Colorimetric Detection of Heavy Metal Ions Using Superabsorptive Hydrogels and Evaporative Concentration for Water Quality Monitoring

Prevalence of high levels of metal ions in naturaland drinking water is a growing problem to both ecosystems andhuman health. Several methods are broadly used for heavy metalmonitoring in water resources, but most of them are laboratory-based. Here, we describe a method that simplifies the measurementprocess by enabling passive aliquoting and preconcentration ofheavy metals. We use superabsorbent polymer beads that can takeup hundreds of times their volume to aliquot the sample andpreconcentrate the ionic species present in them by 2 orders ofmagnitude. We then use commercially available colorimetric dyesthat are sensitive only at high concentrations to reveal a visiblerange change in the bead color that can be measured opticallyusing a camera. Using this approach, we have detected theconcentration of copper(II) ions in water as low as 5.4 ppb. We demonstrate that this method can also be used for drinking waterand tap water samples to assess concentrations of copper and iron. This solid-state method significantly simplifies the analyticalprocedure and provides extremely low detection levels of heavy metals, eliminating the need for expensive equipment and hencecould be useful in remote settings.