apparatus similar to that of Durrum (S), with Whatman No. 1 filter paper (30 cm. long and 15 cm. wide) was used, The electrochromatograms were run for 2 hours with 400 volts; either 1% borax solution or p H 8.6 borax-boric acid-NaC1 was used as buffer. REVEALING SUGARSPOTS. The paper chromatograms or paper electrochromatograms were dried in an oven, sprayed with reagent A and then heated for 20 minutes at loo", when the sugar components were revealed as yellow spots on a colorless background. Care was taken not to leave the chromatograms or paper electrochromatograms exposed t o strong light, since they tended to acquire a blue coloration. DEVELOPINGCOLOR FOR ESTIMATION. Circles 2 cm. in diameter were cut around each revealed spot and introduced in a test tube (25-mI. capacity), 6 ml. of reagent B were added, and the tubes were heated in a briskly boiling water bath for 15 minutes with occasional shaking, then kept a t room temperature for 5 minutes. A colorless blank was simultaneously prepared by
cutting a circle of the same size and subjecting it to the same treatment. MEASUREMENT OF COLOR. The color was measured on either a Unicam SP 500 spectrophotometer (6) at wave length 700 mp or with a Hilger Spekker absorptiometer (6) using Ilford spectrum red filter No. 608 (approximate peak of transmittance a t wave length 680 mp). In both cases, 1-cm. cells were used. DETERMINATION O F CONCENTRATION. Curves of the absorbance were plotted against weight of sugar for the two standard solutions and from the absorbance of the sugar components in the analyzed mixture, their weights were determined. DISCUSSION
Apart from its simplicity, the suggested procedure gives reasonably reproducible results. Thus, the usual error involves differences of about 5 pg. in 100-pg. samples of sugar (Table I). The number of components to be esti-
mated and their nature are limited only by whether they can be satisfactorily separated by paper chromatography or paper electrophoresis. The solvent used for the former does not seem to have any great influence, since it is evaporated. LITERATURE CITED
(1) Aronoff, S., Vernon, L. P., Arch. Biochem. 28,424 (1950). (2) Bl;ck, R. T., Durrum, E. L., Zweig, G., Manual of Paper Chromatography and Paper Electrophoresis," p. 57, Academic Press, New York, 1958. (3) Durrum, E. L., J. -4m.Chem. Soc. 72,2943 (1950). (4) El Khadem, H., Hanessian, S., ANAL. CHEM.30, 1965 (1958). (5) Rlatthews, Maryland Acad. Sci. Bull. 7, 35 (1928). (6) Vogel, A. I., "Quantitative Inorganic Analysis," pp. 621, 629, Longmans, Green, London, 1953.
HASSAN EL KEADEM Chemistry Department WISSAMGIRGIS Faculty of Science Alexandria University Alexandria, Egypt, U.-4.R.
Determination of Ruthenium Tetroxide SIR: -4study of the kinetics of the decomposition of ruthenium tetroxide necessitated determination of the quantity of RuO4 present in sealed Carius tubes containing, in addition to RUO4, other materials such as ruthenium metal, ruthenium dioxide, silica gel, and Anhydrone. Available methods measured the total ruthenium content and were not applicable to this type of sample, since ruthenium dioxide was one of the products of decomposition. Accordingly, a procedure was developed to measure RuO4 content selectively. Sandell reported (6)that ruthenium tetroxide may be extracted with carbon tetrachloride, but the stripping of the RUOa from the solvent is a slow procedure, requiring as much as 2 hours' shaking with sulfurous acid for a quantitative transfer. Marshall and Rickard (1) published a method for determining ruthenium, utilizing the absorbance of the orange-red color of the ruthenate solution. The combination of carbon tetrachloride extraction and colorimetric procedures provided the basis for the present method. The main innovation is the stripping of the tetroxide from the carbon tetrachloride using a solution of potassium hydroxide. Reagents. Ruthenium metal and ruthenium dioxide were obtained from the A. D. Mackay Co. The oxide was ignited at 950' C. to remove volatile impurities. Spectrographic analysis of the ignited sample indicated only trace impurities. The 646
ANALYTICAL CHEMISTRY
RUO4 was synthesized from RuOl via a persulfate oxidation, followed by drying with Anhydrone. Experimental. Capillary micropipets were used to transfer the liquid RuOd to the Carius tube. RuO4 was melted and an appropriate volume was drawn into the pipet with a syringe. The filled pipet was then weighed, and the RuOl was quickly transferred into a Carius tube which was chilled a t the bottom. Any R u 0 4 that remained in the capillary was frozen to reduce volatilization losses by touching the chilled wall of the Carius tube. The pipet was removed and reweighed, and the weight of Ru04 transferred into the Carius tube was obtained by difference. These tubes were sealed and used in a study of the decomposition of To determine the amount of RUO4 not decomposed, one end of the sealed Carius tube was placed in a dry iceacetone bath and the other was warmed with a hair dryer, so that the Ru04 condensed in the cold end of the tube. The top of the tube was cracked, using a hot wire, and opened. Fifteen milliliters of Cc14 was added to the tube, which was then allowed to come to room temperature. The cc14 and the tube contents were transferred with CCl4 washing to a centrifuge tube and centrifuged. The centrifugate was added to a beaker containing 50 ml. of 2N KOH. The residue (RuOz and Anhydrone) in the tube was crushed with a glass rod and re-extracted with CC14. The CCl, extract was added to the original centrifugate. The mixture of CCl4 and alkali was warmed a t about 70" to 75" C. until the cc14 layer was clear
(about hour). The mixture was transferred to a separatory funnel, the two layers were separated, and the CC1, was discarded. The aqueous layer was transferred to the original beaker and reheated to 80' to 90' C. for about 15 minutes. The KOH solution was transferred to a 250-ml. volumetric flask, cooled, and made up to volume with 2N KOH. The absorbance was then measured a t 465 mp with the Beckman DU spectrophotometer. RESULTS AND CONCLUSIONS
The combination of carbon tetrachloride extraction and KOH stripping gave the advantages of high selectivity of the solvent and development of the ruthenate color in a short period of time. The RUOc n-as rapidly extracted by the carbon tetrachloride and presented no problems. A number of tests were conducted to determine optimum conditions for stripping the RuOc from the CC14; 2N KOH a t about 70" C. gave the best results. The relatively rapid stripping with KOH can probably be traced to a combination of factors. In the procedure described, the CCl4 extract is added to a beaker containing warm KOH and is heated. This increases the hydrolysis rate of the RuOc in the aqueous phase, thereby favoring the stripping. The RuOl is also more volatile a t the higher temperature. As it volatilizes, it is absorbed in the layer of KOH and hydrolyzes. There is no appreciable loss during this step. The accuracy of the method was
estimated by analyzing a series of samples in sealed tubes. As shown in Table I, the average RuO4 recovery was 97.9%, with a standard deviation of *1.5%, The greatest loss of RuOc occurred in transferring a weighed amount of RuOl to the Carius tube and subsequent sealing. For this reason, the accuracy of the analytical method is probably greater than that shown in the table. This was demonstrated by recoveries of 99.0 and 99.6y0 when the RuO4 mas dissolved directly in carbon tetrachloride instead of being sealed in a Carius tube. The method was applied to 300 to 400 samples and found to be satisfactory. Typical types of samples are shown in Table I. These contained hod, RuOz, Anhydrone, ruthenium metal, and/or silica gel. The procedure was modified for the latter, since the CC14 extraction of RuOl from the silica gel was very slow and required several extractions. The RuOc and silica gcl were dissolved in 2N KOH (CCll m-as used to wash the silica gel from the tube into the KOH). When the silica gel mas added to the KOH, there was some gas evolution, but a t no time was there an odor of RuOl. Tests with RuOz and silica gel indicated that there was no significant dissolution of RuOz during this treatment. The dissolved silica gel did not interfere with the optical measurements. If any RuOz n a s carried over with the silica gel, it was removed by centrifuging. Marshall and Rickard reported that
Table I. Summary of Results Sample Composition, Mg. Ru RuOz metal Anhydrone ... ... ... ... ... ... ... ... ... 1000 ... ... ... 1000 ... 1000 ... 1000 ... ...
RuO, 52.1 84.5 48.0 39.7 58.7 64.1 40.9 65.5
150
61.1
...
io0
...
... ... ...
...
42.7 36.0 51.9 46.6
‘50
...
1000
1000 ... ... ... ...
% RuOa
Silica gel
Recovered 98.3
...
96.1 96.6 97.1 97.7 96.3
lbbb
1000 1000
1000 Av.
100.0 97.9
c?
potassium ruthenate solutions are unstable but can be stabilized for a t least l/z hour by making the solution 2N in KOH. Rithenate-solutions, prepared using the present procedure, exhibited exceptional stability. For example, the absorbance of a freshly made sample was 0.527, after 1 day 0.528, and after 5 days 0.530. Initially the stability was ve&_ Door. but reneated use of the-same glassware apparently had a beneficial conditioning action. As a result, all new glassware was soaked for several days in KOH-ruthenate solution prior to use. I
ACKNOWLEDGMENT
The authors acknowledge with thanks
1.5
the guidance provided by C. M.Slansky of Phillips during the course of the -program. LITERATURE CITED
(1) Marshall, E. D., Rickard, R. R., ANAL.CHEM.22,795-7 (1950). (2) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” 3rd ed.,
Interscience, New York, 1958. CHARLES J. ANDERSON RICHARD DEL GROSSO
gl”bJl)MARTIN ratoriesH. ORTNER
~ ~ $ - ~ & ~ ~ ~ f
Vitro Laboratories West Orange, N. J. WORKsupported by a subcontract from Phillips Petroleum Co., prime contractor to the Atomic Energy Commission under contract AT(10-1)-205.
N e w Solvent System for Separation of Fatty Acids C,,-C,, by Countercurrent Distribution n-heptane as the upper layer and acetonitrile, methanol, and acetic acid as the lower layer, appears to be equivalent in performance to the new solvent
SIR: Ahrens and Craig ( I ) used the countercurrent distribution principle for the separation of fatty acids using several solvent systems. One system, 3.6 3.2
PALMITIC ACID
2.8
K.0.70
STEARIC ACID K: 1.2
Figure 1 . Countercurrent distribution of fatty acids
2.4
Upper layer. Petroleum ether Lower layer. 9 to 1 dimethyl rulfoxide-octa-
2.o
1.6
no I
system presented here. However, no third solvent is required in the new system. Fatty acids CIO to C18 have been separated from each other by the countercurrent distribution technique in the new solvent system using petroleum ether as an upper layer and a 9 to 1 ratio of dimethyl sulfoxide to 1-octanol as a lower layer. This communication describes the determination of the distribution coefficients of fatty acids in various solvent systems and the separation of the acids in the new solvent system. EXPERIMENTAL
1.2
0.8 0.4
0.0
0
10
20
30
40 5 0 60 TUBE NUMBER
70
80
90
100
Apparatus. Craig-type countercurrent distribution apparatus (,!?), 100 tubes, 40-ml. lower layer capacity, 40ml. upper layer capacity with automatic filling device (H. 0. Post Scientific Instrument Co., Maspeth, N. Y.). Determination of Distribution Coefficients. Before the counterVOL. 33, NO. 4, APRIL 1961
* 647
