We are also indebted to Miss J. McCune for assistance in the laboratory work. LITERATURE CITED
(1) Brochmann-Hanssen, E., Svendsen, A. B., J . Phawn. Sci. 51, 393, 938
(1962). (2) Brochmann-Hanssen, E., Svendsen, A. B., Ibid., 51, 1095 (1962); 52, 1134 (1963). (3) Brooks, C. J. W., Homing, E. C., ANAL.CHEM.36, 1540 (1964). (4) Fales, H. M., National Institutes of Health, Washington, D. C., private communications, 1960-1961. ( 5 ) Fales, H. M., Pisano, J. J., Anal. Bzochem. 3, 337 (1962).
(6) Horning, E. C., Homing, M. G., VandenHeuvel, W. J. A., Knox, K. L., Holmstedt. B.. Brooks. C. J. W.. ANAL.CHEM.36, 1546 (1964). (7) Horning, E. C., Moscatelli, E., Sweeley, C. C., Chem. and Ind., (London), 1959, 751. (8) Homing, E. C., VandenHeuvel, W. J. A., Creech, B. G., in “Methods of Biochemical Analysis,” Vol. XI, D. Glick, Ed., Interscience, New York, 1963.
(9) Kovats, E., Helv. Chim. Acta 41, 1915 (1958). (10) Linstedt, S., Clin. Chem. Acta 9, 309 (1964). (11) Ryhage, R., ANAL. CHEM.36, 759 (1964). ~ - ,(12).Sen, N. P., McGeer, P. L., Biochem. Bzophys. Res. Commun. 13,390 (1963).
(13) Sen, N. P., McGeer, P. L., Ibid., 14, 227 (1964). (14) VandenHeuvel, W. J. A., Gardiner, W. L., Horning, E. c., ANAL. CHEW 36, 1550 (1964). (15) VandenHeuvel, W. J. A., Gardiner, W. L., Homing, E. C., J . Chromatog. 19, 263 (1965). RECEIVED for review August 11, 1965. Accepted December 13, 196Ci. Work supported in part by Grant HE05435 of the National Institutes of Health, Grant Q-125 of the Robert A. Welch Foundation, and by a grant from the Loula D. Lasker estate. Third International Symposium, Advances in Gas Chromatography, Houston, Texas, October 1965.
Electrical Discharge Pyrolyzer for Gas Chromatography JAMES C. STERNBERG and ROBERT L. LITLE Beckrnan Instruments, Inc., Fullerton, Calif.
b A new pyrolytic method employing a low current, high voltage discharge for the fragmentation of solid samples is described. The sample is placed on a porous graphite felt electrode which serves as the downstream electrode in a flow-through tubular discharge chamber. The sample tubes are readily sealed in place and removed from the system by means of a pneumatic actuator through use of a gasketed removable electrode assembly. Breakdown fragments are swept immediately out of the discharge and into a sample loop. A sampling valve permits introduction of the breakdown fragments onto the head of the chromatographic column, and permits the introduction and removal of sample tubes without interruption of the column carrier flow. The system has been shown to give reproducible and highly characteristic breakdown patterns for samples in various states of subdivision. Results obtained for a variety of samples and possible areas of application are discussed. HE technique of gas chromatogT r a p h y has made possible the analysis of complex mixtures of gases and volatilizable materials through separation followed by measurement. Many classes of sample, however, consist of or include components of insufficient volatility for gas chromatographic analysis. Many organic compounds, especially those of biological interest, decompose a t temperatures which are insufficient for their analysis by gas chromat,ography. It has long been recognized that the decomposition of nonvolatile compounds
under controlled conditions could lead to breakdown patterns characteristic of the starting material. Fragmentation of molecules through electron bombardment under vacuum conditions, with mass-based separation of the ionic fragments produced, is the basis of mass spectrometry. With the development of gas chromatography, a technique became available for the separation and measurement of the stable molecular fragments formed during the decomposition of larger molecules. Originally (2, 4 ) , the pyrolysis was carried out in a separate system, with subsequent syringe injection of the volatile products formed into the gas chromatograph. The more convenient technique of carrying out the pyrolysis in the carrier flow stream feeding the chromatographic column was soon introduced (7, 1 1 ) . Since gas chromatography normally operates a t atmospheric pressure or above, fragmentation methods applicable under these conditions have been used in place of high vacuum electron bombardment. For the fragmentation of solids and plastics, most workers have employed thermal pyrolysis, using a hot wire, a heated tube, or a chamber heated to a high temperature. A large number of publications cited in two recent reviews (9,10) describe various versions of this technique and present the results obtained. I n addition, several commercial devices are available for the thermal pyrolysis of solids. Keulemans and coworkers (6) have also employed thermal pyrolysis for characterization of gaseous species, much as we have used discharge pyrolysis. Simon (12) describes the use of high frequency
heating to pyrolyze samples deposited on small wires introduced into a region where the field can be applied. In a prior study (13) we have used a high voltage, low current, glow discharge in an inert gas carrier a t atmospheric pressure or above for the fragmentation and characterization in the gas phase. Because of the usefulness and reproducibility found attainable with the electrical discharge fragmentation technique when applied to vapor samples, it was decided to attempt to adapt this technique to the fragmentation of solids. I n working with vapor samples, the electrical discharge method affords exceptionally efficient coupling of the input power, since the current is carried by the sample and carrier gas itself and very low power levels (about 1 ma. a t 300 volts d.c.) are sufficient to fragment a significant fraction (greater than 10%) of the sample ( I S ) . Coupling of the power to a nonconducting solid material, however, cannot be as efficient as to vapors, since only a fraction of the input power will be transferred to the solid by collision with electrons and with atoms and molecules of gases which have been energized by the discharge. .4t the higher current levels required for volatilizing the solids, fragments passing int,o the vapor phase will tend to undergo appreciable further breakdown, since they find themselves in an environment much more energetic than that normally employed for vapor fragmentation, Thus, the problem of application of electrical discharge fragmentation to solids became much more than simply one of inserting a solid sample in ~i. VOL. 38, NO. 2, FEBRUARY 1966
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u
dA
Air S u p p l y
Helium Supply
t
Therrnotrac 2
Figure 1.
Schematic of system used in preliminary investigation
I
a hydrogen flame ionization detector, electrometer, and recorder. In the preliminary investigations the fragmentation chamber, sample loop, and valve were located in one Beckman Thermotrac programmed temperature chromatographic column oven, and the column was located in a similar oven, with the flame detector mounted directly on the side. This arrangement is shown schematically in Figure 1. In later studies, the fragmentation inlet, valve, and sample loop were located in the thermostated valve compartment of a Beckman GC-4 gas chromatograph, with the column in the programmable column compartment, and the hydrogen flame ionization detector in the thermostated detector compartment of the same instrument. These components, as illustrated in Figures 2, 3, and 4, are now available as standard accessory modules for that instrument. High Voltage Power Supply. The power supply used throughout this work, shown in Figure 2, consisted of a high voltage transformer with secondary voltage controlled by means of a Variac in the primary circuit and with current controlled by means of various limiting resistors (1.5 Mohms, 250 kohms, 50 kohms, 10 kohms) which could be inserted in series with the electrodes of the fragmentation chamber. The transformer could supply voltages up to 3500 volts a x . (peak-to-peak). Since the fragmentation chamber acts somewhat as a voltage regulator which operates a t a voltage characteristic of the composition of the gas within the chamber, the difference between this characteristic voltage and the supplied voltage was dropped across the limiting resistor and determined the current. Currents ranging from less than 1ma. to more than 100 ma. were available. The discharge could be operated from time intervals
d
discharge region. It was necessary to find the means of sample introduction which would provide the most effective volatilization of the solid sample and yet give highly reproducible fragmentation patterns. Several experimental arrangements and sampling procedures were investigated before one fulfilling the desired standards of performance was found. EXPERIMENTAL
The apparatus used consisted of the various forms of fragmentation chamber, a high voltage power supply, the sample loop, a pneumatically-actuated slider valve, a chromatographic column, and 322
e
ANALYTICAL CHEMISTRY
I I
n 040Op.4
-1 --
Figure 2. Schematic diagram of fragmentation power supply
m
I
Vent
fraction is initially contained. When subambient temperature programming is used, even lower boiling components become condensible. A minimum flow rate of 3 to 4 cc./minute (measured a t room temperature and atmospheric pressure) through the fragmentation inlet is desirable, particularly if biclogical or other samples containing water are fragmented, since back diffusion of breakdown products into the discharge a t lower flow rates can otherwise cause erratic firing of the discharge and undesirable secondary hreakdown of the primary breakdown fragments. The volume of the sample loop required is determined by taking the product of the flow rate of the carrier gas and the time allowed for the discharge, adding about 1 cc. for the volume of gas evolved by the sample and for sweeping out the connecting tubing between the inlet and the sample loop, and multiplying the sum by the ratio of the absolute temperatures of the sample loop (valve compartment) and the flow meter (usually room temperature). Thus, if a discharge time of 30 seconds is used with a flow rate of 4 cc./minute and a valve Compartment temperature of 250' C., the sample loop must have a volume of a t le& (2 1) X 523/295 = 5.3 cc. (taking room temperature to be 22' C.). Column Configuration. The column used in the earlier portion of this work was a general purpose 30% SE-30 column, 10 feet X '/&inch o.d., prcgrammed linearly from 50" C. to 250' C. In later runs in the GC-4, a 6foot X '/Anch 0.d. SE30 column was used. Because of the nature of the fragmentation process, a wide boiling range of fragments is obtained. Best results could probably be obtained by use of wide range programming, starting from subambient temperatures. This capability was unavailable in the breadboard instrument, but is available as an accessory for the GC4. Its utility has recently been demonstrated using a 20-foot X '/rfoot 0.d. column containing 3% SE30 on Chromosorb G, programmed from 0' to 250' C. It is desirable to leave the column for several minutes isothermally a t the highest temperature reached during
+
Figure 3.
Sample valve
,-,.
.wl.n,vY,Y.,V,,.
ihe fragmentation inlet
A. Volvs In purge paltion (with fragmontotlon prOdum collecting in sample I-pl B. Valve in inject paition (with fragmentation produch from sample loop swept inM column)
from 1 second up to 1 minute by means of a preset interval timer. Sample Loop and Valve. An eightport pneumatically-actuated linear slider valve of Teflon was used to make possible the removal, introduction, and purging of the sample tubes and fragmentation a t essentially atmospheric pressure without interruption of the normal carrier flow t o the analytical column. The fragmented vapors from the sample were transported by a low flow rate of carrier gas into the samplingloop. Whenfragmentation was complete, actuation of the valve would place the sample loop in the column carrier line, sweeping the sample fragments onto the column. Advantages of this arrangement included the effective compression of sample band width on a time basis by the ratio between sample system and column flow rates, the operation of the discharge under reproducible atmospheric pressure conditions independent of column back pressure, the convenience of sample introduction, purging, and removal without disturbing the column system, the possibility of using any desired gas composition in the discharge to produce specific chemical effects without interfering with normal operation of the column and detector, and the possibility of sampling fractions eluted from another Glumn,
without requiring that the other column be operated with outlet above at. mospherio pressure. It is desirable in general to use a relatively large volume sample loop (5 to 10 cc.) with the fragmentation inlet. In programmed temperature operation, all but the lowest boiling components are effectively deposited onto the bead of the column, so that the peak width is unrelated to the volume of carrier gas in which a condensible
Figure 4. Photograph of fragmentation inlet in valve compartment of
GC-4
I VOL 38, NO. 2, FEBRUARY 1966
323
GASKET
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CARBON FELTSAMPLE SlLl GA WOOL-
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SAMPLE TUBE
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MARKED END
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GASKET
RETAINER --.RING
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ELECTRODE GASKET
Figure 5. Exploded view of sample tube assembly
the program to give the column time to clean up before the next run. Since the sample tubes can be removed without disturbing the column flow, it is convenient to prepare the next sample while the column is cleaning up or cooling down from one sample. Detection System. A Beckman GC-4 hydrogen flame ionization detector and electrometer were used in these studies. The high sensitivity and general response of the flame ionization detector to organic compounds made it particularly suitable for fragmentation work, although there may be situations where a special interest might attach to the determination of nonionizable components such as carbon monoxide or water vapor in the breakdown pattern. Improved Fragmentation Inlet. On the basis of preliminary studies, the following requirements for a suitable fragmentation inlet were specified : a clean flow pattern, for minimum dead volume; a chamber and electrodes that could be readily cleaned, preferably after each sample; a convenient and reproducible means of inserting samples into the discharge zone; and no organic materials in direct contact with the sample or with the high energy particles from the discharge. Proper fulfillment of the first requirement would also be necessary if the inlet were to serve the dual purpose of solids fragmentation and the fragmentation chromatography of vapors. To achieve these aims, a flow-through tubular discharge chamber as shown in Figure 5 appears to be the most suitable solution. To have the electrodes readily accessible and cleanable, they were also made removable with the sample tube and became part of the sample tube assembly. A mechanical arrangement was necessary to permit the ready introduction and removal of the sample tubes within a heated compartment, and i t was decided that a pneumatic actuator, mounted outside of the heated zone, could best be em324
ANALYTICAL CHEMISTRY
Figure 6. Effect of sample position on fragmentation of polyethylene samples Upper curve sample near downstream electrode Lower curve sample near upstream electrode
ployed to seal and release the tubes. A standard pneumatic actuator of the type used with slider valves of Teflon was employed. The push rod of the actuator served as a grounded electrode and as the upstream conduit for carrying the gases from the discharge to the sample loop. The high voltage electrode contacted a metal insert in a ceramic piece, which provided an insulated section of conduit to isolate the grounded valve and sample loop from the high-voltage electrode. A glassinsulated wire carried the high-voltage from the supply to the metal insert. Electrode Assembly. The electrodes (Figure 5 ) are small, machined pieces which are removed and inserted along with the sample tubes. The longer end of the electrode is inserted into the sample tube and held in place by the small steel retaining spring which fits in a narrow groove near the end of the electrode. The shorter end of one electrode seats in a recess in the plunger of the pneumatic ac tuator, while the shorter end of the other electrode seats against the metallized surface of the ceramic portion of the fragmentation inlet. The larger diameter portion of the electrode provides the surface for sealing the gaskets to the electrodes and is made larger than the gaskets to provide for convenient handling without damage to the gaskets. The slight recesses in the electrodes, where each end section adjoins the large diameter section, serve to retain the gaskets and keep them with the electrodes when the tube and electrodes are removed from the system. If gaseous or vapor samples are to be run, the electrodes are modified by the addition of a gold wire, and a constricted sample tube is employed. Sampling Technique. The positioning of the sample within the discharge space was a critical factor if reproduc-
ible results were to be obtained. Since the current in the discharge for volatilizing the solid samples is so much higher than required for appreciable fragmentation of samples introduced in the vapor state, any variability in exposure of the volatilized fragments of the sample to the discharge will lead to a significant variability of degree of secondary breakdown and, hence, of the overall pattern. With the sample placed nearer the upstream electrode, a large and rapid gas evolution was found to occur, and the breakdown pattern was of lower intensity, except for the very early peaks. With the sample nearer the downstream electrode, less gas evolution occurred and a much more prominent and distinctive breakdown pattern was obtained. A practical means of assuring location of the sample adjacent to the downstream electrode, while retaining the capability of handling samples in any state of subdivision, was found through the use of a porous material for the downstream electrode. Carbon or graphite felt was an ideal electrode material for this purpose, with graphite felt preferred because of its higher purity. In the sampling procedure employed, the empty alumina sample tube is used to cut a disk from a piece of carbon felt. The disk is cut with a simple twisting motion of the sample tube, placed enddown on the felt on a firm surface. The felt can then be pushed gently to the desired position within the tube. The felt is laid with its smoother side downward during cutting, so that the smooth side faces up out of that end of the tube which it occupies immediately after cutting. The felt is pushed in slightly, and the sample placed upon it, approximately centered along the tube axis. The sample can be in the
Figure 7.
Lower: fragmentation products of polyethylene. Upper: fragmentation products of polypropylene
For attenuations, a-b means a X 1 Ob and 1 X 1 indicates 5 X 1 0-ls amp. full scale. mosorb G, programmed as indicated
form of a plastic film, a chunk of plastic, granules, or powder. A liquid can be sampled onto an inorganic powder such as firebrick, alumina, silica gel, or sand, and loaded as a solid; even vapors can be retained on adsorbent solids and handled as solids. A thin layer of silica wool is then placed over the sample. If desired, the silica wool and carbon felt sandwich (or the carbon felt alone) can be predischarged in place to remove traces of contaminants. This procedure is particularly important when working with extremely small samples. The gasketed electrode assembly is then inserted into the bottom end of the sample tube and the sample sand-
Column 20 feet X 1 / 8 inch 0.d. 3% SE-30 on 80-1 00 mesh Chro-
wich is pushed gently down into position so that the carbon felt contacts the bottom electrode. The gasketed top electrode assembly is then inserted, and the sample is ready for loading into the inlet. An exploded view of the sample tube with sandwich and electrodes is shown in Figure 5. Since it is essential to have the carbon felt end of the sample sandwich downstream, the sample tube is marked a t one end to be loaded in the upstream direction. It has been found convenient to have a sample tube permanently marked a t one end, and to start the loading process by introducing the carbon felt into the marked end. The felt then properly arrives a t the electrode a t
the unmarked end when the above sequence of operations is followed. The insertion rod ( R ) of Teflon in Figure 4 is used to place the sample tube in position, resting on the ceramic V-block ( V B ) between the fixed ceramic (C) and moving push-rod (PR) ends of the inlet assembly. The insertion rod is used to move the sample tube against the fixed end of the inlet, so that the downstream high voltage electrode ( H V ) moves into the recess of the ceramic piece. The pneumatic actuator ( P A ) is then switched by means of the pneumatic valve control to seal the sample tube and electrode assembly in place. The push rod of the pneumatic actuator serves as the VOL. 38, NO. 2, FEBRUARY 1966
325
B
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1 R
Figure 8.
Fragmentation products of Tygon
Conditions as for Figure 7.
contact for the grounded electrode, through the gaskets ( G ) . Contact to the high voltage electrode is made through the pin ( P ) and the metallized surfaces (144s)of the fixed ceramic end of the inlet assembly. When first inserted, the sample is purged with carrier gas through the exhaust line (EL), and the sampling valve ( S V ) is then actuated to place the sample loop (SL) in series with the inlet. When the column system is back down to starting temperature and ready to accept a sample, the appropriate settings are made on the voltage control and current range switch to provide the desired current, read on the current meter as the voltage drop across the limiting resistor. The time selector control is set for appropriate duration of discharge, and the desired flow rate through the sample loop is set. When the discharge is ready for firing, a soap bubble is started throu h the soap bubble flowmeter, and t i e discharge is triggered by the start time push button when the bubble reaches the starting mark. When the discharge stops, the volume is noted, and additional time is allowed for a sufficient added volume to flow to ensure that all of the sample has passed through the connecting tube and into the sample loop (this requires only about 0.2 cc. of additional flow). The sampling valve is then actuated, introducing the sample loop into the column line and placing the fragments of the sample on the analytical column. The column temperature program is also initiated a t this time. The sample can then be removed a t any time after this without interfering with the development of the fragmentation chromatogram. If there is any question about 326
ANALYTICAL CHEMISTRY
Attenuation 1-4 except as noted
completeness of sample consumption, it may be desirable to leave the sample in place and fire it again after the run is complete; this would be desirable in establishing the size of sample that can be accommodated with a particular discharge current and firing time. If trace samples are to be measured, it is desirable to prepare the sample tube, with carbon felt but without sample, and to fire it two or three times a t the current level to be used, but with the gases just flowing to vent. The sample can then be loaded, and run without concern about extraneous peaks from these sources. RESULTS
In the experiments related to the early development of the technique, polyethylene film samples were used as a standard of comparison. Once a satisfactory technique had been developed, a wide variety of samples in various states of subdivision were fragmented. The results obtained are grouped according to sample type and serve to illustrate some of the range of potential application of the method. A more extensive tabulation of potential applications is given in the discussion section of this paper. Plastic Film Samples. In the long sequence of experiments aimed a t finding a reproducible technique, polyethylene film from a packaging bag was used in the form of a pair of approximately 2-mm. diameter disks punched out through a hole in a steel plate. Each pair of disks weighed approximately 80 pg. Figure 6 shows
the comparison between samples positioned a t the downstream and upstream ends of the sample tube, respectively, These runs were performed on the breadboard instrument. Figures 7-9 show the patterns obtained for several different plastics employing the fragmentation inlet module and an SE-30 column in a Beckman GC-4 gas chromatograph programmed from 0' to 250' C. Samples of Liquids on Inorganic Solid Support. While the basic method has been developed for solids, i t is also applicable to high boiling liquids. A particularly convenient means of sampling such liquids is by depositing them on inorganic solids, such as firebrick, silica wool, or such adsorbents as alumina or silica gel. Less volatile liquids are adequately retained during fragmentation when placed on less adsorbent solids, while more volatile liquids require more adsorbent solid supports if they are to be fragmented rather than merely volatilized, particularly with the valve compartment housing the fragmentation inlet at an elevated temperature. Figure 10 shows an Apiezon L sample on firebrick. Diethylene glycolsuccinate (DEGS) on firebrick is shown in Figure 11. The Apiezon sample in comparison with polyethylene clearly shows the primarily straight-chain paraffin nature of the sample, with some branching suggested by the occurrence also of the principal polypropylene peak. The DEGS sample shows a much less extensive pattern, with
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Fragmentation of products of poly-(methyl methacrylate)
Conditions as for Figure 7.
Figure 10.
WIN
Attenuation 5-3 except as noted
Fragmentation products of Apiezon Conditions as for Figure 7.
L (20%
on 60-80 mesh firebrick)
Attenuation 2-3 except as noted
VOL. 38, NO. 2, FEBRUARY 1966
327
Figure 1 1 .
Fragmentation products of DEGS (20% on 60-80 mesh firebrick) Conditions as for Figure 7.
many tailing peaks, as might be expected for oxygenated products. Powdered Solid Samples. Solids as powders or granules can also be run directly in contact with the carbon felt a t the downstream electrode. As examples, a commercial detergent (Tide) and sucrose are shown in Figures 12 and 13.
Comparison with Thermal 13rolysis. The results obtained with the electrical discharge fragmentation device show an interesting relationship to those obtained with thermal pyrolysis. The flow rate from the discharge as a function of time, shown in Figure 14, illustrates the flash nature of the process, with most of
Figure 12.
Fragmentation products of a detergent (Tide)
Conditions as for Figure 7. ANALYTICAL CHEMISTRY
the gas evolution occurring within the first 2 seconds. This rate of decomposition would be characteristic of a thermal pyrolysis a t temperatures well in excess of 1OOO" C. The patterns of breakdown products obtained in electrical discharge fragmentation, however, are typical of much lower temperatures in thermal
s
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328
Attenuation 2-3 except as noted
Attenuation 2-4 except as noted
8 0
8 8 8
?
pyrolysis. Thus the relative amounts of monomer and of products of more extensive breakdown obtained from the polymethylmethacrylate pattern (Figure 9) indicate that the normal operating conditions employed in this study correspond to isothermal pyrolysis in a closed container (3) a t about 600650' C . , or to flash pyrolysis in a silica boat heated in a coil (6) a t 800-850' C. Even more interesting information on equivalent temperature is obtained by comparing results obtained on Mesoporphyrin IX (Figure 15) with those
' CH3 R
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MESO-PORPHYRIN TX reported recently by Whitten, Bentley, and Kuwada (14, who studied the effect of pyrolysis temperature on the distribution of alkyl pyrrole products. The fractional yield of higher substituted alkyl pyrroles in the present study was found to fall between those obtained by Whitten, Bentley, and Kuwada a t temperatures of 570' and
630" C. This result supports the findings on polymethylmethacrylate, so it may be concluded that the electrical discharge technique furnishes an effective fragmentation temperature of about 600" C. under the present operating conditions. There is no doubt that this is a range of temperature particularly rich in qualitative information (8), preserving large characteristic fragments intact to a large extent, yet giving enough of their breakdown products to permit their characterization. Characterization of Sample Peaks. For the purpose of characterizing the peaks obtained in the fragmentation patterns, it has been found convenient to introduce in place of the sample tube a special injection port, sealed into place with gaskets by the pneumatic actuator in the same manner as the usual sample tubes. Injection of samples into the carrier stream passing through this inlet results in volatilization into the sample loop, so that the samples are introduced into the chromatographic column in a manner identical to that used for fragmentation samples. Gas or liquid samples can conveniently be injected, and, because of the large volume of the gas sample loop, both gas and liquid samples can be included together in a single calibration run. A calibration run employing this technique is shown in Figure 16.
DISCUSSION
Fragmentation of sample substances in an electrical discharge gives highly characteristic breakdown patterns analogous to those obtained in other methods of flash pyrolysis, but with greater flexibility and convenience of handling samples in various forms. The input power required is relatively modest, with approximately 100 watts for 30 seconds typically employed for fragmentation of solid sample?; only about 1 watt is required for samples already in the vapor state. A high degree of reproducibility of the breakdown patterns is obtained by placing the sample in contact with the graphite felt downstream electrode, which is porous and has a surface capable of accommodating samples in a variety of forms. Breakdown fragments are swept out of the discharge zone as they are formed, so that secondary breakdown is negligible, and the more characteristic primary breakdown fragments are obtained. With sufficient care in sample preparation, quantitative reproducibility within a few per cent should be readily attained. The technique of solids pyrolysis has a very broad range of possible applications. A partial list of these includes plastics, elastomers, resins, perfumes and cosmetics, paints and finishes, lacquers, varnisher, inks, distillation VOL. 38, NO. 2, FEBRUARY 1966
0
329
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Figure 15. phyrin IX
Fragmentation products of Conditions as for Figure 7
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Figure 16.
Calibration sample mixture
Conditions as for Figure 7
charge tube. Complete oxidation is readily obtained in the presence of oxygen under discharge conditions. Fragmentation in the presence of hydrogen yields simpler patterns somewhat analogous to those obtained in the carbon skeleton technique (1, IS). LITERATURE CITED
(1) Beroza, M., Sarmiento, R., ANAL. CHEM.35, 1353 (1963). (2) Davison, W. H. T., Slaney, S., Wragg, A. L., Chem. Ind. ( L o n d o n ) 1954, p. 1356. (3) Ettre, K., Varadi, P. F., ANAL. CHEM.35,69 (1963). (4) Haslam, J., Jeffs, A. R., J . A p p l . Chem. ( L o n d o n ) 7 , 24 (1957). (5) Keulemans, A. I. M., Perry, S. G., Fourth International G. C. Symposium, 103, Hamburg (1962).
END OF SYMPOSIUM ANALYTICAL CHEMISTRY
I
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Gas flow from discharge
residues, drugs, bacteria, waxes and polishes, fungi, binders, fertilizers, asphalts and tars, insecticides, bituminous materials, coal, solid fuels, detergents, soaps, paper and fiberboard, tissuese.g., hair, skin-cloth, synthetic and natural fibers, airborne dust, foodstuffs, flavors, and lubricants. The sample handling characteristics of the new electrical discharge fragmentation method suggest some interesting new applications, particularly in the characterization of components eluted in either gas or liquid chromatography. I n glass paper or thin layer chromatography, the eluted spot and its support can be transferred directly into a sample tube and fragmented. In gas chromatography, eluted components can readily be trapped with no high-temperature valving by allowing them to impinge on a cool bed of adsorbent, which may be in a separate individual sample tube for each peak, or may move beneath the exhaust tube at a rate synchronized with the recorder chart drive. In the latter case, the location of each peak in the moving adsorbent bed would then be inferred from the recorder chart. I n either case, the samples trapped on solid adsorbent could be fragmented just as a solid sample, giving the breakdown pattern characteristic of the collected fraction. The fragmentation technique is also open to modification through the addition of chemical reactants to the dis-
0rl'
z N m W
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OFF* *ON '0I SC HARG E. Figure 14. vs. time
Mesopor-
(6) Lehman, F., Brauner, G. M., ANAL. CHEM.33, 673 (1963). (7) Lehrle, R. S., Robb, J. C., Nature 183, 1671 (1959). (8) Luce, C. C., HurnDhrev. E. F..' et al.. ANAL.CHEM.36, 482 (1964). (9) McKinney, R. W., J . Gus Chromutog. 2. 432 11964). (lOj Perry, S. G., Ibid., 2, 54 (1964). (11) Radell, E., Strutz, H., ANAL.CHEM. 31, 1890 (1959). (12) Simon, W.. ACHEMA, Frankfurt. June 1964. ' (13) Sternberg, J. C., Krull, I. H.,
Friedel. G. D.. Fullerton. Calif.. unpublished work; 1964. (14) Whitten, D. G., Bentley, .K. E., Kuwada, D., J . Org. Chem. 31, in press. RECEIVED for review September 9, 1965. Accepted December 27, 1965. Third International Symposium, Advances in Gas Chromatography, Houston, Texas, October 1965.
