Fast Optical Sensing of Metals: A Case Study of Cu2+ Assessment in Soils

Larisa Lvova,Roberto Paolesse,Federica Mandoj,Elisa Acciari,Giuseppe Pomarico

doi:10.1149/2162-8777/aba0d1

Abstract

In this paper we report an application of a novel porphyrin ligand, Zn(II)TPP-BPI-crown (ZnPC), functionalized with two dibenzo-crown-ether moieties as cation-sensitive ionophore. The test on the optical response of ZnPC ligand inside PVC-based polymeric membranes towards different cations (Na+, K+, Li+, Ca2+, Mg2+, Co2+, Cd2+, Pb2+, Zn2+, Cu2+ and NH4+) were performed. The influence of the lipophilic site functionalization on the ZnPC optode response was investigated. The visibly (naked eye) observed color change of sensing material from green to red demonstrated the suitability of the ZnPC-based optodes to perform fast monitoring of Cu(II) ions in the concentration range between 6.6 × 10−7 and 2.4 × 10−2 mol l−1, with a low detection limit (estimated by s/n = 3 method) of 0.03 mg l−1, which is lower than WHO guideline value of 2 mg l−1 for natural waters. The membranes with the best composition were deposited onto paper support and employed for the express analysis of copper(II) ion in aqueous soil extracts. The results obtained were in a good agreement with a standard ASS method, thus suggesting the utility of developed sensors for aims of express environmental monitoring.

Highlights

Transition and heavy metal ions assessment is a topic of intense research, due to their strong impact on natural processes[1,2]; many of them are essential elements in plants, animals and humans, while others are toxic for environment and living beings.[3,4] Occurring both from anthropological and natural sources, these species are present in soil, water reservoirs and ocean environment,[5,6,7] and through accumulation in plants and animals, enter the human food-chain.[8,9,10]
In the novel ZnPC ionophore the ZnTPP unit is expected to act as an optical signalling unit, while the two crownether moieties will serve as guest-binding site
We first have focused our attention on investigating copper ionZnPC interaction, since ZnPC-based optical sensors may be a promising system for Cu2+ detection

Summary

Introduction

Transition and heavy metal ions assessment is a topic of intense research, due to their strong impact on natural processes[1,2]; many of them are essential elements in plants, animals and humans, while others are toxic for environment and living beings.[3,4] Occurring both from anthropological and natural sources, these species are present in soil, water reservoirs and ocean environment,[5,6,7] and through accumulation in plants and animals, enter the human food-chain.[8,9,10]. Copper amount environmental monitoring is extremely important because it can be a toxic pollutants that lead to different pathologies.[13] According to WHO recommendations, the permitted values for copper are 50–140 mg K−1 g−1 (about 7.8 × 10−4 M in the case of full extraction) and 2 mg l−1 (3.10 × 10−5 M) in soils and natural waters respectively.[13,39] Based on above-reported guideline values, we have tested the UV–vis response of ZnPC ligand (9.4 μM solution in THF) upon addition of Cu2+ ions from 0.01 equiv.

Results

Conclusion