A spectrophotometric and polarographic method is proposed for the determination of ruthenium tetroxide absorbed in oxalic acid. Spectrophotometric measurements of ruthenium in 1 N oxalic acid were made at 375 mμ. In the concentration range from 2 to 36 micrograms of ruthenium per milliliter the relative standard error amounted 14 % to 1 %, respectively. The polarographic determination was performed in a supporting electrolyte containing 1 N oxalic acid and 0.006 % thymol (as a maximum suppressor). The determination is applicable in the concentration range from 4 to 120 micrograms ruthenium per milliliter with a relative standard error of 15 do 0.7 %, espectively. Hydrochloric, sulfuric and perchloric acid up to of 0.5 N does not interfere. In the presence of nitric acid spectrophotometric and polarographic determinations of ruthenium are impossible

M. Branica

Š. Mesarić

English

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CR 0 AT I CA CHEM IC A ACT A 30 (1958) 81 CCA -118 546.96 :545.822 :545.33 Spectrophotometric and Polarographic Determination of Ruthenium in Oxalic Acid $. Mesaric and M. Branica Department of Physicai Chemistry, Institute »Rudjer Boskovic«, Zagreb, Croatia, Yugosiavia Received December 25 , 1957 A spectrophotometric and polarographic method is proposed for the determination of ruthenium tetroxide absorbed in oxalic acid. Spectrophotometric measurements of ruthenium in 1 N oxalic acid were made at 375 mµ. In the concentration range from 2 to 36 micrograms of ruthenium per milliliter the relative standard error amounted 140/o to 1 O/o, respectively. The polarographic determination was performed in a sup-porting electrolyte containing 1 N oxalic acid and 0.0060/o thymol (as a maximum suppressor). The determination is applicable in the concentration range from 4 to 120 micrograms ruthenium per milliliter with a relative standard error of 15 do 0.70/o, respectively. Hydrochloric, sulfuric and perchloric acid up to of 0.5 N does not interfere. In the presence of nitric acid spectrophotometric and polarographic determinations of ruthenium are impossible. Ruthenium has always been a very difficult element to determine 'quantitatively. It exists in eight valency states from I to VIII and forms ·complex compounds. The complexes with nitrogen oxides interfere in many analytical methods. Many methods are given for the separation of ruthenium from other metals. The macro m ethod for the separation by volatilization of the tetroxide can be extended to the minute quantities as well. Ruthenium is oxidized to the volatile ruthenium tetroxide by perchloric acid, sodium bromate-sulfuric acid, perchloric acid-sodium bismuthate-fuming -nitric acid, sodium peroxydisulfate-sulfuric acid, potassium permanganate-sulfuric or phosphoric acid, chromium trioxide-sulfuric or phosphoric acid and sodium hypochlorit sodium hydroxide.H The volatile tetroxide is distilled into hydrochloric acid or alkaline hydroxides and is determined gravimetrically or spectrophotometrically.1- 7 Many sensitive colour reactions with organic reagents for the determination of ruthenium can be m entioned. 1•7•8·9 The polarography of + 4 ruthenium in perchloric acid (0.1 to 5 M) scrupulously freed from chloride was already studied10 and three well-formed waves w ere obtained. In 1 M perchloric acid the first diffusion current is .at zero e.m.f., and the half-wave potentials of the second and thir d waves are + 0.21 and -0.34 V with respect to S. C. E. The sum of the first two waves cor responds to an irreversible (I-electron) reduction of two hydrolytic .species of + 4 ruthenium t o the + 3 ruthenium. The third wave is r eversible 82 S. MESARIC AND M. BRANICA reduction of the ruthenium +3 to the ruthenium + 2. Willis11 found that n 0> reduction waves for + 4 or +3 ruthenium are observed with solutions of the chloro complexes, neither from cyanide, thiocyanate, ~mmonia nor pyridine as supporting electrolytes. In contradictions with this investigation, R. . B. Simpson and others12 found a polarographic wave of ruthenium trichloride . and compute from it a small diffusion current constant. In this note spectrophotometric and polarographic determination of rutheniuin in oxalic acid are given. EXPERIMENTAL Apparatus and reagents Spektrophotometric measurements were made in silica cells of 10 mm light path with »Hilger«-Uvispek spectrophotometer operated at constant sensitivity. A Cambridge Polarograph, Pen recording type with a maximum sensitivity of 2.47 X 10- 9 A/mm, has been used. Polarographic cells of the same Company with a satureted colomel electrode (or with a mercury pool anode) were used and kept in a constant temperature water bath at 25.0 ± o.1oc. Oxygen was displaced by bubbling hydrogen through the solution for 15 minutes prior to the polarographic measurement. The r eduction of Ru(VIII) to Ru(IV) probably occured simultaneously5. Hydrogen was purified by passing it through a saturated solution of pyrogallol in. 200/o sodium hydroxide. The capillary had m = 1.87 mg./sec. (at 0.0 V) and t =2.2 sec. (at 0.2 V) in the respective supporting electrolyte. The wave heights were measured in the points of intersection ·;r the extra-polation lines for the residual and the diffusion current and the polarographic wave slope. The apparatus for distillation of ruthenium tetroxide was a distillation flask with three traps connected in series. The following reagents were used: ruthenium trichloride, purissimum (Fluka, A. G. Buchs) ; ruthenium tetroxide, reagent grade (Hopkin & Williams, London); thymol, recrystallised. All other reagents were of analytical grade (Pliva, Zagreb). Preparation and standardization of ruthenium solutions Ruthenium trichloride was dissolved in 1 : 3 sulfuric acid and the solution evaporated under an infrared lamp until sulfuric acid fumes appeared to ensure-removal of traces of chloride ions. The solution was transfered into a 500 ml. washing bottle which served as distilling flask6and diluted to give a 30 to 500/o sulfuric acid solution. Ruthenium tetroxide was prepared by oxidising the sulfate solutions with a twofold excess of sodium peroxydisulfate and traces of silver sulfate. The sodium peroxydisulfate was added in portions during the course of the distillation. The solution was heated t<> boiling. A slow current of air carried the tetroxide into ice-cold 1 N oxalic acid. The absorption solution was transferred in a volumetric flask and adjusted with oxalic acid to 1 N. From this stock solution various solutions of ruthenium for spectrophotometric· and polarographic measurements were prepared. Ruth.enium in the stock solution, was determinep by precipitation with magnesium or with hydrogen sulfide gas, ignated in a current of hydrogen and weighed as metal.7 Spectrophotometric determination The y ellow colour produced when ruthenium tetrox ide is absorbed in oxalic acid has been studied spectrophotometrically. The colour showed m easu-rable change with the time, the temperature and the concentration of oxalic acid. The stable m aximum is reached by 0.05 N and 0.1 N oxalic acid after five DETERMINATI ON OF RUTHENIUM 83 hours and by 1 N oxalic acid after three hours at room temperature. At ele-vated temperature the stable colour developed rapidly. When heated to 80°C the mixture developed an intense and stable colour within ten minutes. The absorption did not change over a period of five hours. All solutions for the spectrophotometric measurements were made in the same way. Appropriate aliquots of the standard solution to give a final concentration of 2 to 36 microgram of ruthenium per milliliter were heated on a water bath at 80°C for ten minutes, and were cooled to room temperature and made up to 10, 25, 50 or 100 milliliters with oxalic acid. The final solution was 1 N oxalic acid. The measurements were made after the solution has been cooled (about 30 min.). Fig. 1 curve 1 shows the 'absorption of ruthenium tetroxide in 1 N oxalic acid and curve 2 represents the absorption of 1 N oxalic acid. UJ u z < t.O m o,s a: 0 U) m < us o.o I I I I I I ~ I. I I I I. I I I ii I h i I v I\ I I \ I I I I I \.. r\ I I t I K \ __ 2 I 3DO 350 'DO 4SO 500 :iSO 600 WAVE LENGTH (m,µ) Fig. 1. Absorption spectra (1) of ruthenium t etroxide in 1 N oxalic acid (afte r three hours at room temperature or after heating on water bath to aooc during 10 minutes), (2) of 1 N oxalic acid. Silica cell, 10 mm. The system has a sharp absorption band at 375 mµ. and a broad absorption band at 475 mµ. The regression of ruthenium concentration upon absorbance (at 375 m µ. ) and the 990/o confidence limits for predictions of concentration of ruthenium from measurE;d values of absorbance are shown in Fig. 2. · The absorbance (at 375 mµ) against concentration of ruthenium showed good agreement with Beer 's law over the range investigated. ..84 S. MESARIC AND M. BRANICA The standard errors (curve 1) and relative standard errors (curve 2) of .spectrophotometric determination of ruthenium in 1 N oxalic aced are given fa Fig. 3. 0 / (J ~ 1 / j ~ / d w / 0 ,,. ~ a: ~ / ; , z :! If) UJ w fE > ~ ~ z ....I :! w a: If) 10 20 30 40 lll RUTHENIUM CONCENTRATION (>Jg/ml) RUTHENIUM CONCEWRATION (,ugµnlJ Fig. 2. The regression of ruthenium concentrat ion upon absorbance at 375 mµ and the 99'/o confidence limits. Fig. 3. Curve 1 shows the change of the standard error and the curve 2 the change of the relative standard error of t he concentration of ruthenium tetroxide in 1 N oxalic acid. In the concentration range from 2 to 36 p. p. m. ruthenium was determ ined with relative standard error from 140/o to 1 O/o. Polarographic determination Experiments showed that 1 N oxalic acid as supporting electrolyte gave a residual current which linearly increased with the potential applied to the e lectrodes in the voltage range where ruthenium exhibits a polarographic wave. By applying the counter current -0.30 11· A/V, the residual current curve was almost parallel to the abcissa (Fig . . 4, curv~ 1). Thymol in a concent ration of 0.0060/o was used for suppressing the polarographic maximum of ruthenium in 1 N oxalic acid. :;( 15 -.... 0 .... .... z L&J 0:: 0:: :::> u 10 5 0 2 I ,,,----I /1 ./ I 1 I I I -100 -200 -300 -400 -500 -600 -700 mV~vs. S.C.E. Fig. 4, Curve 1: Residual current of the supporting electrolyte (applied counter cur rent -0.30 µA/V) consists of 1 N oxalic acid and 0.0060/o thymol. Cur.ve 2: Current - voltage cur ve ':~ r uthenium in the same supporting electrolyte. Sens1tiv1ty of the .recorder .0 .25 X 10 A/mm. (switch 1/10) ; damping 5; rate of recording 3.78 mm/min ; potentials ar.e g.1ven with respect to the saturated calomel electrode and the position of h alf-wave potential is marked (-440 mV) . DETERMINATION OF RUTHENIUM 85 Fig. -1 (curve 2) shows also a typical polarographic wave of ruthenium in 1 N oxalic acid and 0.0060/o thymol as a supporting electrolyte and the position of the half-wave potential (-440 mV) with respect to the saturated calomel electrode. Distilled ruthenium tetroxide was absorbed in oxalic acid (as previously described). From this solution a series of solutions with various concentrations of ruthenium w ere prepared and adjusted to 1 N with respect to oxalic acid (0.0060/o in thymol). ·The concentration of ruthenium in the solution so prepared should be between 2 and 120 µg. Ru/ml. Traces of oxygen tend to distort the residual current curve and dissolved oxygen must be completely removed from the solution by passing hydrogen through the solution for about 15 minutes. With this operation all ruthenium was probably converted to Ru(IV). 3 A linear regression analysis was performed for the diffusion current (mm at S = 1/3, or in 10-1A) 'against the concentration of ruthenium (µg/ml.). The calibration curve in the described conditions was a straight line which passed through the origin. The following regression equation was obtained: c = 3.19 h where h is the height of the polarographic wave (S = 1/3) in mm. and C is the concentration of ruthenium (µg. Ru/ml.) in the solution. The regression of ruthenium concentration C upon polarographic wave height ·and the 990/o-con-fidence limits for predictions of C from the m easured value of h (h is the mean -of two repeated determinations) are shown in Fig. 5. / '?'/ /~ //;'../ / :Y /; ~ 2 -;f:P /"' / /"' . ,. / ·-/~/ . / . "~ . t1I 2' ioV :/" ... %0 0 60 QO 0 " .1 ~ RUTHENIUM CONCENTRATION lpg/rnl)' Fi g. 5. Regression of ruthenium concentration c (µg . Ru/ml.) upon polarographic wave height h. (mm., or in 10- 1 A) and the 99'/o-confidence limits for predictions of c. The plotted pomts h. are the mean values of polarographic wave h eights of two repeated measurements. The standard errors (curve 1) and the relative standard errors (curve 2) of the polarographic determinations of ruthenium are given in Fig. 6, for the concentration range from 3 to 120 µg. Ru/ml. Hydrochloric, sulfuric and perchloric acid up to 0.5 N in the supporting electrolyte exhibit no effects upon the height of the polarographic wave of ruthenium. In presence of nitric acid (or even any traces of nitrites) the polarographic determination of ruthenium in the described supporting electro-lyte is impossible. S6 S. MESARIC AND M. BRANICA The polarographic determination of ruthenium in presence of hydrochloric, sulfuric and perchloric acid, shows that the proposed method is reliable and precise in a very wide range of ruthenium concentration (4-120 µ,g./ml.) with relative standard errors of 15 to 0. 70/o. -l / ~ , // / / , _,/ _,,/" \ / .,,.,,,,-.. .,-/ / -A-=s .--" ..... K_ ...__ z iD zo 40 60 80 11111 1ZD RUTHENIUM CONCENTRATION (),19/ml) Fig. 6. Curve 1 is the standard error and curve 2 is the relative standard error of ruthenium concentration plotted against ruthenium concentration in the solutions used for polarographic measurements. Polarographic wave-heights h used in determinations are arithmetic means of two repeate dmeasurements. Spectrophotometric determinations of smaller concentrations of ruthenium ;are more accurate than polarographic determinations. The polarographic determination has an advantage because it is useful in a greater concentration range of ruthenium. REFERENCES 1. R. Thier s, N. Graydon and F. E. Be am is ii, Anal. Chem. 20 (1948) 831. 2. G. H. Ayres and F. Young, Anal. Chem. 22 (1950) 1277, 1281. :3. P. Wehnerand and J.C. Hindman, J. Am. Chem. Soc .72 (1950) 3911. ·4. W. Ge i 1 man n and R. Neeb, Z. anal. Chem. 156 (1957) 411 . . 5. C. D. Cory e 11 and N. Sugarman, Radiochemical Studies; The Fission Products, lst Ed., New York 1951. pp. 1542, 1557. {) , United States Atomic Energy Commission LA-1566 Collected Radiochemical Procedures, 1953, 123. '7. N. H. Furm an, Scott's Standard Methods of Chemical Analysis, lst Ed., I , New York, 1954. p. 737. 8. R. P. Ja ff and A. F. Voigt, J . Am. Chem. Soc. 74 (1952) 2500. 9. W. Ge i 1 man n and R. Ne eb, Z. anal. Chem. 156 (1956) 96. 10. I. M. Ko 1 t ho ff and J. J. Ling an e, Polarography, 2nd Ed., II, New York 1952. p. 489. 11. J. B. W i 11 is., J. Am. Chem. Soc. 67 (1945) 547. 12. R. B. Simpson and R. L. Evans, J. Am. Chem. Soc. 77 (1955) 1437. IZVOD Spektrofotometrijsko i polarografsko odredivanje rutenija u oksalnoj kiselini S. Mesaric i M. Branica Prikazana je spektrofotometrijska i polarografska metoda odredivanja malih koncentracija rutenijeva tetroksida absorbiranog u oksalnoj kiselini. Zuta boja DETERMINATION OF RUTHENIUM 87 -rutenijeva tetraoksida absorbiranog u 1 N oksalnoj kiselini posluzila je za foto-nietrijsko odredivanje rutenija. Mjerenja su vrsena kod valne duzine od 375 mµ za koncentracijsko podrucje od 2 do 35 µg Ru/ml, uz relativne standardne pogreske ·Od 140/o do 1°/o. Opisana je polarografska metoda za odredivanje niskih koncentracija rutenija u osnovnom elektrolitu, koji saddi oksalnu kiselinu (1 N) i timol (0.0060/o). Rezultati pokazuju da je predlozena metoda osjetljiva i precizna u koncenracijskom podrucju od 4 do 120 µg Ru/ml. Relativne standardne pogreske krecu se u granicama od 15 do '0.70/o, ako se odredivanja vrse s dva paralelna uzorka. Solna, sumporna i perklorna kiselina (do 0.5 N) kod fotometrijskog i polaro-grafskog odredivanja ne smetaju. Odredivanja se ne mogu vrsiti, ako je nazocna -dusifoa kiselina (najmanji tragovi nitrita). FIZICKO-KEMIJSKI ODJEL :INSTITUT »RUDJER BOSKOVIC« ZAGREB Primljeno 25 . prosinca 1957-

Spectrophotometric and Polarographic Determination of Ruthenium in Oxalic Acid

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