Varnish polish functionalized paper as a new solid platform for colorimetric determination of copper (II) in water

In the current strategy, a highly sensitive and fast one-step colorimetric assay for trace determination of Cu2+ in water is presented. The planned assay was based upon the use of varnish polish-modified filter paper printed with 2-[5-(2-hydroxy-5-sulfophenyl)-3-phenyl-1-formazyl] benzoic acid monosodium salt, commercially named zincon. Under optimal conditions, the designed assay readily recognised the formation of blue–purple-coloured Cu–ZI chelate in less than 10 min. The proposed probe was able to detect Cu2+ in the concentration range from 0.04 to 10 μg/mL (6.34 × 10−1 to 1.59 × 103µM), with low limit of detection (LOD) of 0.01 μg/mL (1.59 × 10−1 µM). The LOD was 10-fold lower than the allowable level for Cu2+ in drinking water set by WHO legislation. The assay was applied for Cu2+determination in water with acceptable recoveries (89.6–102.1%) and precision (&lt;3%). Therefore, the proposed sensing assay might be considered as a potential rapid and low-cost candidate for total determination and speciation of Cu2+in water samples.</p