From what I know, an appositive phrase is a phrase that describes or renames the noun before or after it. However, I feel like the positive phrase could be either 'The Chemist' or 'Professor Ramirez' because both are describing each other. But 'The Chemist' also gives more info about Ramirez, so is 'The Chemist' the positive phrase?
Spot on, the chemist is your appositive. YourDict explains:
An appositive can come before or after the main noun. It has to sit beside the noun it defines.
- Former Vice President Walter Mondale died at the age of 93.
- College professor Steve Williams will review the scholarship applications.
(Appositives in bold.)
This article on Appositives from San Jose State University may be helpful for you.