(22) Marcinkiewicz, S., Green, J., J . Chromatog. 10, 184 (1963). (23) Ibzd., p. 366. (24) Ibzd., p. 372. (25) Xarcinkiewicz, S.,Green, J., MeHale, D., Ibid., 10, 42 (1963). (26) llartin, A. J. P., Ann. Rev. Biochem. 19, 517 (1950). (27) >\Iartin, A. J. P., Biochem. Soc. Symp. 3 , 4 (1949). (28) Martin, A. J. P., Synge, R. L. ?*I., Bzochem. J. 35, 1358 (1941). 129) XIartire. D. E.. ANAL. CHEM.33. 1143 (1961'). 130) hIoore. S.. Stein. W. H..' Ann. Rev. ' Biochem. 21, 517 (1952). (31) Aluller, R. H., Clem, D. L., ANAL. CHEM.23,408 (1951). { 32) Perisho, C., Department of Chemis~
try, Mankato College, Minnesota, unpublished data, 1964. (33) Rohrer, A,, Davis, D., Thoma, J., unpublished data, 1964. (34) Ruoff, A. L., Prince, L., Giddings, J., Stewart, G. H., Kolloid-2. 166, 144 (1959). (35) Soczewinski, E., J . Chromatog. 8, 119 (1962). (36) Soczewinski, E., Wachtmeister, C. A., Zbid., 7,311 (1962). (37) Stahl, E., Kaltenbach, U., Zbid., 5, 351 (1961). (38) Thoma, J. A., ANAL.CHEM.35, 214 (1963). (39) Thoma, J. A,, J . Chromatog. 12, 441 (1963). (40) Thoma, J. A., 'Wethods in Carbo-
hydrate Chemistry," R. L. Whistler,
ed., 4, p. 221, Academic Press, New York, 1964. (41) Thoma, J. A., Talanta 8, 829 (1961). (42) Thoma, J. A., unpublished data, 1964. (43) Thoma, J. A., French, D., API'AL. CHEM.29,1645 (1957). (44) Trevylan, W. E., Procter, D. P., Harrison, J. S., Nature 166, 444 (1950). (45) Weill, E. E., Department of Chemis-
try, Rutgers University, Tu'ewark, New Jersey, personal communication, 1964. RECEIVEDfor review JUIY 20, 1964. Accepted February 10, 1965. This research was supported in part by a grant from the General Medical Division of the U. S. Public Health Service GM 08500-04, and in part by a grant from Corn Industries Research Foundation.
Gas Liquid Chromatography at Low Temperatures Resolution of Some Deuterated Ethanes W. ALEXANDER VAN HOOK and MARGARET E. KELLY Department of Chemistry, University o f Tennessee, Knoxville, Tenn.
C4H8-cyclo CrH7T mixtures. The first b A technique for the gas chromatoof these represents the only member of graphic resolution of some of the the saturated hydrocarbon series in deuterated ethanes is described. which complete resolution on packed Chromatograms for the systems C 2 H r CnD6; C2H6-C2H4D2, 1,l d ; and C Z H ~ liquid partition columns has been reported, although Gant and Yang have C2HsDare shown at various temperasucceeded in partially resolving all of the tures between 158°K. and 273°K. intermediate deuterated methanes on The separation factors, S, are calcuGSC columns packed with activated lated from the chromatograms and charcoal. Using a capillary column compared with the vapor pressure Falconer and Cvetanovic (3) have ratios, R. It is observed that InS is conobtained complete separation of a sistently a factor of about 1.3 times saturated hydrocarbon system differing InR over that temperature range where by only four deuterium atoms. Separaa direct comparison can b e made and tions of saturated hydrocarbons from it is pointed out that this result is in their deuterated isomers have in the accord with the statistical theory of isopast been performed a t 0' C. or above. tope effects in condensed systems.
G
LIQUID (GLC) or gas solid chromatographic (GSC) separations of isotopically substituted hydrocarbons are of interest both as a practical analytical tool and as a method for investigating isotope effects in solution (GLC) or during adsorption processes (GSC). Hopefully the latter two phenomena can be ultimately employed to gain a fuller understanding of the intermolecular forces in solution or in the adsorbed state. There are several reports in the literature of the successful separation of various deuterated compounds from their protiated analogs. These have been summarized recently by Gant and Yang (4) and Root, Lee, and Rowland ( 7 ) . [An additional interesting separation of benzene and perdeutero benzene has been reported by Cartoni (.%')I. Root et al. reported the development of a recycle technique employed to separate nC4Hla-nC4Dlo : CH4-CD4; and cyclo AS
508
ANALYTICAL CHEMISTRY
tion times and grossly broadened unresolved peaks were observed. For these reasons the technique of gas liquid chromatography was adopted. EXPERIMENTAL
The gas chromatograph, built in this laboratory, was of conventional design. Helium carrier gas flowed from a liquid nitrogen cooled charcoal trap through the reference side of a Gow-Mac four filament Pretzel thermal conductivity cell, past a rubber septum type injection port, and into the copper column which was coiled and contained in a one-gallon dewar flask. A short section of capillary tubing connected the column exit with the detector and flowmeter. The first separations were performed Vapor pressure measurements on the using molecular sieve supported methylentire series of the deuterated ethanes cyclopentane (MCP) packing a t -78" C. (8) indicated that these isotopic isomers The resolution was a function of the hismight be separable by gas chromatogtory of the packing and appeared to be raphy. The isotope effects are inverse particularly sensitive t o poisoning. Simand all of the vapor pressure ratios, R , ilar results were found for acetone and [defined as R = ( P C ~ H ~ & , / P C ~ H2,3,4-trimethyl ~)] pentane coated molecushow maxima in the temperature range lar sieve columns. I n this respect it 125' to 140' K. It is accordingly most might be noted that molecular sieves carefully dried a t 200' C. under vacuum practical to attempt the separations at and then coated in the absence of water low temperatures. A second advantage vapor and protected from poisoning are of low temperature operation is that ineffective. They give long retention reasonable flow rates can be maintained times and broad unresolved peaks. with smaller pressure drops than are Thoroughly poisoned columns give qhort required a t room temperature and retention times and sharp unresolved above. These advantages are to some peaks while intermediate ones do give extent offset by low sample vapor pressome separation. Our best separations have been persures which increase the retention times formed with columns using MCP supenormously. We have found it imported on firebrick. We have to date practical to work below -115' C. restricted our studies on firebrick colPreliminary experiments were perumns to XICP packings since in the formed at -78" C. using gas solid chromolecular sieve experiments we obmatography with charcoal, alumina, served the best separations with this and molecular sieve columns. I n all substance. MCP is convenient for low cases adsorption on the solid surface was temperature liquid columns because of so strong that inordinately long retenits very wide liquid range and low vapor
Figure 1 .
Figure 2. Chromatograms of C2H6CzHbD mixtures
Chromatograms of C&,-C6De mixtures
(a) 273'K. (No. 9, Table I); ( b ) 224'K. (No. 7, Table I); (c) 195'K. (No. 6, Table I); (d) 158'K. (No. 2,Table I)
pressure [(m.p. - 142.4' C.; vapor pressure 1 mm., -53.7' C.; 40 mm., -0.6' '2.1 (5). The packing was prepared by slurrying together the firebrick (42/60 mesh) and M C P and then pumping off the excess liquid. This material was packed into either 1/4-inch or 3/16-in~h copper tubing which was then compactly coiled. Slightly better resolution was obtained with the column of smaller diameter. The columns were maintained at 273' K (ice-water), 224' K. (CHClrCC14 slush), 195' K. (dry ice-acetone) or 158' K. (ethyl alcohol slush). RESULTS AND DISCUSSION
The results are summarized in Table
I and certain selected chromatograms are shown in Figures 1 through 3. It is
Table 1.
Columna 11 2 I1 31 41 5 I1 6 111 7 11 8 I1 9 I1 10 I1 11 I11 12 I11 13 111
Temp., ' K. 158 158 195 195 195 195 224 224 273 273 158 158 158
Pressure drop, p.s.1.
20 36 11 4 32 34 30 30 29 30 40 38 42
Flow rate,b cc. /min. 102 100 30 12 60 40 41 40 28 30 75 60 70
( a ) 195'K;
to be emphasized that the separation factors are significantly different from the vapor pressure ratios. As expected, the isotope effects are inverse. The resolution between the perdeutero and ordinary isomers (Figure 1) is excellent a t 195' K. and below, while partial resolution persists to 273' K. Attempts to resolve intermediate isomers show some success in Figures 2 and 3 a t the lower temperatures, b u t unfortunately the monodeutero peak is not resolved sufficiently to indicate a separate maximum on the chromatogram. However, the peak a t 158' K. (-30% CaHaD, 70% C2H6)is markedly asymmetric and does indicate substantial enrichment. Since symmetric peaks were obtained in the case of
( b ) 158'K. (No. 1 1 , Table I)
complete resolution (CZH~-CZDB) under the same conditions, we have graphically constructed the deutero and protio peaks as shown by the dotted lines and estimated the separation factor. If the concentration of CzHsD is raised to about equal t o the CzHe, the peaks simply add together producing a symmetrical unresolved peak. The natural logarithms of the chromatographic separation factors, S , (defined as S = corrected retention time of protio compound/corrected retention time of deutero compound) are included in Table I. To have therho. dynamically meaningful data, i t is necessary to correct the observed retention times for the time which the solute spends in the gas space (or dead vol-
Separation Factors for Some Deuterated Ethanes
S (t'C?Hs/t'Deutero) II 2.2 8.7 5.7 11.9 10.8 8.8 13.2 13.4 12.8 12.2 6.6 8.5 7.0
lo3 In R /I
103 In S
l.ll2l 1.1041 1.0891 1.088/ 1.089[ CzHs 1.088/= 1.0821
143.9 486.9 47.7 116.0 88.8 92.3 32.7 34.3 13.7 13.2 409.2 510.8 440.3
75.3 65.1
24.6 75.3 14 111
195
42
56
7.3
76.2
1{
, 0 2 5 1 c2H> 1.088 CiDa
25
21.5
84
65.1
Col. I = 18 foot 1/4-inch 0.d. packed with 17.6y0MCP on firebrick. I1 = 42 foot l/r-inch 0.d. packed with 17.6y0X C P on firebrick. 111 = 50 foot S/16-inch0.d. packed with 19.0% AICP on firebrick. b As measured room temperature and pressure with a soap film flowmeter. c Vapor pressure measured only to 200' K. a
VOL. 37, NO. 4, APRIL 1 9 6 5
509
I
n
1
~
/
1
I
\
40
50 6o
lO;/T
ea
Figure 4. Natural logarithm of chromatographic separation factors (S) (points) or vapor pressure ratios (8b)( R ) (solid line) vs. reciprocal temperature ( O K . ) for the system C Z D ~ / C & Figure 3. tures (a)
Chromatograms of C2Hs-I, 1 CzH4Dz-CzDs
195'K. (No. 14, Table I); (b) 158'K.
ume) of the apparatus. This is conventionally done by injecting some inert material such as air, nitrogen, or hydrogen and subtracting its retention time from the observed retention time. I n chromatography a t low temperatures however, it is often not obvious that a truly inert marker is being used. When the separation factors being determined are small, an improper measurement of the dead time may seriously affect the final results. In our low temperature chromatograms we observe a partial separation of nitrogen and oxygen (nitrogen first) and have been able to adopt nitrogen as a marker only after satisfying ourselves that it, itself, is inert within our experimental error. This was demonstrated by injecting hydrogen and observing that its retention time was identical with nitrogen and more fundamentally by calculating (6) the dead volume in the apparatus from the column dimensions, the measured volume flow rate, the pressure profile across the column, the temperature, and the retention time of air a t high temperatures where it is not adsorbed. Under the assumption that the dead volume is not a function of temperature, the elution time of a nonretained species may then be calculated a t other temperatures, pressures, etc. The calculated times and the observed elution time for nitrogen agreed within experimental error a t all temperatures used in this work. The separation factors in Table I can then be meaningfully compared with the vapor pressure ratios. The hexadeutero data were obtained over the widest temperature range, (158" to 273" K.) since this pair shows the best resolution. Data below 158" K. would be of interert but retention times become inconveniently long because of the low absolute vapor pressure. The precision of the chromatographic data is somewhat more than an order of magnitude 510 *
ANALYTICAL CHEMISTRY
(No. 13, Table I)
mix-
presented in this paper experimental imprecision may mask significant curvature and lead to an assumed and grossly over-simplified straight line relationless than that of the vapor pressure ship.) measurements. It is poorest a t the It is to be expected that similar contemperature extremes because of either siderations will be pertinent to a disminimal separation (273" K.) or peak cussion of separation factors which occur broadening (158" K.) In the region upon vaporization from solution. In where a direct comparison can be the general case, both the zero point made the separation factors are larger energy shifts on condensation and the by a factor of about 1.3 than the vapor lattice frequencies of the solute molepressure ratios. This enhancement is cule will be different from those in the reflected in the mono and. dideutero pure liquid, and separation factors which data. agree identically with the vapor presh theoretical approach to the vapor sure ratios are fortuitous. pressures of isotopic systems exhibiting The natural logarithm of the separahigher order quantum effects has been tion factor S(C2Ds C2He) is plotted made by Bigeleisen ( I ) . Important against reciprocal temperature in Figure contributions arise from the zero point 4. The data are not precise enough to energy shifts on condensation of the high frequency modes (u = hv/kT >, 2 ~ ) distinguish unambiguously between a straight line or a curve. The vapor and secondly from the lower lying pressure data are shown on the same modes (for ethane the lattice modes and graph as a solid line. Substantial the internal rotation should be of this curvature is indicated. In the absence type) and the two types of terms have of more precise data or outside informadifferent temperature dependencies. tion on zero point energy shifts or Significant curvature is therefore exlattice frequencies, it is impossible to pected in l / T plots even over relatively pinpoint the reason for the larger narrow temperature ranges. Bigeleisen separation factors shown by the chroalso demonstrated that the temperature matographic data. One might rsshly dependence of the difference in heats of speculate that the zero point shifts on vaporization of two isotopic species is condensation should be about the same expected to be similar to the behavior of the log of the vapor pressure ratio. For since both ethane and MCP are nonpolar and no specific interactions are hydrocarbons the two types of terms expected in either case. I n that event a contributing to the effect have opposite substantial lowering of the lattice sign, and the theory predicts a frequencies of ethane in the solution as maximum in the inverse isotope effect compared to the pure liquid is demanded which in fact is observed in the ethane by the data. Were a simple cell or cage data (8) (Figure 4 ) . I n view of this model of the liquid adopted, such a development it seems clear that the lowering might be expected as a conslopes of plots of the logarithm of the sequence of a n increased size of the experimental separation factors against ethane containing cage in MCP as reciprocal absolute temperature are not opposed to liquid ethane. I t is amenable to simple interpretation in necessary to keep in mind, however, terms of heat effects. (If the data are that the separation factors are extremely of such precision that the curvature is sensitive to the zero point energy shift3 precisely known a t each point it is clear and that these must be established either that the slope a t such a point may be reby increasing the precision of the data lated to a difference in differential heat or by outside information before quantiterms. However, for data such as are
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 AND MATERIALS
Sampling Equipment. T h e 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
