Biological and chemical comparisons of methods for removing copper from macronutrient solutions used for plant growth investigations

Summary

Two efficient procedures for the removal of copper contamination from molar stock solutions of plant macronutrients, one using the chelating ionexchange resin Chelex 100 and the other using ammonium pyrrolidinedithiocarbamate as a complexing agent followed by solvent extraction with redistilled chloroform have been described and compared biologically and chemically with two established methods of purification, the CaCO₃/PO₄ method of Stout and Arnon¹⁸ and the Al₂O₃ method of Donaldet al.⁶ The legumeMedicago truncatula was used for the biological test where growth responses and copper uptake values were recorded, statistically evaluated and used as a basis for comparison, while chemical tests were used for total heavy metals and residual copper in the individual molar stock solutions.

Results showed the introduced procedures, provided that free iminodiacetic acid was removed from the chelating ion-exchange resin prior to nutrient purification, to be desirable additions to the methods already accepted for work of this type while the method of Donaldet al. ⁶ was least effective. In addition the introduced procedures had distinct advantages over the established methods in the minimisation of heavy metal recontamination and in the apparatus required.

All methods tested produced more severe symptoms of copper deficiency in the test species than were obtained from control solutions prepared from AR. Salts.