Dear Rodrigo Papai

I am not sure, where your "theory" originates from but as such it is not true that higher mass/charge isotope needs to have a higher sensitivity.

In fact, if you consider that a solution having the same mass concentration (e.g. ug/L) of U with atomic mass of 238 and In with atomic mass of 115 contains more than twice as many In atoms would contratict such a general statement.

As a second fact, quadrupole-based ICPMS usually operate in a way that mass resolving power is increased with mass/charge (leading to similar peak width across the mass/charge range), which theoretically would also favor lower mass/charge sensitivities.

It is a fact that sensitivity in ICPMS generally increases with mass/charge if the heaver ion has similar ionization energy. A significant factor is the so-called space charge effect, which attenuates stronger the transmission lighter ions. A second factor is higher mobility of the lighter ions in the ICP and vacuum interface, causing greater loss by diffusion. The actual sensitivities however depend on a large number of factors like ion optics settings, ICP operating conditions etc. Your data seem to indicata a substantial preferences for lower mass/charge isotopes (Li is twice the limit value) so probably your instrument settings are just not comparable to those used in your "theory".

Dear Rodrigo Papai

I am not sure, where your "theory" originates from but as such it is not true that higher mass/charge isotope needs to have a higher sensitivity.

In fact, if you consider that a solution having the same mass concentration (e.g. ug/L) of U with atomic mass of 238 and In with atomic mass of 115 contains more than twice as many In atoms would contratict such a general statement.

As a second fact, quadrupole-based ICPMS usually operate in a way that mass resolving power is increased with mass/charge (leading to similar peak width across the mass/charge range), which theoretically would also favor lower mass/charge sensitivities.

It is a fact that sensitivity in ICPMS generally increases with mass/charge if the heaver ion has similar ionization energy. A significant factor is the so-called space charge effect, which attenuates stronger the transmission lighter ions. A second factor is higher mobility of the lighter ions in the ICP and vacuum interface, causing greater loss by diffusion. The actual sensitivities however depend on a large number of factors like ion optics settings, ICP operating conditions etc. Your data seem to indicata a substantial preferences for lower mass/charge isotopes (Li is twice the limit value) so probably your instrument settings are just not comparable to those used in your "theory".

When that happens in the ICP-MS Perkin Elmer 350 X, I increase the angle of the nebulizer a bit and the situation is fixed.

Are you tried to optimize the torch position and nebulizer gas flow?

Dear researchers,

Thanks for the answers.

The problem was apparently solved. After AutoTUNE, I performed a Tune Manual modifying the potentials (V) applied in Extraction Lens, Angular Deflection and Q1 Focus Lens. This ensured a more robust ICP-MS behavior, improving sensitivity and stability of Uranium.

In fact, the ICP-MS software performs an automatic optimization to then run this performance test. However, the software seems to be struggling to find the optimal TUNE condition. A manual adjustment proved to be more efficient.

In addition, the previously installed nickel skimmer appears to have been manufactured faulty. When it was changed, an improvement in stability was observed.