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ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
Table I. KHF,-Etched WCOT Columns separation no. stationary phase ov-101 ov-101 OV-17 Poly A-103 UCON 50 HB5100 Carbowax 20M SPlOOO
length, mm 22 22 25 20 22 68 18
type of glass flint borosilicate flint borosilicate borosilicate flint borosilicate
Figure 2.
Figure 1. Electronmicrograph (6000 diameters) of a KHF,-etched capillary column
of nitrogen prior to examination in a gas chromatograph. Finally, the column should be further deactivated by techniques such as those previously described ( 3 . 4 ) . T h e entire deactivation process should be monitored at various stages by examination of the peak shapes of undecane, 2-octanone, and 1-octanol a t 190 "C (190 "C and 100 "C for short columns). Success at deactivation is indicated by improvement in the peak shapes of 2-octanone and 1-octanol. Alternatively, the testing procedure of Schomburg (6) may be used. We have examined the etched capillary surfaces a t various stages by scanning electron microscopy; whisker-like formations were not observed. The electron micrograph in Figure 1 is of an etched flint glass column that has been washed with water only. I t is logical that the crystalline material is K,SiF, which is sparingly soluble in water. However, we have not been able to confirm this. Ideally, a general column preparation procedure should meet certain requirements, such as those established by Grob
deactivation method silanization silanization Carbowax 20M Carbowax 20M Carbowax 20M Carbowax 20M none
c,
3-c14
40 38
32 23 18 48 19
Chromatogram of Patchouli Oil
( 7 ) . We feel that the procedure described above comes close to satisfying these criteria. T h a t is, the method is applicable t o both flint glass and borosilicate glass columns, does not require sophisticated equipment or reagents, and is suitable for a wide variety of coating materials. However, as with other techniques, success with this method is somewhat sensitive to the nature of the glass in each length of capillary tubing. Table I shows some typical results for several 0.25-mm i.d. WCOT columns prepared by static coating of capillary columns that were etched and deactivated by the above method. T h e chromatogram in Figure 2 was obtained with a borosilicate glass column (0.33 m m i.d. x 40 m) that was etched with KHF, and coated with SP1000. T h e column had a separation number (C15-C1G)of 40 a t 100 "C. A flow rate of 3 mL/min was used with linear temperature programming from 50-210 "C @ 2'/min. LITERATURE CITED (1) F. I. Onuska, M. E. Coneba, T. Bisticki, and R. J. Wilkinson,J. Chromatcgr., 142, 117 (1977). (2) M. Novotny and A . Zlatkis, Chromatogr. Rev., 14, 1 (1971). (3) D. A . Cronin, J , Chromatogr., 97, 263 (1974). (4) Th. Welsch, W . Engewald, and Ch. Klancke, Chromatographia, 10, 22 (1977). (5) J. G. Nikelly, Anal. Cbem., 46, 2249 (1974). (6) G. Schomburg, H. Husmann, and F. Weeke, Chromatographia, 10, 580 (1977). (7) K . Grob and G. Grob, J . Chromatogr., 125, 471 (1976).
RECEIVED for review July 5, 1978. Accepted August 11, 1978.
Compact, Variable Volume, Liquid/Liquid Extractor William A. Hoffman, Jr.' Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830
"Continuous" liquid/liquid equilibration between two immiscible solvents provides a convenient way to exhaustively 'Permanent address,Department of Chemistry, Denison University, Granville, Ohio 43023. 0003-2700/78/0350-2158$01 OO/O
extract components from solution even if the distribution coefficients of the solutes are not favorable. Commonly, either the lighter or the heavier density liquid is boiled, condensed, and allowed to percolate repetitively through a companion solvent which contains the solute. Many continuous extraction C 1978 American Chemical Society
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falls on the dispersing head, and percolates through the lighter solvent. As heavy solvent accumulates at the bottom of the apparatus, it moves up the annulus, over the adjustable tube top, and back into the still pot. A recycle rate of 4-5 mL/min was obtained with a CH,C12/H20 solvent pair.
LL
SECTION a-A
ADJUSTABLE T U B E 2 m m TO 3 m m
r
-HEAVY DENSIT
DISCUSSION Solvents and solute(s) employed determine how long an extraction should proceed. Microgram amounts of di-2ethylhexyl phthalate, di-2-ethylhexyl adipate, and various chlorohydrocarbons have been identified from 20-200 mL of rainwater samples after a 24-h extraction with methylene chloride (CH,Cl,) using this unit. Under the same conditions, quantitative isolation of n-Cs and n-C8acids from prepared aqueous solutions also was obtained. T h e apparatus is well suited for extractions from aqueous solutions with chloromethanes. T h e extractor was fabricated from standard glass tubing and rods. Diameters of the tubing chosen constrain the variable volume limits. From Figure 1 ( V = .;rr2h); volume circumscribed by outer wall: (3.14)(2)2(24) y 300 c m 3
-lOcm
HOLE
VI-ON O-RING
Figure 1. Continuous extraction device
devices have been designed on this ebullioscopic principle and are described in reference and commercial publications (1-3) T h e impetus to produce yet another device of this kind is limited; perhaps this heavy-solvent design (Figure 1) will appeal to those who like variety. T h e extractor has these useful features: (1) variable volume of light-liquid, (2) minimum volume of heavy-liquid, and (3) compactness. This extractor design requires that the heavy extracting solvent have a lower-boiling point than the light solvent. Rainwater samples, for which the unit was built and successfully used, vary widely in volume and solute concentration, and a small extracting liquid volume is particularly helpful in minimizing contamination when minor components are to be recovered.
EXPERIMENTAL Filling. With the adjustable tube inserted in the apparatus, sufficient heavy solvent is added through the top to cover the inner wall holes at least 1-2 cm (l(kl.5 mL in this unit). The adjustable tube is moved with a screwing motion through the O-rings to its highest position in preparation for the addition of the low density solvent solution. The solution to be extracted is carefull) poured into the extractor; care needs to be taken in adding light solvent to prevent its introduction into the annulus through the inner wall holes. As light solvent is added, heavy solvent rises in the annulus between the adjustable tube and the inner wall. After both solvents are added, the adjustable tube is turned down until the level of heavy solvent in the annulus and the level of the tube top coincide. If the heavy solvent level in the outer tube is more than 1-2 cm above the inner wall holes at this point, the excess may be drained through the stopcock. Extracting. The filled extractor is attached to a small still pot containing about 25 mL of heavy solvent (bottom), and to a Friedrich's condenser (top). The still pot is heated until full reflux is established. As reflux begins, heavy solvent condenses,
volume circumscribed b y inner wall: (3.14)(1)2(24)g 'is cm3 n e t volume: E 200 c m 3 Using the same dimensions of length, an outer tube with a diameter of 80 mm would provide an aqueous volume of about 1 L for extraction. Two O-rings were used to ensure stability of the adjustable tube. T h e design requires that grooves be machined on the inside of the supporting glass. Viton O-rings were chosen over Neoprene and Buna-N because of Viton's stability toward organic solvents. Because of lot variability of Viton, it is advisable to soak the O-rings in the heaky solvent several days before use and to check for leachable material. Machined Teflon O-rings proved too inflexible to compensate for t h e 0.d. variability of commercial tubing and, when the adjustable tube was machined to h0.005 cm, the Teflon-glass interface proved too rigid to permit the tube to be adjusted with safety. A single Teflon Wilson seal did not provide a uniform annulus. T h e apparatus also was constructed as a f i x e d volume extractor with the elimination of seals altogether.
ACKNOWLEDGMENT The author thanks Richard W. Poole, ORNL, for his helpful discussions and fabrication suggestions. LITERATURE CITED (1) G. H. Morrison and H. Freiser, "Solvent Extraction in Analytical Chemistry", John Wiley and Sons, New York, 1957. (2) L. C. Craig and D. Craig, "Technique of Organic Chemistry", A. Weissberger, Ed., Interscience, New York, 1956,Vol. 3,pp 248-300. (3) Aldrich Chemical Co., Inc., Technical Information Publication #ZlO,156-7, 940 W. St. Paul Ave., Milwaukee, Wis. 58233, 1978.
RECEIVED for review July 17, 1978. Accepted August 21, 1978. Research Supported by t h e Division of Biomedical and Environmental Research, U.S. Department of Energy, under Contract W-7405-eng-26 with Union Carbide Corporation. Publication No. 1244, Environmental Sciences Division, ORNL.
