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

A conductometric enzyme biosensor for determination of formaldehyde in aqueous solutions has been developed using interdigitated thin-film planar electrodes and immobilised alcohol oxidase from Hansenula polymorpha. The biosensor steady-state response was reached after about 1min. Its dynamic range can vary from 0.05 to 500mM formaldehyde and depends on the time of enzymatic membrane cross-linking by glutaraldehyde and on the buffer concentration used. The biosensor developed was not completely specific and selective. It demonstrated no response to primary alcohols and other substrates alone. Unfortunately, the response of this biosensor in a mixture of formaldehyde and methanol was decreased in comparison to the one observed for pure formaldehyde, even if no response was obtained with the interfering specie alone. The operational stability was not <20h and the relative standard deviation appeared to be about 3%. Moreover, the storage stability was more than 1 month.