Use of a Polymer Inclusion Membrane and a Chelating Resin for the Flow-Based Sequential Determination of Copper(II) and Zinc(II) in Natural Waters and Soil Leachates

A bi-parametric sequential injection method for the determination of copper(II) and zinc(II) when present together in aqueous samples was developed. This was achieved by using a non-specific colorimetric reagent (4-(2-pyridylazo)resorcinol, PAR) together with two ion-exchange polymeric materials to discriminate between the two metal ions. A polymer inclusion membrane (PIM) and a chelating resin (Chelex 100) were the chosen materials to retain zinc(II) and copper(II), respectively. The influence of the flow system parameters, such as composition of the reagent solutions, flow rates and standard/sample volume, on the method sensitivity were studied. The interference of several common metal ions was assessed, and no significant interferences were observed (<10% signal deviation). The limits of detection were 3.1 and 5.6 µg L⁻¹ for copper(II) and zinc(II), respectively; the dynamic working range was from 10 to 40 µg L⁻¹ for both analytes. The newly developed sequential injection analysis (SIA) system was applied to natural waters and soil leachates, and the results were in agreement with those obtained with the reference procedure.

Molar absorption coefficients and stability constants of Zincon metal complexes for determination of metal ions and bioinorganic applications

Zincon (ZI) is one of the most common chromophoric chelating probes for the determination of Zn²⁺ and Cu²⁺ ions. It is also known to bind other metal ions. However, literature data on its binding properties and molar absorption coefficients are rather poor, varying among publications or determined only in certain conditions. There are no systematic studies on Zn²⁺ and Cu²⁺ affinities towards ZI performed under various conditions. However, this widely commercially available and inexpensive agent is frequently the first choice probe for the measurement of metal binding and release as well as determination of affinity constants of other ligands/macromolecules of interest. Here, we establish the spectral properties and the stability of ZI and its complexes with Zn²⁺, Cu²⁺, Cd²⁺, Hg²⁺, Co²⁺, Ni²⁺ and Pb²⁺ at multiple pH values from 6 to 9.9. The obtained results show that in water solution the MZI complex is predominant, but in the case of Co²⁺ and Ni²⁺, M(ZI)₂ complexes are also formed. The molar absorption coefficient at 618 nm for ZnZI and 599nm for CuZI complexes at pH7.4 in buffered (I=0.1M) water solutions are 24,200 and 26,100M^-1cm^-1, respectively. Dissociation constants of those complexes are 2.09×10^-6 and 4.68×10^-17M. We also characterized the metal-assisted Zincon decomposition. Our results provide new and reassessed optical and stability data that are applicable to a wide range of chemical and bioinorganic applications including metal ion detection, and quantification and affinity studies of ligands of interest.

SYNOPSIS

Accurate values of molar absorption coefficients of Zincon complex with Zn²⁺, Cd²⁺, Hg²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Pb²⁺ for rapid metal ion quantification are provided. Zincon stability constants with Zn²⁺ and Cu²⁺ in a wide pH range were determined.