In the era when metals were analysed by spectrophotometry, many chelating ligands were developed that selectively formed brightly coloured complexes with particular metal ions.  This methodology has been eclipsed with the introduction of inductively coupled plasma methodology.  Salicylaldoxime can be used to selectively precipitate metal ions for gravimetric determination.  It forms a greenish-yellow precipitate with copper at a pH of 2.6 in the presence of acetic acid.  Under these conditions, this is the only metal that precipitates; at pH 3.3, nickel also precipitates.  Iron (III) will interfere.
  It has been used as an ionophore in ion selective electrodes, with good response to Pb and Ni.