Take the purchase order to Alessandro Luca in the Undercity.
The Royal Apothecary Society needs your assistance. Listen closely, and both of us may profit from my plan.
Apothecary Keever in the next room may be... touched... but his research does potentially bear fruit if it were pursued by a clever researcher. Fortunately, I am such a researcher. I want you to take this purchase order to Alessandro Luca, the proprietor of Blue Moon Odds and Ends; he'll give you a testing kit. When you have it, bring it back to me and I'll outline your task in detail.