procedures. It is also ideally adaptable to routine quality control in viscose plants. The method depends On the finding Of this work that the by-product sulfur in undiluted viscose is almost entirely in the form of trithiocarbonate. Other postulated sulfur-containing by-products, namely sodium sulfide (18) or cellulose dixanthogen ( 5 ) are present in negligible amounts, if at all. -.
(18) E. Kline in “Cellulose and Cellulose Derivatives,” E. Ott, H. M. Spurlin, and M. W. Grafflin, Ed., 2nd ed., Part 11, Interscience, New York, N. Y . 1954, p 991.
ACKNOWLEDGMENT
I thank Messrs. A. F. Turbak, M. N. O’Brien, and D. J. Bridgeford for stimulating discussions during this work. Technical assistance of Mrs. M, E. coxand Mr. J, A. Lynch is gratefully acknowledged. RECEIVED for review April 22, 1971. Accepted June 29, 1971. Presented before the Cellulose, Wood, and Fiber Chemistry Division at the 160th National Meeting of the American Chemical Society, Chicago, Ill., September, 1970. Acknowledgment is due to the Management of Tee-Pak, Inc. for permission to publish this work.
Isolation and Analysis of Carbonyl Compounds as Oximes James W . Vogh Bartiesoilie Energy Research Center, Bureau of Mines, U . S. Department of the Interior, Bartlesoille, Okla. 74003
Analysis of carbonyls in complex mixtures, such as automotive exhaust, is seriously hampered by interference problems. Methods for isolating carbonyls from interfering components exist but render mixtures that are not readily analyzable. In the present study, procedures were developed for collectinq and isolating carbonyls from complex mixtures as oximes, and for subsequent chromatographic analysis of the oxime mixture. The isolation procedure was based on the weak-acid properties of oximes, which permit separation from hydrocarbons and other neutral materials by extraction with pentane. Retention of oximes in the basic phase was improved by addition of alcohols and by extraction at low temperatures. Chromatographic analysis of oximes was accomplished using an all-glass system. Oximes were decomposed to nitriles by hot metal surfaces but were stable in glass equipment that had been cleaned to remove heavy metal oxides. The most satisfactory chromatographic column had a glass tube filled with glassbead support that was coated with a polyglycol liquid phase. In chromatograms, most aliphatic aldoximes showed double chromatographic peaks that were due to the ryn and anti isomers. These were identified, and the isomer peak ratio was shown to be affected by steric interference. Phenols were recovered in the isolation procedure and could be analyzed in the same chromatographic system. Applications in diesel- and gasoline-engine exhaust are discussed. THERE ARE numerous procedures for collection, isolation, and analysis of mixtures of aldehydes and ketones. However, the choice of method may be limited when experiments involve dilute sample and complex mixtures. In these cases, isolation of the carbonyl compounds or their derivatives from interfering components is the most critical part of the procedure. These problems are found in engine exhaust gas analysis because the aldehydes and ketones are quite complex but are only a minor part of the organic components. Hydrocarbons in the engine exhaust interfere seriously in direct gas chromatographic analysis and generally prevent determination of the higher-molecular-weight carbonyls. These problems led to a review of carbonyl analysis methods and to the development of new procedures for isolation and detailed determination of the aldehydes and ketones present in engine exhaust gases. The best known methods that serve both collection and isolation of the carbonyl compounds are based on the solid 1618
dinitrophenylhydrazone derivative (1) and the soluble ionic bisulfite (2, 3) and Girard (4) derivatives. The Girard reagents provide the best available procedure for the collection and isolation steps. These reagents react quite generally and readily with carbonyls, although some sterically hindered ketones react poorly.(5). The isolation is usually based on extraction of a water solution of the derivative by a nonpolar solvent, and the separation is specific and complete. The Girard derivative of some carbonyls decomposes to a considerable extent during ordinary extraction procedures, but a method for extraction under anhydrous conditions has been developed to prevent this (6). This method may not be useful if the original sample contains water. Other problems in the Girard procedure are incomplete recovery of some carbonyl derivatives (4) and the need to regenerate and recover the carbonyls for gas chromatographic analysis. Conversion to oxime derivatives is a particularly useful technique for collecting and isolating carbonyls. The derivative-forming reaction is quite rapid for most carbonyls and occurs in all carbonyl classes, including the sterically hindered ketones. The high reaction speed is particularly helpful in sample collection from gas streams by high-speed scrubbers. Further, oximes are weak acids (pK 10-12) (7)-a property that could be used to isolate them for analytical purposes. Because oximes are stable in basic solution (8) and may be recovered without apparent loss, they can be separated from hydrocarbons and most other neutral compounds by extraction from a paraffinic solvent by dilute base. Detailed analysis of the carbonyls may be carried out either directly on the oximes or o n the carbonyls regenerated from the oximes. Although several methods have been developed (1) R. J. Soukup, R. J. Scarpellino, and E. Danielczik, ANAL. CHEM., 36, 2255 (1964). (2) D. A. Levaggi and M. Feldstein, J . Air Pollut. Control Ass., 20, 312 (1970). (3) . . C . F. Ellis, R. F. Kendall, and B. H. Eccleston, ANAL.CHEM., 37, 511 (1965). (4) . , D. F. Gadbois, J. M. Mendelsohn, and L. J. Ronsivalli, ibid., p 1776. ( 5 ) 0. H. Wheeler, Chem. Reu., 62, 205 (1962). (6) S. F. Osman and J. L. Barson, ANAL.CHEM., 39, 530 (1967). (7) E. F. Degering, “An Outline of Organic Nitrogen Compounds,” University Lithoprinters, Ypsilanti, Mich., 1945, Chap. 13, p 180. (8) Ibid., p 194.
ANALYTICAL CHEMISTRY, VOL. 43, NO. 12, OCTOBER 1971
for converting the oximes t o carbonyls (9), direct analysis of the oxime mixture is preferable in that it avoids the extra effort and error involved in regeneration. Information o n gas chromatography of oximes is limited; there is only one report (10) of successful analysis. Other reports indicate failure (11) or suggest that the oximes be converted to another form (12). The latter reference suggests conversion of oximes t o the 0-methyl ethers, but this seems unsuitable since methylation attacks both the N and 0 atoms of the oxime (13) and, furthermore, has the objectionable characteristics associated with carbonyl regeneration. The major difficulty in gas chromatography of oximes is decomposition at the working temperature of the injection port or
column. This report covers work done at the Bartlesville Energy Research Center to develop procedures for collection and isolation of carbonyls as oximes and for subsequent chromatographic analysis of the oxime derivatives. A study of factors contributing t o the decomposition of oximes during chromatography showed that oximes are stable if heavy metals and their oxides are avoided. The procedures that are discussed in this report provide a general method for detailed analysis of aldehydes and ketones. While initial interest was in analysis of exhaust from internal combustion engines, no restrictions in the scope of the analytical method were found and it is likely that the procedures may be applied t o other samples. EXPERIMENTAL
Hydroxylamine Reagent Solution. The hydroxylamine solution was prepared by allowing a saturated solution of NH20H-HC1 in methanol to react with an equivalent amount of potassium hydroxide dissolved in a small amount of water and a half equivalent amount of glacial acetic acid. The mixture was filtered a t 0 "C to remove potassium chloride. The saturated methanol solution contained 0.124.1 3 gram/ ml NH20H-HC1 a t room temperature. Oximes are generally soluble at moderate concentrations in methanol. Isolation Procedure. After the sample had been collected (e.g., for exhaust, by passing a known volume of exhaust gas through a scrubber containing the methanol-hydroxylamine solution), the methanol-hydroxylamine solution was made basic by adding sodium hydroxide. Solid NaOH is recommended for this since it avoids dilution. Sufficient NaOH was added to make the solution about 1-2N and to react with the acetic acid. This solution was then washed with n-pentane to remove hydrocarbons and other neutral materials. The number of extraction steps required depends on the quantity of contaminant present and the completeness of phase separation. Recovery of Oximes and Other Acid Components. The oxime and other weak acid salts and the excess sodium hydroxide were neutralized with either carbon dioxide or acetic acid. Use of carbon dioxide avoids any question of release of carboxylic acids and subsequent extraction with the oximes. Neutralization with acetic acid to pH 8-9 achieves the same result and is more convenient. The neutralized solution was then diluted with sufficient water to reduce the alcohol concentration below 35 %, and the solution was saturated with sodium chloride. The oximes and other components including phenols were extracted with (9) A very extensive list of conversion methods is given by E. J. Corey and J. E. Richman, J . Amer. Chem. SOC.,92, 5276 (1970). (10) J. Cason and E. R. Harris, J . Org. Chem., 24, 676 (1959). (11) L. J. Lohr and R. W. Warren, J . Chromatogr., 8, 127 (1962). (12) H. M. Fales and T. Luukkainen, ANAL.CHEM., 37, 955 (1965). (13) E. F. Degering, ibid.,p 182.
ethyl ether. When necessary, the ether solution was concentrated to prepare it for gas chromatography. A suitable internal standard may be added to the ether solution of oximes. The distribution of several oximes between ethyl ether and a solution of 33% methanol in water saturated with sodium chloride was determined by the method of successive extractions (14). The solutions contained 0.1-0.2Z of the oximes of formaldehyde, acetaldehyde, propanal, butanal, and acetone. Extractions were made using equal volumes of liquids and were carried out a t 0 "C. Oximes in the ether phase were analyzed by chromatography on the UCON column described below. Chromatography. The injection port and chromatographic column must be free of heavy metals and their oxides. Since glass does not cause decomposition of oximes up to 230 "C (highest temperature used), the injection port liner and column were constructed of borosilicate glass. Decomposition of oximes did not occur when clean glass beads were used for support. Since variable and unpredictable results were obtained with diatomaceous support, glass beads were preferred. The glass bead support has advantages of lower elution temperature and less peak tailing that are not generally found in other supports. Smooth glass beads suitable for gas chromatography may be used if they are cleaned with aqua regia; however, Corning textured beads (GLC-100, Corning Glass Works) are recommended because they produce a more efficient column and are easier to handle (15). They require no aqua regia cleaning because of the method of their preparation, and, in fact, should not be so treated since they appear to be slightly water soluble. Satisfactory oxime separations were obtained using Carbowax 20M and UCON-50-HB-660 at a 0.1 % level on the glass beads. The UCON column was preferred in work with low-molecular-weight oximes since these appeared to be well resolved at a convenient temperature and retention time. The retention times of oximes on the Carbowax column were appreciably shorter so that this column was more useful in analysis of high-molecular-weight oximes. The useful range of the Carbowax column extended through the oximes of naphthaldehyde and octadecanal, the highest molecular weight carbonyls examined. The columns were 42-inch long, 4-mm-i.d., borosilicate glass tubing. They had a square form, about 7 inches on each side, with broadly rounded corners. The columns were filled by vibration and by immersion in an ultrasonic cleaning vat while under vacuum. Nitrogen was used as carrier gas and was passed through a bed of hydrated sodium sulfate at room temperature before entering the column. The flow rate was 20 cc/min. If the column is to be used for analysis of phenols, it should be conditioned for an extended period at 180-200 "C. Phenol peaks may remain quite broad compared with the oxime peaks under conditions that produce good oxime chromatograms. In this case the column should be conditioned before each run by injecting 5-10 pl of water at column temperature of 75 "C, held at that temperature for 5 min, and brought to the desired temperature for sample injection and start of chromatogram. This will usually produce a good phenol chromatogram, but the procedure is not recommended if the sample contains only oximes. The chromatogram was run at a temperature rise program rate of 2 or 6 "C/min, depending o n the resolution required and the maximum temperature needed to develop the sample. The lower temperature program rate was used for complex
(14) L. C. Craig and D. Craig in "Technique of Organic Chemistry," Vol. 111, A. Weissberger, Ed., Interscience, New York, N. Y.,1950, p 182-184. (15) A. M. Filbert and M. L. Hair, J. Gas Chromatogr., 6 , 218 (1968).
ANALYTICAL CHEMISTRY, VOL. 43, NO. 12, OCTOBER 1971
1619
solution. It was held at 0 "C during the sampling. Its performance in removing various components from gas streams has been reported previously (16). The oximes of the exhaust carbonyls were isolated and chromatographed by the procedures described above.
Table I. Extraction of Alcoholic Base Solutions by nPentane for Isolation of Oximes Results shown are per cent retention in the basic phase on extraction by an equal volume of n-pentane 3N
DISCUSSION
NaOH. 50%
'
methanol, 3N NaOH, 50% ethanol 20 "C 20 "C 0 "C -20 "C Aldehyde oximes n-Nonanal n-Tetradecanal m-Tolualdehyde 1-Naphthaldehyde Cinnamaldehyde Ketone oximes 2-Heptanone 2-Pentadecanone 8-Pentadecanone 2,4-Dirnethyl-3-pentanone 3-Methyl-3-pentene-2-one
4-Methyl acetophenone Alcohols, phenol 1-Octanol Benzyl alcohol p-Cresol Hydrocarbons Pentadecane 2-Ethyl naphthalene
...
91 85 99 99 99
96 99 99 99 99
99 99 99 99 99
96
99 90
90 99 99
99 66 1 99 99 99
99 99 99
8 91 99
65 92 99
72
85
95 99
98
1 1
1 1
1 1
... ...
35
...
... ...
...
... 98 75
... , . .
...
... ... I
.
.
mixtures (the exhaust samples) and for those containing highmolecular-weight carbonyls. An F and M model 810 gas chromatograph equipped with a flame ionization detector was used to monitor the chromatogram. Examination of the Isolation Procedure. The distribution of several oximes and other materials between the pentane and basic phases was determined to show the effectiveness of the isolation procedure. Solutions of these materials made up in pentane a t 0.2 to 1.0 wt % concentrations were contacted with equal volumes of 3 N NaOH in 50% methanol or 50% ethanol. Extraction temperatures were 20, 0, and -20 "C. The pentane solutions were analyzed before and after extraction in order to delermine the amount of each component transferred into the basic phase. These analyses were made by means of the gas chromatographic techniques described for oxime analysis. Stability of Oximes. The formation of nitriles in the decomposition of oximes and the conditions for decomposition were observed by means of mass spectrometric methods. In one system the chromatograph effluent was coupled to a Bendix T.O.F. mass spectrometer by means of a 4-foot-long, 0.01-in.-id., stainless-steel tube. Benzaldoxime was chromatographed, and the 121 and 103 m / e peaks were monitored to detect benzaldoxime and benzonitrile. The second system used a molecular leak sample device with dual borosilicate glass and stainless-steel reservoirs held at 150 "C and coupled to a CEC model 103 mass spectrometer. Benzaldoxime was held in each reservoir, and the 121 and 103 m / e peaks were monitored over a 1-hour period. Applications-Engine Exhaust Carbonyl Compounds. Diesel exhaust was sampled directly from the engine exhaust manifold. The absorber containing the hydroxylamine reagent solution was attached to a short sample probe in the manifold and the exhaust sample was drawn into the absorber by vacuum without filtering. Automobile exhaust was sampled from the tailpipe in a similar manner. Exhaust from both the automobile and the diesel engine were drawn through the absorber at 4.5 liters per minute for 10 minutes. The absorber used for this sampling was a liquid lift type scrubber and contained 15 ml of the hydroxylamine reagent 1620
Isolation Process. Certain oximes are partially extracted from the basic solution into the pentane phase, This is particularly significant for the higher aliphatic ketoximes in which both alkyl groups are large. Both the temperature of extraction and the basic solution solvent affect the degree of extraction by pentane. Table I shows the results of distribution measurements of a variety of oximes and other materials between alcohol base solutions and pentane. The aldoximes appear to be fairly easily extracted into the basic phase using either of the alcohols and at any temperature. The ketoximes are not so well extracted, perhaps indicating that they are weaker acids than the aldoximes. The high-molecular-weight aliphatic ketoximes are difficult to extract, and those in which both of the alkyl groups are large are retained in the pentane to the greatest extent. Use of ethanol-base mixture at low temperature permits separation of these ketoximes from contaminating hydrocarbons. They are extracted from the base solution as free (acid form) oximes rather than as the sodium salt. This evidently is the result of hydrolysis of the anion as the conjugate base form of a very weak acid. The decreased hydrolysis at low temperature is probably due to the lowering of the dissociation constant of water. Alcohols have dissociation constants in the range 10-18 to 10-lg (17) and presumably should be extracted by pentane from the basic solution. However, the results of extraction measurements shown in Table I indicate some tendency of alcohols to be retained in the base. Benzyl alcohol and related alcohols cannot be separated from the oximes, but other higher aliphatic alcohols can be removed by repeated pentane washing of the methanol-water solution at 20 "C. The oximes are recovered from the neutralized solution by extraction with ethyl ether. Some of the lower molecular weight oximes are not completely extracted and the best procedure for collection of these oximes is repeated extraction by small volumes of ether. The distribution constants at 0 "C for several oximes are : formaldoxime-4 ; acetaldoxime-5 ; propanaldoxime-19; acetone oxime-21 ; butanaldoxime->75. Temperature does not appear to have an appreciable effect on the distribution constants. The recovery of the oximes depends on the number of extractions and the relative liquid volumes and may be calculated on the basis of the distribution constants by the methods of reference (14). If the procedure is carried out in three extractions using a volume ratio of ether to neutralized solution of 0.1, about 64% of the formaldoxime and 97% of the acetone oxime should be recovered. The higher molecular weight oximes are generally recovered with good efficiency. Phenols remain with the oximes through the extraction procedure. Oximes are only slightly weaker acids than the phenols, and it is not practical to attempt separation during the neutralization step. Unless the phenols are present in excessive variety and amount, they do not interfere with the oxime chromatographic analysis. Examples are shown of analysis of engine exhaust which contain phenols and carbonyls. (16) J. W. Vogh, J . Air Pollut. Control Ass., 19, 773 (1969). (17) W. F. McEwen, J . Amer. Chem. SOC.,58, 1124 (1936).
ANALYTICAL CHEMISTRY, VOL. 43, NO. 12, OCTOBER 1971
~
~~
Table 11. Retention Times of the Oximes of Aldehydes and Ketones on the GLC Carbowax-20M Column Time. minutes First or Peak height Peak time, Second peak ratio (ho/hl) only peak Aldehydes Ketones minutes ... 2.9 ... Acetone Formaldehyde 6.7 4.2 5.4 Butanone 1.10 10.5 Acetaldehyde 7.1 2-Pentanone 0.66 8.6 14.9 Propanal 12.9 11.2 3-Pentanone 0.69 Butanal 12.5 17.2 15.8 2-Heptanone 0.69 Pentanal 25.0 22.4 20.9 3-Heptanone 0.66 Hexanal 21.7 27.3 25.6 2-Pentadecanone 0.69 Heptanal 59.7 32.2 30.6 0.69 8-Pentadecanone Octanal 56.8 35.4 0.66 37.0 3-Methylbutanone Nonanal 12.8 41.7 40.0 4-Methyl-2-pentanone 0.62 Decanal . 17.4 59.0 57.5 0.72 4-Methyl-3-hexanone Tetradecanal 19.3 66.4 65.0 0.63 Hexadecanal 2,4-Dimethyl-3-pentanone 17.0 73.6 72.3 :not sep.) 25.7 Octadecanal 2,2-Dimethyl-3-heptanone 7.7 2-Methylpropanal 8.8 2,4-Dimethyl-3-heptanone 0.35 25.6 ... ... 2,2-Dimethylpropanal 10.0 2,6-Dimethyl-4-heptanone 24.6 16.5 3-Methylbutanal 14.6 0.87 3,5-Dimethyl-4-heptanone 25.9 18.4 19.5 2-Ethylbutanal 0.43 Cyclopentanone 23.9 16.9 2-Methylpentanal 0.36 18.0 Cyclohexanone 27.7 23.5 2,3-Dimethylpentanal 22.3 0.54 Cyclododecanone 55.1 21.1 2-Ethyl-3-methylbutanal 3-Buten-Zone 20.0 0.28 18.5 31.2 Cyclohexane car boxaldehyde 3-Methyl-3-buten-2-one 30.1 0.41 26.1 Phenylacetaldehyde 3-Methyl-3-penten-2-one 47.1 0.90 48.8 39.8 Hydrocinnamaldehyde 51.1 52.8 ... Acetophenone 48.6 13.8 15.2 Propenal 4-Methylacetophenone 52.6 0.22 2-Butenal Benzophenone 20.1 22.2 76.0 0.24 15.9 ... 2-Methylpropenal 9-Fluorenone 95.9 2-Methyl-2-butenal 23.3 ... p-Methoxyacetop henone ... 64.0 Cinnamaldehyde 63.5 63.8 Butanedione (monoxime) (not sep.) 36.0 46.2 ... Benzaldehyde ... Butanedione (dioxime) 59.5 49.8 ... o-Tolualdehyde ... 2,CPentanedione (dioxime) 58.8 m-Tolualdehyde 50.3 ... ... 2,3-Hexanedione (dioxime) 64.1 50.1 ... p-Tolualdehyde ... 2,s-Hexanedione (dioxime) 63.7 2-Methoxybenzaldehyde 60.1. ... ... 3,4-Dimethoxybenzaldehyde 74.0 ... ... 1-Naphthaldehyde 76.1 .,. ... 76.2 . , . 2-Naphthaldeh yde
The lower carboxylic acids are not liberated during the neutralization and do not interfere with the chromatographic analysis. Chromatography. A wide range of oximes and phenols may be analyzed by either the Carbowax 20M o r UCON columns. The aliphatic aldehyde oximes examined range from formaldehyde to octadecanal, and the aromatic aldehydes through I-naphthaldehyde. The ketone oximes elute earlier than the aldoximes of corresponding structure and presumably may be analyzed over an equivalent range. Phenols ranging to I-naphthol may also be resolved, although the more acid phenols tend to show broad and tailing peaks. Table I1 contains retention times determined for the Carbowax column for a number of oximes. The columns were temperature programed at 2 "C/min following sample injection at 50 "C. An unusual characteristic of the oxime chromatograms was the occurrence of double peaks for most of the aliphatic aldoximes. The aliphatic aldoximes examined included oximes of conjugated unsaturated aldehydes and phenyl acetaldehyde along with normal and branched saturated aldehydes. Only formaldehyde, 2,Z-dimethyl propanal, 2methyl propenal, and 2-methyl-2-butena1, among those examined, failed to show the double peak. Oximes of ketones and of aromatic aldehydes with the carbonyl o n the ring showed only single peaks. Pejkovic-Tadic et al. (18) showed that the syn and anti (18) I. Pejkovic-Tadic, M. Hranisavljevic, and S. Nesic, J. Chromatogr., 21, 239 (1966).
isomers of aliphatic aldoximes can be separated by thin-layer and liquid-solid chromatography. The two peaks found in this work evidently represented these isomers. This 'is confirmed by the partial conversion of the isomer mixture to the syn form. This was done by treatment of butanaldoxime with 1.2N NaOH for 18 hours at room temperature followed by neutralization with solid NaH2P0, and extraction with ether. Figure 1 shows the chromatogram of the butanaldoxime before and after base treatment. The first peak is seen to increase at the expense of the second. The first peak should therefore be the syn isomer (19). The isomer mixture obtained by this base treatment is not stable and will revert over a period of hours or days to the isomer composition found before base treatment. Figure 2 shows a chromatogram of a mixture of the oximes of acetaldehyde, propanal, 2-methyl pentanal, and 2,2-dimethyl propanal. The anti acetaldoxime isomer (second peak) is the larger part of the acetaldoxime and therefore may be the more stable isomer form if no steric interference effect is present. The relative amounts of each isomer are evidently sensitive to steric interference as alkyl groups are substituted for alpha hydrogens, as was shown by the increasing amounts of syn isomers for propanal and 2-methyl pentanal. Only one peak is found for 2,2-dimethyl propanal oxime, and this is the pure syn isomer. This compound has been shown by N M R studies (20) to exist only in the syn form. A detailed
-
(19) E. F. Degering, ibid., p 189. (20) G. G. Kleinspehn, J. A. Jung, and S . A. Studniarz, J . Org. Chem., 32, 460 (1967).
ANALYTICAL CHEMISTRY, VOL. 43, NO. 12, OCTOBER 1971
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20
30
4
MINUTES
Figure 2. Chromatogram of aldoxime mixture, UCON 50 HB 660 column, temperature programmed a t 2 "C per minute
,
L'
IO
0
L
1, 1'.
Acetaldoxime
2, 2'. Propanaldoxime 3. 2,2-Dimethylpropanaldoxime 4, 4'. 2-Methylpentanaldoxime
5
MINUTES
Figure 1. Chromatogram of butanaldoxime, Carbowax 20M column, 65 OC temperature A . Stock solution treated with 1.2NNaOH 18 hours, neutralized
with solid NaHd'O,, and chromatographed immediately B. Stock solution in ether, aged
list of isomer ratios is shown in Table 11. These are given as the peak height ratios and represent the antilsyn isomer ratio. The same trend in isomer ratios with alpha substitution and similar specific ratios has been determined previously (21) by NMR methods, Stability of Oximes. The mass spectra studies both showed the formation of benzonitrile from benzaldoxime and indicated that hot metal surface caused the decomposition. Both compounds were found in the chromatographed benzaldoxime peak. Since pure benzonitrile had a much lower retention time than benzaldoxime, it would appear that the post-column decomposition occurred in the metal system connecting the column to the mass spectrometer source. In the other mass spectrograph system, the 103 and 121 mje peaks were determined for benzaldoxime stored in the glass or metal reservoirs. Results of this showed that benzaldoxime in the sample contained in the borosilicate glass reservoir remained at 82% of the total over a one-hour period. In the stainless-steel reservoir, the benzaldoxime was 66 of total at the initial measurement, 4 6 x after 20 minutes, and 2 6 z at one hour. Benzonitrile was detected in material from both reservoirs, and it is possible that the 103 m/e peak is a normal part of the benzaldoxime mass spectra. No
(21) F. C. Nachod and W. D. Phillips, "Determination of Organic Structures by Physical Methods," Vol. 2, Academic Press, New York, 1962, p 444-5. 1622
significant change in composition occurred while the benzaldoxime was held in the glass reservoir. This would indicate that the benzaldoxime was not decomposing within the glass container. Applications. The methods described were applied to the isolation and analysis of carbonyls in automotive and diesel exhaust. Engine exhaust contains numerous organic components at low total concentration. The predominant materials are hydrocarbons that may be either unburned fuel or combustion products. The molecular weight range of the hydrocarbons is broad and may in some circumstances include engine lubricant materials. Carbonyls (aldehydes and ketones), prominent in the oxygenated organic classes, have been found at total levels of up to 100 ppm. Figures 3 and 4 show the oxime chromatograms for gasoline engine exhaust and diesel exhaust, respectively. The gasoline engine exhaust sample was obtained during cyclic mode operation. The total carbonyl level was about 60 ppm. The diesel exhaust sample was obtained during idle mode operation of a precombustion-chamber type of engine. The total carbonyl level was about 100 ppm. The two types of exhaust differed in carbonyl compound composition, both in principal components and in total amounts of the carbonyls. The carbonyl composition of each exhaust varied with operation mode, so that the patterns indicated by Figures 3 and 4 d o not generally represent gasoline and diesel exhaust carbonyl composition. The analysis of engine exhaust carbonyls is based on both the isolation and the chromatographic procedures for oximes. Other problems in analysis, preparation, or chemical reactions of the oximes may use either procedure alone. The isolation procedure for oximes is a convenient and general purification process; it may be used to prepare material for other oxime or carbonyl studies or may be used with other analytical
ANALYTICAL CHEMISTRY, VOL. 43, NO. 12, OCTOBER 1971
RETENTION TIME, MINUTES
-
Figure 3. Gasoline engine exhaust sample, Carbowax 20M column, programmed a t 2 "C per minute 1. Formaldehyde; 2, 2'. acetaldehyde; 3. acetone; 4, 4'. propanal; 5. butanone; 6. 2-methylpropenal; 7. benzyl alcohol; 8. o-cresol; 9. phenol; 10. rn-cresol; 11. p-cresol; 12. benzaldehyde; 13. tolualdehydes; 14. 1-naphthol (internal standard)
0
10
20
30
40
3
50
MINUTES
/'
Figure 4. Diesel exhaust sample, Carbowax 20M column, temperature programmed at 2 "C per minute 1. Acetone; 2, 2'. propanal; 3. isobutanal; 4. butanone; 5, 5'. propenal; 6. 2-methylpropenal; 7. 3-butenal; 8. phenol; 9. benzaldehyde; 10. tolualdehydes
methods. The gas chromatographic procedure for oximes is more convenient than methods Previousb developed and should be useful in studies of oxime chemistry and properties. ACKNOWLEDGMENT
neauthor thanks Donald seizinger for conducting and interpreting the mass spectrometric experiments and for many useful discussions.
R E C E I V Ereview D ~ ~April ~ 12, 1971. Accepted June 29, 1971. Trade names are used in this report for identification purposes only and d o not necessarily imply endorsement by the Bureau of Mines. Work supported by the Environmental Protection Agency (formerly, National Air Pollution Control Administration, U. s. Department of Health, Education and Welfare).
ANALYTICAL CHEMISTRY, VOL. 43, NO. 12, OCTOBER 1971
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