Q: How should the first affiliation of a paper be defined where the first author and the first corresponding author are not in the same organization?

The primary affiliation should be for the organization or institution where the greater portion of the research took place. As the definition of the first author is the one who made the most extensive and significant contribution to the research (among other criteria), the first author’s name should be prime on the paper and therefore also their affiliation. The corresponding author’s affiliation too needs to be there, as the corresponding author is typically a senior researcher who would have provided invaluable guidance and direction for the research. Of course, the affiliations of the other authors need to be mentioned as well.

Having said that, note that there is usually not much agreement on affiliation. So, in case there is some disagreement on the order of authorship and therefore affiliation, you may also wish to consult with the editor of your selected journal.

For more insights into affiliation, you may also find it useful to go through these previous queries by other researchers:

• Which of the two affiliations I have should I prioritize in my manuscript?
• How to put senior author affiliation after changing institution?
• Do I need to add my company's name as affiliation in my PhD thesis?

All the best for your submission!