A Method for Sampling and Determination of Organic Carbonyl Compounds in Automobile Exhaust Mario F . Fracchia, F . J. Schuette, and Peter K. Mueller
Air and Industrial Hygiene Laboratory, State of California Department of Public Health, 2151 Berkeley Way, Berkeley, Calif. 94704
m Automobile exhaust was sampled at 1 liter per minute through a water trap and two bubblers in series. The bubblers contained aqueous acidified 2,4-dinitrophenylhydrazine (2,4-DNP). The carbonyl compounds in the water trap were precipitated with the hydrazine reagent. The hydrazones in the trap and in the bubblers were collected by filtration and extraction, dissolved in carbon disulfide, and analyzed by gas chromatography using a flame ionization detector. The water trap contained mostly formaldehyde. All aldehydes were quantitatively trapped in the first bubbler, and the ketones were determined from the hydrazones in the second bubbler. The role of potential interferences has been evaluated. Sampling efficiencies and analytical errors have been established for several compounds. Alkyl and aromatic carbonyl compounds obtained from selected automobiles under several operating modes are compared. More sensitive methods are needed for analyzing carbonyl compounds in air, but a methodology is now available for studying combustion sources,
C
arbonyl compounds are a class of highly reactive compounds formed by the combustion of organic materials, by the operation of motor vehicles (Barber and Lodge, 1963; Ellis, Kendell, et a/., 1965), and by the photooxidation of hydrocarbons (Nicksic, Harkins, et a/., 1964). The carbonyl compounds have odor thresholds a t parts per billion concentrations (Guadagni, Buttery, et a/., 1963a; 1963b). Their identification and concentration in air pollution sources, their effects on living organisms, and their role in photochemical air pollution are largely unknown because convenient methods with sufficient specificity and sensitivity have not been available. The status and application of methods for the analysis of carbonyl compounds in air pollution and source effluents have been reviewed (Lodge, 1961; Altshuller, 1963, 1965). Since the work reported here was completed, Oberdorfer (1967) determined carbonyl compounds in automobile exhaust gas by recovering and weighing 2,4-dinitrophenylhydrazine derivatives from a gas scrubber. The sampling tubes from the exhaust pipe were heated to prevent condensation, and the scrubber, containing a saturated 2,4-DNP solution in 2 N HCI, was kept at 0" C. A temperature-programmed gas chromatographic method for separating these 2,4-DNP derivatives has been presented (Camin and Raymond, 1967). However, a comprehensive description of their method has not been made available. Formaldehyde and total aliphatic alde-
hydes have been determined in automobile exhaust recently by a colorimetric determination employing the 3-methyl-2-benzothiazolone hydrazone test (Sigsby and Klosterman, 1967). Soukup, Scarpellino, et a/. (1964) demonstrated that numerous 2,4-dinitrophenylhydrazine derivatives could be separated by gas chromatography. This paper deals with further investigation of that method for purposes of quantitation, the development of a 2,4-DNP reagent suitable for selective and quantitative sampling of carbonyl compounds, and a description of their occurrence in automobile exhaust. Experimental
Gas Chromatography. A Model 600B Varian Aerograph gas chromatograph was equipped with a flame ionization detector and l-mv. Minneapolis-Honeywell recorder operated at a chart speed of 1 inch per minute. A glass insert was used in the injection chamber. The instrument conditions for hydrazone analysis are given in Table I. Three different conditions of column temperature and carrier gas flow rate were used to optimize the separation. Condition I gave optimum resolution for C1to C4carbonyl derivatives; C5to C7aliphatic derivatives were best separated by condition 11; condition I11 was chosen for separating aromatic carbonyl derivatives and aliphatic derivatives greater than C7. To calibrate the gas chromatographic analysis of hydrazones, 2,4-DNP derivatives of carbonyl compounds were prepared by known methods and tested (Shriner, Fuson, el al., 1957) until constant melting points were obtained. An infrared spectrum was obtained for each derivative. The data were in reasonable agreement with known literature
Table I. Gas Chromatographic Conditions for Hydrazone Analysis Item
Carbonyls Carrier gas, N ? ml. per minute Column temperature,
c.
Sample size, pl. Injection port temperature, C. Co'umn Packing
Condition IJ
I
~ ~ _ _ _ 111
C1to C4 C5to CI Aromatics and >C: Aliphatics 60 70 80 230
250
260
5
5
5
270
270
270
O
Detector
6 feet X 0.085-inch I.D. stainless steel 10% SF 96 o n 60- to 80-mesh acidwashed Chromosorb W F I w i t h H2 at 35 ml. per minute
Volume 1, Number 11, November 1967 915
values. Individual hydrazone solutions in carbon disulfide a t four concentrations ranging from 0.005 to 0.125 pg./pl. were chromatographed to obtain the retention times and flame ionization response factors. Another gas chromatographic method was used to measure the concentration of single carbonyl compounds directly in calibrating gas streams which were generated to determine the efficiency of the gas sampling procedure. In some cases, it was possible to monitor mixtures of three carbonyl compounds. This method is not suitable for formaldehyde, for which the collection efficiency determination is described below under Sampling Train Performance. Two-milliliter samples of the gas stream were injected into a column (5 feet X 0.1-inch I.D.) employing N2carrier gas at 25 ml. per minute and Hf flow to the detector a t 25 ml. per minute. For the analysis of Cpto C4 carbonyl compounds, a column packing of &B'-oxydipropionitrile on 60- to 80-mesh firebrick was used. The injection port temperature was 110" C., and the column temperature was 30" C. 2-Pentanone and 2hexanone were monitored using 5 % diethylene glycol succinate (DEGS) on 60- to SO-mesh Chromosorb W. The injection port and column temperature were 150" C. and 85" C., respectively. Benzaldehyde in the calibrating stream was determined with a column containing 5 z Carbowax 20M o n 60to 80-mesh acid-washed Chromosorb W. The column temperature was 115" C. with an injection port temperature of 204OC. Standard gas dilutions of the individual aldehydes and ketones were prepared in two stages. The purity of each liquid carbonyl was checked prior to use, and no significant contamination was found. A 1000-p.p.m. primary standard was prepared by injecting the appropriate quantity of the liquid carbonyl into an evacuated, temperature-regulated, 2-liter volumetric flask (Figure 1). The heating mantle was regulated to maintain a temperature of 120" i 2' C. for dilutions of CI to C4 carbonyls and a t 200" 2" C . for benzaldehyde. The appropriate injection volume to produce 1000 p.p.m. (v.,'v.) a t 25" C. and 760 torr was calculated from known densities. The carbonyl compound was drawn into a 10-p1. syringe calibrated to include the syringe needle volume. The entire liquid volume was drawn into the barrel of the syringe to prevent losses from the needle on the septum upon injection. The volumetric flask was evacuated to about 250 torr, and the liquid was injected by inserting the needle completely through the center septum. The plunger was removed from the syringe, and the reduced pressure in the flask caused the incoming air to sweep any residual carbonyl in the syringe needle and barrel into the flask. The syringe was removed, and a No. 23 syringe needle was inserted into the center septum to allow displacement air to enter during the withdrawal of aliquots. A similar temperature-regulated volumetric flask was used to prepare 1- to 10-p.p.m. standards. An appropriate aliquot was withdrawn from the 1000-p.p.m. standard through the upper septum by means of a 10-ml. gas syringe. This volume was immediately injected into the center septum of the second flask. After injection, the syringe was withdrawn, filled with room air, and again injected into the flask several times to ensure the complete transfer. Finally, a No. 23 syringe needle was placed into the center septum. Two-milliliter aliquots were taken through the upper septum with a 2.5-ml. gas syringe for injection into the gas chromatograph.
Sampling Procedure. The sampling reagent was prepared by adding 3 ml. of concentrated H2SOI (reagent grade) to 300 mg. of 2,4-DNP (Eastman No. 1866) in a 250-ml. Erlenmeyer flask. After five minutes, 10 ml. of distilled water were added dropwise, and then the solution was diluted to 50 ml. with shaking and tap-water cooling. To obtain exhaust samples, a stainless steel or glass probe
5z
Figure 1. Temperature-regulated volumetric flask
*
916 Environmental Science and Technology
Figure 2. Mixed gas stream generator
r
EJ3eL;:'.
Figure 3. Test sampling trains
was led from the exhaust pipe to a water condensation trap and from there through glass tubing to two tall-form bubblers in series. The bubblers were equipped with extra coarse frits, and each contained 15 ml. of the sampling reagent. A silica gel desiccant tube followed the second bubbler to prevent moisture condensation in the flowmeter calibrated in situ. The needle valve following the flowmeter was used to control the sampling rate a t 1.0 liter per minute. The 2,4-DNP derivatives were recovered from each of the two bubblers by similar procedures. The contents of the bubblers were vacuum filtered on fine sintered glass. The bubbler and frit were rinsed several times with distilled water, and the washings were transferred to the filter, keeping the volume of the filtrate to less than 25 ml. The filtrate was extracted twice with dichloromethane in a separatory funnel. The bubbler, frit, and filter were washed with the dichloromethane filtrate extract. The solution was added to a 50-ml. volumetric flask. The apparatus was rinsed several times with more dichloromethane, and the rinsings were added to the volumetric flask which was then made up to volume. Depending on the concentration judged by the intensity of the color and the amounts of the residues, either a n aliquot or the total volume of the solution was evaporated to dryness and volumetrically dissolved in carbon disulfide in preparation for gas chromatographic analysis. Sampling Train Performance. An apparatus (Figure 2) was devised for generating constant gas phase concentrations of several carbonyl compounds in the range of 1 to 10 p.p.m. Five to 10 ml. of each compound were placed in two midget impingers connected in series and placed in a constant temperature water bath. The water bath was held a t 0" C. for eight of the compounds tested. The impinger tube terminated within 2 mm. of the liquid surface. A stream of N P passed through the impingers at approximately 20 ml. per minute. This gas mixture was diluted up to 500-fold with Nzin the first chamber. A portion of this mixture was metered to the second dilution chamber from which the gas was removed a t 2 liters per minute with a corresponding amount of filtered room air providing further dilution up to 100-fold. The dilution ratios were controlled by adjusting flow rates through flowmeters ( F M ) 1, 2, and 3. F o r generating formaldehyde, crotonaldehyde, and benzaldehyde gas streams, the water bath was held at 23" 2" C., and the impinger outlet was connected directly to the second dilution chamber. The apparatus for testing the performance of the sampling train is illustrated in Figure 3. Train A was used for all carbonyl compounds except formaldehyde. The bubbler arrangement in train A was similar to that described for sampling automobile exhaust. In each case, the sampling period was 40 to 120 minutes. Samples were withdrawn from ports P1, P2, and P3 at 3- to 5-minute intervals so that each port was sampled every 9 to 15 ininutes and analyzed by the gas phase gas chromatographic procedure. At the end of each sampling period, the hydrazones in bubblers A I and A 2 were analyzed by gas chromatography. From the differences in the concentrations at each port, the amount of each carbonyl compound trapped in bubblers A1 and A2 was calculated. The trapping efficiency, TE1, for the first bubbler is given by
*
(21 -
TE1 =
GZ
77-
An analogous expression defines the trapping efficiency for the second bubbler. d p ,and are the mean concentrations obtained a t P1, P2, and P 3 during the entire sampling period. The hjdrazone recovery efficiency, HRE1, is the amount of hydrazone found in the bubbler compared with the calculated amount based on trapping efficiency and volume sampled. Thus
cl,
ca
where 81is the mean quantity of carbonyl calculated from three determinations of the hydrazone recovered from a bubbler for a single sampling period, and V is the total volume sampled. An analogous expression can be written for the hydrazone recovery efficiency corresponding to the second bubbler. The amount of carbonyl found in the first bubbler compared with the amount of the carbonyl that has entered the bubbler is the over-all efficiency, El. The efficiency of the first bubbler is the product of its trapping efficiency and hydrazone recovery efficiency. E1 = (TEd(HRE1) (3)
A direct means of measuring and G, during the sampling of formaldehyde was not available. Therefore, its trapping efficiency and hydrazone recovery efficiency could not be determined. However, its over-all efficiency was obtained because gl and (2, could be determined. The formaldehyde calibrating stream was split and monitored by the simultaneous use of sampling trains A and B (Figure 3). Fifteen milliliters of a 1% NaHSO3 sampling reagent were placed in each bubbler. Sampling was performed at 1.0 liter per minute for 15 minutes for three consecutive sampling periods. The amount of formaldehyde passing through both trains was the same by the chromotropic acid method (Altshuller, Miller. et al., 1961), showing that the stream was split equally. The efficiency was determined by placing the 2,4-DNP sampling reagent in bubblers A1 and A 2 while the remaining bubblers contained the bisulfite solution. The split stream was sampled for 90 minutes at 1.0 liter per minute. Gl was calculated by the summation of the formaldehyde trapped in the train B bubblers. 8, was calculated from the amount of hydrazone found in the first bubbler. The sampling efficiency, El, for formaldehyde was calculated from Equation 3. Sampling and Analysis of Automobile Exhausts. To assess the occurrence of carbonyl compounds in automobile exhaust, three vehicles in good operating condition and tuned to manufacturers' specifications were selected for study. Car A was a 1960 model, medium V8 with 74,000 miles, from which samples were obtained at two modes of operation: normal and fast idle. Fifty to 100 liters of exhaust were sampled at each operating mode. Cars B and C were 1966 models with medium V8 engines. B had been driven 4900 miles and was equipped with an air injection exhaust control system. C , with 1090 miles, was equipped with an engine modification exhaust control system. Two successive samples of 50 to 100 liters of exhaust were obtained from each vehicle operated a t 35 to 40 m.p.h. o n a low load dynamometer. All were operated with regular gasoline which was otherwise undefined. Volume 1, Number 11, November 1967 917
Table 11. Retention Times and Flame Ionization Response of Hydrazones FI Responses,” Retention Mm.* X Attn. X lo4 Time,a Per Pg. Compound Minutes Hydrazone Condition I Formaldehyde 3.1 1.7 Acetaldehyde 4.6 3.0 Acetone 6.1 3.1 Acrolein 6.1 1.6 Propionaldehyde 6.1 2.9 Isobut yraldehyde 6.8 n.v.‘ 2-Butanone 8.2 2.5 Butyraldehyde 8.2 2.6 Crotonaldehyde 10.2 1.2 Condition I1 Valeraldehyde 5.6 2.9 Hexanal 7.3 2.6 Heptanal 9.8 n.v. Condition I11 Nonanal 11.0 n.v. Benzaldehyde 11.2 0.4 Propiophenone 11.3 n.v. a
Conditions as given in experimental section. Slope of calibration line. n.v. = no value
Sampling was performed after engine warm-up. After sampling, the water trap condensate was added to the first bubbler. The contents of the second bubbler were analyzed separately to determine the ketones. Each hydrazone solution was chromatographed in duplicate, and the averages are reported. Representative total hydrocarbon, carbon monoxide, and carbon dioxide emission data for cars B and C were used to make exhaust volume adjustments. Results and Discussion Separation and Quantitation of Hydrazones. Retention times and flame ionization response data for the 2,4-DNP derivatives investigated are given in Table 11. Under condition I, eight compounds were separated into five fractions. Acetone, acrolein, and propionaldehyde appeared as a mixed fraction as did butanone and n-butyraldehyde. Formaldehyde, acetaldehyde, and crotonaldehyde were resolved. Condition I1 resolved valeraldehyde, hexanal, and heptanal. Correlation coefficients of detector response and concentration for the 11 hydrazones varied from 0.964 to 0.997 indicating a high degree of response linearity for each compound. The response data in Table I1 were obtained from the slopes of the calibration lines. Some of the response factors were not determined because the compounds did not occur in our samples. There were some significant response differences among the different compounds. Excluding formaldehyde, there appeared to be a decreasing response from saturated to unsaturated to aromatic carbonyl compounds. But even within these classes there were significant differences in response among individual compounds. The response factor also varied with changing column characteristics. Therefore, accurate quantitative analysis 918 Environmental Science and Technology
requires the determination of the response factor for each hydrazone a t the time of sample analysis. In sequential duplicate determinations of 0.025 bg./pl. standard hydrazone solutions for all the carbonyls found in the exhaust gases, deviations were less than 10%. Analysis of Calibration Streams. The procedure for determining the carbonyl compounds directly in the gas phase is suitable only for the separation of two or three compounds in a mixture. This procedure was used in the present work primarily to quantitate a single gas phase carbonyl in the determination of collection efficiencies. Correlation coefficients of detector response for concentrations from 1 to 10 p.p.m. for each of the carbonyl compounds varied from 0.975 to 0.999 among different compounds indicating linearity in response, which shows good precision in the preparation of the standard gas mixtures. The stability of the gas phase dilutions in the heated volumetric flasks was investigated with a 5-p.p.m. propionaldehyde mixture and 2-, 4-, 6-, 8-, and 10-p.p.m. mixtures of 2-pentanone in air. No significant change in concentration was observed for a period of three hours. The time of transfer by syringe from the flask to the chromatograph was varied from 15 to 120 seconds. No losses occurred during transfer. It was assumed that a similar transfer accuracy was obtained with the other carbonyl compounds. Samples taken from the bottom, center, and top of the volumetric flasks gave similar responses, indicating that no stratification of the carbonyl compounds occurred during the calibration process. Collection Efficiencies. The trapping efficiencies. hydrazone recovery efficiencies and the over-all efficiencies obtained with the first bubbler are given in Table 111, together with the mean inlet concentration, GI, Trapping efficiencies for the aldehydes were nearly 100%. The C3to Cs ketones were collected with considerably less efficiency, and significant amounts were found in the second bubbler. Therefore, only ketones will appear in the second bubbler, furnishing a means of differentiating aldehydes from ketones unresolved by gas chromatography. The applicability of this principle for resolutions of carbonyl compounds beyond Cs has not been investigated. The effects of concentration and sampling rate on trapping efficiency for acetaldehyde, n-butyraldehyde, and acrolein were investigated. Concentrations ranged between 1 and 20 p.p.m., and sampling rates varied from 0.5 to 2.0 liters per minute. Concentration had no effect on trapping efficiency Table 111. Trapping Efficiency and Hydrazone Recovery Efficiency, First Bubbler Sampling rate, 1 liter per minute
81,
Compound
TEi,
z
HREi,
z
El,
P.P.M.
Formaldehyde Acetaldehyde Acetone Acrolein Propionaldehyde 2-Butanone Butyraldehyde Crotonaldehyde 2-Pentanone Benzaldehyde
18.50 5.35 3.50 3.17 3.95 3.30 7.85 3.93 3.51 4.17
... 97 18 97 92 34 99 100 71 100
...
90 99 23 75 85 30 102 97 79 80
102 128 78 92 90 103 97 111 80
z
(Table IV). However, trapping efficiencies decreased above a sampling rate of 1.0 liter per minute (Table V) while trapping efficiencies of + 5 % are probably within experimental error, the consistent sequential decrease in TE1with increasing sampling rate is considered significant. Trapping efficiency for ketones was increased by decreasing the sampling rate. The trapping efficiency for 2-pentanone is 71% when sampled a t 1.0 liter per minute and 84z a t 0.85 liter per minute. Therefore, maintaining a sampling rate of 1.0 liter per minute is very important for quantitative analysis. The trapping efficiency of each bubbler for the ketones is given in Table VI. The trapping efficiency increased with a n increase in molecular weight. There was a concentration effect o n trapping efficiency for ketones heavier than acetone. The trapping efficiency decreased with a decrease in the ketone
Table IV. Concentration Effects on Trapping Efficiency for Three Aldehydes Sampling rate, 1 liter per minute Gas Phase Concn., TEi , Compound P.P.M. 72 Acetaldehyde 5.35 97 15.2 100 Acrolein 3.17 97 9.65 100 Butyraldehyde 7.85 99 16.70 100
Table V. Trapping Efficiencies (Per Cent) at Different Sampling Rates for Three Aldehydes Sampling Rate, Acetaldehyde. Acrolein, Butyraldehyde, Liters per Min. 11 to 17 P.P.M. 6 to 10 P.P.M. 11 to 20 P.P.M.
100 100 96 90
100 100 99 97
0.5 1. o 1.5 2.0
I O 7-
100 100 99 91
concentration. The relationship between concentration and trapping efficiency remains to be determined for quantitation of the ketones which are found in automobile exhaust. Hydrazone Recovery Efficiency. The hydrazone recovery efficiencies for most of the aldehydes were within =t 10% of 100% recovery (Table 111).With the exception of acrolein and benzaldehyde, a statistical analysis of the data for each of the other carbonyl compounds indicates that the deviations in the hydrazone recovery efficiencies were no greater than the precision of determining GI and Gz during the course of each sampling period. The relatively low hydrazone recovery efficiencies for acrolein and benzaldehyde of about 80% are related to the insolubility of their hydrazones in carbon disulfide. This led to incomplete removal of precipitates lodged in the frits. Accordingly, dichloromethane is used to wash out the frit in all cases, and the assumption is made that the current procedure recovers nearly 100% of the acrolein and benzaldehyde derivatives as well. Acetone exhibited the largest deviation from 100% recovery. Recovery values are dependent on the accuracy of the d, and G, values. F o r acetone, deviations of about 2 0 z were observed for individual values of G,. Since GIminus was only 20% of GI, the apparent high recovery can be ascribed to difficulties in accurate measurements of acetone leaving the bubbler. The hydrazone recovery efficiencies for other ketones tested-namely, 2-butanone and 2-pentanone-yielded results within the experimental error of the standard curves. Composition of Automobile Exhaust. Car A had no exhaust control devices and was tested at normal and fast idle. No qualitative differences were noted. The carbonyls found and their concentrations are given in Figure 4. Bars corresponding
c2
Table VI. Trapping Efficiency for Ketones First Bubbler Second __ Bubbler __ e 1 TE, . G? , TEz, 0Ketones p.p.m. /o p.p.m. Acetone 3.50 18 2.90 15 2-Butanone 3 30 34 2.12 21 2-Pentanone 3 51 71 1.02 61 1
z
0Car P , normal ,d!e
,v 5 in N
+m 3 IO E, a c
e + e + S W
8 6 4
L: 0
0
2 Acetaldehyde
Acetone Acrolein 2-Buta- Butyr- Croton& Unknown BenzalPropion- none aldehyde dehyde dehyde aldehyde Nonanal, Propiophenone
Decanal Unknown Phenyl-
propion-
aldehyde
Figure 4. Organic carbonyl compounds in automobile exhausts Volume 1, Number 11, November 1967 919
Table VII. Organic Carbonyl Compounds in Automobile Exhaust Concentration, P.P.M. Formal- Other organic Car dehqde carbonyls Total ~
to more than one compound represent carbonyls not resolved by the gas chromatographic procedure. However, acrolein was identified by thin-layer chromatography (Schwartz and Parks, 1963). Of the aliphatic ketones, only acetone and 2butanone were detected. The concentration of formaldehyde with respect to other carbonyls is given in Table VII. At fast idle, the concentration of carbonyls other than formaldehyde was almost doubled while the formaldehyde concentration was increased by only 4 0 z . Cars B and C were equipped with exhaust control systems differing from each other. The chromatogram for car C contained one peak corresponding to high-boiling compounds not found in the exhaust of B. Acetone was the only aliphatic ketone found. Figure 5 shows a chromatogram of the hydrazone standards and the hydrazones in the first bubbler collected from the exhaust of B. Peak A in the exhaust sample is the solvent, and peaks B to D are noncarbonyls trapped by condensation during sampling. Peaks F and G are formaldehyde and acetaldehyde, respectively. Peak H is acetone-acrolein-propionaldehyde. A thin-layer chromatographic analysis of the hydrazones confirmed the presence of acrolein (Schwartz and Parks, 1963). The amount of acetone was determined by analysis of the hydrazones collected in the second bubbler. Peak I shows a slightly shorter retention time than the n-butyral-
A. No exhaust controls, normal idle A. No exhaust controls, fast idle B. Exhaust control, 35 to 40 m.p.h. cruise C. Exhaust control, 35 to 40 m.p.h. cruise
20.4
7.6
28.0
28.8
14.0
42.8
69.3
23.6
92.9
44.6
14.6
59.2
dehyde standard. This shift may be due to nondetectable quantities of butanone which has a slightly reduced retention time from n-butyraldehyde. Although peak J is within the retention time variability for crotonaldehyde, a thin-layer chromatographic analysis did not confirm its presence. From the retention times given by Soukup, Scarpellino, et al. (1964), isovaleraldehyde is a possibility. Another possibility is methyl acrolein which has been found in exhausts from an experimental engine burning isooctane (Alperstein and Bradow, 1966b). Identification of peak K was attempted at optimum gas chromatographic conditions for valeraldehyde, hexanal, and heptanal hydrazone standards. The chromatogram showed that peak K did not correspond to any of these compounds. Other likely possibilities are isohexanal (Soukup, Scarpellino, et a ( . , 1964) and trimethylacetaldehyde (Alperstein and Bradow, 1966b).
CAR B EXHAUST C A R C EXHAUST
K
~
4x
~
A
J a:
I -Solvent
S
n
2 -Formaldehyde 3 -Unidentified
HYDRAZONE STANDARDS
2
U
0
+ u e, + e, n
I -Solvent I A - Solvent impurity j 2 -Formaldehyde I 3 - Unidentified 4 -Acetaldehyde \ 5 - Acetone. Acrolein; Propiohldehyde 6 - A u t a n o n e . Butyraldehyde 7 - Crotonaidegyde 8 - Benzaldehyde ~
HYDRAZONE STAN D A R D S
4 -Acetaidehyde 5 -Acetone Acrolein;
i
~
Propiohalde h y d e
~
6 - 2-8utanone. Butyraldehyde
/, ~
7 - Crotonaldehyde
~
U I
I
0
2
Figure 5.
I
I
I
(
I
I
1 0 1 2 1 4 ReteQtion T i m e - Minutes
4
6
8
Identification of C1 to
C4
carbonyl compounds
Gas chromatographic condition I (Table I)
920 Environmental Science and Technology
I
\
\
!
0
2
4
6
Figure 6.
I
l
\
I
8 IO I2 14 Retention Ti me - Mi i~ tes
)
I
J
I6
18
20
Partial identification of aromatic carbonyl compounds Gas chromatographic condition 111 (Table I)
Chromatograms obtained at optimum conditions for determination of aromatic carbonyl compounds are shown in Figure 6. Based on its retention time, peak L may represent benzaldehyde, nonanal, and/or propiophenone. Although peak L does not appear in the second trap chromatogram, propiophenone cannot be excluded as a possibility because the trapping efficiency for aromatic ketones has not been determined. Decanal and 3-phenylpropionaldehyde have retention times identical to peak M. Peak N represents one or more carbonyls heavier than decanal. Car B produced 60% more total carbonyls than C. N o significant difference was noted in the acetone emission. Individual aliphatic aldehydes were increased in B by factors ranging from about 1.5 to 4 times that occurring in the exhaust of C. The greatest increase was in the propionaldehydeacrolein fraction. However, the aromatic carbonyl compound concentrations in car B exhaust were approximately half those in the exhaust of C. Interferences. Possible interferences of high molecular weight compounds in automobile exhaust were considered such as polycyclic hydrocarbons (Begeman, 1962), cyclic ethers (Alperstein and Bradow, 1966a; 1966b), and undefined carbonaceous matter. The polycyclic concentration ( p g . per liter) in exhaust is approximately half the carbonyl concentration. Pyrene, fluoranthene, coronene, chrysene, benz[a]anthracene, and benzo[a]pyrene were chromatographed. Several had retention times near but not identical to those of the hydrazones. To determine if these compounds were trapped by condensation, exhaust from car A at fast idle was sampled using aqueous 2 N H2S04 without 2,4-DNP. Some precipitate having a carbonaceous appearance and soluble in carbon disulfide was recovered and injected into the column used for the hydrazones. No peaks were observed. A similar control is recommended for source sampling. The specificity of the 2,4-DNP reagent minimizes the interferences from other compounds. Hydrazones may be formed with sugars, 5-membered heterocyclic compounds, hydroxy aromatics, esoteric alcohols, and ketols (Gallard-Schlesinger Chemical Mfg. Corp., 1966). If these compounds were present, the corresponding hydrazones would have much greater retention times than those observed. Cyclic ethers cleave in acidic 2,4-DNP solution to form aliphatic and aromatic carbonyl hydrazones (Buchi, Inman, et a [ . , 1954). Cyclic ethers have been found in the exhaust of an experimental engine burning isooctane (Alperstein and Bradow, 1966b). However, the amounts were below the detectable limit of this procedure (0.1 p.p.m.). Cyclic ethers in exhaust from standard engines using gasoline have not been reported. Sensitivity. Sensitivity depends on the volume of the sample
and dilution of the recovered hydrazones. Under the stated conditions of sampling and analysis, the lower limit of detection and quantitation was about 0.1 p.p.m. Since the optimum sampling rate appears t o be 1.O liter per minute and it is not practical to increase the sampling time beyond 1 hour, these factors cannot be manipulated to increase the sensitivity. It would be desirable to decrease sampling time to about 5 or 10 minutes. Decreasing the dilution of the recovered hydrazones by a factor of 10 appears to be feasible but laborious. Alternatively, the required volume could be pumped into a plastic bag following a water trap (Altshuller, Wartburg, et a / . , 1962), and the samples could be withdrawn through the bubbler train thereafter.
Conclusions
Automobile exhaust gas apparently contains about 20 carbonyl compounds with up to 10 carbon atoms. Their concentrations are relatively unaffected by type of commercial fuel, but operating mode and other engine variables are important
Table VIII. Mole Per Cent Composition of Several Exhaust Gases Automobile OberA, A, dorfer normal fast Compound (1967) idle idle B Formaldehyde 70.2 72.9 67.3 7 5 . 6 Acetaldehyde 7.2 8.5 7 . 7 11.0 Acrolein 9.8 6.4a 7.5a 7 . 6 a Crotonaldehyde 0.4 0.4’ 0.7’ 0.8’ Methacrolein Trace n.m.’ n.m. n.m. Isovaleraldehyde Trace n.m. n.m. n.m. Butyraldehyde Trace 1.7 1.4 1.6 Unknownd n.m. n.f. n.f.e n.f. Benzaldehyde All >Ci. as Ci n-Decanal Unknown, >Clo Acetone Acetone and propionaldehyde 2-Butanone
8.5 2.5 n.m. n.m. n.m. 0.4a
n.f.
C
71.8 6.7 2.9a 0.6b n.m. n.m. 5.8 0.8
4.31 n.m. 2.53 n.f. 2.1
n.f. 1.8’ 5.9’ n.m. n.m. n.m. 7.7O 1 . 4 3 4.6’ 6 . 1 n.f. n.f. 0.9 0.3 0.8
n.m. 1.1
n.m. 0.5
n.m. n.m. n.f. n.f.
Includes propionaldehyde. Could include methacrolein and isovaleraldehyde. n.m. = not measured in this analysis. Could be isohexanal and trimethylacetaldehyde. e n.f. = not found. J Could include nonanal and propiophenone. Could include 3-phenylpropionaldehyde and other compounds. Q
Volume 1, Number 11, November 1967 921
(Oberdorfer, 1967). The mole per cent composition of samples obtained from different kinds of automobile operation are compared in Table VIII, including the data published by Oberdorfer (1967) ; significant differences are detected. Insufficient data have been obtained for generalizing about how various factors affect the carbonyl compound composition. However, the data are sufficiently consistent in demonstrating that formaldehyde is the major component (about 70 mole %) and other aldehydes are not negligible. Acetaldehyde and acrolein occurred in the range of 3 to 10 mole %. Butyraldehyde was present only as a trace in Oberdorfer’s (1967) sample, but in the authors’ samples it occurred at greater than 1 mole %, with almost 6 mole % occurring in the exhaust gas of the cruising vehicle equipped with the modified engine. Compounds tentatively identified and measured in terms of benzaldehyde and n-decanal also occurred in varying concentrations greater than 1 mole %. Only two ketones have been found. Acetone appeared consistently, but 2-butanone was found only at idle with car A. If a gas chromatography column could be developed to separate acetone, propionaldehyde, and acrolein, it might not be necessary to use the second bubbler for the separate collection of the ketones. Among the three-carbon compounds, the authors could not quantitatively distinguish between acrolein and propionaldehyde. Oberdorfer (1967) could not separate acetone and propionaldehyde. Because his combined value is about the same as our values for acetone, and there is substantial agreement between us concerning acrolein, propionaldehyde may be a minor constituent (less than 0.1 mole Optimum separation was obtained by using a single column a t three constant temperatures. A single temperature-programmed column would simplify the procedure. Despite several attempts by the present authors and by Camin and Raymond (1967), satisfactory separations of mixtures with CI to CIOcarbonyls in exhaust gas have not yet been achieved on a single column. The analysis of carbonyl compounds in automobile exhaust gases has primarily been limited to the determination of formaldehyde, total aliphatic, and total aldehydes in terms of formaldehyde. From the data in Table VIII, a n average molecular weight of about 42 was calculated for all the simples. Thus, Oberdorfer’s (1967) gravimetric determinations of total aldehydes calibrated with formaldehyde are about 40% too large. Sigsby and Klosterman (1967) indicated formaldehyde is 34 to 44 mole % of the total aliphatic aldehydes in several runs with several vehicles. They used colorimetric methods calibrated with gas-phase mixtures. While the total aliphatic aldehyde concentrations by the 3-methyl-2-benzothiazolone hydrazone method appear to yield results in substantial agreement with the total aldehydes by the 2,4-DNP methods, their formaldehyde concentrations determined by the chromotropic acid method seem low. Presumably, for that method there are negative interferences in exhaust gases (U. S . Public Health Service, 1965; Oberdorfer, 1967). In estimating the contribution of automobile exhaust emissions to acute air pollution episodes, the assumption has been made that the carbon monoxide pollution comes primarily from the operation of automobiles. The ratio of carbon monoxide measured in automobile exhaust to the carbon monoxide measured in ambient air provides a n estimate of the dilution of automobile exhaust under prevailing meteor-
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922 Environmental Science and Technology
ological conditions. The average carbon monoxide concentration in automobile exhaust prior to control devices was 3.8% (State of California, 1960), and ambient levels of 60 to 100 p.p.m. have been reported during severely smoggy days in Los Angeles. During such episodes, there may be only a 300- t o 600-fold dilution of exhaust gases. If the additive effect of subthreshold concentrations of aldehydes is valid (Guadagni, Buttery, et a/., 1963b), then the odor thresholds of aldehydes in air originating only from automobiles could be exceeded. Also aldehydes are generated in other combustion processes, and by the photochemical oxidation of hydrocarbons and aldehydes of molecular weight greater than formaldehyde (Calvert and Pitts, 1966). While a methodology is now available for studying combustion sources, more sensitive methods are required for the analysis of carbonyl compounds in the atmosphere. Literature Cited
Alperstein, M., Bradow, R. L., SOC. Automotice Engrs. Pub. No. 660410,1966a. Aluerstein. M.. Bradow. R. L.. SOC.Automotice Enars. Pub. No. 660781,1966b. Altshuller, A. P., Anal. Chem. 35, 3R-1OR (1963). Altshuller, A. P., Anal. Chein. 37, llR-20R (1965). Altshuller, A. P., Miller, D. L., Sleva, S. F., Anal. Chem. 33, 621-25 (1961). Altshuller; A. P., Wartburg, A. F., Cohen, I. R., Sleva, S. F., Intern. Air Water Pollution 6, 75-81 (1962). Barber, E. D., Lodge, J. P., Jr., Anal. Chem. 35, 348-50 (1963). Begeman, C . R., SOC. Automotice Engrs. Pub. No. 440C, 1962. Buchi, G., Inman, C. G., Lipinsky, E. S., J . Am. Chem. SOC. 76.4327-31 (1954). Calvert, J. G.‘, Pitis, J. N., Jr., “Photochemistry,” Wiley, New York, 1966. Camin, D. L., Raymond, A. J., Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., March 1967. Ellis, C. F., Kendell, R . F., Eccleston, B. H., Anal. Chem. 37, 511-16 (1965). Gallard-Schlesinger Chem. Mfg. Corp., Carle Place, Long Island, N. Y., “2,4-Dinitro-Phenyl-HydrazineBulletin,” 1966. Guadami. D. G.. Buttery. R . G.. Okano. S.. J . Sci. Food Agr .io,’ 76 1-5 (19634. Guadagni, D. G., Buttery, R . G., Okano, S., Burr, H. K., Nature 200. 1288-9 (1963b). Lodge, J. P., Anal. Chem. 33,’ 3R-13R (1961). Nicksic, S. W., Harkins, J., Fries, B. A., J . Air Pollution Control Assoc. 14, 158-60 (1964). Oberdorfer, P. E., SAE Automotive Engrs. Congr., Detroit, Mich., January 1967. Schwartz, D. P., Parks, 0. W., Microchem. J . 7,403-06 (1963). Shriner, R . L., Fuson, R. C., Curtin, D. Y., “The Systematic Identification of Organic Comuounds.” 4th ed.. v . 219, Wiley, New York, 1957. Sigsby, J. E., Jr., Klosterman, D. L., 153rd Meeting, ACS, Miami Beach, Fla., Ami1 1967. Soukup, R . J.; S c a r p e h o , R . J., Danielczik, E., Anal. Chem. 36, 2255-59 (1964). State of California Department of Public Health, Berkeley, “Technical Report of California Standards for Ambient Air Quality and Motor Vehicle Exhaust,” 1960. U. S. Public Health Service “Selected Methods for Measurement of Air Pollutants,” Cincinnati, Ohio, 1965. v
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Receiced for reciew May 22, 1967. Accepted October 9, 1967. Dii‘ision of Water, Air, and Waste Chemistry, 152nd Meeting, A C S , New York, N . Y., September 1966.
