A high performance potentiometric sensor for lactic acid determination based on molecularly imprinted polymer/MWCNTs/PVC nanocomposite film covered carbon rod electrode

Abstract

A novel nano-sized imprinted polymer/multi-walled carbon nanotube (MWCNTs)-based potentiometric sensor is introduced for lactic acid (LA) sensing in dairy products. The imprinted polymer was synthesized using allyl amine (AA) and ethylene glycol dimethacrylate as functional monomer and cross-linker, respectively. It was demonstrated that the amide linkage was created between LA and AA during copolymerization reaction which was finally hydrolyzed when removing template from the synthesized MIP. It was also shown that the MIP cavities, compatible with LA anion, were created during polymerization reaction which influenced the potentiometric response behavior of the MIP-based electrode. This novel potentiometric sensor is a carbon rod electrode, coated with a membrane consisting of the MIP nanoparticles (2.5%), MWCNTs (2%), dibutylphthalate (DBP) (65%), poly-vinyl chloride (PVC) (28.5%) and tetra phenyl phosphonium bromide (TPPB) (2%). The active ion sensed by the electrode is the LA anion formed at elevated pH condition. The sensor exhibited Nernstian slope of 30.3 ± 0.4 mVdecade−1 in the working concentration range of 1.0 × 10−1to 1.0 × 10−6 mol L−1 with detection limit of 7.3 × 10−7 mol L−1. The sensor displayed a stable potential response in the pH range of 5–8 and fast response time of less than 60 s. It exhibited also high selectivity over the interfering species. The proposed sensor was successfully applied for the determination of LA in real samples (milk and yoghurt).