(IV) are quantitatively cluted from an etliylcnedianimonium-form column but are retained on a hydrogen-form column (0.1M HF). Bismuth(II1) and thorium (IV) are slowly and ineomplctely eluted from an ethylenediammonium-form column but are quantitatively retained on a hydrogen-form column when the column is eluted n i t h 0.1Ji hydrofluoric acid. Cadmiuni(I1) is quantitativcly retained on an ethylenediammonium-form column but completely eluted from a hydrogen-form column. SVhen a hydrogen-form column is used, elements are eluted more rapidly with 1.061 than with 0.1M hydrofluoric acid. I n addition bariuni(II), iron(III), mcrcury(IT), manganese(II), strontium( 11), vanadium(IV), and zinc (IT) are quantitatively eluted with 1.OM hydrofluoric acid. Thcse elements have a break-through volunie of 180 ml. or
morc \\lien (>luted with 1.0X hydrofluoric acid. However, the use of 1.0M hydrofluoric acid causes several additional elements to be partially eluted, thus increasing the number of interfercwes. A summary of the elution behavior of metal ions is given in Table IV. *ilthough the alkaline earth metals, rare earths, and thorium form insoluble fluorides, no precipitation is expericnced, provided samples containing these metal ions are taken u p by the ion exchange column from a solution that does not contain fluoride. On elution n ith hydrofluoric acid, the equilibria for rare earths and thorium apparently favor the resin-metal ion “complex” rather than the fluoride precipitate. For the alkaline earths. the acidity of tlie hydrofluoric acid eluent is wfficient to prevent precipitation of fluorides.
LITERATURE CITED
(1) Faris, J. P., ANAL.CIIEM,32, 520
i 1w n ) (2) Freund, H., Miner, T. J., Ibid., 2 5 , \ - - - - I .
564 (1953). (3) Fritz, J. S., Karraker, S. K., Ibid., 31, 921 (1959); 32, 957 (1960). (4) Hettel, H. J., Fassel, V. A., Ibid., 27, 1311 (1955). (5) Hibbs, L. E., Wilkins, D. H., Talanta 2,16(1959). (6) Kraus, K. +4.,Selson, F., A S T M Spec. Tech. Pub., KO.195, 27 (1958). (.7,) Nelson. F.. Rush. R. BI.. Kraus. K. A., J . A h . Chem. Soc. 82, 339 (1960). (8) Schindenolf, U., Irvine, J. W., Jr., A x . 4 ~ .CHEILI. 30, 906 (1958). (9) Strelow, F. IT. E., Ibid., 32, 1185 (1960). (10) Wilkins, D. H., General Electric Co., private communication, 1960. (11) Wish, L., h A L . CHEM. 31, 326 (1959). RECEIVED for rcview November 9, 1960. Accepted hlarch 15, 1961. Contribution 932. Work performed in the Ames Laboratory, U. S. Atomic Energy Commission.
Spectrophotometric Determination of Ruthenium by Thiocyanate W. L. BELEW, G. R. WILSON, and L. T. CORBIN Analytical Chemical Division, Oak Ridge National laboratory, Oak Ridge, Tenn.
V A method i s presented for the spectrophotometric determination of ruthenium using sodium thiocyanate as a color reagent. The ruthenium is oxidized to the tetroxide and extracted into carbon tetrachloride. The ruthenium tetroxide i s stripped from the CCI4 with an aqueous solution of sodium thiocyanate and determined as the deep blue ruthenium thiocyanate complex, [Ru(CNS)~] +*. This method provides a simple and efficient method foi. the separation and determination of ruthenium when interfering substances are present.
A
review of the numerous spectrophotometric methods available for the determination of ruthenium has been published by Beamish and AIcUryde ( 1 ) ; however, none of the methods currently available are directly applicable to samples containing HNOe or stainless steel constituents. The ruthenium is usually separated from interfering substances by the conventional distillation as the tetroxide(6). The difficulties encountered in separating niicrogram quantities of ruthenium from solutions containing HSOa and stainless steel constituents led to the development of the faster and less complicated procedure presented here. By using an extraction procedure inN EXCELLENT
886
ANALYTICAL CHEMISTRY
stead of the corlventional distillation method the separation of ruthenium can be simplified. The extraction of rutlienium tetroxide into carbon tctrachloride has been tlioroughly investig a t d bj- Martin ( 3 ) . The chief problems in the analytical application of this extraction are in oxidizing the ruthenium to the 8 state and stripping the RuOl from the organic phase. Surasiti found argentic oxide to be a suitable oxidant for oxidizing the ruthenium to tlie tet’roliide (4, 5 ) . To strip the RuOi from tlie CCla he used a reagent of H2S04and SO,. The extraction is slo~v,taking about 2 hours t o reach equilibrium. This difficulty is overcome i n the method presented here by extracting the RuO4 as the thiocyanate complcx ( 7 ) . The extraction is rapid and reproducil,le quantitative results are obtained. REAGENTS A N D APPARATUS
A standard Ru solution was prepared by d,issolving ruthenium nitrosohydroxide in 1 S HS03, diluting to volume with distilled water, and standardizing b y the method given in Scott ( 2 ) Thc rutlieilium nitrosohydroxide, RuKO3(OH),, is available from A. D. Xlackaj-, Inc., 198 Broadway, Kew York 38 S . P. Sodium thiocyanate solution was prepared by dissolving 81 grams of
reagent KaCSS in water and diluting to 1 liter with distilled water. The argentic oxide (Ago, trade name Divasil) is available from hlerck 8: Co., Inc. 7’0 prepare the 1.251 X1(S03)3-0.2V HKOa reagent. 452 grams of A ~ ( N O S ) ~ 9H20 as dissolved in water, 12.6 ml. of concentrated IISO, added, and the solution diluted to 1 liter with distilled water. Since RuOl is easily reduced by contact n i t h stopcock grease, separatory funnels n i t h Teflon stopcocks are recommended The absorbance measurements \$ere made on a Beckmail Model B spectrophotometer a t 590 mg in 1-cm. cells. EXPERIMENTAL PROCEDURE
-1 calibration curve was prepared by the follon-ing procedure. .iliquots containing from 20 to 100 gg. of Ru were taken from the standard Ru solution and transferred to separatory funnels -ontaming nppro\imately 5 mi. of the ;\l(SOj)a reagent. -4pproximately 30 mg. of A g o vas added to each funnel. Ten milliliters of CCll n as pipetted intc each funnel and the funnel was then shaken for 2 minutes. Immediately after the phases had separated, the CCld layer n a s drained into a second separatory funnel containing 10.0 ml. of the 1 M KaCSS reagent. The extraction was repeated uith 5 ml. of CC1, and the extracts nere combined. The funnel containing the combined
::pJ 0.90
A
i
0.60
$52 1
0.50
+
1
1
a z -
E
0.6
r ,
-
1 -
T e 5 1 s o 1 u l i o n ~:
Curve A , reagent blank
C u r v e B , 1 2 . 5 pg.of
Rut'
~
O 2 t per mi.
I 0L 475
A
500
-
.
-
525
-
5 5 0 575 600 WnVE L E l v G T H , rnp
04
Figure 2. Effect
''
extracts and the KaCNS reagent was shaken for 1 minute and the NaCNS layer drained into a centrifuge cone. The color was allowed to develop for 30 niinutes and the absorbance of the solutions measured at 590 mp. The calibration curve was then prepared by plotting Ru concentration against absorbance. The test solutions were analyzed by this procedure and the R u content was determined from the cnlibration curve. DISCUSSION
IInrtin found the distribut'ion coefficient of RuO, between CC1, and water to 1ia1.e thc vnluc (3): (RuO4)ccI,,'(RUO~]H?O = 58.4 (25'
02
C.)
The coefticmient is approsiinately the same in acid solutions, since the tetroxide has essentially no basic characteristics ($). ;it low R u concentrations ( 2 p g . per 1111. or less) i t was found necessary to have a salting agent present in the aqueous phase to assure complete extraction of the Ru. -41though HSOa would perhaps serve a s a suitable salting agent, a high concentration of HNOa (>4M) tends to cause interference in the formation of the R u thiocyanate complex and, therefore, a solution of d l ( S 0 3 ) 3and H N 0 3 \vas found more satisfactory for this purpose. Solutions containing l to 231 -&1(503)3 and 0.1 to 1-11 " 0 3 gave quantitntive recoi-ery of 10 k g . of Ru. Tlie data presented here \?-ere obtained n i t h a reagent 12.U in -il(S03)3 and 0.2J1 in HK03. Tlie oxidation of the R u to tlie tetroxidc is a critical step in the extraction. Surasiti has found argentic oxide to be a suitable oxidizing agent for this purpose ($, 6 ) . Only a small excess of Ago should be added and care should be taken to avoid entrainment of the excess AgO into the K a C S S reagent. The ruthenium t'hiocyanate complex in pcrcchloric wid medium has been
I I 12 14 06 08 10 M O L A W T Y OF NaCN S !
700
1 . Absorbance spectrum of [Ru(CNS)I]
Figure
I I
0 653
-I
O1/-
Reference s o l u t i o n , reogent b l a n k
I
I
46
18
2 0
of molarity of NaCNS on absorbance 0.625 mg. per ml. of Ru
studied by Yaffe and T'oigt ( 7 ) . They found t h a t both Rut3 aiid R u + form ~ a Table 1. Effect of Time on Absorbance deep blue complex wit'h thiocyanate, (Absorbance measured a t 590 mp on a the Rut4 complex being reduced to the solution containing 5.0 pg./ml. of ruthenium) R u + ~complex a t the expense of the ligand. They postulated the formula Time, >hi. Absorbance for the complex to be [RU(CNS),]+~. When a solution of R u + ~nitrate reacts 1 0.190 5 0.195 with thiocyanate, a pink to violet 10 0.198 colored complex is formed; however, 1.5 0 205 -~ if a n aqueous solution of thiocyanate is 25 0,210 brought in contact witli the R u 0 4 in the 24 hours 0.210 CCll phase, the deep blue complex observed by Taffe and Voigt is obtained in the aqueous phase. The complex Table II. Effect of Diverse Ions forms alniost immediatcly, being sample AIetaIs Tested _ Ruthenium, M _ _g approxiinately 90% complete n-ithin one KO. M g . Present Found minute. The color develops to maxi1 Tht4 20 0 050 0 050 mum intensity in approsiniatcly 30 2 b7+6 2 0 050 0 049 niinutes and is stable for a t least 24 0 050 0 050 2 3 oS+4 hours thereafter, as shown in Table I. 4 Th+4 12 0 200 0 212 U 2 The spectral absorbance curve of the 5 Stainless 404 0 050 0 047 complex obtained by nieans of a Warren steel Spectracord is shown in Figure 1. The 6 Stainless 40 0 200 0 214 adsorption of the complex obeys Beer's steel law in t'he range of 1 to 15 p.p.m. of 7 Stainless 40 0.025 0 024 steel ruthenium. Tlie molar absorptivity is approximately 40,000. a 204 stainless stec.1 dissolved in 6 M The effect of thiocyaiiate conccntraI3,SOa. tion on the absorbance of the solution is shown in Figure 2 . llaximuni absorbance is obtained a t alq>rosiniately Table 111. Determination of Precision 0.3-11 concentration of thiocynnate. (Analysis of ruthenium nitrate solution Excess thiocyanate has 110 cffect on tlie approximately I N in nitric acid) absorbance. Ruthenium, The method proposed here has several Sample Rig /SIl. 7 0 advantages over present spectrophotoNo. Present Found Error metric methods available for tlie deter-1 5 1 0 200 0 197 mination of ruthenium. The extraction -3 0 2 0 200 0 194 of RuOl into CCli is relatively specific 0 0 3 0 200 0 200 3 o 201) o 194 -3 0 and no interference from diverse metal d 0 200 0 202 +1 0 ions is expected unless they are present 6 0 200 0 205 +2 S in large excess. Table I1 present's some 7 0 200 0 202 +I 0 data collected in the presence of various 8 0 200 0 204 +2 0 metal ions. Most spectrophotometric 9 0 200 0 210 $0 5 -2 0 10 0 200 0 196 methods for ruthenium require heating 11 0 200 0 202 +l 0 a t a specific temperature for a specified 0 190 -5 0 12 0 200 lrngth of time with the color reagent to obtain a reproducible color. The blue Relative stand dev. 1.967, ruthenium thiocyanate complex forms VOL. 33, NO. 7,JUNE 1961
887
~
quickly at room temperature when the thiocyanate is brought in contact with RuOc as in this method, Nitric acid, which is a serious interference in most spectrophotometric methods for ruthenium, can be tolerated in this method. A number of analyses were made of a ruthenium nitrate solution containing 200 pg. of ruthenium per ml. Aliquots containing from 40 to 60 pg. of ruthenium were analyzed (Table 111). The standard deviation obtained is for the most favorable concentration range and may not apply to different ruthenium concentrations.
ACKNOWLEDGMENT
The authors gratefully acknowledge the suggestions of R. R. Rickard and P. F. Thomason during this work. Thanks are also due to Lonas Guinn, Grant Hickey, and R. L. Lewis for some of the data presented.
LITERATURE CITED
(1) Beamish, F. E., McBryde, W. A. E., Anal. Chim. Acta 9, 349 (1953); 18,
562 (1958).
(2) Furman, N. H., ed., “Scott’s Standard Methods of Chemical Analysis,” 5th ed., Vol. I, p. 740, Van Nostrand, New York, 1950. (3) Martin, F. 8.. J . Chem. SOC. 1954. 2564. (4) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” 3rd ed., p. 779, Interscience, New York, 19.59. -__I.
(5) Surasiti, C., Ph.D. thesis, University of Minnesota, 1957. (6) Westland, H. D., Beamish, F. E., ANAL.CHEM.26,739 (1954). (7) Yaffe, R. P., Voigt, A. F., J . Am. Chern. SOC.74, 2500 (1952). RECEIVEDfor review August 4, 1960. Accepted March 27, 1961.
Titrimetric Determination of Ferrous and Ferric Iron in Silicate Rocks and Minerals CHARLES V. CLEMENCY and ARTHUR F. HAGNER Department o f Geology, University o f Illinois, Urbana, 111. The automatic derivative spectrophotometric titration method of Malmstadt and Roberts ( 5 ) for the determination of iron in titanium and its ores, using coulometric generation of titanous ion as the titrant, has been adapted successfully to the determination of total iron in silicate rocks, magnetite, pyrrhotite, pyrite, or mixtures of these, and to the determination of the ferrous-ferric ratio of silicate rocks, magnetite, or mixtures of these. The method measures the amount of ferric iron present. Using a rapid method of sample dissolution b y a hydrofluoric-sulfuric acid mixture, both total iron and the ferrous-ferric ratio ccn b e obtained within one hour. U. S. Geological Survey rock samples G-1 and W-1 were used as rocks of known iron content. Evidence is presented that reduction of ferric iron during dissolution of the sample may b e a major cause of error in the conventional wet method of analysis for the ferrous-ferric ratio. Results of higher precision and accuracy are obtained in a shorter time using smaller sample sizes than with conventional methods.
iron in small samples of silicate rock, The method described is an adaptation of the automatic spectrophotometric titration method of Malmstadt and Roberts (6) for the determination of iron in titanium sponge, alloys, and ores. Because of the importance of the ferrous-ferric ratio of silicate minerals and rocks as a parameter in the interpretation of likely environments of formation of these rocks, the method
+ 7
BERZELIUS
PLAT F O R M
I
N A STUDY of the Sterling Lake, N. Y., magnetite deposit by Hagner and Collins (3) and Hagner, Collins, and Aye (4),it was necessary to determine the total iron content of 100-mg. samples of metamorphic silicate minerals and rocks. Gravimetric methods similar to those described by Washington (8) proved unsatisfactory for routine analysis of such small samples. The purpose of this investigation was to develop a new method for the analysis of total
888
ANALYTICAL CHEMISTRY
Figure 1 . in beaker A.
Arrangement of electrodes
Platinum foil half cell electrode, Sargent Catalog No. 5-3051 5 6. Platinum gauze electrode, Sargent Catalog NO.S-29672 Gauze screening 1 ’/, Inches high and 1 inches In diameter
was extended to provide a new and better means of obtaining this ratio than was previously available. PROCEDURE FOR DETERMINATION O F TOTAL IRON I N SILICATE ROCKS
Apparatus. A Sargent-Malmstadt automatic titrator and titrator control unit; a Sargent Model I V coulometric current source; and a commercially available Sargent platinum gauze electrode were used (Figure 1). Reagents. Titanium Sponge Solution. Dissolve 40 grams of low-iron content titanium sponge (obtained from Cramet, Inc., Chattanooga, Tenn.) in a mixture of 1200 ml. of 5 M sulfuric acid and 100 ml. of 48% fluoboric acid and dilute to 2 liters with water. A 50-ml. aliquot contains 1 gram of titanium. Standard Iron Solution. 1.00 mg. per ml. Mallinckrodt 99.97% pure iron wire in hydrochloric acid. Leuco Methylene Blue Solution (and other reagents) as described in (6). Blanks. Blank values were obtained by running two standard iron solutions at the beginning, and one a t the end of the day. The standard solutions each contained 5.00 mg. of iron. The number of microequivalents needed t o titrate these solutions was calculated (e.g., 89.5 at 100 ma.) and the standards were run for total iron. The difference between the average number of microequivalents actually used to titrate the standards (e.g., 93.5) and the calculated number was taken as the blank. I n this case the blank would be 93.5 - 89.5 = 4.0 peq. This procedure also checks on the efficiency of the electrodes. When the electrodes need regeneration, the number of microequivalents needed to titrate the same standard solution increases. When the number becomes
