Uranium determination in process chemicals: on the way to sub-pg/g concentrations

The detection limit of ICP-MS is affected by the sensitivity, the height of the blank and its relative stability i.e. precision, the accuracy and additionally by a bias or systematical error. The improvement of a single factor will improve the efficiency of the whole analytical system. For the example of uranium determination in process chemicals such as concentrated HF and HNO₃ the improvement or deterioration of the factors given above is demonstrated. The applied methods are matrix removal by evaporation, highly efficient nebulization with a USN, isotope dilution and use of a double-focusing instrument (ICP-SFMS_LR). The increase or decrease of each factor is compared to conventional nebulization ICP-QMS. To take full advantage of each single method, they can be combined with each other. Possible drawbacks of a single method are compensated by another method. Detection limits for uranium in concentrated process chemicals in the sub-pg/g range can be achieved.     

An Effective Zeta Potential Fitting Model for Sphere-Plate Interaction Force in Nanoparticle Suspensions

The silica sphere-plate interaction forces in zirconia nanoparticle suspensions have been successfully measured to explain how negligibly charged silica microspheres can be stabilized through the addition of highly charged zirconia nanoparticles. However, the influence of nanoparticle volume fraction on the stabilization as well as how various forces (the attractive van der Waals force, repulsive electrostatic force, and depletion force) contribute to the total interaction force still remains unclear. Therefore, an effective zeta potential fitting model is developed to explain the experimental interaction force curves based on a variable effective Debye length and a measured effective zeta potential using a continuum assumption.