Development of a microfluidic paper analytical device for the measurement of iodide in briny wastewater

Flowback water is a major byproduct of hydraulic fracturing for oil and gas production and is undrinkable because of contamination from radioactive species, trace organic species and high concentrations of ions. Therefore it must be captured and contained or treated. Once contained, often in large storage tanks or lined pits, it is possible for these sources to leak into nearby ground or surface water. While iodide itself is not toxic, iodide is a good "tracer" ion that, when detected at high concentrations, could be indicative of contamination from flowback water. This paper describes an inexpensive microfluidic paper-based analytical device (µPAD) to detect iodide by reacting starch and sulfuric acid with contaminated water under UV light to induce a colorimetric reaction. This method uses smartphone image analysis for quantitative detection in the range of 7.6-34.4 ppm iodide with high linearity and sensitivity, and UV-vis analysis in the range of 11.5-45.9 ppm iodide. Validation using simulated flowback water confirms intra- and inter-day reproducibility with 1.2% error and 7.2% precision.