ANALYTICAL CHEMISTRY
1185 metric samples, and is applicable to microanalysis of dilute .. solutions. ACKNOWLEDGMENT
The authors indebted to D, 8,h l a c ~ n n e sand Theodore Shedlovsky for advice in use of the method and criticism of the manuscript. LITERATURE CITED
(1) Brown, A. S., J . Am. Chem. Soc., 56, 646 (1934). (2) Cunningham, B., Kirk, P. L., and Brooks, S. C., J . Bzol. Chem., 139, 11 (1941).
(3) Foulk, C. W., and Hollingsworth, XI., J . Am. Chem. SOC., 45, 1220 (1923). (4) International Critical Tables, Vol. VII, p. 266, AlcGraw-Hill, New York, 1930. (5) Kirk, P. L., “Quantitative Ultraniicroanalysis,” Wiley. Xew York, 1950. (6) Lange, E,, and Schwartz, E,, z,Elektrochem., 32, 240 (1926), (7) MacInnes, D. A , , and Dole, II.,J . Am. Chem. Soc., 51, 1119 (1929). (8) AIacInnes, D. A,, and Jones, P. T., Ibid.,48, 2831 (1926). RECEIVED for review Noveiiiber 26, 1954.
Accepted January 26, 1955.
Spectrophotometric Determination of Ruthenium GRAHAM A. STONER1 M a i n Laboratory, The Dow Chemical Co., Midland, M i c h .
.i procedure is given for determining ruthenium by measuring the absorbance of potassium perruthenate in alkaline solution at 380 mp. The method may be employed for amounts of ruthenium from 0.1 to 12 mg. Osmium, the only element known to interfere, may be removed by preliminary distillation.
R
UTHENIUM may be determined spectrophotometrically as a thiourea complex ( 1 ) or as potassium ruthenate (4)) a hich has an absorption maximum a t 465 mp. I n the course of R ork on the ruthenate procedure in this laboratory, conversion to perruthenate was found to offer several advantages. Potassium perruthenate is more stable than the ruthenate and can be determined with greater sensitivity. Its absorption maximurn in alkaline solution is a t 380 mp, Distillation of ruthenium (4) by a slightly modified method, followed by photometric determination of perruthenate, provides a reasonably rapid, sensitive, and precise procedure for the analysis of minerals and alloys containing this element. The proposed method involves distillation of ruthenium tetroside from a solution of perchloric acid, phosphoric acid, and sodium bismuthate containing a trace of chloride. Phosphoric acid must be present to prevent the distillation of molj bdenuni ( 3 ) . The tetrovide is collected in a 2.054 potassium hydroxide solution. (This separates ruthenium from all interfering elements except osmium. If osmium is present in the sample it should be removed first, by distillation from a nitric acid solution ) The ruthenium distillate in alkaline solution is diluted to a knov n volume and its absorbance is read a t 380 nip after standing for 0.5 hour. The mechanism of the reaction is assumed to involve oxidation of the ruthenium compound to ruthenium tetroxide by the perchlorate-bismuthate mixture, as well as the simultaneous oxidation of the chloride to free chlorine. Both the ruthenium tetroxide and the chlorine are absorbed in the potassium hydroxide solution, forming potassium ruthenate and potassium hypochlorite. The potassium ruthenate is attacked by the hypochlorite to form potassium perruthenate. The reaction is not instantaneous, however, and about 0.5 hour was found to be required for complete conversion to the perruthenate:
2KzRu04
+ Clz
+
2
I Y
U
Z
2
5
P
4 ‘
0
+
2 K R ~ 0 4 2KC1
This transformation can be detected by the color change from the orange red of the ruthenate to the greenish yellow of the perruthenate. The effect of chloride ion in the distillation is shown by comparison of curves I and I1 in Figure 1. Curve I1 presents the 1 Present address, Chemistry Orleans, La.
absorption curve of potassium perruthenate formed by the distillation of ruthenium trichloride (10 mg. of ruthenium) into alkaline solution. Curve I s h o w the absorption curve of potassium ruthenate formed by distilling an equivalent quantity of ruthenium sulfate without chloride but under otherwise similar conditions. A further verification of the effect of chloride ion was made by adding an excess of silver nitrate solution to ruthenium chloride prior to distillation, in order to remove all free chloride. The absorption spectrum of this distillate coincided with curve I. h small amount of chlorine was then passed through these solutions and after standing their absorption spectra were identical with curve 11. The quantity of chloride ion in the sample must be carefully controlled, since hypochlorite absorbs strongly a t 296 mp and large amounts of hypochlorite will interfere with the 380-mp perruthenate peak. Figure 1 indicates that the perruthenate peak is much more sensitive
Department, Tulane
University,
New
0
525
425
5
W A V E LENGTH (mr)
Figure 1.
Spectrophotometric curves
I.
Potassium ruthenate, 10 mg. of ruthenium per 100 ml. 11. Potassium perruthenate, 10 mg. of ruthenium per 100 ml. L
1187
V O L U M E 2 7 , NO. 7, J U L Y 1 9 5 5
w
assembled with each of the absorption bulbs containing 50.0 ml. of 2.OM potassium hydroxide. The second absorber is used only as a precaution. If the solution in it turns yellow during distillation, some ruthenium tetroxide is escaping the first bulb. This has never been observed in the tests conducted so far. One gram of sodium bismuthate, 1 ml. of phosphoric acid, and 10 ml. of perchloric acid were added as rapidly as possible; the distilling head was inserted immediately, and air was bubbled through the train a t a rate of about 2 bubbles per second. The flask was then heated and the distillation mixture allowed to boil gently for 0.5 hour or until distillation was complete. Then the first absorber was removed, its contents were transferred to a 100-ml. volumetric flask, and the solution was brought to volume with water. After a thorough mixing the solution was allowed t,o stand a t least 0.5 hour and its absorbance was read a t 380 mp. The data obtained from the series of standards yielded a straight line when plotted. PROCEDURE
Figure 2. All-glass distilling apparatus for ruthenium tetroxide
than the 465-mp ruthenate peak. The perruthenate solutions were found to be stable even after overnight standing or boiling, whereas potassium ruthenate solutions are not stable over long periods. EXPERIM EYTA L
Reagents. Ruthenium trichloride from the American Platinum Works was dissolved and standardized. Osmium tetroxide was obtained from the Fisher Scientific Co. Sodium bismuthate, -4CS reagent. Potassium hydroxide solution, 251. Dissolve 112 grams of reagent grade potassium hydroxide in 1 liter of water. Hydrochloric acid, sulfuric acid, nitric acid, sodium carbonate, and sodium bisulfate were ACS reagent. Perchloric acid, 70’%, reagent grade. Phosphoric acid, 85%, reagent grade. Apparatus. During the development of this method all spectral curves were recorded on a Cary recording spectrophotometer. A standard calibration curve was prepared from absorbance measurements made on a Beckman Model DU spectrophotometer using 1.001-em. matched Corex cells and with water as the reference solution. Its linearity indicated excellent agreement viith Beer’s law. All distillations were carried out in the special allglass distillation apparatus illustrated in Figure 2. The distillation flask has a capacity of 500 ml. and the receivers of 125 ml. each. Preparation and Standardization of Ruthenium Solutions. Ruthenium trichloride n-as dissolved in water which contained 1% (by volume) of hydrochloric acid. The solution was then diluted to contain approximately 2 mg. of ruthenium per ml. This solution was standardized by pipetting a known amount of solution into a tared porcelain boat and evaporating slowly to dryness on a hot plate. The boat was allowed to cool and then placed in a Vycor combustion tube. Hydrogen gas was passed through the tube for 15 minutes to remove all the air from the tube and the boat was ignited in the hydrogen atmosphere a t the full heat of a Meker burner to constant weight. Duplicate samples were analyzed and found to agree very well. The solution which was used for the preparation of the standard curve had a concentration of exactly 2.00 mg. of ruthenium per ml. Preparation of Calibration Curve. Suitable aliquots of the standard ruthenium solution prere pipetted into 500-ml. distilling flasks and diluted with 10 ml. of water. The distilling train as
Table I.
Sample
Preparation of Sample, Osmium Absent. If the sample is an alloy, dissolution in hydrochloric or nitric acid is usually necessary. Dissolve a sample of suitable size in a minimum of nitric or hydrochloric acid and filter off any insoluble material using a close textured paper (Whatman No. 42). Transfer the insoluble material and paper to a clean platinum crucible. Dry, burn off the paper, and ignite a t 950” C. for 0.5 hour. Cool the crucible, and fuse the residue with sodium bisulfate at 400” C. Dissolve the fusion melt in the original filtrate with sulfuric acid or until the final solution is strongly acid, and evaporate to fumes of sulfur trioxide. This step is necessary to remove all hydrochloric and nitric acid. If the sample is a eilicat,e rock or mineral in which a basic fusion is necessary to effect solution, fuse the sample with sodium carbonate a t 1000” C. for 1 hour in a platinum crucible. Then dissolve the melt in water and sulfuric acid ( 1 ml. of acid for each gram of sodium carbonate in the fusion melt). Distillation. Transfer the sample as prepared to the distilling flask (Figure 2). Add 5 drops of concentrated hydrochloric arid, 1 ml. of phosphoric acid, 1 gram of sodium bismuthate, and 10 ml. of iOyoperchloric acid. Rapidly attach the flask to the absorption train. Pass air slowly through the train, heat the solution to a gentle boil, and continue the distillation for a t least 0.5 hour. When distillation is complete detach the absorption bulb, and transfer its contents to a 100-ml. volumetric flask diluting to volume with water. Allow the solution to stand 0.5 hour or longer and read its absorbance a t 380 m+, Compare the reading with the standard curve and calculate the per cent of ruthenium. Alternative Procedure if Osmium Is Present. In the presence of osmium the solution step is modified to remove the osmium prior to distillation of ruthenium tetroxide. After solution of the sample is complete, add 25 ml. of concentrated nitric acid and boil gently while bubbling a slow stream of air through the solution. One hour is usually sufficient to remove osmium when it is present as the osmate or bromoosmate. However, when it is present as the chloroosmate. 7 or 8 hours are said to be required ( 3 ) . After removal of the osmium as the tetroxide, add sulfuric acid, evaporate to fumes of sulfur trioxide, and proceed with the bismuthate distillation as already described. APPLICATIONS
The method was applied to the determination of approximately 0.1% ruthenium in a uranium alloy. The alloy also contained small amounts of molybdenum, neodymium, and zirconium. Duplicate results agreed within 0.002%. Several sedimentary rock samples were also analyzed. Their ruthenium contents n-ere found to be negligibly small, but known additions of ruthenium could be recovered almost quantitatively, as indicated in Table I. The results of such work indicate that this method should be adaptable to both mineral and alloy analysis.
Determinations of Ruthenium Added to 2.0 Grams of Calcareous Shale (Fused with 7.0 grams of sodium carbonate) Ru Ru Added, Recovered, Xlg. Absorbance hlg. 0.00 0.006 0.01 2.00 0.273 2.00 3.00 2.95 0.400 4.00 0.543 4.03 6.00 0.800 6.00 8.00 1.08 8.07 10.00 1.35 10,08
REFERENCES
Ayres, G . H., and Young, F., ANAL.C m x . , 22, 1 2 i i (1950). Coryell, C. D., and Sugarman, N., “Radiochemical Studies: The Fission Products,” paper 260, p. 1549, hIcGraw-Hill, New York, 1951. ( 3 ) Hillebrand, W. F., Lundell, G. E. F., Bright, H. A., and Hoffman, J. I., “Applied Inorganic Analysis,” p. 3 i 2 , Wiley, New York, (1) (2)
Error, hlg.
.
-0 -0
+o
, .
01 06
02 01 +o 06 + O 07
-0
1953.
(4) Marshall, E. D., and Rickard, R. R., ANAL. CHEM.,22, 795
(1950). R E C E I V E for D review Kovember 1, 1954. Accepted January 2 6 , 1955.
