is joined to the stainless steel tube by a Teflon tubing connection, The eluting solvent may also be d e aerated when the nine-chambered variable gradient device (Autograd. Technicon Corp., New York) described by Peterson and Sober (4) is used to produce a gradient. This is accomplished by heating the solvent in the chamber immediately preceding the pump with an insulated heating tape wrapped around the bottom third of the chamber. The heating tape is held in place by Teflon adhesive tape. Because each chamber is already vented, no special precautions for the release of gases are required. Disruption of 100-em. columns of silica gel with hydration which varied between 3.8 and 5.2 ml. of aqueous phase to 8 grams of silica gel was eliminated by the use of solvents deaerated as described here.
i
LITERATURE CITED
Figure 1.
(1) Keener, L., Muntwyler, E., Griffin, G. E., Abrams, J., Federation Proc. 21 (No.2), 1 (1962). (2) Moore. S.. Stein. W. H..J . Bid. 'Chem. 211,893(i954j. (3) Mowery, D. F., Jr., ANAL.CHEM.31, 1911 (1959). (4) Peterson, E. A., Sober, H. 8., Zbid., 31,857(1959). (5) SDackman. D. H..Stein. W. H.. 'Moire, s.,Ibid., 30,1190(1958j. (6) Woods, K. R., Engle, R. L., Jr., Ann. N . Y . Acad. Sci. 87,764(1960).
Deaeration of a multiple chamber gradient device A. 8. C. D. E.
F. G. H. I.
Deaeration flask Gas vent Narrow gauge Teflon tubing Solvent reservoir Magnetic stirrer Heating mantle Thermometer Preliminary mixing chambers Column
is delivered to the pump from the heated deaerator flask A through a */8-inch by 10-inch stainless steel tube. To this tube are soldered 34 cooling
fins prepared from 2-inch squares of thin copper sheeting. Also, to avoid trapping any of the released air bubbles in the pump inlet tube, a glass U-tube
Gravimetric Introduction Device for Gas Chromatography.
SUPPORTED in part by a grant from NIH H-1657 Taken in part from Ph.D. thesis submitted by Leo K~~~~~to the Graduate Educational Program of the State University of New York Downstate Medicalcenter.
Application to Pyrolysis Studies
Roger S. Porter, Allan S. Hoffman, and Julian F. Johnson, California Research Corp., Richmond, Calif.
QRAVIMETRIC
introduction system
A for gas chromatography has sev-
eral potential advantages. It offers the most precise approach for calibration of gas chromatographic detection. With the design offered here, the gravimetric method may be used for a variety of studies-for example, .po!ymer pyrolysis. Decomposition is indcced under controlled conditions, the volatiles are gas chromatographed, and the residues are weighed and recovered. The advantage of using gas chromatography for studying pyrolysis has been widely noted. Pyrolysis has been conducted separately with the trapped volatile products being injected into a gas chromatograph (2). Decomposition studies performed on hot filaments in an injection system of
chromatographic columns (3) give quantitative analyses for certain s e lected systems, notably polymers which decompose entirely to volatile products. Techniques utilizing a weighable holder are advantageous in pyrolysis studies because of ease in handling the sample and residue. I n this way, a variety of systems may be studied under controlled decomposition conditions (1, 3). A useful method suggested for performing decompositions in the gas sample loop of a commercially available chromatographic injection system ( I ) has limitations in the precGion of weighing, in ease of cleaning, and inability to recover pyrolysis residues. This technique has been modified for more careful sample hmdling, but the procedure is more elaborate (3).
The new gravimetric introduction device for gas chromatography shown in Figure 1 has advantages in pyrolysis studies over both commercial equipment and techniques cited in the literature. The introduction system is easily connected to most chromatographs. Its small, compact design enables it to be thermostated closely and heated and cooled rapidly. Samples may be accurately weighed and varied from a few milligrams to about 1 gram. Catalysts or special liners may be used with samples to prevent or induce surface reactions. Both liquids and solids are conveniently loaded and weighed with precision using a threaded lower portion of the movable injection plunger (Figure 1). The carrier gas sweeps over the sample by passing through four symmetrically placed ports which are in the indented portion of the plunger just VOL. 34, NO. 9, AUGUST 1962
1179
CIRCLE SEAL
MOVABLE I N J E C T I O N
O-RING VALVE
AMPLE THERMOCOUPLE SHAFT
L A S S INSULATED HEAT1 NG WIRE
-
CARRIER GAS
IGRAPH
THERMOCOUPLE
Figure 1.
Gravimetric introduction device for gas chromatography
above the threads for the detachable sample chamber (Figure 1). The decomposition residues are also easily weighed and recovered. Successive samples can be run as fast as in conventional gas chromatography using multiple, replaceable introduction plungers and sample chambers. Figure 1 is drawn to scale; the diameter of the plunger and sample chamber is s/lo inch. The plunger is snug fit to the injection shaft. Before decomposition, samples are purged of air while held in a stream of helium before heating the block to decomposition temperatures. Samples may also be dried in the chamber a t any desired temperature by heating the
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64
j
block and/or the helium stream. After such pretreatment, the plunger is raised and the block is preheated to the desired temperature for pyrolysis. Then the plunger is rapidly lowered back to where the sample chamber is within the heating block. Alternately, the block may be heated over a fixed temperature program while the plunger remains in the lowered position. Because no separate sample pretreating or sealing techniques are required, vacuum systems, drying ovens, and/or capsulation used in other methods (1) are avoided. Temperatures for decomposition may be rapidly attained and controlled from ambient to over 500" C. with a maximum variation of *5' C. The py-
This new gravimetric introduction system is easily and inexpensively constructed and requires little or no maintenance. The inert atmosphere decompositions, attained by using h e lium as the chromatographic carrier gas, simulate pyrolysis conditions in vacuo. The decomposition atmosphere may also be oxidizing or reducing depending on choice of carrier gas. Patent rights are reserved on this gravimetric introduction device for gas chromatography.
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rolysis chamber is wound with 9 feet of 0.024inch insulated Nichrome wire controlled through a variable voltage transformer. The tight fit of the movable steel injection plunger and sample chamber ensure close control of maximum desired pyrolysis temperature. Temperatures may be read closely from thermocouples in the chamber and in the heating block close to the decomposition section. Volatile products of decomposition are rapidly swept into the column by the helium stream, thus minimizing secondary reactions. The rate and timing of chromatographic introduction can be controlled with valves. The introduction device can be used in either the direct-through or bypass arrangement. The direct-through procedure is facilitated by the use of an 0ring valve on the injection shaft which prohibits gas escape during all phases of sample handling. Figure 2 illustrates an application of the gravimetric device in the study of polymer decomposition. The volatile pyrolysis products from 0.0200 gram of a polybutene degraded a t 425' C. are shown in the chromatogram; the column was 50 feet of 28 weight % propylene carbonate on firebrick a t ambient temperature. The helium carrier gas flow rate was 35 ml./minute. The custom-built chromatograph was of conventional design. Three isothermal columns and three thermal conductivity detectors were used. The major products were resolved on the second column (Figure 2). The polybutene studied is a commercial product which is synthesized from a monomer mixture containing principally isobutylene. Decompositions, as in the case in Figure 2, may be rapid enough, taking place in a few seconds so that virtually no resolution is lost because of degradation time. Thus, eluted components may be identified by direct injection of pure compounds through a conventional septum system or through this introduction device.
ACKNOWLEDGMENT
The authors express appreciation for the contributions of K. E. Thompson. LITERATURE CITED
10
I5
20
25
TIME, MINUTES
Figure 2.
Pyrolysis of a polybutene
Second chromatogram of a three-column separation
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ANALYTICAL CHEMISTRY
30
35
(1) Radell, E. A., Stmtz, H. C., ANAL. CHEW 31, 1890 (1959). (2) Stramburger, J., Brauer, G. M., Tryon, M., Forziati, A. F., Ibid., 32, 454 (1960). (3) Swmn, W.B., Dux, J. P., Ibid., 33, 654 (1961).
