Spectrophotometric determination of traces of ruthenium with o-tolidine

Atialytkw

CItitrricu Acru. 65 ( 1973) 2 13-2 f 5 PubIishio~ Company, Amsterdam

0 Elsevier Scientific

SHORT

in The Netherlands

COMMUNICATION

Spectrophotometric

RAirL

213 - Printed

determination

of traces

of ruthenium

with o-tolidine

S. DE PABLO

Dianwml (Rcceivcd

Sitnnvvck

Corporatiolr.

20th October

P.O. Box 345, Paiuesuille,

Ohio (U.S.A.)

1972)

o-Tolidine is known to react with free chlorine, gold(IXI), osmium tetroxide, ruthenium salts, tungstates, etc. la2 but it has not been applied to the determination ofruthenium via its reaction with rhthenium tetroxide. This procedure is less sensitive than the catalytic cerium-arsenic method 3, but is more sensitive than any of the following methods: thiourea, diphenylthiourea, dithiooxamide, diphenylthiosemicarbazide, o-phenanthroline, p-nitrosodimethylaniline3.

Experimental Apparatus.

Microgram amounts of ruthenium were readily distilled from a ZOO-ml all-glass Claisen flask in a stream of air; the all-glass sidearm of the flask was placed into a test tube in an ice-bath. Before use, the apparatus was washed with hot cleaning mixture (15 g of potassium dichromate dissolved in about 500 ml of concentrated sulfuric acid) followed by a water rinse and a steam cleaning. Otherwise, traces of organic impurities might reduce the ruthenium tetroxide and lead to low results. The joints of the distillation apparatus should not be lubricated. A Beckman B spectrophotometer was used with 5cm cells. a-To&line soZzlt~o~_Suspend 0.200 g of pure o-tolidine dihydrochloride in about 100 ml of distilled water, add 30 ml of concentrated hydrochloric acid, dissolve, make up to 200 ml and mix well. Prepare fresh daily. This solution should be colorless. Ruthenium standard solution. Pure ruthenium trichloride hydrate is analyzed for total ruthenium via reduction under hydrogen or atomic absorption. Weigh the proper amount, dissolve in 2 M hydrochloric acid, make up to the desired volume, and calculate the exact concentration. By dilution, prepare another solution containing 1 p.p.m. of ruthenium. Procec;lure. Treat the sample so as to bring all the ruthenium into sofution4. Transfer an aliquot (containing not more than 10-12 pg Ru) to a beaker. Add sufficient concentrated hydrochloric acid to react with any nitrate present (if any was used) and to leave an excess of 20-25 ml. Add sufficient (1 + 1) sulfuric acid to transform all the salts into neutral sulfates and to leave an excess of 5-7 ml of the concentrated acid. Mix well, heat to fumes of sulfur trioxide without boiling, and fume for 4-5 min. Cool to room temperature. Carefully transfer all the solution to the distillation apparatus. Dilute to about 80-100 ml. Add 0.243 g of ammonium cerium(IV) sulfate without leaving any particles stuck to the walls. Place IO ml

SHORT

COMMUNICATION

of o-tolidine solution and 10 ml of water in the receiver test tube, mix, cool to about O-+ 5” with an ice bath, start a flow of clean air (3-4 bubbles s- ‘), heat the flask solution to the boiling point and boil for about 25-30 s after the sidearm of the distillation flask becomes hot. Remove the receiver tube, make up to 50 ml and mix well. Wait for 5 min after boiling begins and determine the absorbance at 430 nm in S-cm cells versus water. Run a calibration curve by the same procedure, using aliquots of the standard solution.

Resiitts Seer’s law was obeyed over the range O-10.8 j(g Ru. The reagent blank was cu. 0.010 absorbance units. The sensitivity according to SandelI was about 10d3 jig cmV2. Under the recommended conditions, osmium was the only likely interfering element. The results obtained with various concentrations of osmium are shown in Table I. With osmium, the absorbance increased after the specified 5-min period, whereas the absorbance caused by ruthenium began to decrease slowly (Table II). When osmium is added as the tetroxide, most is eliminated in the fuming step; but, when it is added as potassium osmate or potassium chlorosmate, most or all remains in the system. If desired, the osmium may be separated by some suitable procedure3q4. TABLE

I

INFLUENCE

OF OSMIUM

OS added (pg)

Added

9.000 100

oso,

as

K,OsO, K,OsO, K,OsO, K,OsO, K ,OsO, K20sCl, K,OsCl,

500 700 l.ooo 3,200 2,090 6,640 TABLE

IN ABSENCE Rtt

Jblorti

OF RUTHENIUM

(jiy

j

0.5

0.2 0.4 0.6 0.8 2.0 < 1.0 f3.0

II

VARIATION TIME

OF TWE ABSORBANCE

OF THE OSMIUM

AND

RUTHENIUM

JO00 pg Us tts K,0s04

11.7 pg Rti

The

Absorbance

Time (rttirr j

Absorbirtrce

0.10 0.19 0.35 0.48 0.59 0.77

5 10 IS 26 3s 54

1.21 1.20 1.18 1.14 1.10 1.04

5 15 30 45 60 80

(mitt)

COLORS

WITH

SHORT

215

~OMM~NI~AT~ON

This reaction seems to involve the oxidation of o-toiidine by ruthenium tetroxide, with simultaneous reduction of ruthenium(VIII) to one or more lower valences. This mechanism is supported at least in part by the fact that the absorption curve of the yellow compound obtained coincides in shape and absorption maximum with that obtained from+tolidineoxidized by other reagents like sodium hypochlorite, in the absence of ruthenium (Fig. I).

330

370

390

410

430

WAVELENGTH

Fig. 1. Spectral absorption ruthenium in 50 ml solution.

curves.

430

470

(

0

(nm)

(A)

15.8 ~cg sodium

hypochlorite

in 50 ml solution;

(B)

6.3 erg

REFERENCES I 2 3 4

W. B. Pollard, Artulyst, 44 (1919) 94; Bull, Itrst. Min. Metals., 223 (1923). See, e.g. K. Kodttma, Methods oJ ~i~;t~~tit~ttiue l?zor~irrfic Amlysis, Wiiey-Interscienc~, New York, 1963. E. B. Sandell, Colorinretric Determitmfiott of Traces of Metals, Interscience, New York, 3rd Ed., 1959. F. E. Beamish, Tire Anal_Wicul Chemistry of the Noble Metals. Pergamon Press, Oxford. 1966, p. 156.