AIDS FOR THE ANALYST ball-and-socket joints are lubricated with water.) B has a small opening at the top of the bend and a trap on the outer descending arm, to prevent siphoning of the solvent from the reservoir into the distilling flask. A small hole in G prevents a positive pressure in the distillation system.
liquid-liquid Continuous Extractor for Solvents Heavier Than Water Charles E. Pierce and Ralph E. Peterson, National Institute of Arthritis and Metabolic Diseases, National Institute of Health, Bethesda, M d .
modifications of the original Wehrli liquid-liquid M continuous extractor for solvents heavier than v-ater have been described. Attempts to improve the Wehrli-type ('7)
ANY
extractor have been directed toivard increasing the surface area for contact of the two solvent, phases, so that the solvent leaving the extraction chamber is more nearly in equilibrium with t'he aqueous solution. This has been accomplished by mechanical stirring in the extraction chamber ( 6 ) , stirring by injection of the vapors from distillation (J), injection of the solvent from a fine jet (Q), addition of long spiral for the solvent to be in contact with the aqueous phase ( I ) , and provision of a diffuser plate (2) to disperse the solvent condensate. However, these modified extractors are still relatively inefficient because the extracting solvent does not extract sufficient solute to satisfy the partition ratio during a single passage through the aqueous phase. Thus, there is still a need for a liquid-liquid estractor for solvents heavier than water, n-hich has more versatility and gives a more efficient extraction rate. The folloTving apparatus meets many of t.hese requirements. A greatly increased boundarj- surface for contact of the two solvent phases has been achieved by the continual exposure of the organic solvent t o a rapidll- changing thin film of the aqueous solvent through the use of a rot,ating glass hall.
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Figure 1.
OPER4TION
Assembled extractor
The extractor is assembled as shown in Figure 1.
A few hundred milliliters of solvent (dichloromethane has been used in all of these experiments) are placed in a 1-liter roundbottomed distillation flask which is then attached to the ground joint a t the lower end of 6. Approximately 500 ml. of dichloromethane are added to the reservoir, A , which has a capacity of about 4500 ml. with the 1liter round glass ball in place. The aqueous phase (water or urine in these experiments) is carefully introduced into '4. From 200 ml. t o a maximum of 4000 ml. of aqueous material may be used in a reservoir of this size. Urine should be a t room temperature or slightly higher (25" to 40" C.) during the entire operation of this extractor. Cold urine has a tenaency to form- emulsions, but no troublesome emulsions have been experienced with warm urine. The adjustable side arm, B , is set a t the proper angle, depending upon the volume of urine added to the reservoir. The angle should be adjusted so that between 300 and 350 ml. of dichloromethane remain in the bottom of the reservoir. This should bring the level of dichloromethane in 9 to just below the center of the circular ball, D. The heating mantle for the distilling flask is connected to a variable transformer and distillation of the solvent is begun. A few boiling chips may be added t o the distillation flask to achieve a more even distillation of solvent. The solvent vapors pass up the side arm, C, and the condensate collects a t the condenser, G . This condensate then drops into the sidearm tube and mixes with the solvent in the bottom of the reservow. After the solvent has started to distill over, the variable-speed electric motor with the magnet is started. This in turn rotates the magnet encased in Teflon in the hollow glass ball, D, enclosed in the reservoir. As the ball turns, it carries a thin film of the aqueous phase through the solvent, and produces a very efficient and continuous mixing of the upper phase. The ball, operating at the slowest speed that is necessary to keep it turning continuously, must turn a t a rate of approximately 50 r.p.m. Faster rates produce no more efficient extraction, and too rapid turning may produce emulsions. The dichloromethane-soluble solutes in the urine reach the distilling flask via the adjustable side arm, B. ( N o stopcock grease is used on any of the ground-glass joints of this equipment. The
male ball joints a t bottom 20-mm. tubing 29*/2 inches high from top of bend to bottom of 24/40 eround ioint. 35/20 male ball joint a t toD. - 28/15 . female ball j o h t a t bottom ' D. I-liter round-bottomed bor,osilicate flask, w-ith 20-lb . pull Tefloncoated magnet embedded in glass flask E . 24/40 ground-glass joint with Teflon adapter F . 50-lb. pull magnet to attach t o variable-speed motor G . Modified Friedrichs condenser with 35/20 female ball joint a t toD and 35/20 male ball joint a t bottom, 6-mm. air vent near bdttom C.
After the extraction operation has been completed, the solvent in the reservoir may be drained directly into the distillation flask by closing the small opening in the tip of the adjustable side arm and lowering the angle of the side arm. This adjustable side arm is similar to that described by Ifland (S), but makes it possible to adjust the liquid level in the extractor over a wider range of volumes. The reservoir may be completely emptied by placing a finger over the air vent and lowering the side arm. After the solvent has drained into the distilling flask, the side arm is returned to a vertical position, and the urine drained out through the stopcock at the bottom of A . RATE OF REMOVAL OF STEROIDS FROM WATER
A graphic plot on semilogarithmic coordinates of the fraction of steroid removed from the water per unit time produced a single straight line (Figure 2). This demonstrates the exponential nature of the removal process and the efficiency of the mixing of the aqueous solution. The rate of removal n-as found to be a function of the volume of the aqueous phase. Using the standard Hershberg-Wolfe extractor ( 8 ) with 1000 ml. of water. hydrocortisone was removed a t a rate that indicated a half-time of 84 minutes as compared with 18 minutes with the rotary film extractor and 1000 ml. of water. In all experiments with this extractor and the Hershberg-Wolfe extractor, the dichloromethane was distilled a t a rate of approximately 14 ml. per minute.
2029
ANALYTICAL CHEMISTRY
2030 This adjustable side arm is similar to that described by Iffland (S), but makes it possible to adjust the liquid level in the extractor over a wider range of volumes. The reservoir may be completely emptied by placing a finger over the air vent and lowering the side arm. The rate of removal of the steroids from the water was correlated with the partition coefficient of the particular solute be-
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tn-een mater and dichloromethane. The higher the partition concentration upper phase coefficient ( K = with solvents equilconcentration lower phase' ibrated with each other a t 25" C.), the slower the rate of removal of solute. Figure 3 shows the removal rates for three different steroids, using a constant volume of water ( 2 liters), and also the partition coefficients of the various steroids between water and dichloromethane.
4
ADVANTAGES
1
The extraction rate is rapid because of the large surface area of fresh aqueous phase continuously exposed to solvent by the turning of the glass ball, and the continuous mixing of the aqueous phase by the turning of the glass ball. Thus, a rapid equilibration of the solute between the two solvent phases is achieved. There is little tendency t o emulsion formation, because air is not introduced into the system. Various volumes of urine (200 t o 4000 ml.) can be extracted v i t h a small volume of solvent. The extractor may be designed to extract even large volumes of urine. This extractor, like any continuous extractor, permits extraction of a solute from a large volume of water into a small volume of solvent, especially desirable where the solute is not particularly soluble in the solvent.
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ACKNOF LEDGMENT
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The authors are indebted to T. D. Perrine for many helpful suggestions regarding the design of this extractor, and t o the Rinco Instrument Co., Greenville, Ill., for aid in the construction. The extractor is commercially available from the Rinco Instrument Co
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LITERATURE CITED
Figure 2.
(1) Friedrichs, F . , J . An?.ChLm. SOC.34, 285 (1912). (2) Hershberg, E. P., Wolfe, J. K., J . Bid. Chem. 133, 6G7 (1940). (3) Iffland, D. C., ANAL.CHEM.25, 1577 (1953).
Rate of removal of hydrocortisone from water
E. R., Fulmer, E. I., Underkofler, L .I., ENG.C H E M . . h A L . ED 16, 473 (1944). ( 5 ) N a m e l i , G., Gam. chim. ital. 361, 1 2 3 (1906). 6) Keuberger, A., Biochem. J . 32, 1435 (1938). (7) Wrhrli, S , Helu. C h i n . Acta 20, 927 (1937). (4) Kolfenbach, J. J., Kooi,
Extracting solvent, dichloromethane Time in minutes required for one half of steroid t o hr rxtracren 1112.
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Feliability, system: good regulation, easy temperature selection, and simplicity of design. The regulator described
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Rate of removal of corticosteroids from 2 liters of water
Extracting solvent, dichloromethane K . Partition coefficient t ~ / x .Time in minutes required for one half of steroid t o be removed from water
permits temperature control to i.0.01" C. in an uninsulated bath operating 15' above room temperature, a dial setting gives the desired operating temperature. The unit has been in use intermittenti>- for a year a t temperatures from 0' to 80' C. with no change in calibration, and the circuit is less complicated than a small "hi-fi" preamplifier The thermistor is the most responsive of the temperaturesensitive resistance elements. Its thermal coefficient of resistance is about 47, per degree Centigrade, compared vith 0.39% for the platinum resistance thermometer. A thermistor does not have the pon-er-handling capability of the metallic resistance elements, PO that a much smaller bridge voltage must be used. The bridge output signal for a 0.01" change in temperature may thus be lomer Tvith a thermistor than with a metallic resistance thermometer. This loner output can be compensated by slightly higher gain in the amplifier. The lower cost of the thermistor and associated low-power bridge elements, combined vith its low thermal lag, makes it a logical choice for the temperature-sensing element. -4two-stage resistance-coupled amplifier using a 12.4X7 gives
