Spectroscopic Properties of Methylene Blue Dispersed in Paper and Its Application for Oxygen Indicators

Abstract

In order to apply methylene blue (MB) dispersed in paper as oxygen indicators, reflectance spectra were studied for MB dispersed in papers. From the spectral characteristics of the papers dipped in neutral MB solutions, an increase in the monomeric MB in comparison with dimeric MB was observed during the drying process. The increase in the monomeric MB was attributed to the adsorption of MB to the pore surfaces of cellulose during diffusion and drying of MB solutions. The N-demethylation of MB in basic solutions occurred by the effect of hydroxide ions and MB changed to azure C after about 1 hour. On the other hand, the N-demethylation reaction in the papers dipped in basic MB solutions proceeded more slowly, resulting in the formation of azure C after about a month. Oxygen indicators were prepared by dipping papers in solutions containing MB, glucose, and sodium hydroxide. The blue color of oxygen indicators due to MB disappeared in deoxygenated condition. When the deoxygenated condition was broken after 103 days, the sample revealed a blue color again after 5 min and the same spectrum as that of MB. It was considered that the N-demethylation reaction of MB was suppressed in a leucomethyleneblue structure.