1596
Anal. Chem. 1906, 58,1596-1597 VORTEX GENERATOR I
NOZZLE
'
HOT OUTLET
COLD WTLET
VORTEX GENERATION CHAMBER
Figure 1. Schematic drawing of a Ranque-Hlisch vortex tube.
escape (approximately 40430% of the total volume), while the remainder of the air returns through the (previously empty) center of the tube in a counterflowing stream. This counterflowing stream in the center of the tube forms a second vortex having the same angular velocity as the first vortex, traveling in the opposite linear direction. The principle of conservation of angular momentum requires that a particle in a vortex increase its speed as it moves toward the center of the vortex. Since both vortices are locked together at the same angular velocity, the inner stream must lose energy upon its formation. This energy leaves the stream as heat, carried by the fraction of air escaping from the needle control valve. The inner stream must therefore be cooled to compensate for this energy loss. This cooled air will emerge from the cold air outlet on the right-hand side of Figure 1. The air escaping from the hot end of the tube can have a temperature as high as 90 "C, while that escaping from the cold end may be as cool as -40 "C. The actual temperature obtained may be regulated by adjusting the needle control valve at the hot end of the tube. Thus, with most of the air flow escaping from the hot end, minimum temperature is obtained at the cold end. To utilize vortex cooling for subambient chromatographic column operation, the cold end of the vortex tube was fitted with a machined titanium adapter that was then attached to the column oven through an auxiliary port. This allows the
cold air stream to be directed inside the column oven. The low thermal conductivity of titanium ensures that the fitting will cause minimal heat leakage into or out of the oven. The hot air stream, which is set (using the needle control value) to comprise about 40-50% of the total air flow, was allowed to escape into the room. It is not possible to direct the cold stream of the vortex tube into the solenoid valve, which typically accepts the cryogen transfer line on commercial instruments. This is because any interference to the flow of the cold stream of the vortex tube will disrupt the operation of the tube. The equilibration time, which depends on insulation of the oven, is approximately 15 min. The only disadvantage experienced with this approach to cooling was the continuous noise of escaping compressed air (at a leJel of 78 dB). To remedy this problem, the acoustic spectrum was measured with a frequency analyzer. The noise spectrum was found to have two major peaks between 2 and 8 kHz and between 12 and 16 kHz. Subsequent installation of an appropriate baffle muffler to the hot air outlet of the tube and the use of sound-absorbing foam around the tube reduced the noise to an acceptable level of 25 dB. The compressed air supplied to the vortex tube can be taken from the house air supplied in most laboratories. It is important, however, that the air supply be free of moisture and oil vapor. Thus, it is necessary that the vortex tube be preceded with both a particulate filter and a coalescence filter. With these precautions, a vortex tube and ordinary compressed air can be a convenient substitute for many liters of cryogenic fluids.
LITERATURE CITED (1) Bruno, T. J.; Hume, G. L. Int. J . Thermophys., In press. (2) Brettell, T. A.; Grob, R. L. Am. Lab. (Fairfield, Conn.) 1985, 17(10), 19. (3) Zabetakis, M. 0. Safety with Cryogenic Fluids; Plenum: New York, 1987. (4) Aronson, R. B. Mach. D e s . 1978, 4 7 , 6.
RECEIVED for review January 13, 1986. Accepted February 14, 1986. This work was supported by the Gas Research Institute.
Radlometrlc Method for Determining Solubllity of Organic Solvents in Water J. M. Lo,* C. L. Tseng,and J. Y. Yang Institute of Nuclear Science and Nuclear Science & Technology Development Center, National Tsing Hua University, Hsinchu, Taiwan 30043, Republic of China Cobalt-60 labeled cobalt(II1) pyrrolidinecarbodithioate (eoCo(PDC)3)has a peculiar stability during storage in organic solvent and when its organic solution is shaken with an aqueous solution containing different acids or ions (1-3). Using these characteristics, we have attempted to use 6oCo(PDC)3as a radioagent for determining solubilities of various organic solvents in water. The radioagent was first dissolved in the organic solvent under investigation before pure water was added. The solution mixture was shaken vigorously in order to let the organic phase contact with water sufficiently. Some of the organic solvent would dissolve in water after shaking, resulting in volume reduction of the organic phase. However, the radioagent was found not to accompany the organic solvent molecules going into water; i.e., all the radioactivity of 6oCo(PDC)3would be retained in the organic phase. Solubility of the organic solvent in water therefore can be calculated from the value of the volume change of the organic phase divided by the water volume. Direct mea0003-2700/88/0358-1596$01.50/0
surement of a small change in volume of organic phase with high accuracy is generally very difficult; alternatively, we have measured the specific activities of 6oCo(PDC)3(cpm/mL) in the original and the final organic solutions, and the counting results were used to estimate the decrease in volume of the organic phase. Several commonly used organic solvents were selected to test the applicability of the proposed radiometric method. The solubilities of the organic solvents selected for this study range from very small values (lo4) to relatively large values (
EXPERIMENTAL SECTION The volume of water in our experiments was much greater (at least 100-fold)than that of the organic solvent investigated. Both of the liquids were placed in a 1000-mL separation funnel. 6oCo(PDC)3 was concentrated in the organic solvent at about 1 X IO" M with a specific activity of 10 fiCi/mL. The radioagent was prepared by adding a suprastoichiometric amount of ammonium pyrrolidinecarbodithioate into 6oCo2+(New England 0 1988 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 58, NO. 7, JUNE 1986
Nuclear Co. product) at pH -4 ("OB). The labeled complex, @%O(PDC)~,was extracted into chloroform. Part of the organic solution was withdrawn and evaporated at 60 "C for several hours to dryness. Then the organic solvent under investigation was added to dissolve the solid %o(PDC),. Before analysis the organic solution was washed with water by shaking to remove any possible radiolytic product, e.g., e°Co2+.The organic solvents studied in this work were purchased from E. Merck; pure water used was demineralized and then subboiled around 90 "C. All experiments were performed at room temperature (-25 "C). Only 5 mL of the low-solubility organic solvent containing GOCo(PDC)3 was placed together with 1000 mL of water into the separation funnel. For high-solubility organic solvents, up to 100 mL of solvent containing 6oCo(PDC)3was placed with 1000 mL of water. The mixture was shaken by hand vigorously for 5 min; this shaking time was found to be enough for the organic solvents to reach saturation in water for all the cases. After a 30 min wait to permit separation of the two phases, part of the organic phase was withdrawn for activity measurement by a NaI(T1) scintillation detector. The activity in the original organic solution was also measured. For each set of experiments, part of the aqueous phase was also withdrawn for activity measurement after extraction. It should be noted here that several factors, such as the total activity of 6oCo(PDC)3as well as the volumes of the two phases (the organic solvent and the water), could be adjusted to obtain a significant difference between the specific activities in the original and final organic solutions, leading to accurate solubility measurements.
RESULTS AND DISCUSSION The solubilities of the organic solvents investigated were calculated from the observed experimental data by
"( 5) vw
1-
x 100
or
-vo As x 100
v, S'
(indicated by % by volume) and
-vo Asp x 100 vw
s1
(indicated by % by weight) where V , and V , are the volumes of original organic solution and water, respectively, So,S', and A S are the specific activities of the original and final organic solutions and the difference between them, respectively, p is the specific gravity of the organic solvent investigated. The solubilities of various organic solvents obtained by the proposed method were summarized in Table I. Most of the values obtained from this study are in good agreement with those reported and collected in the text edited by Riddick and Bunger ( 4 ) except chlorobenzene, n-butyl acetate, and ethyl acetate. However, our measured solubilities of n-butyl acetate and ethyl acetate are close to those that appear in the Merck Index (5). A higher value for chlorobenzene shown in the literature ( 4 ) might be due to the fact that the datum was obtained a t a higher temperature (30 OC). Most of the previous measurements used gas-liquid chromatographic techniques to which water sampled after extraction is directly injected into a gas chromatograph and analyzed for ita organic content. One drawback of this method is that small organic solvent droplets, difficult to observe, may still stay in the water sample and be falsely counted as the soluble material. It was mentioned by McAuliffer (6) that in the case of vigorous shaking, the solution was allowed to stand for a long period of up to 2 days to permit separation of the organic droplets from water. Our method uses an indirect method by sampling the organic solution rather than water for analysis by radiometry. Here, it is not necessary to con-
1597
Table I. Solubility in Water at Room Temperature (25 "C) of Vivious Organic Solvents organic solvent p-xylene o-dichlorobenzene chlorobenzene toluene carbon tetrachloride benzene carbon disulfide n-butyl acetate chloroform methyl isobutyl ketone ethyl acetate
solubility, % by wt this work ref 4 ref 5 0.019 f 0.001~ 0.019 0.017 f 0.001 (0.026 0.035 k 0.002 0.0488* 0.052 f 0.002 0.0515 0.080 f 0.007 0.077 0.181 f 0.015 0.178 0.286 f 0.025 0.294' 0.840 f 0.02 0.43c 0.82 f 0.02 0.815O 1.77 f 0.04
9.50 f 0.25
Standard deviation of mean. done at 20 O C .
1.7 8.08
0.83
9.02
Work done at 30 "C. 'Work
sider the same problem inherent in the direct method as mentioned above. As long as the two phases becomes visibly separable, part of the clear organic solution (usually about 60%) could be sampled for specific activity measurement. The standing time was short for all the solubility measurements carried out in the study. It should be emphasized that any water content soluble in the final organic solution would only give a negligible fluctuation to the volume decrease of organic phase from the dissolution of organic solvent in water. This is reasonable when a great volume of water and a small volume of organic solvent are added for extraction, as are all the cases in the study. In fact, the larger the volume ratio, the greater the sensitivity of the solubility measurement. This situation is particularly useful with the application of those low-solubility organic solvents. A direct method by liquid-gas chromatography cannot achieve such an advantage. The distribution coefficient of 6oCo(PDC)3between two phases is important in assessing the limiting measurable value of solubility by the proposed method. Usually the total activity of 6oCo(PDC)3added to the organic solvent for our experiment was on the order of lo5cpm. However, the activity in the aqueous phase after extraction was generally found to be very few, i.e., very close to the counting background. When the total activity of 6oCo(PDC)3added was enhanced to lo6 cpm, the total activity of cobalt-60 that appeared in the aqueous phase was around lo2cpm. Consequently, the distribution coefficient of "Co(PDC)3 is calculated to be on the order of lo5 for all the extraction systems in the study. Accordingly, the detection limit of solubility of organic solvent in water can reach ca. 10-5.
ACKNOWLEDGMENT We are indebted to C. M. Wai of the Chemistry Department at the University of Idaho and Chung Chien of the Institute of Nuclear Science a t the National Tsing Hua University for their advice. Registry No. 6oCo(PDC)3,77885-64-4. LITERATURE CITED (1) Wei, J. C.; Lo, J. M.; Yeh, S. J. Radiochem. Radioanal. Lett. 1978, 35, 121-126. (2) Tseng, C. L.; Lo, J. M. Radiochem. Radioanal. Lett. 1978, 33, 315-322. (3) Lo, J. M.; Wei. J. C.; Tseng, C. L.; Yeh, S. J. Int. J . Appl. Radiat. Isot. 1981, 32, 251-253. (4) Riddick, J. A.; Bunger, W. B. Organic Solvents: Physical Properties and Methods of Purification, 3rd ed.; Why-Interscience: New York, 1970. (5) Windholz, M. The Merck Index, 10th. ed.; Merck 8 Co., Inc.: Rahway, NJ, 1983. (6) McAuiiffer, C. J. Phys. Chem. 1966, 7 0 , 1267-1275.
RECEIVED for review March 19,1985. Resubmitted February 13, 1986. Accepted February 13, 1986.
