Nikelly, J. B., -4s.4~.C H E x 34, 472 (1962). (5) Shaw, W. H. R., Grushkin, B., J.Am. Chem. SOC.82, 1022 (1960). RECEIVEDfor review May 2, 1963. Accepted October 14, 1963.
