The EI mass spectra of several arylhydroxyoximes and of their coordinated complexeswith transition metals,Cu,Ni,Co and Fe have been studied using high resolution mass spectrometry,metastable ion measurements and the stable isotopes ~(15)N,~(63)Cu and ~(65)Cu labelling to elucidate thefragmentation pathways.It has been found that the spectra of all compounds 1-24 except Fe-complex 24 show molecular ions.The relative intensity of molecular ions of the complexes,whichcontained the same kind of metal and the arylhydroxyoximes with different substituents R,is closelyrelated to the electronegativity of R.In all metal-complexes 9-22,the main decomposition pathwaysinvolve the successive loss of O,NO and then H_2O or LH.In these spectra the fragmentions of non-metal-containing species resulting from the cleavage of the dioxime ligands can be discriminated. The EI mass spectra of several arylhydroxyoximes and of their coordinated complexes with transition metals, Cu, Ni, Co and Fe have been studied using high resolution mass spectrometry, metastable ion measurements and the stable isotopes (15) N, ~ (63) Cu and ~ (65) Cu labelling to elucidate the fragmentation pathways. It has been found that the spectra of all compounds 1-24 except Fe-complex 24 show molecular ions. The relative intensity of molecular ions of the complexes, which contracted the same kind of metal and the arylhydroxyoximes with different substituents R, is closely linked to the electronegativity of R. In all metal-complexes 9-22, the main decomposition pathways in volve the successive loss of O, NO and then H_2O or LH. these spectra the fragmentions of non-metal -containing species resulting from the cleavage of the dioxime ligands can be discriminated.