The Vampire Academy (series) first encounters Alchemists in Blood Promise, when Rose Hathaway is in Russia. Rose meets Sydney Sage in an alley behind the Nightingale club. A Strigoi attacks Sydney and Rose stakes him with her silver stake and intends to leave him there. When it is obvious to Sydney that Rose doesn't know what her job is, she takes out a vial that disintegrates the dead Strigoi leaving behind only a pile of ashes. Sydney and Rose then go to a restaurant, order food, and Sydney explains to Rose what the Alchemists are and what they do.
A Quote From Vampire Academy: The Ultimate GuideEdit
"[Alchemists] are given a special tattoo made from gold and Moroi blood, which gives them traits similar to those of the Moroi themselves: a long life and excellent health. Because the tattoo is also charmed with water and earth compulsion magic, it prevents the Alchemist from speaking about Moroi in any way that could endanger or expose them." -- Vampire Academy: The Ultimate Guide. Pages 283-284.