Monitoring the rate of osmium(VIII) catalyzed arsenic(III)vanadium(V) reaction by potentiostatic stat method using an automatic measuring system: An approach to the determination of osmium

The rate of reaction between arsenite and vanadate, catalyzed by osmium(VIII) was monitored using an automatic potentiostatic stat method. This was carried out by maintaining the preset potential of a platinum indicator electrode by addition of a 2 x 10(-3) M vanadate solution (titrant). The rate of addition of titrant was considered as a criterion for the reaction rate and for this purpose the plots of Vi, (volume of titrant added) versus time (duration of titrant addition) were recorded, by an automatic measuring and control system. The slopes of linear part of these plots were used for the evaluation of the reaction rate. The experimental variables influencing the reaction rate were investigated by two methods, the one-at-a-time method and the Simplex method. As the rate of the osmium(VIII) catalyzed arsenite-vanadate reaction is linearly dependent on the osmium(VIII) concentration, a kinetic catalytic method was developed for the determination of trace-osmium. Under the optimized conditions, the calibration plot was linear over the concentration range 7 x 10(-8)-2.5 x 10(-6) M of osmium(VIII). The limit of detection of osmium was 3 x 10(-8) M. The interference of 28 cations and anions on the osmium determination was studied. The method was applied to the determination of osmium in synthetic osmiiridium samples with trace amount of osmium as typical example of application.