Department of Chemistry, Sant Longowal Institute of Engineering and Technology, Longowal-148 106, India E-mail : b.kanungo@vsnl.com Fax : 91-1672-3280057 Department of Chemistry, Punjabi University, Patiala-147 002, India Manuscript received 10 April 2001, revised 26 June 2001, accepted 1 September 2001 Complexation of Coll, Nill, Cull and ZnIl involving CDTA (trans-1,2-dinitrilocyclohexanetetraacetic acid) and 1,2,2-trimethyl­1,3-cyclopentanedicarboxylate (camphorate) has been studied by pH-metric method. The formation constants are determined at ionic strength, µ = 0.1 M and 27° in aqueous medium. The order of stability in mixed ligand complexes is Coll < NilI> CuII < ZnII.