The present invention provides a novel carbamazepine hydrazide compound suitable for covalent attachment to a polymer particle reagent, having general formula (1). The present invention also provides a novel carbamazepine acid compound suitable for attachment to proteins for the production of carbamazepine immunogens. The carbamazepine antigen of the present invention has general structure (2), where X is C=O, CH2 or SO2; Y is C=O, CH2, SO2; R is an alkyl and P is a protein or a hapten.