Investigating the mechanism that reduces the memory effect of Li on MC-ICP-MS†

The memory effect significantly impacts the precision and accuracy of lithium isotope measurements using MC-ICP-MS. This study evaluates the origin of the memory effect, identifying the cones, especially the skimmer cone, as the primary site responsible for lithium memory accumulation. To investigate the type and optimal concentration of sodium-containing solutions, scanning electron microscope (SEM) and cone elution experiments were conducted. Results demonstrated that a 0.5% NaNO₃ solution was the most effective based on the high signal-to-blank ratio, less impacted signal intensity and non-interferences. Combined with the SEM results and KCl elution experiments, the mechanism by which the Na solution reduces the lithium memory effect can be attributed to two aspects. First, a nanoscale particle coating is formed on the cone surface, preventing the deposition of Li material on the cone. Second, Na/K solutions are preferentially ionized due to their low ionization energies, reducing or even eliminating the ionization of the analyzed Li. Based on these findings, we infer that high-concentration rinse solutions of alkali or alkaline earth metals may effectively reduce the memory effect of other related elements.