(3) Bruderreck, H., Schneider, W., Halbz, I., ANAL. CHEM.36, 461 (1964). (4) Brunner, H., Pharm. Ind. 20, 581 (1958). (5) Carman, P. C., “Flow of Gases through Porous Media,” p. 8, Butterworths, London, 1956. (6) dal Nogare, S., Juvet, R. S., Jr., “Gas-Liquid Chromatography,” p. 135, Interscience, New York, 1962. (7) Desty, D. H., Godfrey, F. M., Harbourn, C. L. A. “Gas Chromatography 1958, Amsterdam,” p. 200, Butterworths, London, 1958.
(8) Desty, D. H., Goldup, A., Swanton, W. T., “Gas Chromatography 1961, Lansing.” N. Brenner. J. E. Callen. ,ds., p.’ 105, Academid Press, N ew York, 1962. (9) Desty, D. H., Haresnape, J. N., Whvman. B. H. F., ANAL.CHEM.32. ,.-Luu,
302”(1960). (10) Ettre, L. S., “Open Tubular Columns
in Gas Chromatography,” p. 34, Plenum Press, New York, 1965. I ) Glueckauf, E., ‘‘Vapour Phase Chromatography 1956, London,” p. 29, Butterworths, London, 1957. 2) Golay, M. J. E., “Gas Chromatography 1958, Amsterdam,” D. H. Desty, ed., p. 36, Butterworths, London, 1958. 3) Golay, M. J. E., “Gas Chromatography 1961, Lansing,” N. Brenner, J. E. Callen, M. D. Weiss, eds., p. 11, Academic Press, New York, 1962. (14) Halhz, I., Hartmann, K., Heine, E., “Gas Chromatography 1964, Brighton,” A. Goldu , ed., p. 38, Institute of Petroleum. Eondon. 1965. (15) Hal& I., Heine, E., ANAL.CHEM. 37, 495 (1965). (16) Halbz, I., Heine, E., Nature 194, 971 (1962). (17) Halbz, I., Schreyer, G., Chem. Ing.Tech. 32, 675 (1960).
(18) Keulemans, A. I. M., Kwantes, A., “Vapour Phase Chromatography 1956, London,” p. 15, Butterworths, London, 1957. (19) Littlewood, A. B., “Gas Chromatography 1958, Amsterdam,” D. H. Desty, ed., p. 23, Butterworths, London, 1958. (20) Litt,l,ewood, A. B., “Gas Chromatography, p. 145, 187, Academic Press, 1962. New Yo,!r (21) Reisch, J. C., Robison, C. H.,
Wheelock, T. D., “Gas Chromatography 1961, Lansing,” p. 91, Academic Press, New York, 1962. (22) Scott, R. P. W., “Gas Chromatography 1958, Amsterdam,” D. H. Desty, ed., p. 189, Butterworths, London, 1958. RECEIVED for review September 30, 1965. Accepted December 6, 1965. Third International Symposium on Advances in Gas Chromatography, Houston, Texas, October 1965.
I .
.
I
Flame Ionization Detector for Liquid-Liquid Chro matogra phy ARTHUR KARMEN Department of Radiological Science, The Johns Hopkins University, Baltimore, Md. A detection system for liquid-liquid chromatography (LLC) has been developed. The effluent of a LLC column is deposited on a continuously moving metal chain from which the solvent is evaporated. The residue is then carried into a heated tube filled with nitrogen in which high boiling compounds are volatilized and nonvolatile compounds are pyrolyzed. The resulting vapors and pyrolysis products are detected by a hydrogen flame ionization detector that was designed to aspirate vapors into its hydrogen-nitrogen line at a brisk rate with only a modest input of gas. Lipid substances ranging in volatility from methyl esters of fatty acids to nonvolatile sterol esters and triglycerides were quantitatively detected.
M
COMPOUNDS that are not sufficiently volatile to be analyzed by gas-liquid chromatography (GLC) can readily be separated by thinlayer (TLC) or liquid-liquid chromatography (LLC). TLC and LLC also supplement GLC even in analyses of moderately volatile compounds because 3f the variety of separations that can oe performed. Because many of the advantages usually ascribed to GLC are attributable to the sensitive and automatic GLC detector, the utility of the other forms of chromatography should be increased if comparable detection methods were available. One of the few generally applicable approaches to quantitative LLC detection is to use eluting solvents that are appreciably more volatile than the
286
ANY
ANALYTICAL CHEMISTRY
compounds to be separated and to detect those compounds in the column effluent by evaporating the solvent and assaying the residue. This approach is useful even if the composition of the solvent is changed during the course of the analysis, a circumstance in which detection based on monitoring a physical property of the effluent is impractical. It is also useful when not all of the compounds to be detected have a single functional grouping that might form the basis of a specific chemical test. A sensitive method for assaying the residue is to vaporize it and deliver the vapors to a gas chromatography detector. Several methods for accomplishing this have now been described (2-4, 7, 8). The objective of this study was to devise a system for LLC that would detect rapidly and with high and reasonably uniform sensitivity both volatile compounds and compounds that required pyrolysis to be volatile. The column effluent was deposited on a continuously moving, endless metal chain. Solvent was removed by a stream of heated air. The residue was then carried by the chain into the cross limb of a T-tube from which air was excluded by separate flows of nitrogen delivered to each end. Within this tube the residue was subjected to increasingly high temperatures so that volatile materials were evaporated from the chain first followed by the pyrolysis products of nonvolatiles. Each compound was thus subjected to a temperature just sufficient to volatilize it and carbonization was minimized. T o ensure quantitative delivery of the vapors from the open T-tube to the detector
and quantitative detection, the sidearm of the tube was connected to the intake of a n aspirating hydrogen flame ionization detector. EXPERIMENTAL
Methods and Materials. A schematic drawing of the aspirating detector is shown in Figure 1. The electrical conductivity of the gas between the ring electrode and the remainder of the detector was monitored in the usual manner. The flame jet was a 1-inch length of ‘/lBinch 0.d. stainless steel hypodermic tubing which was silver-soldered into a hole bored along the axis of a 1/2-inch length of a 1/4-inch 0.d. stainless steel rod. The rod, in turn, was silver-soldered into the bore of the ‘/,-inch N P T connection of a Swagelok TNT, stainless steel 1/4-inch T-connector which was bored out to receive it. Metered flows of nitrogen and hydrogen were delivered to the detector in l/lc-inch tubing. The flows were combined in the l/l&nch diameter bore of a l / p inch 0.d. stainless steel tube that was fastened into the arm of the Swagelok T opposite the jet. The gas was delivered close to the center of the bore of the flame jet, 1/2 inch below its tip, in 0.020-inch 0.d. stainless steel hypodermic tubing that was silver-soldered into the bore of the */(-inch 0.d. tube. The ‘/(-inch tube leading from the center of the pyrolysis tube was fastened into the sidearm of the T. The entire detector cell, from just below the sidearm of the T, was maintained at approximately 200’ C. The pyrolysis tube and its connection to the detector were constructed of ‘/(-inch tubing (Figure 2). I n one prototype, all tubing was type 304 stainless steel welded together. I n
Figure 2.
Schematic diagram of
pyrolysis tube
Chain travel is in direction indicated
Figure 1 . Schematic diagram of aspirating flame ionization detector
another prototype, stainless steel tubing connected in Swagelok '/a-inch T connections was used. In still others, the tubing was made of borosilicate or Vycor glass, in which case the aspirating tube was connected to the sidearm of the T with silicone rubber O-rings. An endless stainless steel chain, 36 inches long, was moved through the straight portion of the tubing by a 1.5-inch i.d. aluminum pulley with a knurled shaft that was driven by a small constant speed motor. The chain was supported on the far side of the tube by a second aluminum pulley freely rotating on a ball bearing suspension. The direction of chain travel and the position of the electrical heaters and thermal insulation were as shown. Calibration. T o calibrate the system for quantitative detection of organic compounds, a heated glass T-connection fitted with two 1-hole silicone rubber stoppers for gas inlet and outlet and a puncture-type silicone rubber seal for injecting samples was placed in the nitrogen line leading to the detector. Samples of aqueous solutions of acetone, 1 to 2 pl., could thus be delivered directly to the detector to calibrate it, and minor adjustments in the hydrogen to nitrogen ratio could be made to maximize its response. The conditions necessary for pyrolyzing and quantitatively detecting a number of lipid substances were then studied. These included triglycerides and long-chain fatty acid esters of cholesterol, considered representative
of compounds that were not volatile unless pyrolyzed; free cholesterol and other steroids, considered examples of barely volatile compounds; and free, long-chain fatty acids and their methyl esters, considered examples of known volatile compounds that had vapor pressures sufficiently low that losses during evaporation of solvent were minimal. Dimensions of Aspirating Detector. The effects of varying the diameters of the flame jet and the tube delivering gas to its bore and of the position of one within the other on the rates of aspiration were measured using a 7-mm. o.d., 11/2-inch long glass T-tube fitted with silicone rubber seals t o simulate the detector body. The aspiration rate was measured by connecting the sidearm of the T to the top of a soap bubble flowmeter. The minimum gas flow necessary to cause aspiration and the maximum rate of aspiration that could be achieved using gas flows up to 500 ml. per minute were determined. Detector Gas Flows. The gas flow necessary t o cause a given detector to aspirate briskly was determined with the pyrolysis tube detached by connecting the top of a soap bubble flowmeter t o the sidearm of the Swagelok T a t the detector with 1/4inch tubing. Flows of approximately 7 5 ml. per minute each of hydrogen and nitrogen caused approximately 150 ml. per minute to be aspirated with a detector constructed as described. The pyrolysis tube was then attached. The flow of nitrogen to each end of the pyrolysis tube was then slowly increased until the detector no longer responded to an open vial of ether placed a t the end of the pyrolysis tube. Pyrolysis Tube Temperature and Calibration. With the chain moving a t approximately 4 inches per minute through the tube, the temperature of the pyrolysis tube was gradually increased until the response of the detector to 2-pl. samples of a solution of methyl palmitate, 1% w./v. or less, deposited directly on the chain was maximal. This response, with the detector aspirating properly, was always greater than the response to an equal volume of an equal concentration of acetone in water as predicted from the known behavior of the flame detector (IO). It was used as a basis for determining the maximal response to be expected from samples of the other lipids. The temperature of the pyrolysis tube was then gradually increased until the
responses of the detector to the compounds to be analyzed reached a maximum, Solutions of cholesterol were generally used to determine the temperature to be used in analyses of higher boiling but definitely volatile substances, such as steroids; solutions of triolein and cholesterol palmitate were used to determine the temperature for compounds requiring pyrolysis. The relationship between the response of the detector and the quantity of a given material deposited on the chain was determined by placing 2 4 . aliquots of serial dilutions of individual lipids in ether directly on the chain. The same method was used to compare the relative responses of the detector to equal quantities of different compounds. To assess the performance of the system as a continuous detector in the effluent of a column, simple mixtures of lipids were separated on silicic acid columns varying in length from 8 to 15 cm. and 1- to 2-mm. i.d. Mixtures containing cholesterol esters and methyl esters of fatty acids, triglycerides, and free cholesterol were separated using mixtures of petroleum ether and diethyl ether as eluting solvents. The entire column effluent, usually less than 1 ml. per minute was deposited on the chain, rather than only a portion of it. Solutions containing approximately 20 pg. each of cholesteryl palmitate, triolein, and cholesterol were analyzed on the silicic acid columns by eluting the least polar compound, the cholesteryl ester, first with the least polar solvent (petroleum ether 95%, diethyl ether 5%, v./v.); as soon as the peak had been recorded, the solvent was changed to petroleum ether 75%, diethyl ether 25%, which eluted the triglyceride. The solvent was then changed to lOOyodiethyl ether to elute the free cholesterol. RESULTS
Tubing Dimensions and Geometry of Aspirating Detector. I n each experiment, as the gas flow was gradually increased, a flow was reached a t which the detector just began to aspirate. Further increase in flow then increased the aspiration rate a t first rapidly and then slowly until a rate of aspiration was reached a t which further increases in flow caused a minimal increase. With the same 0.016-inch 0.d. tubing delivering the gas to the flame jet, increasing the diameter of the jet in steps from 0.045 inch VOL. 38, NO. 2, FEBRUARY 1966
8
287
beyond these limits decreased the aspiration rate. A nitrogen flow of 150 ml. per minute to a detector with the dimensions described yielded an aspiration rate of approximately 150 ml. per minute. System Performance. When the aspiration rate was less than 40 ml. per minute, only a fraction of a known volatile compound such as methyl palmitate deposited directly on the chain reached the detector. This was determined by comparison of the results obtained with those obtained by injecting an equal weight of acetone directly into the detector. iln even smaller fraction reached it when the temperature of the pyrolysis tube was increased. It thus appeared that vapors could be flashed by heat in a direction opposite to the flow of gas in the
A
C
Figure 3. Analysis of equal aliquots of serial dilutions of cholesteryl palmitate in diethyl ether deposited directly on the chain Samples A were 0.7 pg. each; 8, 2 pg. each; C, 6 fig. eoch. Full scale wos 3 X lo-* ampere
to 0.080 inch increased the minimum gas flow necessary to cause aspiration but made greater maximal rates of aspiration available. Decreasing the diameter of the inner or gas supplying tube from 0.024 inch to 0.012 inch had little effect on the aspiration rate when the larger diameter tubes were used, but increased the aspiration rate slightly when smaller jets were used. As measured with a simple water manometer, a lower pressure was developed in the sidearm of the T-connection when a smaller diameter jet was used under conditions of no flow in the aspiration tube. However, the aspiration rate measured under the same conditions was greater when the larger tube was used, indicating that the increased resistance to flow of the smaller tube played an important role. The detector aspirated effectively if the tip of the inner or gas supply tube penetrated the base of the jet tubing a t least inch and was more than approximately 3/8 inch below the tip of the jet, Raising or lowering the jet Table
1.
1.
2. 3. 0
Each
Responses
Analysis of
triolein,
20
pared with acetone, 6, 20 pg. delivered directly to the detector by injection into the gas line in aqueous solution
tube and were probably condensed and retained on the cool portions of the tube. Placing a quantity of a volatile, colored compound on the chain confirmed that this occurred. When the higher aspiration rates were used, this effectwas overcome and quantitative recoveries were obtained. The responses of the system to given weights of different lipids were grossly similar, although there was somewhat greater variability than could be explained from the known differencesin the response of the hydrogen flame ionization detector to different compounds (Table I), The gross similarity of the responses indicated that the yield of detectable fragments from the pyrolysis of the compounds tested was high.
delivered directly to the detector (Figure 3). The response of the system to different lipids was directly proportional to the quantity of lipid deposited on the chain (Figure 4, Table I). The responses to certain compounds, including some of the biologically important steroids, mere sometimes noted to be less than expected. When this occurred it was accompanied by a decrease in sensitivity as the size of the sample was decreased. Both of these effects were associated with the use of chains and pyrolysis tubes made of stainless steel that had accumulated an oxide coating and was not observed when glass or Vycor pyrolysis tubes and noble metal chains were used. The usual base line current observed with the entire system operating ranged a t approximately 3 to 4 x 10-lo ampere. The sensitivity of the system was such that samples of lipids less than 0.01 pg. deposited directly on the chain could conveniently be quantified. When the pyrolysis tube was operated at higher temperatures, the detector responded markedly to the deposition of samples of alkali metal salts on the chain. This response was often greater than predicted from tht. expected vapor pressure of the salts a t the temperature used. It was necessary to keep the tube leading from the pyrolysis tube to the detector hot to prevent condensation of the lipids within it. Compounds such as cholesterol, which were presumably volatilized promptly upon entering the intensely heated zone of the pyrolysis tube, apparently left the chain as intact molecules. If the tube leading to the detector were kept a t less than 200°, the cholesterol peak showed
C
(sq. mm.) to Application of 2-pl. Aliquots of Solution of Lipids Directly on Chain
Peak area Compound” 1% ‘/a% l/S% a. Methyl stearate 3028 1032 3198 1064 355 b. Methyl palmitate 3711 1231 353 c. Cholesterol palmitate 3337 1396 459 a. Cholesterol palmitate 2813 1114 432 b. Methyl stearate 2975 1280 427 a. Methyl palmitate 2798 1075 356 b. Triolein number is average of three determinations; 1, 2, 3 were performed on different
Figure 5. Analysis of samples of cholesterol, 2 and 6 pg., compared with cholesteryl palmitate (CP), 2 and 6 pg. Both materials were chain in ether solutions.
days.
288
Figure 4.
pg., deposited on the chain, A, com-
The response of the system to each
of the different lipids tested was greater than that to an equal weight of acetone
ANALYTICAL CHEMISTRY
deposited directly on Full scale lo-* ampere
IlO
CP
TO
C 1’5
b
JMINUTES
1’0
Figure 6. Analysis of approximately 2 0 fig. each of cholesteryl palmitate (CP), triolein (TO), and cholesterol (C) on a 120-mm. long, 2-mm. i.d. silicic acid column Solvent changed at times indicated b y arrows. Solvent 1, 95% petroleum ether, 5% diethyl ether; solvent 2, 75% petroleum ether, 25% diethyl ether; solvent 3, diethyl ether. Full scale sensitivity, 1 0 - 8 ampere
marked tailing. Although compounds such as cholesterol palmitate required a greater degree of cracking to be volatilized, once volatilized they were less likely to condense. As a result, the peak for cholesterol palmitate frequently showed less tailing than the cholesterol peak (Figure 5 ) . If the temperature of the aspirating tube were reduced markedly] however, the symmetry of the cholesterol peak increased again although the response was still less than that predicted. That the cholesterol did not condense out and thus escape detection was attributed to the formation of an aerosol a t the low temperature. When the system was used to monitor the separation of simple mixtures of lipids on the crude, semimicro silicic acid columns, the areas of the peaks were comparable to those obtained when an equal quantity of material was deposited directly on the chain. The level
C TO k-3-------1-2.--------ICl-l 1’0
C
7 0
CP
-3-2-1+ I
15
1‘0
MINUTES
I
0
Figure 7. Analysis of a mixture similar to that in Figure 6 using an 85-mm. long, 2-mm. i.d. column and the same sequence of solvents Solvent changes shown b y arrows.
of base line noise was increased somewhat by the deposition of the column effluent on the chain. This noise originated from two sources: a slow component of noise was attributed to variation in the concentration of nonvolatile solvent impurities reaching the detector; short bursts of noise were attributable to the deposition of small silicic acid particles on the chain and their subsequent delivery to the detector in the flowing gas. These short bursts of noise were accompanied by short bursts of yellow light in the flame as the particles passed through it. Mixtures containing cholesteryl esters, triglycerides, and free cholesterol were separated in 10 to 20 minutes depending on the length of the column used (Figures 6, 7, 8). Even faster analyses were possible if the solvent was changed before the elution of each peak
Full scale sensitivity,
ampere
was complete. Even though the entire column effluent was deposited on the chain, it was delivered more dropwise than continuously because of the low solvent flow rate. This intermittency in the delivery of sample was reflected in the curves obtained. It could be reduced by adding a small additional flow of solvent to the column near its orifice. A longer time constant (about 8 seconds) could also be used to record the analyses (Figure 9). DISCUSSION
I n our first attempt to develop a detection system for LLC (6),the effluent of a column was deposited on a continuously moving wire which passed first through a zone in which the solvent was evaporated and then through the flame of a hydrogen flame ionization detector. We noted that as nonvolatile lipid residues approached the flame, they melted, retreated along the wire, and formed droplets that fell off the wire thus partially escaping detection. Other nonvolatile conipounds that formed crystals as they approached the flame were spattered by the heat and lost. Volatile compounds such as longchain fatty acid esters were vaporized before reaching the flame and were detected with poor sensitivity. One objective of our second approach (6)
CP
&MINUTES
b
Figure 8. Analysis of a mixture similar to that in Figures 6 and 7 using a 77-mm. long column, 2-mm. i.d. and the same sequence of solvents changed as indicated by the arrows. Full scale sensitivity, 3 X 1 0-8 ampere
B
A
Figure 9. Analysis of mixture containing about 50 pg. each of cholesterol and cholesteryl palmitate on a 120-mm. long, 1 -mm. i.d. column Full scale sensitivity, 3 X 10-8 ampere; time constant, 8 seconds VOL. 38, NO. 2, FEBRUARY 1966
289
was to ensure delivery of all volatilized material in the effluent to the detector. These experiments indicated that reasonably equal responses could be obtained for equal weights of high boiling compounds and pyrolysis products of nonvolatile compounds. They thus demonstrated the feasibility of using pyrolysis as a means of quantitatively transforming volatiles into a form suitable for detection by a gas detector. In the system used, volatilization and pyrolysis were performed sequentially. This limited the frequency with which successive samples could be analyzed. While the speed of response of the system was adequate for the usual LLC analysis, it was too slow for the rapid LLC analyses of the type described by Bayer (1) which may require a speed of response almost as high as that of a detector for GLC. The hydrogen flame ionization detector was selected for this work because its response to organic compounds is not adversely affected by the presence of water vapor, carbon dioxide, or traces of atmospheric gases and, because of all the highly sensitive gas chromatography detectors, its response to similar quantities of different molecular species varies least. Its response to the pyrolysis products of a given compound thus seemed least likely to be changed by a small change in the conditions of pyrolysis. The insulator of the flame detector described was mounted outside the heated zone below the remainder of the detector. The air supply to the detector, which entered the shielding tube just above the level of the insulator, prevented contact between the products of combustion and the insulator. In this design, the electrostatic shielding of the electrode and its electrical leads was complete, and water could not condense at the insulator, even though the insulator was kept at ambient temperatures. A hydrogen flame detector designed this way has been described previously (4). James, Ravenhill, and Scott used an argon ionization detector in their LLC detection system (3) and reported that it was insensitive to salts. Because the ionization potentials of the alkali metals are among the lowest of all substances, one might reasonably expect them to be ionized efficiently in an argon ionization detector. In the system described, however, the effluent of their pyrolysis tube was brought to ambient temperature before delivering it to the detector. It may be that alkali metal salts condensed out and did not reach the detector. In the system described here, the high sensitivity of the flame detector to alkali metal salts will require that special measures be used in analyses of mixtures that contain them. Because the pyrolysis tube was open 290
ANALYTICAL CHEMISTRY
to the atmosphere, quantitative delivery of vapors to a conventional flame detector by gas under pressure would require that the tubing leading from the pyrolysis tube offer appreciably lower resistance to gas flow than the points of entry and exit of the chain. Because this seemed difficult to achieve in the usual flame detector, the aspirab ing flame detector was designed. A hydrogen flame can be made to aspirate by operating the entire detector a t a reduced pressure. This possibility was not investigated because of the feeling that a detector designed this way would require much more careful control of operating parameters for stable operation. It was also possible to design an aspirating flame detector in which the aspiration was accomplished by the air supply rather than the nitrogenhydrogen supply. However, organic vapors delivered to the usual hydrogen flame detector in its air supply are detected with much lower sensitivity than those delivered in the nitrogenhydrogen lines. Experiments with premixed flames, such as those used in flame photometers, indicated that comparatively large gas flow rates mere required if the flame were to be stable and to aspirate properly. These considerations led to the choice of the design described here. The geometry of the pyrolysis tube was chosen after extensive trials indicated that temperatures in excess of 600’ C. were required for maximal response to triolein, which can be considered to have undergone cracking prior to volatilization, while volatile compounds, which were flashed back from an intensely hot area, were best detected when exposed to temperatures not over 250’ C. The system described here was designed and operated so that low boiling compounds were aspirated before the residue reached the intense heat, while the triglycerides and other nonvolatiles were driven off the chain slightly later in its travel. As the temperature of the pyrolysis tube was gradually increased, the responses to the more volatile compounds increased and reached a maximum first, followed by the responses to less volatile compounds, and finally by the compounds requiring pyrolysis. To avoid unnecessary shortening of the life of the components, the tube was operated at a temperature only high enough for maximal response to the classes of compounds being analyzed. The great potential of continuous liquid-liquid chromatographic detection was hardly suggested by the results of the analyses performed with the crude silicic acid column described here. The sensitivity of the detection system, although somewhat lower than the sensitivity of the flame detector used with a
nonbleeding gas chromatography column, was more than adequate for detecting the quantities of material ordinarily analyzed in thin-layer chromatography. Combination of these two techniques required either that the chromatography be carried out so that all the materials are eluted from the plate-i.e., that the plate be used as a column is used-or that an alternative method of delivering the materials be devised. It would seem ideally suited for use with the capillary liquid chromatography columns described by Bayer. The system can also be used for measuring the quantities of nonvolatile materials in volatile solvents, by depositing several microliters of the solution directly on the chain. Although some resolution is sacrificed, the sensitivity of this discontinuous system as a detector for LLC, in terms of the smallest quantities of materials that can be detected, is greater than that of the system operated as a continuous detector. S o t only can the solution to be analyzed be concentrated prior to depositing an aliquot on the chain, but more of the effluent can be delivered to the detector in a shorter time period. ACKNOWLEDGMENT
The author expresses his appreciation to Maurice Lofters for expert assistance in performing this work, to Joseph Vokroy for constructing the detection system, to Sally Donovan for preparing this manuscript, and to the Engineering Department of the Packard Instrument Co., Inc. (which is developing a similar detection system) for technical advice. LITERATURE CITED
(1) Bayer, E., 2nd International Sym-
posium on Advances in Gas Chromatography, Houston, Texas, March 2326. 1964. - - I
(2) Haahti, E. 0. A., Nikkari, T., Acta Chem. Scand. 17,2665 (1963). (3) James, A. T., Ravenhill, J. R., Scott, R. P. W., Chem. Ind. 1964, p. 746. (4) Karmen, A,, J . Gas Chromatog. 1965, p. 180. ( 5 ) Karmen, A,, Tritch,.H. R., Bowman, R. L., “National Institutes of Health, Review of Intramural Research, 1960,” p. 88, U. S. Dept. Health, Education, and Welfare, U. S. Govt. Printing Office, 1961. (6) Karmen, A., Walker, T., Bowman, R. L., J . Lipid Research 4, 103 (1963). ( 7 ) Lieberman, S., U. S. Patent 3,128,619, (March 24, 1961). (8) Stouffer, J. E., Kersten, T. E., Krueger, P. M., Biochem. Biophys. . A c t ~93, 191 (1964). (9) Sternberg, J. C., Carson, L. M., J . Chromatog. 2,63 (1959). (10) Sternberg, J. C., Gallaway, W. S.,
Jones, D. T. L., “Gas Chromatography,” N. Brenner et al., eds., p. 231, Academic Press, 1962. RECEIVED for review August 27, 1965. Accepted November 12, 1965. 3rd International Sym osium, Advances in Gas Chrornatograpiy, Houston, Texas October 1965. Study supported by d. I. H. Grant GM 1153.5.
