Selective Determination of Phosphate with PhoE Porin-Lecithin Membrane Electrode

Abstract

The presence of phosphate in the environment originating from detergent and fertilizers causes water pollution. The determination of phosphate in water is, therefore, important in environmental analysis. The phosphorus-molybdate blue method can be employed for the determination of phosphate¹, but requires a complicated procedure and is not suitable for on-line measurements. An enzyme sensor based on the inhibition of alkaline phosphatase by phosphate has been developed². However, this sensor requires additional glucose and glucose-6-phosphate. The outer membrane of gram-negative bacteria acts as a molecular sieve with defined exclusion limits. This property results largely from an outer membrane protein, called porin, which forms a large water-filled pore through the hydrophobic core of the outer membrane³. The PhoE porin protein is produced as a major outer membrane protein under condition of phosphate deprivation⁴. The PhoE porin has a specific permeability function in enhancing the uptake of phosphate into the periplasm. In this study, PhoE porin-lecithin membranes were prepared on a basal plane pyrolytic graphite electrode and an anion-selective polymer membrane electrode. The selectivity of the PhoE porin-lecithin membrane was studied by applying cyclic voltammetry to the porin graphite electrode. The PhoE porin-lecithin membrane electrodes were used for the selective determination of phosphate and phosphocompound.