Table I. Retention Data for Plasticizers Studied
Plasticizer Dibut 1 phthalate Benzyf but 1 phthalate Dibenzyl pgthalate
Retention Time 72 aeca. 204 aeca. 576 aeca.
grease-coated Embacel as above. Retention times were excessively long (&benzyl phthalate not eluted after 1 hour), and the peaks were of a poor shape for accurate quantitative work. T o decrease retention times shorter columns were tried. This lead eventually to the development of a 9-inch column which gave the desired properties.
The retention times for the three plasticizers using the 9-inch column are given in Table I. The retention times were meaaured from the point of injection. Figure 1 shows a number of samples of benzyl butyl phthalate submitted by various suppliers. From these graphs the suitability of the sample can be assessed readily. Symmetrical peaks were obtained for each plasticizer (Figure 1) under the conditions specified. This allowed the normal triangulation method for the determination of peak areas to be used. A calibration graph was constructed for dibutyl phthalate which allows this component to be determined to an accuracy of 2% at a concentration of 5 to 10%. Prior to the development of this gas
chromatographic method, benzyl butyl phthalate samples were tested under practical conditions in the finished lacquer. This testing procedure could take up to 3 months to complete. Thus the gas-liquid chromatographic method offers enormous saving in time as well as a positive and accurate analysis of the constituents of commercial benzyl butyl phthalate. ACKNOWLEDGMENT
The authors express gratitude to the Management of Balm Paints Pty. Ltd., for permission to publish this paper. LITERATURE CITED
(1) Desty, D. H., “Vapour Phase Chromatography,” p. 319, Butterworth Scientific Publications, London, 1957.
Efficient Procedure for Solvent Deaeration in Column Chromatography Leo Kesner, Edward Muntwyler, Grace E. Griffin, and Joan Abrams, Department of Biochemistry, State University of New York Downstate Medical Center, Brooklyn, N. Y.
in chromatographic G solvents frequently interfere with column chromatographic procedures ASES DISSOLVED
(9, 6, 6). The problem is intensified when air or nitrogen is used to force solvents through the column a t increased flow rates. The dissolved gases may be released a t the lower part of the column, upon approaching atmospheric pressure, resulting in disruption and channeling. To circumvent this difficulty Mowery (3) substituted a pump for gas pressure. However, gases dissolved in the solvent a t room temperature and atmospheric pressure will be released if the temperature of the solvent is raised a t any point in the system after the pump m o d u l e f o r example, by jacketing the column (1, 6) or during color development (6). I n addition, a solvent should be deaerated prior to introduction into the pump to maintain accurate delivery volumes (6). The present communication describes simple procedures for deaerating solvents used during column chromatography. APPARATUS
Figure 1 illustrates a multichamber gradient device in which gas pressure is used to force solvents through a column. The three-necked deaeration flask A is the final mixing chamber prior to solvent delivery to the column. With a single mixing chamber system, the solvent reservoir D is positioned in one of the three necks of flask A . When solvents of higher density are to 1178
ANALYTICAL CHEMISTRY
be delivered from the reservoir a t slow flow rates, it is advisable to insert a &inch length of I-mm. bore ‘capillary in the stem of the reservoir chamber to avoid solvent mixing (5’)- Tube B acts as a vent for released gases in chamber A where constant volume is maintained. It consists of I/lrinch wall Teflon tubing attached to a glass tube whose outside diameter is equal to or slightly greater than the inside diameter of the Teflon tubing. An 8-mm. tube is a convenient size for the glass portion of tube B. The lower end of this glass tube is packed with 0.022inch Teflon tubing of nonuniform lengths varying between a/4 inch and ‘/zinch. Gas is thus released in small bubbles and any possible transfer of liquid from flask A to reservoir D is eliminated. In operation the solvent in flask A is warmed to the experimental temperature before insertion of tube B. The connection of Teflon to glass is readily accomplished as follows: Bevel the inside edge of the Teflon tubing and round the outer edge of the glass tubing. Heat the glass component below its softening point and force it into the Teflon tubing. This will cause the Teflon tubing to expand in order to accommodate the glass. Upon cooling, a gas-tight connection results. If the joint is not properly made, it can be secured with a hose clamp tightened over a piece of rubber tubing. Flask A is maintained a t an elevated temperature, the latter being determined empirically for each system used because i t is dependent upon the solvents, pressure, nature of the gas, and temperature to which the solvent is
maximally subjected. Although the illustration indicates, that flask A is heated with a mantle, other methods of heating are possible-e.g., the use of hot water circulating through a jacketed flask and a silicone rubbercoated heating tape wrapped around the flask and held in place by Teflon adhesive tape (Temp-R-Tape T, Connecticut Hard Rubber Ca., New Haven 9, Conn.). Tube C consists of a narrow boree.g., 0.047 inch-Teflon tubing which is forced through the stopper. This is accomplished by first drilling a hole in the stopper of a slightly smaller diameter than the tubing. A needle is then inserted into the lumen of the tubing to facilitate passage of the latter through the stopper hole. Silicone rubber stoppers (Size 24, The West Co., Phoenixville, Pa.) are useful and, when inserted into 24/40 ground joints, withstand up to 2 atm. of pressure a t temperatures up to 95’ C. However, under some circumstances it may be necessary to wire or clamp the stoppers. Also, depending upon the solvents used, swelling may be encountered, sufficient to close off the Teflon tubing C by compression. In such cases, insertion of a hypodermic needle through the Teflon tubing a t the point of compression will keep the lumen open. In those precedures where a pump is preferred for propelling the liquid, tube B may be opened to the atmosphere a t some point above the level of the solvent reservoir D. The solvent reservoir D, usually positioned about 2 feet above the pump, may be connected directly to flask A or to other mixing chambers prior to flask A . The solvent
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
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