Got this from Wowhead, hope it helps

This fight doesn't require a main-spec tank, so don't worry if you can't find one to come along - it's probably faster to take four DPS and a healer (or even a fifth DPS with healing abilities, if they're good).

Tactics:
Hummel has a purple aura that does about 2k per second to anyone near him, unless they've drunk the purple anti-perfume potion. Similarly, Baxter has a green aura that does the same to anyone who hasn't drunk the green anti-cologne potion. Frye has no aura, but throws cologne and perfume on the floor frequently, leaving pools on the ground that deal damage to anyone who is standing in them if the player doesn't have the relevant anti-potion effect on them. The pools are color-coded same as your potions - if you drank the purple anti-potion, a purple pool on the floor won't hurt you. Additionally, Crazed Apothecaries will keep running up and suicide-AoEing on you, this is the only real source of damage if everyone's alert with the perfume/cologne stuff, but should be easy enough for anyone with healing, even off-spec, to deal with.

Choose two members of your party with reasonably high health. They will be your tanks. One will chug the purple anti-perfume potion, and get ready to tank Hummel where he stands (the one with the purple aura). The other will chug the green anti-cologne potion and be ready to tank Baxter (the one with the green aura, who runs to Hummel's 2 o'clock when the fight begins). Everyone else will chug whichever potion they fancy, just so they don't need to worry about moving out of Frye's thrown poison half the time.

When the fight is activated, Hummel is first to become attackable, followed in a few seconds by Baxter and a few seconds more by Frye. The tanks should point Hummel and Baxter towards the walls of this room, to avoid their cologne/perfume spray cone attack hitting the rest of the party. Tanks should run away temporarily when Hummel or Baxter start casting Chain Reaction, as the damage from this is not mitigated by the anti-perfume or anti-cologne potions.

It's generally best for the rest of the DPS to kill Frye first as he has no aggro table and is the most annoying. If Frye runs up close to one of the other alchemists, melee should either chug a potion of that alchemist's aura, or wait for Frye to move on - don't get close to Hummel or Baxter without the right anti-potion up.

Once Frye is dead, move on to either Baxter or Hummel, remembering to drink the correct anti-potion first if you need to.

The alchemists' perfume and cologne effects are nature-damage, so any nature resistance auras you have might be useful here.

Potential causes of failure:
■Not getting the hell out of the perfume/cologne pool on the ground when you should do.
■Forgetting to drink the correct anti-perfume or anti-cologne when meleeing Baxter or Hummel.
■Not pointing Baxter and Hummel away from the rest of the party.
Don't make these mistakes and it'll be easy as cake.