638 SHORT COM~WNICATI~NS

3-NITROSO-4-HYDROXY-5,6-BENZOCOUMARIN AS A SELECTIVE REAGENT FOR THE SPECTRQPHOTOMETRIC

DETERMINATION OF RUTHENIUM(II1)

(Received 2 October 1973. Accepted 8 seceded 1973f

Various reagents for the calorimetric determination of ruthenium have been reviewed.’ ’ Some of the important and recently introduced reagents are 2,3diaminopyridine,5 24,6-tris(2’-pyridyl)-5-triazine,6 chrome azurol S,’ 3&diaminobenzoic acid,’ acenaphthenequinone monoxime,9 oximidobenzotetronic acid” and 3-nitroso-2.6- p~id~edio1.”

3-Nitroso-ehydroxy-S,,6_benzocoumarin (NHBC) is a chelating agent which has already been used for the spectrophotometric determination of nickel” and as a spot-test reagent for the detection of cobalt.” It reacts with ruthenium(lII), giving a pinkish-violet complex, which is extractable mto n-butanol. Under suitable conditions, the reagent can be used for the spectrophotometric determination of ruthenium in the presence of all other platinum metals.

Reagents

NHBC solution in acetone, OOOZM.

EXPERIMENTAL

Ruthenium(llZ) stock solution, O-OlM. Ruthenium(II1) chloride was dissolved in doubly distilled water con- taining sufficient hydrochloric acid to give a final acidity of 1M and the solution standardized by precipitating ruthenium as the hydrated oxide, igniting it carefully in air, reducing in hydrogen and cooling in an atmos- phere of carbon dioxide. Working solutions were prepared by dilution of the stock soiution.

All other chemicals used were of reagent grade.

Procedure

To a sultable aliquot of solution containing 1 l.O-63.0 II& of ruthenium(II1) in a SO ml Pyrex glass-stoppered bottle, add 1 ml of 2M sodium perchlorate and an excess of the reagent solution (5 ml). Adjust the pi-i to 5.5-8-O and dilute to 10 ml. Heat the mixture for 40 min on a steam-bath. Cool and dilute to 1Oml with doubly distilled water. Extract the pinkish-violet complex with 10 ml of n-butanol. Centrifuge the organic layer and measure its absorbance at 520 nm against a reagent blank prepared under identical conditions.

Absorption spectra

RESULTS

The absorption spectrum of the pinkish-violet complex extracted into rl-butanol is shown in Fig. 1. The absorption ~imum is at 520 nm where the absorbance of the reagent IS low.

Reaction conditions

Solutions containing fixed amounts of ruthenium and reagent were prepared, of which the pH was varied from 3.5 to 10.0, and extracted as described. The absorbance at 520 nm was constant over the pH range 5.5-8.0. At lower and higher pH the absorbance decreased.

For maximum colour development, heating for at least 20 min on a steam-bath was found to be necessary. Further heating for 2 hr had no effect on the colour of the complex. Heating for 40 min is recommended to ensure complete complexation. The colour of the complex was found to be stable for at least 92 hr at room temperature.

Increasing amounts of reagent were added to 1 ml of 5 x lo-“M ruthenium at pH of 6.5 (acetate buffer). After the extraction, the absorbance was measured at 520 nm against corresponding reagent blanks prepared under identical conditions. The study showed that at least a 12-fold molar excess of the reagent is required for full colour development.

The system obeys Beer’s law up to 7.4 ppm of ruthenium. The optimum range for the accurate determination of ruthenium, as evaluated from a Ringbom plot, is 1.1-63 ppm. The molar absorptivity is 1.04 x 10“

SHORT COMMUNICATIONS 639

0.6

400 440 480 520 560 600 640

WAVE LENGTH (rim) -

Fig. 1. Absorption spectra. (At-Reagent blank vs. n-butanol (reagent 1 x 10Y3M). (Bt--Ruthenium complex t’s, reagent blank [Ru(III) 5 x 10e5M; reagent 1 x 10m3M).

l.mole- ’ .cm- ‘. The precision of the method was tested by measuring the absorbance of 10 samples each containing a final ruthemum concentration of 5.05 ppm. The mean absorbance was 0.520 with a standard deviation of OGO4.

Molar composition of the complex

Jobs method of continuous variations and the logarithmic method of Bent and French both indicate the formation of a 1 : 2 complex (metal : ligand).

Efict of other ions

The effect of various ions was studied. With 5.05 ppm of ruthenium, the following ions present in the amounts (in ppm) shown m parentheses did not cause a deviation of more than _+2% in absorbance from that expected: chloride (3000), bromide (2000). iodide (2000), fluoride (250), citrate (200), thiocyanate (1500), oxalate (150). nitrate (3000). phosphate (50), thiosulphate (KM)), borate (250), sulphate (5000) sulphite (lOO), Hg(I1) (100). Cd(I1) (250). Zn(I1) (25). Th(IV) (125), Cr(II1) (200), Al(II1) (15) Mn(I1) (250), Pb(I1) (150), Mo(V1) (25). Bi(II1) (100). U(V1) (IOO), Mg(I1) (200), Ca(I1) (250), Ba(I1) (25O), Sr(I1) (250), Ag(1) (5O), Ce(IV) (80). As(II1) (150), Sb(II1) (150). In(II1) (60) V(V) (5), Ni(I1) (25), Pd(I1) (25), Cu(I1) (20), Pt(IV) (5O), Os(VII1) (45). Ir(IV) (20) Rh(II1) (50) Ir(II1) (35), Os(IV) (45) and Au(II1) (50).

EDTA. nitrite. thiourea. cobalt(I1) and iron(II1) were found to interfere in the determination of ruthenium. Interference due to 10 ppm of iron(I11) could be removed by adding 200 ppm of fluoride. Attempts to mask cobalt(I1) were unsuccessful.

Determinatiott in ores

Synthetic mixtures contaming platinum metals (e.g.. corresponding to osmiridmm or syserkite) were prepared and the ruthenium content determined (Table 1).

Procedure. Mix the sample with sodium chloride and heat the mixture to redness in a current of chlorine. Extract with water. filter and add concentrated hydrochloric acid. The platinum metals form soluble chloro-complexes. Reflux the solution m presence of concentrated hydrochloric acid and ethanol to reduce any Ru(IV) which may be present, to Ru(II1). Evaporate the solution to a small volume, cool and make it up to 50 ml with 1M hydrochloric acid. Determine the ruthenium content in the sample by the procedure already described in the experimental section,

640 SHORT COMMUNICATIONS

Table 1. Determination of ruthenium in synthetic mixtures corresponding to osmiridium or syserkite

Ruthenium Ruthenium present, Rh, Ir, OS. Pd, Pt, found,

ppm ppm ppm ppm ppm ppm ppm

2.75 - 5.24 2057 - O-06 2.78 4.19 - 8.00 32.97 - 0.09 4.16 SOS - 9.64 39.66 - @l 1 4.99

CONCLUSION

Although many reagents are known for the calorimetric determination of ruthenium. comparatively few are well suited for the purpose. Thiourea’ has proved to be satisfactory for the determination of about 2-15 ppm of ruthenium and the tolerance for iridium, rhodium, platinum and nickel offers some advantage but the sensitivity is very low and palladium interferes. l,lO-Phenanthroline and 4,7-diphenylphenanthroline’ give sensitive colour reactions but the intensity of the colour depends upon several factors that require control to produce precise results. Considerable interference is caused by other metals and a time-consuming prior separation of ruthenium by distillation is necessary. p-Nitrosodimethylanilinei4 is highly sensitive (00l28 pg/cm’) but perhaps the most objectionable feature in this method is the narrow pH range, which is also the pH required for precipitation of ruthenium as the hydrated oxide. Osmium and nitrate interfere seriously and should be absent.

Recently 2,3_diaminopyridine,’ 2,4,6-tris(2’-pyridyl)-S-triazine,6 oximidobenzotetronic acid” and 3,4_diamino- benzoic acids have been used for the determination of ruthenium. In the case of 2,3-diaminopyridine, prior separation of ruthenium from other metals is necessary. Oximidobenzotetronic acid is selective but the sensitivity is low. 3+Diaminobenzoic acid is a sensitive reagent but the pH range is narrow (40-4.5) and other platinum metals interfere.

The present procedure, involving the use of NHBC as spectrophotometric reagent for ruthenium, is fairly sensitive. None of the platinum metals interferes in the determination. Among the group VIIL metals only cobalt interferes in the &termination. The major advantage of this method is that the reagent can be used as such for the determination of ruthenium in presence of large quantities of other platinum metals in readily attainable oxidation states, without the use of masking agents.

Acknowledgement-The authors are thankful to the Council of Scientific and Industrial Research (India), for the award of a fellowship to one of them (N.K.).

Department of Chemistry University of Delhi Delhi-l 10007, India

NITIN KOHLI R. P. SINGH

REFERENCES

1. F. E. Beamish, Analytical Chemistry of Platinum Metals, p. 366. Pergamon, London, 1966. 2. D. F. Boltz and M. G. Mellon, Anal. Chem, 1972, 44, UW)R; 1970, 42, 152R; 1968, 40, 2SSR; 1966,

38, 317R. 3. F. E. Beamish, Talanta, 1965. 12, 789. 4. F. E. Beamish and W. A. E. McBryde. Anal. Chim. Acta, 1953.9, 349; 1958, 18, 551. 5. G. H. Ayres and T. Eastes, ibid., 1969, 44, 67. 6. W. A. Embry and G. H. Ayres, Anal. Chem, 1968,40, 1499. 7. K. K. Saxena and A. K. Dey, Indian J. Chem., 1969,7, 75. 8. G. H. Ayres and J. A. Amo, TaIanta, 1971, 18, 411. 9. S. K. Sindhwani and R. P. Singh, Anal. Chim. Acta, 1971, 55, 409.

10. G. S. Manku, A. N. Bhat and B. D. Jain, Talanta. 1967, 14, 1229. 11. C. W. McDonald and J. H. Badenbaugh, Mikrochim. Acta, 1970, 474. 12. N. Kohli and R. P. Singh, Curr. Sci. Calcutta, 1973, 42, 142. 13. N. Kohli B. S. Garg and R. P. Singh, Mikrochim. Acta, (accepted for publication). 14. C. V. Banks and J. W. O’Laughlin, Anal. Chem., 1957, 19, 1412.

Summary-The pinkish-violet complex developed on interaction of ruthenium(II1) with 3-nitroso- 4-hydroxy-5,6_beruocoumarin (NHBC) in the pH range 5.5-8.0 can be extracted into n-butanol. The complex has an absorption maximum at 520 nm. Maximum colour development takes place

SHORT COMMUNICATIONS 641

after heating for 20 min on a steam-bath and the extracted complex is stable for at least 92 hr. Beer’s law IS followed up to 7.4 ppm of ruthenium. The molar absorptivity is 1.04 x 10“ l.mole-‘.cm-‘. The composition of the complex is 1 : 2 (ruthenium : NHBC). None of the other platinum metals was found to interfere in the determination of ruthenium, even though present in large excess.

Zusammenfassung-Der rosaviolette Komplex aus Ruthenium(II1) und 3-Nitroso-4-hydroxy-5,6- benzocumarin (NHBC) bei pH 5,5-&O kann in n-Butanol extrahiert werden. Der Komplex hat ein Absorptionsmaximum bei 520 nm. Die maximale Farbentwicklung findet nach 20 min Erhitzen auf dem Dampfbad statt; der extrahierte Komplex ist mindestens 92 h lang stabil Das Beersche Gesetz gilt bis hochstens 7,4 ppm Ruthenium. Der molare Extinktionskoefiizient betrtigt 1,04 x IO4 I.mol-‘.cm-‘. Die Zusammensetzung des Komplexes ist 1 :2 (Rut- henium : NHBC). Keines der anderen Platinmetalle stijrt bei der Bestimmung von Ruthenium, such nicht in groDem UberschuR.

R&atm&-Le complexe violet-rositre dbveloppe par interaction du ruthtnium(II1) avec la 3-nitroso 4-hydroxy 5,6-benzocoumarine (NHBC) dans le domaine de pH 5,5-&O peut etre extrait en n-butanol. Le complexe a un maximum d’absorption a 520 nm. Le dtveloppement maximal de la couleur se fait aprbs chauffage pendant 20 mn au bain de vapeur et le complexe extrait est stable pendant au moins 92 h. La loi de Beer est suivie jusqu’8 7,4 ppm de ruthinium. Le coefficient d’absorption molaire est 1,04 x 10” l.mole- ‘. cm- I. La composition du complexe est 1 : 2 (ruthenium : NHBC). On a trouvit qu’aucun des autres mitaux du platine n’interfkre dans le dosage du ruthtnium, m&me p&sent en grand exds.

Talanta, Vol. 21, pp. 641-645. Pergamon Press. 1974 Prmed m Great Briram

ZUR ENTMISCHUNG DER LijSUNGSMITTEL BET DER CHROMATOGRAPHISCHEN TRENNUNG-IV*

SELEKTIVE SORPTION DER FLIEDMITTEL AN DER SILICAGEL- UND ALUMINIUMOXIDS~ULE SOWIE AN PAPIERSTREIFEN

(Eingegangen am 27. M&z 1973. Revidiert am 12. September 1973. Angenommen am 30. November 1973)

Friiher verijffentlichte Untersuchungenl-’ haben gezeigt, daB esim Verlaufdes chromatographischen Prozesses an der Cellulosed\ule zur Entmlschung der Losungsmittel kommt und dafi man die Verhiltnisse an der Grenze zwischen der festen und der fliissigen Phase offensichtlich nicht nur mit der Bildung eines Cellulose-Wasser- Komplexes erkliiren kann. Es war nun interessant zu erfahren, ob das fiir Cellulose erkannte Verhalten der FlieDmittel fir andere Trhger gilt oder ob sich der Charakter der Sorption von Fall zu Fall iindert. Darum wurde eine Versuchsreihe angesetzt. bei der einige schon friiher an Cellulosesiiulen durchgefihrten Experimente an Silicagel- und an Aluminiumoxiddiulen sowie an Streifen von Chromatographiepapier durchgefihrt wurden.

EXPERIMENTELLER TEIL

Filr die Versuche wurden die friiher beschriebenen Siiulen’ verwendet.

ReageCen

SdicageI. KorngriiBe 0.3 bls 0.6 mm. gewaschen. bei I10 C getrocknet. 4Ifrrllirlirrrllosicl. REANAL fin chromatographische Zwecke. Dieeingesetzten Alkohole wurden durch mehrfache Destillation gereinigt. Tabelle 1 gibt die Zusammensetzung

der untersuchten Alkohol-Wasser-Mischungen an. Die Bestimmung des Wassergehalts der Lbsungen erfolgte durch. Tltratlon mlt Karl-Fischer-Lisung mit

blamperometrischer Endpunktsanzeige.4 Die papierchromatographischen Untersuchungen wurden auf Streifen von Whatman Papier Nr. 3 MM durchgefiihrt. die entweder zwischen zwei 7 cm langen mikroskopischen Objekttrilgern oder zwischen zwei Glasplatten von 24 x 2 cm lagen, die durch Anritzen mit einem Diamanten in 2 cm lange Abschnitte geteilt worden waren.

* Mitteilung III: Talanta, 1965. 12. 171.