Multifactorial analysis of ion concentration polarization for microfluidic preconcentrating applications using response surface method

Abstract

Ion concentration polarization (ICP) in a microfluidic device requires a precise balance of forces on charged molecules to achieve high concentrating efficiency. It is, thus, of considerable interest to study the impact of all governing parameters on ICP performance. Experimental study of the ICP multifactorial phenomenon seems impractical and costly. We report a systematic approach to understand the impacts of governing parameters on the ICP phenomenon using a robust numerical model established in COMSOL Multiphysics®. We varied the buffer concentration, applied voltage, and microchannel length to study their impacts on the ICP phenomenon. Then, we developed a statistical model via the response surface method (RSM) for the numerical results to study the direct and interactive effects of the mentioned parameters on ICP optimization. It was found that the buffer concentration (Cbuffer) plays a key role in the enrichment factor (EF); however, simultaneous impacts of the applied voltage and channel length must be considered as well to enhance EF. For low buffer concentrations, Cbuffer < 0.1 mM, the ionic conductivity was found to be independent of Cbuffer, while for high buffer concentrations, Cbuffer > 1 mM, the ionic conductivity was directly linked to Cbuffer. In addition, the RSM-based model prediction for a certain buffer concentration (∼1 mM) highlighted that an electric field of 20 V/cm–30 V/cm is suitable for the initial design of experiments in ICP microdevices.