Hello there.

I've a question regarding a parameter in Agilent MassHunter Qualitative Analysis.

I'm working on flow injection ESI-MS of methyl linoleate to study its degradation and oxidation products. When trying to understand the raw formulas, I use the Mass Calculator tool in MassHunter. However, I'm not sure about what to do with the parameter "allow both even and odd" for MS ion electron state.

I suppose that I should set it "odd", because my ions are losing an electron? Or maybe not?

Thanks for your time and patience

Based on your description, it sounds like you are using the Formula Calculator tool to generate possible formulas, in place of the Mass Calculator tool. In the Formula Calculator tool and in Generate Formulas in Qual Methods, the MS ion electron state options are a way to filter out possible formulas based on the nitrogen rule after taking into account the electron state of the ion. The ”allow both even and odd” option is the broadest and will present any formula that meets the criteria specified in the tool where the “odd electron” and “even electron” options limit the formulas further.

I'll use your example to explain the electron state options a bit. ESI usually results in even electron ions due to the way the ions are formed. For example, a hydrogen loses its one electron becoming positive resulting in the whole ion having an even number of electrons. Applying the "even electron" filter to m/z fragments from an ESI-generated spectrum results in a list of potential formulas where an even integer mass has no or an even number of nitrogen atoms and an odd integer mass has an odd number of nitrogen atoms.

The “odd electron” state option would apply the appropriate nitrogen rule filter for ions that have an odd number of electrons. The typical example for using the “odd electron” option would be identifying formulas for ions formed in an EI source.

Going back to your example, in the Formula Calculator tool, a reasonable set of parameters for your example would be choosing “H” for the positive ions, since H

^{+}is the common charge carrier in ESI, and “even electron” for the MS ion electron state. Since only one charge carrier can be considered at a time in the Formula Calculator tool, I would also suggest trying different, reasonable charge carriers to explore those options as well.