tamination; periods from 45 to 120 minutes result in nearly constant absorbance. With decreasing acid concentrations below 1.80N, during precipitation, thorium begins to interfere seriously ;with increasing concentrations above 1.80N, zirconium recovery decreases. Between 1.75 and 1.85N, the resulting absorbance is essentially constant. For the optical measurements, the less sensitive wavelength of 560 mp is used because the absorbance
(2) Hayes, W. G., Jones, E. W., IND. ENQ. CHEM., ANAL. ED. 13, 603
a t the absorption maxlmiim near 500 mp is generally too high to be measured. The precision of the procedure was calculated from the values obtained on analyzing six solutions containing 400 l g . of zirconium and amounts of thorium ranging from 25 to 250 mg. The relative st,andard deviation was 0.8%.
(1941). (3) Russell, E. R.. U. S. Atomic Energy Comm. Rept. DP-161 (1956). (4)Stehney, A. F., Safranski, L. W.; U. S. Atomic Energy Comm. Rept. AECD3097 (declassified 1951). A. R. EBERLE L. PINTO M. W. LERNER
LITERATURE CITED
New Brunswick Laboratory U. S. Atomic Energy Commission New Brunswick, N. J.
(1) Grimaldi, F. S., White, C. E., ANAL.
CHEM.25,1886(1953).
Gas Chromatographic Analysis of High Boiling Point Plasticizers Using a Short Column C. D. Cook, E. J. Elgood, G. C. Show, and D. H. Solomon, Balm Paints Pty. Ltd., Melbourne, Australia is used as a in the manufacture of acrylic lacquers. Some methods of preparation of this plasticizer lead to a product which is contaminated with both dibutyl and dibenzyl phthalate. The former is a particularly undesirable impurity as it tends to distil out of the lacquer film on exposure, and this can lead to embrittlement. For this reason it was necessary to develop a, method for the analysis of incoming stocks of benzyl butyl phthalate and also for the analysis of samples submitted by new suppliers. The requirements of the method would be the accurate determination of the dibutyl phthalate and the approximate determination of other impurities-e.g., dibenzyl phthalate-present. Because of the similarity in the compounds and their molecular weights (dibutyl phthalate 278.34, benzyl butyl phthalate 312.36, dibenzyl phthalate 346.37) the normal chemical tests of purity-e.g., saponification value-will be of little value. An equimolar mixture of dibutyl and dibenzyl phthalate would give an identical saponification value to benzyl butyl phthalate. Even if the benzyl butyl phthalate was contaminated with only one of these impurities to the extent of loyo,the difference in saponification value would be very small. For these reasons physical methods of analysis were examined, and gas liquid chromatography proved to be the most satisfactory technique.
;
ENZYL BUTYL PHTHALATE
B plasticicer
EXPERIMENTAL
Apparatus. The apparatus consisted of a Perkin-Elmer Vapor Fractometer Model 154C fitted with a thermistor bridge detector and a Leeds & Northrup recorder set for
10
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Figure 1. Chromatograms of commercial samples of benzyl butyl phthalate I. Graph of accepted standard II, 111, IV. Graphs of submitted samples from alternative saurces A, Unknown; E, dibutyl phthalate; C, benzyl butyl phthalate; D, dibenzyl phthalate
1 millivolt full scale deflection. The column finally selected was of stainless steel, 9 inches long and l/c-inch external diameter. It was packed with Embacel80- to 125-mesh (May and Baker) coated with 25y0 w./w. of silicone grease treated according to a procedure published previously (1). Procedure. The column was operated a t the maximum temperature obtainable with this instrument (approximately 235' C.). Helium was
used as the carrier gas at an inlet pressure of 10 p.s.i. which gave a flow rate through the column of 110 ml. per minute. Samples of 1 11. in size were injected into the apparatus using a &pi. Hamilton microsyringe. RESULTS AND DISCUSSION
Initial work was carried out on a 2meter column packed with siliconeVOL 34, NO. 9, AUGUST 1962
* 1177
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
