Evaluation of Nebulizer Performance within the ICP-MS Measurement System for Analysis of SRS Radiological Waste Tank Simulated Solutions

High level radioactive waste tanks at the Savannah River Site are high in salt content. The average Total Dissolved Solids (TDS) content is approximately 25%. For ICP-MS optimum signal stability and to reduce blockage of nebulizers and sampling orifices, it is usual to limit analyte solutions to a TDS content of nominally < 0.2%. Dilution to this level to reduce the matrix effect may push some analytes of interest below detectable levels. Five commercially available nebulizers were evaluated in a field study as part of the ICP-MS measurement system for their performance in a high salt matrix. The nebulizers surveyed were a meinhard concentric, cross-flow, micro-concentric (MCN), V-groove, and a direct injection nebulizer (DIN). Analytes spiked into non-radioactive diluted salt solutions ranging from nominal 0.25 – 1.0% TDS were repetitively analyzed with the goal of determining stability of response signal and magnitude of any signal loss/suppression resulting from the diluted salt matrix. The cross-flow nebulizer provided the most stable signal for all salt matrices with the smallest signal loss/suppression due to this matrix. The DIN exhibited a serious lack of tolerance for TDS; possibly due to physical de-tuning of the nebulizer efficiency.