Spectrophotometric Study of the RutheniumDithio-oxamide Complex GILBERT H. AYRES A N D FREDERICK YOUNG The University of Texas, Austin, Tex. The blue color produced when solutions of ruthenium(1V) or ruthenium(II1) chloro complexes are treated with dithio-oxamide (rubeanic acid) has been studied spectrophotometrically. In hot solutions containing hydrochloric acid and ethyl alcohol the color develops rapidly, and is stable for 24 to 48 hours. Measured a t 650 mp against a reagent blank with a Beckman spectrophotometer (1-cm. cells), best accuracy is obtained when solutions contain about 2 p.p.m. (micrograms per milliliter) of ruthenium; in this region the relative analysis error
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S A previous paper ( 2 ) the authors presented a spectrophotometric study of the ruthenium-thiourea color system, evaluated the optimum range and maximurn accuracy of the photometric process, a n d determined the tolerance of the system for certain interfering substances. Among t h e various color reactions of ruthenium t h a t have been reported, i t appeared t h a t the blue reaction product with dithio-oxamide (rubeanic acid) ( 5 , 6) would be suitable for spectrophotometric determination. It is t h e purpose of this investigation t o make a study of the ruthenium-dithio-oxamide reaction to define t h e best conditions for color development, to evaluate t h e optimum range and the accuracy of t h e photometi% process, and to determine t h e nature and extent of interferences, especially of other platinum metals.
is 2 . i ' q ~per 1%absolute photometric error, or about 0.8% relative error for a precision of 0.3% (standard deviation) in the photometric process. In the range 1 to 5 p.p.m. of ruthenium the relative error does not exceed 1%. Interference tolerances are given for other platinum metals, common cations which are colored, and anions t h a t might be present in certain separation procedures. Osmium is the only platinum metal that interferes extensively a t 650 mp; hence a sharp prior separation of osmium, if present, is required for determination of ruthenium.
several concentrations of ruthenium are shown in Figure 1. T h e curves have a very broad transmittancy minimum a t 650 mp, a maximum at 460 mp, and a second sharp minimum a t about 3iO mp, below which the transnlittancy again rises sharply; the second minimum showed a shift ton-arc1 longer wave lengths as the concentration of ruthenium increased. A plot of log transmittancy, at 650 mp, against concentration showed good agreement with Beer's law; transmittancy values a t the minimum centered about 370 mp were not in good agreement with Beer's Ian-. IO(
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R E A G E N T S AYD APPARATUS
The ,Gtandard ruthenium solution [ ruthenium(1V) and/or rutheniuni(II1) chloro complexes], and the solutions of the various cations and anions used in the determination of interferences were the same as those employed in the study of the ruthenium-thiourea system ( 2 ) . Dithio-oxamide, Eastman chemical S o . 4394, was used in the form of a 0.2% solutionin glacial acetic acid. Transniittrtncy measurements were made, in Corex cells of 1 001-cni. light path, with a Beckman Model D U spectrophotometer, o p c r , i t d a t constant sensitivity, using slit widths of the order of 0.02 to 0.10 mm., corresponding to band widths of about 1 to 4 ni+.
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Development of Color. Preliminary experiments showed t h a t a high concentration of acid was required, and that a large amount of ethyl alcohol \vas dcsii~ahic~ to prevent formation of precipitates :ind to give a more stahle ~0101,system. At room temperature loped very s l o ~ l y(over a period of a feLv days), b u t at elevatctl temperatures deyeloped rapidly.
Appropi'iate aliquots of the stock standard solution, t o give a fiiial coiicc~ntrat~or~ of 0.3 to 8 p.p.m. of ruthpniuin, were treated with 40 ml. of 1 to 1 (hl- volume) mixture of concentrated hydrochloric acid and 95y0 ethyl a!cohol, and 15 ml. of the dithio-
oxamide rc:jgent. T h e n i h u r e was heated on a water bath at 85' C. for 30 minutes, and \WS then cooled and made u p t o 100 ml. with a 1 to 1 misturc of 6 .TI hydrochloric acid arid ethyl alcohol. Blanks contained the same amounts of reagents. Spectral Characteristics. Data for the spectral curves were ohtaincd b y measuring the trensmittancy a t frequent wavelength intervals over the range of 800 t o 360 mp. Curves for
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Figure 1. Spectral Curves for Ruthenium with Dithio-oxamide Stability of Color. Solutions containing various amounts of ruthenium showed no measurable change in transmittancy in 21 hours, and a change of only about 0.470 (absolute) in 48 hours. On longer standing a black precipitate separated. This behavior was essentially identical with t h a t found for the rutheniumthiourea system ( 2 ) . Effect of Temperature. I n the range 25' to 40" C. the effect 1281
ANALYTICAL CHEMISTRY
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tion of ruthenium. The curve has ma.;iinum slope a t about 63y0 absorptancy, in agreement with derivations from Beer's law (1). Graphical evaluation of maximum photometric accuracy gives a value of 2.i% relative error per 1% absolute photometric error, or about 0.8% relative error, on the concentration measured, for A photometric error of 0.3Yo (the standard deviation previously mentioned); this accuracy is attainable a t a concentration of about 2 p.p.ni. of ruthenium. In order to keep the relative error within lY0, the concentration must be within the limits 1 to 5 p.p,m. These limits were evaluated as follows: Assuming- the photometric error to be O.3y0absolute, a relative error of 1% on the concentration measured would correspond to 3,4y0 'Table , I . Tolerance of Ruthenium for Interfering Substances relative error per 1% absolute photoDithio-oxamide Method Thiourea Method metric error. This error corresponds to (7.1 P.P.M. Ruthenium) (2.2 P.P.M. Ruthenium) a slope of 230/3.4 = 68% absorptancv 7Visual color. % Visual color. interfering relaiive interfering relaii\.e change per log cycle on the concentrsInterfering substance + Tolerance, to substance + Toleranee, to Substance reagents p.p.m. ruthenium reagents p.p.m. ruthenium tion axis-i.e., a tenfold concentratiori Osmium change. A line having this slope i, (Iy, Olive green 0.05 2 Rose red 0.2 3 tangent to the calibration curve a t about Rhodlum (111) Orange 0.5 23 Colorless K Ointerference 1 p.p.m. on the lower portion and a t Iridium (IV, Yellow 0.9 41 Colorless No interference about 5 p.p.m. on the upper portion of Palladium the curve. The range can be evtended to (11) Yellow 10 455 Yellow 0.7 10 Platinum higher concentrations, with an increase Orange red 2 91 Colorless N o interference(IV) 5 230 Amber 5 40 Iron(II1) Amber in accuracy, by comparison of a sample Cobalt(I1) Blue 2 91 Blue 0.5 7 solution with a reference standard inNickel(I1) Light green 1 45 Light green 20 ?SO Copper(I1) Greenish stead of a blank (1, $). yellow 2 91 Greenish yellow 5 70 A plot of per cent absorptancy a t 230 Green 1 1-1 Chromiuma Green 5 3 i O rnr (the second minimum) against log 0 Chromium(V1) was reduced to chromium(II1) by reagents. concentration of ruthenium gives a curve almost parallel to the curve shown in Figure 3, but displaced slightly toward Effect of Diverse Ions. Solutions of the other platinum metals higher concentration. However, measurements of unknowns a t were developed with dithio-oxamide in the usual way, and their 3 i O me would be unsatisfactory on account of interference froni other platinum metals. spectral curves determined in order to predict what interference During the course of making measurements for the spectral might be expected. These curves, shown in Figure 2, indicate curves for osniium-dithio-oxamide, a striking anomaly \vas that at 650 mp the measurements for ruthenium should not be subject to appreciable error from moderate amounts of the other encountered. When measured a t once, after development in the usual way, the transmittance of the solutions (containing 5 and platinum metals except osmium. At the second ruthenium mini10 p.p.ni. of osmium) was very much higher than that of the blank mum, 370 mp, palladium and rhodium would interfere seriously; other platinum metals would interfere to a considerable extent. solution in the region between about 365 and 400 mp. I n this region the transmittancy was changing very rapidly with time T h e extent of interference by the other platinum metals, as during the first hour or more, and reached a stable value only well as by the common colored rations, was determined by measuring the transmittancies of color-developed solutions con100 taining a constant amount of ruthenium (2.2 p.p.m., which is in the optimum range for measurement) and varying amounts of the interfering ion. Transmittancy measurements were made over a considerable wave-length region on either side of 650 mp; no shift in the minimum was observed. The tolerance of the 80 ruthenium-dithio-oxamide system for the interfering substance was taken as the largest amount of t h a t substance which would give a transmittancy not more than 0.4% absolute different from 0 > t h a t of the ruthenium alone. Table I lists the interfering sub2 60 c stances tested, their individual colors after treatment with the reE agents, and the tolerance as defined above. For comparison, I colors and tolerances for the ruthenium-thiourea method ( 2 ) are z K 4 included. 40 2 os 10 I n a previous article ( 2 ) i t was shown t h a t b y the use of various 3 Rh 20 fl 4 Ir 20 procedures for t h e dissolution and/or separation of ruthenium, 5 Pd 10 t h e only anions (beside chloride) t h a t could be present in analytical amounts are bromide, sulfate, nitrate, hypochlorite, or per20 chlorate; t h e study of anion interference was therefore limited to these anions. I n solutions containing 2.2 p.p.m. of ruthenium, all these anions are without effect up to 100 p.p.m., hence were not studied further. of temperature was found to be about +0.0370 absolute transmittancy per 1 ' C. Reproducibility. A statistical treatment was made of the transmittancy measurements on 4i samples (2.2 p,p.m. of ruthenium, transmittancy 39.37c),developed as described previously. The data, collected over a period of several weeks, included all analysis errors accumulating in the procedure from the point at which the aliquot of the standard solution was taken; no results were rejected. The average deviation was 0.23% and the standard deviation was 0.30% absolute transmittancy.
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DISCUSSION
I n the calibration curve, Figure 3, per cent absorptancy (100 yo transmittancy) a t 650 mp is plotted against log concentra-
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Spectral Curves for Platinum Metals with Dithio-oxamide
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V O L U M E 2 2 , NO. 10, O C T O B E R 1 9 5 0
siderably higlicr concentrations thaii \yere 1,cquired in the study of interferences in the present in\-estigation. Kelrher ( J ) , apparently referring to the work of Kolbling and Steiger, states, “It is important to know that osmium, which in its other analytical reactions resembles ruthenium, does not react’with rubeanic acid; for this reason rubeanic acid can be used for the detection of ruthenium in the presence of osmium.” T h e original article by Wolbling and Steiger states, “Osmium salt solutions give, with rubeanic. acid, no essential color change; with large amounts, the ethyl acetate estract is brown.” In the present work, no estraction procedures with organic solvents \Yere used. Rather large amounts of ethj*l alcohol and strong acid, and elevated teniperatures, were required to give rapid development of the blue ruthenium-dithio-oxamide color; under these conditions osmium gave a color; when the reagents were mixed the solution assumed a greenish color, which on heating changed rapidly to a brownish red, then more slowly to a n olive green color. By the proposed method, therefore, reasonably sharp prior separation of osmium from ruthenium, by a n appropriate distillation procedure ( 2 ) , would be required. Compared with the thiourea method, the dithio-oxamide method has a slightly lower optimum concentration range, although the difference in ranges is hardly large enough to be of importance in application to analyses. T h e choice between the two methods probably would be based upon the kind and amount of interfering substances present in the sample.
CONCENTRATIOI+, P P Y . R u
Figure 3. Calibration Curve for Ruthenium w i t h Dithio-oxamide, 650 mw
after several hours. Between 450 and 800 mp, stable readings were obtained from the start. After about 2 hours the transmittancies in the lower w a v e - h g t h region had undergone a reversal, so t h a t the transmittancy of the 5 p.p.m. solution was considerably lower than t h a t of the 10 p.p.m. solution; the spectral curves for the two concentrations crossed at about 410 mp. Above 450 mp the two curves were still parallel in their proper relation to concentration and at the same transmittancies as when first measured. This behavior was checked throughout; no explanation has been found as yet, and the effect should be studied further. T h e osmium curve shown in Figure 2 was plotted from data taken about 2 hours after color development. Kolbling and Steiger ( 6 ) found t h a t palladium and platinum salts yield red precipitates with dithio-oxamide. These precipitates form only when palladium and platinum are present in con-
ACKNOW LEDGM E S T
T h e authors hereby acknowledge their thanks to the American Platinum Works for providing samples of ruthenium metal and ruthenium trichloride used in p a r t of this investigation. LITERATURE C I T E D
(1) Ayres, G. H.. Axar.. CHEM.,21, 652 (1949). (2) Ayres, G . H., and Young, Frederick, Ibid., 22, 1277 (1950). (3) Hiskey, C. F., Ibid., 21, 1440 (1949). (4) Welcher, F. J., “Organic Analytical Reagents,” Vol. IV, p, 154, iXew York, D. Van Nostrand Co., 1948. (5) Wolbling, H.. Ber., 67B,773 (1934). (6) Wolbling, H., and Steiger, B., Mikrochemie, 15, 295 (1934).
RECEIVED January 24, 1950. Condensed from a thesis submitted b y Frederick Young t o the faculty of t h e Graduate School of t h e University of Texas i n partial fulfillment of the requirements of the degree of master of arts, 1950.
Determination of Sodium Monoxide in Sodium LEONARD P. PEPKOWITZ A N D WILLIAM C. JUDD Knolls Atomic Power Laboratory, General Electric Company, Schenectady, ,V. Y .
T
HE initial attempt by the authors to devise a method for the determination of sodium monoxide in sodium n-as to use the water formed by the reaction of sodium monoxide with dry hydrogen chloride a t high temperatures. The water formed immediately reacts with the excess sodium to form sodium hydroxide, which is reduced by the sodium a t the elevated temperatures t o reform sodium monoxide ( 4 ) . 2YaOH
+ 2Ka --+ 2 S a 2 0 + HS
sodium-vapor phase reactions at elevated temperature and in dry benzene ivvith iodine, bromine, and hydrogen chloride. Dry glacial acetic acid has some promise as a reagent, if a method could be developed for detecting the small quantity of water formed and if the glacial acetic could be dried reproducibly. 2Sa NazO
(1)
I n all such reactions the total sodium sample must react completely before the water equivalent to the oxygen present will be released. The determination of the small amounts of water produced in the presence of the very large quantity of sodium chloride is as difficult a task as the primary determination. Such exploratory attempts made without success included reactions with dry hydrogen chloride or carbon tetrachloride in liquid
+ 2 H . 4 ~+2SaAc + H, + 2HAc +2SaAc + H20
(2)
(3) The measurement of the water conductometrically appeared to be very sensitive b u t nonreproducible because of the original variable water content of t’he glacial acetic acid. The simple method reported in this paper depends on the physical separation of sodium from the sodium oxide by repeated extractions with mercury. The sodium oxide is insoluble in the resulting sodium amalgam and floats on the surface of the amalgam, Folloiving the extraction, the sodium monoxide is dis-
