An integrated centrifugal microfluidic chip for in situ chemical oxygen demand by improving the conventional dichromate method

Abstract

This study proposed automated centrifugal microfluidic chips (CMCs) as advanced Lab-on-a-Chip systems for water quality analysis, taking chemical oxygen demand (COD) as an example. The CMCs minimize reagent use, reduce hazardous waste, and enable precise reaction control through optimized geometric designs by leveraging centrifugal and Euler forces to enhance particle filtration, liquid transfer, and in situ monitoring. Our novel settling chamber isolated large particles in digested samples, improving the efficiency of COD detection. Simulations were conducted to optimize the inclination angle and angular acceleration of the siphon valve, ensuring stable liquid transfer. The system achieved a 6.85 % improvement in COD detection accuracy, an 88 % reduction in sample volume, and a 55 % decrease in analysis time. Precision increased by 64.10 %, and uncertainty was reduced by 47.04 %, maintaining a detection range of 0–150 mgL⁻¹ with a Limit of Detection of 4 mgL⁻¹ and a Limit of Quantification of 12 mgL⁻¹. With a compact, portable design (250 mm × 280 mm × 315 mm, 13 kg) and low power consumption (33.9 W), the device is well-suited for environmental monitoring and remote water quality testing. To ensure coherence with the novel CMC chip, we developed the customized CMC microfluidic equipment in our laboratory. Its adaptability for other difficult water quality parameters, such as total nitrogen or phosphorus, could boost its applications in public health and sustainable water management.