Highly selective simultaneous determination of Cu(ii), Co(ii), Ni(ii), Hg(ii), and Mn(ii) in water samples using microfluidic paper-based analytical devices

Abstract

A new paper-based analytical device design was fabricated by a wax printing method for simultaneous determination of Cu(II), Co(II), Ni(II), Hg(II), and Mn(II). Colorimetry was used to quantify these heavy metal ions using bathocuproine (Bc), dimethylglyoxime (DMG), dithizone (DTZ), and 4-(2-pyridylazo) resorcinol (PAR) as complexing agents. The affinity of complexing agents to heavy metal ions is dependent on the formation constant (K_f). To enhance the selectivity for heavy metal ion determination, the new device was designed with two pretreatment zones, where masking agents remove the interfering ions. It was found that two pretreatment zones worked better than a single pretreatment zone at removing interferences. The reaction time, sample and complexing agent volumes, and complexing agent concentrations were optimized. The analytical results were achieved with the lowest detectable concentrations of 0.32, 0.59, 5.87, 0.20, and 0.11 mg L⁻¹ for Cu(II), Co(II), Ni(II), Hg(II), and Mn(II), respectively. The linear ranges were found to be 0.32–63.55 mg L⁻¹ (Cu(II)), 0.59–4.71 mg L⁻¹ (Co(II)), 5.87–352.16 mg L⁻¹ (Ni(II)), 0.20–12.04 mg L⁻¹ (Hg(II)), and 0.11–0.55 mg L⁻¹ (Mn(II)). The lowest detectable concentration and linearity for the five metal ions allow the application of this device for the determination of heavy metal ions in various water samples. The sensor showed high selectivity and efficiency for simultaneous determination of Cu(II), Co(II), Ni(II), Hg(II), and Mn(II) in drinking, tap, and pond water samples on a single device and detection with the naked eye. The results illustrated that the proposed sensor showed good accuracy and precision agreement with the standard ICP-OES method.