ODM2 Variable Name Controlled Vocabulary ODM2 Working Group A vocabulary for describing the name of Variables. Nitrogen, dissolved (free+ionized) Ammonia (NH3) + (NH4) Dissolved (free+ionized) Ammonia Originally from the CUAHSI HIS VariableNameCV. See: http://his.cuahsi.org/mastercvreg/edit_cv11.aspx?tbl=VariableNameCV.