DETERMINATION OF THE STABILITY OF OSMIUM(VI) HEXACHLORIDE ICP-OES STANDARDS IN HCl ACID MATRIX

The ideal HCl concentration used in stabilizing osmium standards was investigated in this study. Additionally, mathematical models were tested to predict the decomposition rate of osmium standards at room temperature. Osmium(IV) hexachloride stock solutions stabilized in 7 and 15% HCl were used to assess the decomposition rate using ICP-OES. Several sets of calibration standards were prepared from the original stock solutions. The first calibration set was prepared with no additional HCl added to the final solutions and other sets with a total HCl acid concentration of 0.2, 0.4, 0.6, 1.0 and 1.5% v/v. Emission intensities were measured at 0, 24, 48, 72 and 96 hours. Standards with no additional HCl acid added kept at room temperature showed increase in emission intensities after 24 hours. These changes in emission intensities indicated chemical instability of osmium standards at low acid concentration levels. Standards stabilized in 1.0-1.5% HCl and refrigerated below 10 degrees C showed consistent emission intensities and had a shelf life of up to 48 and 72 hours, respectively. Four mathematical models were tested to determine the decomposition rate of the osmium standard. The first used rate of change concept and the second a stochastic approach. Both failed to capture osmium decay. The third was based on non-local operators with power law kernel and was able to capture the decay at earlier, but not later stages. The fourth, based on non-local operators with non-singular kernel was able to capture earlier and later decay due to its crossover properties in waiting time distribution.