Trace analysis on chromium (VI) in water by pre-concentration using a superhydrophobic surface and rapid sensing...

Heavy metal ions in water resources present great threats to human health. Chromium (Cr), as the frequently used heavy metal in industrial processes and everyday life, requires a low-cost, fast and effective means to determine its concentration, especially in drinking water. Conventional colorimetric paper-based analytical devices (PADs), due to the limited sensitivity, are unable to quantify the most harmful heavy metal ions to the drinking water standard. In this work, we present a method of using a superhydrophobic (SH) paper to concentrate Cr⁶⁺ from solutions of very low concentration to obtain the precipitated Cr⁶⁺ salt particulates. A known volume of Cr⁶⁺-containing solution was concentrated to "a spot" on the SH paper through drying, so that trace amount of Cr⁶⁺ can be quantified via the application of a specifically-designed chemical-responsive adhesive tape (CAT) sensor, loaded with Cr⁶⁺- specific indicator, on to the concentrated Cr⁶⁺ spot. The detection limit of the SH-CAT method for Cr⁶⁺ is 0.05 mg/L, which is the permitted maximum concentration in drinking water and is significantly lower than that of conventional PADs. The interference and the accuracy studies also show the reliability of this method for measuring trace amounts of analytes.