[en] Tritium-labeled amine-containing derivatives of the crown ether (CE) 18-crown-6 (18C6) were synthesized, which were used to determine the possibility of covalent modification of the surface of nanodiamonds (ND). Tritium-labeled CEs were fixed on the ND surface by generating an amide bond between the amino groups of the ethers and the carboxyl groups of the surface. The degree of ND surface modification and the change in physicochemical parameters: specific surface area, aggregate sizes, and ζ-potential in water, pH of suspensions were measured.