Design of pH microelectrodes based on ETHT 2418 and their application for measurement of pH profile in instant noodles Original Research Article

A new pH selective microelectrode has been developed and tested. The described microelectrode is based on the neutral chromoinophore ETHT 2418 which is incorporated into a liquid membrane of variable composition. The microelectrode is based on an optimized membrane composition and exhibits a linear dynamic response function from pH <1 to 9, a response time <3 s, and resistance of about 35±8 (n=7) GΩ for a tip diameter of about 1 μm. These characters make the electrode suitable for measurements at normal physiological intracellular pH as well as in acidic physiological media. Such electrodes with tip diameters from 0.5 to 5 μm display a sensitivity of 57.5±0.5 mV/pH unit from pH <1 to 9. The discrimination of Na+, K+, Mg2+, and Ca2+ is sufficient for extra- and intracellular measurement of pH at the typical ionic backgrounds encountered. The influence of the composition of the solvent polymeric membrane, the plasticizer, the additives, and the H+-selective carrier on the electrode’s response was studied. The electrode shows a wide dynamic range, high stability and good reproducibility. Finally, pH profiles of a wet instant noodle was revealed for the first time with the presented pH microelectrode. The average pH in the noodle is around 4.14.