Zero-field magnetic resonance spectra of halogen nuclei in amine and amino acid hydrohalides, partially deuterated at the exchangeable positions, show multiple spectral lines, each one corresponding to a particular pattern of deuteron replacement in the coordinating protonated groups, We have analyzed this isotope perturbation using two-dimensional I-127 zero-field NMR spectroscopy (NQ-COSY). The principal values of the electric field gradient tenser for each isotopomer are obtained from the corresponding resonance frequencies of two connected transitions. The difference between the electric field gradient tenser for isotopomers differing by a single isotope substitution is treated as an axially symmetric perturbation along the hydrogen bond between the substituted proton and the halide : under this assumption, we have determined the orientation of the electric field gradient tenser principal axis system.