Abstract
A novel platform of microfluidic paper-based analytical device (μPAD) with colorimetric acid-base titration for cooking oil quality evaluation was created and oleic acid was selected as a model analyte. Graphene oxide (GO) was used to modify cellulose paper for improved visualization and increased hydrophobicity of the colorimetric sensor. μPAD with colorimetric acid-base titration was prepared by immobilizing phenolphthalein and primary standard of Na2CO3 on GO-modified cellulose paper and applied for oleic acid detection. The neutralization of oleic acid on the cellulose paper was illustrated by color disappearance from pink to colorless. This platform provided a linearity of (0–2% v/v), covering a cut-off oleic acid level (1.0%) for evaluation of cooking oil quality. This device, designed with 3D-μPAD, created the automatic lateral-flow channel for semi-quantitative analysis of cooking oil without instrumental requirement. The content of oleic acid equated to the number of pink-detection area disappearing. Ultimately, this device was successfully applied for cooking oil quality evaluation in real waste cooking oil samples.
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