Low-Range Detection of the Phosphate Group by a Molecularly Imprinted Polymer-Modified Carbon Paste Electrode

A series of size-selective polymeric sensors for the phosphate group was designed and synthesized using the molecularly imprinted polymer (MIP) technique based on the noncovalent interaction of the template dipentyl phosphate with the functional monomer methacrylic acid. Very low-range specific electrochemical detection of phosphate molecules was performed by square wave voltammetry with a modified carbon paste electrode (CPE). Calibration curves were obtained within the linear range of 20-300 nmol L^-1 for all modified CPEs, with the lowest detection limit determined as 8.82 nmol L^-1. Potential inorganic interferents, such as carbonate, nitrate and sulfate ions, were investigated and no signal disturbance was observed for relative concentrations 100 times higher than the phosphate concentration. Furthermore, the modified electrodes also showed good selectivity for phosphate molecules containing alkyl chains up to five carbon atoms. The selectivity study confirmed that imprinted sites were successfully synthesized and only structures that are the same size or smaller than those of the template molecule are selected by maximizing intermolecular interactions at the MIP binding site. Moreover, the sensors presented good stability, maintaining the same degree of selectivity for several months. These sensors were also applied in the determination of phosphate in a cola soft drink.