Determination of zinc in plants by flow injection spectrophotometry with ion-exchange separation

Abstract

A flow injection system is proposed for the spectrophotometric determination of zinc in plants. Ashed samples dissolved in 2.0 M hydrochloric acid are injected into a slightly acidic sodium chloride carrier stream flowing through an anion-exchange resin (Dowex 1-X8, 100–200 mesh) where zinc chloro complexes are retained. Elution is accomplished with dilute sodium hydroxide solution and on-line measurement is carried out after addition of zincon. Schlieren noise is overcome by using dual-wavelength spectrophotometry. Reagent constitution, chloro-complexation conditions, resin operation, system dimensions, interferences and commutating times were investigated. The proposed system handles 45 samples per hour with zinc contents in the range 0.00–2.00 mg l^–1. The results are precise (relative standard deviation usually <0.02) and in agreement with data obtained by atomic absorption spectrometry.