achieved may be rather costly in terms of the increased operating difficulties arising from the higher inlet pressures required, increased carrier gas consumption, and the greater amount of labor involved in measuring and calculating the quantities required to design a system for minimum time operation. The quantitics w, B, C, ki, and a affect the analysis time under minimum plate height conditions in substantially the same fashion as under minimum time conditions. The conclusions drawn in the preceding sections regarding the influence of these quantities on analysis
time apply equally to either type of operation. LITERATURE CITED
(1) Bohemen, J. Pimell, J. H., in “Gaa Chromatograph D. H. Desty, ed., pp. 12-13, Acagmic Press, New York, 1968. (2) DeFord, D. D., Lyndrup, Ma, unublished results. (3rDeaty, D. H., ,$hldup, A., in “Gaa Chromatography, D. H. Desty, ed., p. 162-83, Butterworths, London, 1960. (4P Giddinga, J. C., Seager, S. L., Stucki, L. R., Stewart, G. H., ANAL.CHEM.32, 867 (1960). (5) Hishta, C., Messerly, J. P., Reschke, R. F., Fredericks, D. H., Cooke, W. D., Zbid., 32,880(1960).
(6) Keulemana,, A. I. M., “Gaa .Chromatography, pp. 13C-8, Remhold, New York, 1957. (7) Kieselbach, R., ANAL. CHEM. 32, 880 (1960). (8) Lo d R. J., Ayers, B. O., Karaaek, F. tbzd., 32,698 (1900). (9) Purnell, J. H., Nalurs 184, 2009 (1969). (10) Purnell, J. H., Quinn, C. P.,in “Gas Chromatography,” D. H. Desty, ed., pp. 184-98, Butterworths, London, 1960. (11) Scott, R.P. W., Hazeldean, C.S. F., Ibid., pp. 144-61.
d,
RECEIVEDfor review November 21, 1960. Accepted March 30, 1961. Presented in part before the Division of Anal ical Chemistry, 137th Meeting, ACS, &veland, Ohio, April 1960.
Automotive Exhaust Gas Analysis by Gas-Liquid Chromatography Using Flame Ionization Detection Determination of
C1
to
c 6
Hydrocarbons
RAYMOND FEINLAND, A. 1. ANDREATCH, and D. P. COTRUPE’ Central Research Division, American Cyanamid Co., Stamford, Conn.
b Gas chromatographic techniques using the flame ionization detector have been applied to the determination of automotive exhaust gas hydrocarbons including C1 to Cg compounds and several Ca compounds. Because of the high sensitivity of the detector, it is possible to analyze a 1-ml. gas sample without a concentration step. Two columns are used to resolve the components. The minimum detectability using a 1 -ml. sample is estimated to be 0.01 p.p.m. for n-butane. The standard deviation for n-butane standards at the 10- to A com100-p.p.m. level is 4%. parable level of reproducibility may be expected for various components in exhaust gas samples which are not subject to peak overlap.
T
HE DETERMINATION of automotive exhaust gas hydrocarbons is an important problem in air pollution studies. Most of the previous work employing gas chromatography has been done with the conventional thermal conductivity detector which necessitated a concentration of the trace hydrocarbons (3, 8, 9). Heaton and Wentworth (6) analyzed the hydrocarbons directly by oxidizing them to
Present address, Chemical Research Laboratories, Amcrican Machine & Foundry, Springdale, Conn.
COZ and passing the latter into an infrared analyzer. This technique requires the use of expensive equipment and, moreover, the sensitivity leaves something t o be desired. Previous workers have used dimethylsulfolane a t 0” C. for determining C1 to CS hydrocarbons (3, 4). The resolution of components was good but the retention time was excessively long. Moreover the presence of Cs saturated hydrocarbons introduces overlapping peaks. The use of a flame ionization detector for the direct determination of exhaust gas hydrocarbons including CI to Cg compounds and several Ca saturated compounds is described. The detector is more sensitive than any previously applied to this problem. Two columns at 25’ C. are employed to give adequate resolution in a reasonable period of time, EXPERIMENTAL
Flame Ionization Detector. An inexpensive rugged detector was designed in our laboratories employing a simple direct current amplifier ( 1 ) . Its sensitivity measured on the basis of the S factor as defined by Dimbat, Porter, and Stross (9)is of the order of 108 mv. ml. per mg. with a noise level of 10 pv. This sensitivity is several thousand times greater than that of the thermal conductivity detector.
Apparatus and Procedure. T o determine the C1 to Cs exhaust gas hydrocarbons, two column packings were used: 20% by weight of dimethylsulfolane on 60- to 80-mesh Chromosorb solid support and 10% by weight of diisodecylphthalate on 60- to SO-mesh Chromosorb W solid support. Each material was packed into 4 meters of l/d-inch copper tubing which was coiled and inserted into a water bath thermostated a t 25.0’ C. The columns were connected in parallel. Hydrogen and nitrogen were mixed in equimolar amounts and passed throug!i the columns a t a total flow rate in each column of 50 cc. per minute. Capillary restrictors (thermometer tubing) were placed in the hydrogen and nitrogen inlet lines to help regulate the gas flow rates and to eliminate back pressure. Thermometer tubing was also used as a restrictor following the column t o regulate the relative flow rate of each. An inlet port was ins+illed a t the entrance of each column for sample injection. Each column was connected to a flame ionization detector and the response of each detector measured by the same IO-mv. recorder, having a chart speed of 48 inches per hour. The dimethylsulfolane substrate has sufficient vapor pressure to cause an extremely high background signal. This signal may be offset by electrical means, but a high noise level would still be present. A trap immersed in a dry ice-acetone slurry was inserted between this column and the detector to condense the dimethylsulfolane vapor. VOL. 33, NO. 8, JULY 1961
0
991
Table 1.
u
Relative Retention Data at
ffFCOffOER
25.0" vs. n-Pentane Relative Retention on Dimethylsulfolane Compound 0.00 Methane 0.040 Ethane 0.040 Ethylene 0.466 Acetylene 0.116 Propane 0.202 Propylene 1.60 Propyne 0.69 Propadiene 0.226 Isobutane 0.346 n-Butane 1-Butene 0.58 0.60 Isobutene 0.75 trans-%Butene cis-2-Butene 0.88 1,a-Butadiene 1.35 0.76 180 entane 1.00 n-&ntane 1.63 1-Pentene %Methyl-1-butene 1.83 1.03 3-Methyl-1-butene 2.44 2-Methyl-2-butene 1.91 trans-2-Pentene cis-2-Pentene 2.08 2,3-Dimethylbutane 1.95 2-Methylpentane 1.97 2.34 3-Methylpentane n-Hexane 2.74
Relative Retention on
Diisodecyiphthalate 0.00 0.021 0.018 0.034 0.088
0.093 0.204 0.178 0.191 0.313 0.314 0.315 0.431 0.489 0.431 0.74 1.00 0.99 1.10 0.66 1.48 1.24 1.31 2.14 2.14 2.66 3.08
Glass wool was inserted in the trap to prevent fog formation. Total volume of the trap was approximately 1.3 ml. No complications resulted from its use as long as the accumulated substrate was removed eve two days. A schematic diagram of t e apparatus is shown in Figure 1. Exhaust gas samples were collected
x
Table
II.
Figure 1. Apparatus for determination of exhaust gas hydrocarbons
in a 125-ml. gas bulb containing an injection port sealed with a rubber stopple. A 1-ml. sample was taken by h podermic syrin e and then ejected. $his wtm repeatef eeveral times to prevent any ossible loas of trace componenta by a&orption on the walls of the syringe. The sample was then injected' into one of the columns. After elhtion of the desired components, a 1-ml. sample waa injected into the other column.l'wo recorders would permit simultaneous elution on the two columns. Gas standards were prepared as described previously (1). RESULTS AND DISCUSSION
In Table I, the relative retention data of the components a t 25.0" C . are given
Hydrocarbons Determined in Automotive Exhaust Gas
Components Obtained on Dimethylsulfolane Methane Ethane Ethylene Acetylene Propane Propadiene n-Butane Isobutene + 1 Butene
+
cis-%Butene 1,3-Butadiene
Components Obtained on Diisodecylphthalate Iaopentane tram-ZPentene n's-%Pentene 2-Methyl-1-butene 3-Methyl-1-butene %Methyl-2-butene 2,3-Dimethylbutane ZMethylpentane 3-Methylpentane n-Hexane
+
Componenta Obtained by Difference Propylene
+ ropylene (DIDP) (DRs)
Propane Propane Difference
propylene trans-2-Butene 1,3-Butadiene trans-2-butene (DIDP) 1,3-Butadiene (DMS) Difference = trans-2-butene 1-Pentene n-Pentane 1- entene (DIDP) n-Pentane (by Jfference) Difference = 1-pentene =
+
+
992
0
ANALYTICAL CHEMISTRY
n-Pentane 3-Methyl-1-butene n- entane (DMS) 3-Methyl-1-butene (DID!) Difference = n-pentane Isobutane Propylene isobutane (DMS) Pro ylene (by difference) DifPerence = isobutane Propyne 1-Pentene pro yne (DMS) 1-Pentene (by diierence) Difference = propyne
+
+
+
for the two columns using n-pentane the internal standard. The elution times or distances are measured from the methane peak instead of the air peak because air produces little or no signal in the flame ion detector. The d a h in Table I are in good agreement with similar data recently reported by Hively (6). Overlap of some components is observed on each column. However, by using the columns in combination, practically every component in the region investigated is obtained aa shown in Table 11. It is necessary to calculate six components by difference, namely, n-pentane, propylene, propyne, isobutane, trans-2-butene, and l-pentene . The chromatograms of the exhaust gas hydrocarbons are shown in Figure 2. The elution time of 1-pentene is 7 minutes on dimethylsulfolane and the elution time of n-hexane is 31 minutes on diisodecylphthalate. The total elution time required is thus 38 minutes. The number of theoretical plates of each column is: dimethylsulfolane, 3300 (n-pentane) ; diisodecylphthalate, 3200 (n-hexane). Two peaks observed on the diisodecylphthalate column were not identified. An upward drift may be observed on the diisodecylphthalate column which wm probably caused by the elution of higher boilers from a previous run. This base line drift, which was observed in some chromatograms, waa not serious enough to lower the accuracy of the method. The systems were calibrated using 10 and 100 p.p.m. by volume n-butane standards in nitrogen, of which 0.50, 0.75, and 1.00 ml. of each was injected. The volume injected multiplied by the concentration (parts per million) was plotted os. area under the recorded
-
I
20
Figure 2. Dlmethybulfolone colurnlrc 1. Methane 2. Ethane ethylene 3. Propane 4 . Propylene bobutane 5. n-Butane 6. Acetylene 7. 1 -Butene 8. lrobutene 9. Propodlene tronr-2-butene 10. lropentane
+
+
+
peak.
This is equivalent to plotting
a function of the number of moles injected vs. the peak area. Linearity was obtained for both systems. The areas of the peaks were found by multiplying peak height by the width a t half peak height. It is necessary to use only n-butane for calibration because the response of the detector is proportional to the number of carbon atoms. Thus the molar response of propane is s/, the molar response of butane; that of hexane a / t the response of butane, etc. This property of the detector has been established in previous work on 17 hydrocarbons in the CI to CI range where a linear carbon response was obtained which is within the limits of accuracy desired in exhaust gas analysis ( 1 ) . The high sensitivity of the flame ion detector enables one to inject 1-ml. samples of exhaust gases without any preliminary concentration steps. A 1-ml. n-butane sample of 10-p.p.m. concentration produced a signal of 8 mv. on the dimethylsulfolane column and 3 mv. on the diisodecylphthalate column. Since the noise level is approximately 0.01 mv., the minimum detectability of n-butane is estimated to be 0.01 p.p.m. on dimethylsulfolane and 0.03 p.p.m. on diisodecylphthalate. This estimation of minimum detectability does not apply in cases where overlapping peaks are obtained, a condition that occurs frequently in exhaust gas analysis. A trace component is most likely to be undetecb able when i t is overlapped by the tail of a larger peak. The flame ion detector is insensitive to gases such as No, 0 , CO, CO, and
Chromatograms of
exhaust
gas
5
0
hydrocarbons
1 1. cis-2-Butene 3-methyl-1 -butene 12. n-Pentane 13. Butadiene 1 -pentens 14. Propyne Diirodecylphtholate colurnnr 1. Propylene propane Irobutane propyne 2. Propadiene 1-butene lrobutene n-Butane 3. 4. Butadiene frons-2-butene 5. cis-2-Butene 6. 3-Methyl-1 -butene
+ + + +++
-
0
IO ELUTION T M E , M " E S
++
HzO (1). This property enables one to determine the light hydrocarbons in the presence of B large excess of air. The results of the analysis of two typical samples of automotive exhaust gas are given in Table 111. One of the samples had been passed over a combustion catalyst to lower the hydrocarbon level. The concentrations of n-prntane and propylene obtained by subtracting a small number from a large number are as accurate as those components obtained directly. The concentrations of propyne, isobutane, trans-2-butene, and 1-pentene arc less accurate than the other components. The reproducibility of the detectors was tested over a period of 9 days. Sample sizes of 0.25, 0.50, 0.75, and 1.00 ml. were taken. The standard deviation of the area under the nbutane peak was 4% and the day-today variation was the same as the within-day variation. This standard deviation includes the uncertainty in injecting the sample volume reproducibly. For exhaust gas samples, the accuracy will be reduced in many cases due to overlapping peaks. The accuracy is difficult to estimate under this condition, but it would probably decrease by a factor of two or more in cases of extreme overlap. Fredericks and Brooks (4) have discussed the use of diisodecylphthalate and dimethylsulfolane columns in series to resolve CIto CShydrocarbons. The over-all resolution and specd of analysis is improved by using the columns separately. Moreover, the identification of the components is simplified when fresh columns have to be prepared
7. Isopentane 8.
n-Pentane
+ 1-pentene
9. 2-Methyl-1 -butene 10. trans-2-Pentene
11. cis-2-Pentene 12. 2-Methyl-2-butene 13. 2,3-Dimethylbutone 14. Unknown 15. 3-Methylpentane 16. Unknown 17. n-Hexane
+ 2-methylpentane
Table 111. Exhaust Gas Analyses Automotive engine exhaust at 40 m.p.h. cruise Concentration, P.P.M. by V o a TJn-
triited sample
Compound 450 Methane 420 ethylene Ethane 300 Acetylene 1.2 Propane Propylene 88 5.9 Propyne 10.0 Propadiene 3.5 Isobutane 41 n-Butane I-Butene isobutene 26 5 trans-2-Butene cis-%Butene 1,3-Butadiene Isopentane n-Pentane 1-Pentene 6.8 2-Methyl-1-butene 4.5 3-Methyl-1-butene 3.8 2-Methyl-2-butene 13.5 trans-2-Pentene 4.7 cis-2-Pentene 1.6 2,3-Dimethylbutane Zmethylpentane 17.5 3-Methylpentane 7.5 +Hexane 12.1
+
+
+
Treated sample 360
179 48
Trace 17.3 1.4 1.9 0.4 11.4
4.2
0.7 1 .o
0.6 2.1
0.6 0.2
3.3 1.1
2.5
because the relative retention times of components will be the same even though the amount of substrate varies from column to column. The daily loss of dimethylsulfolane was 0.1% of the total. The background signal caused by this vaporization was effectively reduced by a cold trap a t -80" C. This may be a general method for reducing the signal caused by the vaporization of substrate. Two VOL. 33,
NO. 8, JULY 1961
993
conditions must be fulfilled: The solute should not be condensed in the cold trap and the solvent that condenses in the cold trap should not contribute appreciably to the retention time of the solute. A plot of the vapor pressure of n-hexnnc 09. temperature indicated that no hydrocarbon in the exhaust gas up to the Ce saturates could condense a t -80" C. a t the concentrations encountered. This was confirmed experimentally from the peak shape of n-hexane in the chromatograph because no tailing or broadening of the peak was observed. The retention times of the components were identical immediately after installing the cold
trap and after a period of several days. This indicates that the condensed substrate did not contribute to the retention times. Some recent work has shown that a considerable portion of exhaust gas hydrocarbons may consist of compounds above CS (7) Determination of these compounds, if desirable, mould necessitate longer elution times and/or a third column.
Isen. F. M..
I
LITERATURE CITED
(1) Andreatch, A. J., Feinland, R., ANAL. CHEM.32, 1021 (1960). (2) Dimbat, M., Porter, P. E., Stross,
F. H., Ibid., 28, 290 (1956).
tion. (8) Hurn, R. W., Chase, J. O., Hughes, K. T.. Ann. N . Y . Acad. Sn'. 72. 675
ANAL.CHEl
RECEIVED for review October 4, 1960. Accepted A ril 6, 1961. Division of Analytical 138th Meeting, ACS, New September 1960.
8 yo%^?^.,
Separation of Trace Elements in Plant Materials from Ferric Iron by Cation Exchange Chromatography F. W. E. STRELOW National Chemical Research Laboratory, South African Council for Scientific and lndusfrial Research, Pretoria, South Africa
b In a recent study of the equilibrium distribution coefficients of cations with AG 50W-X8 resins in nitric acid, differences between the Kd values of Fe(lll) and many of the bivalent heavy metals were noticed. This fact was used to develop a cation exchange chromatographic procedure for the separation of trace amounts of Pb(ll), Mn(ll), Cu(ll), Ni(ll), Co(ll), Zn(ll), and Ti(lV) from larger amounts of iron in South African plant materials. The method can be extended to 100- to 150-mg. amounts in the case of the separation of Ti and Ni from iron. Mo(V) and V(V) are separated from iron at the same time, and the method can be modified to separate tin(lV) as well. Percentage recoveries for about 100-pg. amounts of the trace elements are given.
T
HE SPECTROGRAPHIC DETERMINATION of the trace metals Pb, Mn,
Cu, Ni, Co, Zn, Ti, Sn, Mo, and V in plant materials is hampered by the presence of large amounts of alkalies, alkaline earths, and iron. Stetter (9) extracted the above trace metals plus some others as the pyrrolidine dithiocarbamate complexes into chloroform, and thus separated them from the alkalies and the alkaline earths. Iron, which is often present in fairly large amounts in South African plant materials such a8 citrus leaves, is extracted with the trace metals. Strasheim (9) showed that the amount of iron present influences the measured intensity of the spectrographic lines 994
ANALYTICAL CHEMISTRY
used for the determination of the concentration of the trace metals. Furthermore, the sensitivity of the determination of the trace metals is depressed in low dispersion spectrographs because at very low concentrations their lines are obscured by the complex iron spectrum. Gorbach (1) developed a procedure for the separation of some trace metals from iron, the alkalies, and alkaline earths. The method is complicated and includes a benzoate precipitation at accurately controlled pH, ether and dithizone extractions, a tartrate destruction step, and an oxine extraction. It proves to be time consuming under actual working conditions. The relatively high I
