SEPARATION AND PRECONCENTRATION OF IRON(II) AND IRON(III) FROM NATURAL-WATER ON A MELAMINE-FORMALDEHYDE RESIN

A combined method for the preconcentration and selective spectrophotom etric determination of both valencies of iron, i.e., Fe(II) and Fe(III ), down to 0.4 mu g l(-1) has been developed. Iron(III) from synthetic and natural water samples has been concentrated on a melamine-formald ehyde resin at pH 5; iron(II) was not retained under identical conditi ons. The oxidized iron was concentrated on a second resin column. The iron in both columns was eluted with 1 M HCl solution and separately a nalyzed by the 1,10-phenanthroline-citrate spectrophotometric method. The effect of pH, adsorption and elution rates, and interferences on t he developed procedure were investigated. Metal ions that can be retai ned by the resin at moderate concentrations, e.g., Al3+, do not cause interference in more dilute solutions encountered in natural water sam ples. At least 160-fold volume enrichment can be easily obtained using an adsorption flowrate of 50 ml min(-1). A hydrothermal water sample was analyzed by the recommended procedure and by a literature method, and the results were statistically compared by t- and F-tests. (C) 199 7 Elsevier Science B.V.