A novel and highly sensitive single‐sweep oscillopolarographic method for the determination of ultratrace amounts of ruthenium

Abstract

A novel and highly sensitive oscillopolarographic method is described for determining ruthenium as low as 7.9 X lo-" M, based on its catalysis of the redox reaction between Ce(Iv) and As(II1). The changes in concentration of As(II1) in the reaction is traced by single-sweep oscillopolarography. The influence of 34 foreign ions is considered. Ruthenium in ore samples was analyzed by the method, and good results were obtained. . A thermometer has been used to determine 0.7-41 X g/mL Ru by measurement of the temperature rise in the Ce(IV)-As(II1) system [ 26). We have found that the reaction can be monitored by singlesweep oscillopolarography through the As(II1) wave at -0.65 V (vs. SCE). In the present work, a novel and highly sensitive method has been developed for the determining ultratrace amounts of Ru at levels higher than 7.9 x lo-" M. EXPERIMENTAL ApparatusA JP-2 model single-sweep oscillopolarograph (Chendu Instrumental Factory) was used for the polarographic measurements. The settings on the JP-2 single-sweep oscillopolarograph were: dropping mercury period 7 s; scanning rate 250 mV/s; scanning potential range 500 mV in the negative direction;I: (second derivative wave); and a three-electrode system-DME, SCE, and platinum electrode. An-5OlB model thermostat and a 10-mL thermostatic polarographic cell were used to control the reaction temperature. ReagentsA 100 pglmL As(II1) solution and 0.004 M Ce(N) solution containing 0.10 M H2SO4 were used.A standard solution of Ru (10 pg/mL) was prepared according to the following procedure: weigh out 16.45 mg of (NH,),Ru(H,0)C15 and place in a 250-mL beaker. Add 50 mg ferrous ammonium sulfate and 50 mL of 10 M H,S04 solution, heat until fumes have evolved for 5 min, cool, then transfer to a 500-mL volumetric flask and dilute to the mark with double distilled water. Prepare working solutions by dilution shortly before use. General ProcedureIn the polarographic cell, place 1.0 mL of 2.0 M H,SO,, 0.50 mL of 0.01 M mercuric sulfate and 0.20 mL of 100 pg/mLAs(III) solutions, and 8.0 X lo-" -4.0 X lo-* g Ru, then dilute to 9.0 mL with water. Keep the temperature of the cell at 25°C. After about 5 min add 1 . O mLof 0.004 M 0 1991 VCH Publishers, Inc.