tative (or in fact qualitatively definitive) calculations can be made. Gas liquid chromatographic separations offer a convenient tool for the study of isotope effects in solution. Both more extensive, and more importantly, more precise data than that presented here are needed for a n unambiguous theoretical treatment. It is to be hoped that the latter can be obtained by the use of capillary columns at low temperatures. Increased resolution is to be expected under these conditions perhaps even to the point of allowing the temperature coefficient of the CzHsD/CzH6system to be measured. At low enought temperatures one might also hope to separate equivalent iso-
mers-e.g. 1,l- and l,2-C2HlD2-in view of significant vapor pressure differences between such molecules (8). Another possible advantage is that effects caused by interactions with the solid support should be minimized with the use of such columns. LITERATURE CITED
(1) Bigeleisen, J., J . Chem. Phys. 34, 1485
(1961). (2) CartEni, G. P., in “Gas Chromatography, M. Von Swaay, ed., p. 221, Butterworths, London, 1962. (3) Falconer, W. E., Cvetanovii., R. J., ANAL.CHEM.34, 1064 (1963). (4) Gant. P. L., Yang, K., J . Am. Chem. SOC.86, 5063 (1964).
( 5 ) “Handbook of Chem. & Phys.,” Chem.
Rubber, 35th ed., p. 2196, Cleveland, Ohio. - ~~. ..
(6) Porter, P. E., Deal, C. H., Stross, F. H., J . Am. Chem. SOC.78,2999 (1956). (7) Root, J. W.. Lee, E. K. C.. Rowland, ‘ F. S.. Science ’143. 678 (1964j. (8) VahHook, W. A., ( a j J . Chem. Phys. 40, 3727 (1964); ( b ) unpublished data, 1964. RECEIVEDfor review October 14, 1964. Accepted January 25, 1965. Work supported in part by the National Science Foundation and in part by the Petroleum Research Fund administered by the American Chemical Society. One of us (M. E. K.) was a participant in a National Science Foundation Summer Undergraduate Research Program at The University of Tennessee in 1964. Conversations with Sayeed Akhtar were helpful.
Identification of Some Oxygenates in Automobile Exhausts by Combined Gas Liquid Chromatography and Infrared Techniques C. F. ELLIS, R. F. KENDALL, and B. H. ECCLESTON Bartlesville Petroleum Research Center, Bureau of Mines,
A method for identifying certain oxygenates in automobile exhausts by gas liquid chromatography with confirmation b y infrared spectra is described. The oxygenates were separated from exhaust gases by scrubbing solution of NaHS03. with a 1% Then, oxygenates which eluted ahead of water were separated from the solution in a preparatory column. The carbonyls indicated in the chromatograms were derived from the thermal decomposition of the bisulfite complexes of these compounds in the chromatographic column. The eluted oxygenates were collected in a cold trapping needle and charged to an analytical GLC unit employing thermal conductivity detection. A chromatogram was thus obtained, and the individual components indicated in the sample were collected in separate plastic bags and transferred to a 10meter infrared cell for confirmation of the GLC identifications. Acetaldehyde, propionaldehyde, isobutyraldehyde, n-butyraldehyde, acetone, methyl ethyl ketone, methanol, and ethanol were present. Acrolein cannot b e detected by this method. After identification of the oxygenates present, GLC analyses employing flame detection were made directly upon the scrubber solutions and also on preparatory column effluents.
Q
U. S . Department of
UALITATIVE and
the Interior, Bartlesville, Okla.
quantitative analyses of the oxygenated compounds in automobile exhaust gases are needed in air pollution studies. A GLC qualitative analysis has been reported for exhaust gases produced from n-hexane and isooctane fuels (7) and colorimetric quantitative methods have been developed to determine acrolein (6), formaldehyde (5), crotonaldehyde ( I ) , and total aliphatic aldehydes (2). Quantitative analyses for classes of oxygenates and for formaldehyde (6) and a qualitative analysis for carbonyls in exhausts have been reported wherein acetaldehyde, acetone, methyl ethyl ketone, acrolein, and crotonaldehyde were detected (4). Hughes and Hurn (7) have shown that GLC techniques are not satisfactorily applied to cold trap condensates of exhausts which include interfering hydrocarbons. Thus, a separation of the oxygenates from the hydrocarbons was made by scrubbing the exhausts with either water or sodium bisulfite solution. The identification of the oxygenates was made from infrared spectra of fractions recovered from GLC separation of the oxygenates from the bisulfite solution. This work was undertaken to demonstrate the feasibility of obtaining confirmed GLC identifications of some of the oxygenates present in automobile exhausts produced from a regular grade gasoline.
APPARATUS A N D MATERIALS
Sampling Equipment. The exhaust gas used as a sample was produced using a late model light sedan equipped with a 283-cubic-inch V-8 engine a n d operated on a chassis dynamometer. T h e fuel used was a regular grade gasoline. The glass scrubbing train used to collect the oxygenates from a n exhaust sampling stream consisted of an opentube, water condensing trap followed by three scrubbers each using a Corning gas dispersion tube with extra coarsefritted cylinder immersed in a 1% solution of sodium bisulfite. The glass train was 23 cm. high, 25 mm. in outside diameter for the open tube trap, and 17 mm. in outside diameter for the scrubbers. Ice baths were provided for the trap and the three scrubbers. The scrubbed exhaust gas was collected in an evacuated 35-liter receiver for volumetric measurement. A trapping needle, shown in Figure 1, was used t o collect the oxygenates in the effluent of the preparatory GLC unit by condensation a t liquid nitrogen temperature. This facilitated transfer of the oxy enates to a custom-built analytical b L C unit to obtain GLC identifications and to collect individual compounds for infrared confirmation. Plastic bags of approximately 1.5liter capacity were used to collect the effluents from the GLC units for transfer to the I R long-path cell or to another GLC unit. The bags were made of 200-mil Tedlar, a polyvinyl fluoride VOL. 37,
NO. 4,
APRIL 1965
51 1
GC-2
froction collector
0 /Swogelok
connecfor
f-$..-
Luer-lok
Swagelok connector Tygon tubing
Connectors
Luer -lok
Luer-lok
Stopcock
stoiniess steel tubing
$lo
'w
a
\
A
S i l a s t i c plug-,
Septum-,
I
M
Sideport injection n e e d l e (.04I'II.D.)
0
Silostic plug
Helium
T o GLC column
Figure 2. Figure 1. unit
Trapping needle for preparatory
film, and equipped with stainless st'eel and fittings of D u Pont Teflon so that the contents of the bags were in contact only with the plastic film, Teflon, and stainless steel. GLC and Infrared Equipment. A preparatory unit consisting of a Beckman GC-2 chromatograph with a column inch in diameter and 2 feet in length conbaining 9 wt. yo Carbowax 600 on unsized Teflon was used for separating oxygenates from water. h custom-built analytical GLC unit employing a thermal conductivity detection system was used t'o separate the oxygenates obtained from the preparatory GLC unit. This unit contained a 1l4-inch by 20-foot column of 9 mt. 7, Carbowax 600 on unsized Teflon. A flame ionization unit with a column 3 l I 6 inch in diameter and 2 feet in length which contains 9 wt. yo ,Carbowax on unsized Teflon was used with a FIAD 512
o
ANALYTICAL CHEMISTRY
Injection system for thermal conductivity GLC unit
GLC
hydrogen flame detection unit. The column was housed in a Perkin-Elmer vapor fractometer. Two Beckman 10-meter infrared cells, a reference and a sample cell, were used with a Beckman IR-7 spectrophotometer. PROCEDURE
The point of sampling from the vehicle's exhaust system was about 2 feet from the front end of the exhaust pipe and about 6 inches ahead of the muffler, About 2 feet of lI4-inch 0.d. stainless steel tubing heated to approximately 150" F. with a heating tape to prevent water condensation waq used as the sampling line. Each of the three gas-dispersion scrubbers was charged with 3 ml. of 1% sodium b i d f i t e solution, and then all four units of the scrubbing train were placed in icewater baths. The exhauat gases were
drawn through the scrubbing system into the evacuated vessel. The scrubbing of exhaust gases for this work was done with two modes of engine operation : a standardized cycle mode of various cruise speeds, accelerations, decelerations, and idle conditions ( 0 ) ; and a 40-1lLp.h. cruise mode. During a cycle of engine operation, exhaust gases are produced at varying rates and t'he flow through the scrubbing system will vary in some manner with the rate of exhaust gas production. An average sampling rate of 1 =t 0.1 liter per minute was maintained by occasional adjust'ment of the regulating value on the receiver for both the cycle and the 40-m.p.h. cruise modes of operation. A closely representative, or proportional, sample of gases for t,he cycle mode cannot be obtaincd in this way. However, g a m from all ])arts of the cycle were sampled, and for the qualitative st,udy this is satisfactory. The total amount of gases collected was 100 i 10 liters and the time re-
quired for sampling was about 2 hours. Only two gas-collecting vessels were required, one being evacuated for use
17u rn l COMPOSITE OF FOUR TRAPS
870 0
1100
IO00
1775 1725 OPEN-TUBE,WATER CONDENSING TRAP
80 70 C
-
w
1100 No I N o H S O 3 SCRUBBER
Z 4 50
1000
1L L 2 L l - J I
IZ:m 40
1775
1725
HOO
io00
No 2 No H SO3 SCRUBBER
80
70
1775
I100
1725
1000
No 3 N o H S O 3 SCRUBBER
90
1775
1100
1725
1000
WAVENUMBER, cm-1
Figure 3. Selected parts of infrared spectra of various preparatory column effluents
45
35
40
while the other was in use. Following the scrubbing operations, the volumes of the solutions contained in the individual units of the scrubbing train were measured and the separate solutions were filtered, placed in small dark-glass containers, and stored in a refrigerator a t 0' to 5' C. The preparatory column was charged with 2.5 ml. of scrubber solution injected at a rate of 1 ml. per minute. The preheater of the preparatory unit was operated a t 125' C. and the column a t 80" C. The flow rate of the helium carrier gas was 40 ml. per minute. Water appeared in the effluent about 10 minutes after the liquid injection was started. The flow of effluent into the plastic-film bag was allowed to continue for 2 minutes after the first appearance of water as indicated by recorder deflections. Preparatory GLC effluents were collected in separate plastic bags from solutions of the four individual units of the scrubber train and from a composite sample of solution from the four units. The separate effluents were transferred totally to the evacuated 10-meter, 4liter sample infrared cell; atmospheric pressure flattens the bags because the volume of the cell is much greater than that of the sample charge. This procedure was adopted to determine which scrubber contained the highest concentration of oxygenates and to provide efficiency data for the scrubbing train. The outlet of the preparatory GLC unit was connected to the trapping needle as shown in Figure 1. The vertical trapping needle was cooled in a Styrofoam container filled to the half-
25
30
height level of the trapping needle with liquid nitrogen. The preparatory column was charged with 2.5 ml. of the solution from the No. 1 NaHS03 scrubber and the oxygenates were trapped in the cold needle. Stopcock A was closed, the trapping assembly removed from the preparatory unit, and the side-port injection needle, with a sliding silastic plug, quickly attached. The trapping assembly was then connected to the inlet of the thermal conductivity GLC unit as illustrated in Figure 2, except that the injection needle was not inserted into the system. With the helium flowing through the bypass, the trapping needle was allowed to warm to about 0' C. Stopcock B was then turned to open the trapping system to the helium line. The sideport injection needle was inserted through the septum C and stopcock A was opened simultaneously to permit the trapped oxygenates to be flushed into the GLC column. As the thermal conductivity chromatogram was being produced, the individual emerging components were trapped in separate plastic bags. Five cycles of the sequence of scrubbing, separation of water from the oxygenates within the GLC preparatory column, trapping of the oxygenates in the cold needle, and charging of these oxygenates to the GLC unit were made to provide material for infrared confirmation for each mode of operation. Where the oxygenates were of high concentration, only two or three cumulative trappings in the plastic bags were necessary. I t is estimated that the collection efficiency from the preparatory unit was 50 to 70y0 for the various oxygenates.
15
20
5
10
0
[L
W 0 K
0 W u K
I
hi
I
/
Acetaldehyde
3
lsobutyraldehyde
6
Methyl Ethyl Ketone
/a 2
Unknown
4
Acetone
7
Methanol
Propionaldehyde
5
n-Butyraldehyde
6'
Ethanol
Figure 4.
Chromatograms of oxygenates trapped for infrared confirmation VOL.
37, NO. 4, APRIL 1965
51 3
Compound Identified Peak No
ACETONE 4
ISOBUTYRALDEHYDE 3
99
80
1775
wyq
97
UNIDENTIFIED la
2900 2700 WAVENUMBER, cn?
80
98
I725
PROPIONALDEHYDE 2
- - - z k&o 7
ACETALDEHYDE I
I : : m
80
2900
2700
2700
96
95
90
80
2900
2700
y 1 I775 1725
mlml
1250 12001 WAVENUMBER, c 6
90
1775 1725 WAVENUMBER, C m '
Compound Identified Peak No.
-05
ETHANOL 98
WAVENUMBER, cm
I725 1775 WAVENUMBER, cm-' METHANOL 7
METHYL ETHYL KETONE
5
100 96
90 80
R -
s lox
-
Reference spectrum Sample spectrum Scale expansion, ten times
n-BUTYRALDEHYDE
1775
1725
1200
1150
95
70
e: 60
50
z a
92 90
1075
IO 25
93
40
1200 1150 WAVENUMBER, cm'
91 90-
1-
2900
2700
loo 90
WAVENUMBER C 6 '
Figure 5.
Infrared spectra associated with GLC peaks of Figure 4
The flame detection GLC column was used in two distinct ways. In one, 10 pl. of a scrubber solution was injected into the preheater operated a t 110' C. to obtain a chromatogram a t a column temperature of 80" C. In the other, 5 to 25 ml. of the effluent from the preparatory column was charged to obtain a chromatogram a t a column temperature of 45' C. RESULTS A N D DISCUSSION
Water is a less efficient scrubbing agent for the collection of oxygenates than 1% sodium bisulfite solution at the relatively high scrubbing rate of 1 liter per minute. However, the qualitative composition of the oxygenates collected is identical in either case. The bisulfite complexes of the aldehydes and methyl ketones observed in this work thermally decompose at the temperatures used to give the original carbonyl compounds (8). In a typical scrubbing operation of the exhaust produced during a cycle 514
ANALYTICAL CHEMISTRY
1725 1775 WAVENUMBER cri'
operation, 4.6 moles of water-free exhaust gas were passed through the scrubbers. The open tube trap, which was initially dry, contained 7.5 ml. of solution and the three scrubbers, with an initial charge of 3 ml. of bisulfite solution, contained, respectively, 4.5, 3.5, and 3.0 ml. of solution. Selected parts of five infrared spectra of the preparatory column effluents derived from the solutions in the four separate elements of the scrubbing train and from a composite sample from these are shown in Figure 3. The concentration of the oxygenates is highest in the No. 1 NaHSOa scrubber. A high efficiency of removal of the oxygenates from the exhaust gas was obtained as indicated by the relatively weak infrared absorption associated with the final scrubber. Typical thermal conductivity chromatograms of the preparatory column effluents, one from the cycle mode and another from the 40-m.p.h. cruise mode
of engine operation, are shown in Figure 4. The two chromatograms are qualitatively alike except that there is an additional minor peak labeled 1-a in the 40-m.p.h. cruise case. The concentrations of oxygenates in the exhausts for the cycle mode as sampled are considerably higher than those for the 40-m.p.h. cruise mode. I t was possible t o confirm by infrared spectra all eight of the compounds indicated by the chromatogram for the cycle mode-acetaldehyde, propionaldehyde, isobutyraldehyde, acetone, n-butyraldehyde, methyl ethyl ketone, methanol, and ethanol. The major oxygenates were acetaldehyde, methanol, and acetone. For the 40-m.p.h. cruise mode there was insufficient trapped material to confirm the compounds associated with peaks 5, 6, and 8 corresponding t o GLC retention times of n-butyraldehyde, methyl ethyl ketone, and ethanol. Figure 5 shows pertinent portions of the infrared spectra of the compounds
8
9
L
L
1
1
7
1
1
6 1
5
1
4 1
1
IO
15
RETENTION
2 1
1
/
[
I
I
5 TIME,
minutes
/ Acetaldehyde
4 Acetone
2 3
Propionaldehyde
5 n-Butyraldehyde
7 Methanol 8 Ethanol
lsobutyraldehyde
6 Methyl Ethyl Ketone.
9 Unknown
Figure
6.
Chromatogram
collected, represented as peaks in Figure 4, compared with reference spectra.
All the compounds confirmed by the IR spectra as shown in Figure 5 came from the cycle mode. The material associated with the peak 1-a, found only with the 40-m.p.h. cruise mode, was unidentified. According to GLC residence times, this material can be neither ethylene oxide nor propylene oxide.
from
1 0-PI. solution charge
Although the retention times for acrolein and methyl acrolein fall within the limits of those of the compounds identified, these compounds were not found. According to Smith ( 8 ) , acrolein reacts with water and also forms a bisulfite complex which is not thermally decomposed. A freshly prepared water solution containing 100 pl. of acrolein per liter, when injected into
a hydrogen flame detection GLC unit containing Carbowax 600 on Teflon at a column temperature of 90" C. and a t a preheater temperature of 110" C., gave a relatively small GLC peak corresponding to the emergence time for acrolein. However, on standing 15 minutes, acrolein was not indicated when the solution was again injected. When a 1% sodium bisulfite solution of the same acrolein concentration was charged to the GLC unit operating under the same conditions, no indication of a GLC peak was obtained; the same was found for methyl acrolein in sodium bisulfite solution, Acrolein has been found in automobile exhausts (4, 5 ) . Formaldehyde (6) and crotonaldehyde (4) also have been found in exhaust gases, but neither of these can be detected by the methods of this study because they do not elute ahead of water in the procedure prescribed. Figure 6 shows a chromatogram obtained by the injection of 10 111. of a composited sample of the solutions contained in the four units of the scrubbing train when the exhaust gases were produced a t the 40-m.p.h. cruise mode. Elevated column temperatures of 80' to 90" C. were used for the decomposition of the bisulfite complexes. At these
30
25
20
15
10
5
0
30
25
20
15
10
5
0
/
2
3
Acetoldehyde Propionaldehyde lsobutyraldehyde
Figure 7.
RETENTION TI ME. minutes 4 Acetone 5 n- Butyraldehyde 6 Merhyl Ethyl Ketone
7
8
Methonol Ethonol
Chromatograms of preparatory column effluents VOL. 37, NO. 4, APRIL 1965
51 5
temperatures the isobutyraldehyde peak was not separated from the acetone peak. The concentrations of the various oxygenates in the composite sample used to produce this chromatogram were of the order of low3to gram mole per liter. The procedure of direct injection of the bisulfite solution into the GLC unit provides a rapid qualitative analysis. After a confirmed GLC qualitative analysis has been established, the procedure of direct solution injection could provide a basis for studies in quantitative analysis. This procedure in its present development, however, can provide a means for ascertaining the relative amounts of the oxygenates. The chromatograms shown in Figure 4, based on a trapping procedure, are subject to the effects of distortion of the relative amounts of the oxygenates
caused by varying partial condensations which most likely occur in the cold trapping needle. Figure 7 shows two chromatograms obtained by the injection of bag-trapped effluents from the preparatory GLC unit. One chromatogram (top panel) was derived from the cycle mode of engine operation and the other from the 40-m.p.h. cruise mode. At 45’ C., good resolution was obtained with the 20-foot Carbowax-Teflon column at 55 ml. per minute helium flow. The qualitative identity of the oxygenates for the two modes of engine operation is noted. This method, in contrast to direct solution injection, has the advantage of permitting an unmodified aliquot of the preparatory column effluent to be charged to a GLC unit operating a t lower temperatures where greater resolution can be obtained.
LITERATURE CITED
(1) Altshuller, A. P., Cohen, I. R., ANAL.
CHEY.33, 1180 (1961).
( 2 ) Altshuller, A. P., Leng, L. J., Ibid., 35, 1541 (1963).
(3) ~, Altshuller. A. P.. Miller. D. L.. Sleva. S . F., Ibid.,’33, 621 (1961j. ( 4 ) Barber, E. D., Lodge, J. P., Jr., Ibid., 35, 348 (1963). (5) Cohen, 1. R., Altshuller, A. P., Ibid., 33, 726 (1961). (6) Ellis, C. F., BuMines Rept. of Investinations 5822. 35 DD.. 1961. (7) Hughes, K. Ji’Hur
