LAUSR

A simple one-step assay for the trace determination of Co2+ was developed on filter paper modified with solubilized polymethyl methacrylate (PMMA) and arrays of 3-[(2-mercapto-vinyl)-hydrazono]-1,3-dihydro-indol-2-one (MHDI) reagent. The paper modified with a thin film of PMMA transformed its surface wettability from hydrophilic (θ ∼ 0°) to hydrophobic (θ ∼ 92°). Goniometry and scanning electron microscopy confirmed modification of cellulose fibers. On a low-wetting surface, analyte droplet could be confined onto the MHDI spot, allowing visual detection of 1 μM concentration of Co2+ within 10 min. The limit of detection (LOD) was three orders of magnitude superior to that of a similar assay executed on unmodified paper. The established method is the first of its kind for Co2+ determination with a wide linear dynamic range (101 to 104 μM) coupled with good reproducibility, ruggedness and point-of-use testing. Due to high selectivity towards Co2+ and minimum interference from diverse ions, the developed probe was successfully applied for the trace analysis of Co2+ in tap and industrial wastewater samples. The established method was successfully validated using ICP-OES analysis. The proposed assay could be compared favorably to most of the reported methods for Co2+ determination in terms of ease, cost-effectiveness and analysis time. The recoveries from the recognized method were >90%, confirming its potential use for sensing Co2+.