Development of a dye nanoparticle-loaded test strip for the Zn(II) determination in metal plating wastes

Zincon/Latex-NR₃⁺ nanocomposite-loaded dye nanoparticle coated test strip (Zincon/Latex-NR₃⁺ DNTS) was fabricated to detect Zn(II) in plating wastewater by a unique color change from red-purple to deep blue and evaluated its detection performance in actual plating samples. The 5 × 5 mm square-cut DNTS attached sticks were immersed into 10 mL aliquots of aqueous solutions containing Zn(II) ion and 0.01 M TAPS buffer at pH 8.4 with stirring at 250 rpm for 60 min. The calibration curve for Zn(II) was prepared based on the integrated area intensity of reflectance by TLC at 620 nm with the 3σ detection limit was 48.61 ppb, and the quantitative range was approximately up to 1000 ppb. Although Cu(II), Mn(II), Ni(II), and Co(II) showed competitive interference due to complex formation with Zincon, a mixture of masking reagent including thiourea, 2-aminoethanthiol, and o-phenanthroline was effective in removing the contamination. To eliminate Cr(III) interference based on the incorporation of Zn(II) into Cr(III) hydrolyzed polymer, adding KBrO₃ and H₂SO₄ under boiling for several minutes was required. With appropriate pretreatment, all results of actual plating water samples by Zincon/LatexNR₃⁺ DNTS were close to those of ICP-OES.