Mass Production and Outside Test of Microfluidic Paper Based Analysis Devices for Determining Chromium Ions in Industrial Wastewater

Hexavalent chromium ions in industrial wastewater can bring serious pollution to the environment and a variety of harms to human health. It is necessary to develop a novel technique to determine the heavy ions. In this work, we designed a special machine to enhance the production of microfluidic paper based analysis devices (μPADs, ∼1000 μPADs/h), which could be used to determine the industrial wastewater. We optimized the diphenyl carbamide solution and the volume of liquid to be tested. Finally, we established a fitting curve of the standard Cr concentration and color intensity from the μPADs. We carried out outside experiments in an industrial park, which needed a great amount of stable and repeatable devices for the test. In the concentration range of 250–600 mg/L, 74% of the measurement results had a relative error of less than 20%; in the concentration range of 50–250 mg/L, 72% of the measurement results had a relative error of less than 20%. Our results demonstrated that the accuracy and repeatability satisfied the requirements for wastewater detection, which could be extended to industrial application.