Would putting a mutagen in to nauseate enemies be possible?
For a build, which would be better, using syringe spears or injection spears (or both?)
For the injection spear, would it also take a minute to reload? A minute per dose? A standard action per dose?
How about using a bomb in one? (unlikely but seems worth considering)
the problem is the base Potions description (see Brew Potion) as the imbiber is considered the caster and is in control of the spell effect.
For instance, using Poisoner's Gloves with a Potion of Gaseous Form. Hitting the taget on your action would inject the potion and they would go gaseous (a good de-buff). On their turn as their standard action they may dismiss the spell. So the penalty only lasts a short time but it does burn their action.
Alchemists have other options and after failing a save nausea can occur. Still, it's not as good as the original effect.
I am fairly sure there is a FAQ that says that at least some of the Range: Personal spells without a save get a save if used as infusions. Finding it is another matter, as it was made as an answer to a relatively unrelated question.
Paizo FAQ pages aren't easy to consult for a specific answer.
About the Mutagen:
A non-alchemist who drinks a mutagen must make a Fortitude save (DC 10 + 1/2 the alchemist’s level + the alchemist’s Intelligence modifier) or become nauseated for 1 hour
If you are injected with the Mutagen, you aren't drinking it.