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

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.