NOVEL DYE-SOLVENT SOLUTIONS FOR THE SIMULTANEOUS DETECTION OF OXYGEN AND CARBON-DIOXIDE

The effects of the compositions of N,N-dimethyl-p-toluidine/N,N-dimethylformamide (DMT/DMF) solvent mixtures, the types of bases, the initial base concentrations, and the water content on the performance of alkaline fluorescein (FL)-DMT/DMF (dye-solvent) solutions in determining oxygen (O-2) and carbon dioxide (CO2) have been investigated, Increased [O-2] causes the absorbance of dye-solvent solutions at 400 nm to increase because of a contact charge transfer existing between DMT and O-2 molecules, and increased [CO2] produces a nonlinear decrease in absorbance at 520 Mn as the color of FL changes from its orange dianion (FL(2-)) to the colorless, neutral, lactonic forms, The sensitivity to O-2 can be enhanced by increasing [DMT] in the DMT/DMF solvent mixture, A linear equation (i.e., log(A(o) - A)/A = 2 beta log [CO2] + log(alpha(2)/k), where A(o) and A are the absorbances of dye-solvent solutions with nitrogen and CO2 standards passing through, respectively, alpha and beta are constants, and K is the dissociation constant for FL) is derived to relate the change of absorbance and applied [CO2], The sensitivity of dye-solvent solutions to O-2 is independent of the types of bases, but the sensitivity to CO2 is not. Increased base concentration causes a change in the sensitivity to CO2 but has mo effect on O-2, The higher water concentration in dye-solvent solutions has two effects, First, dye-solvent solutions are more sensitive to CO2. Second, there is a hypsochromic shift of FL(2-) ions in DMT/DMF solvent mixture, A fiber-optic detecting system based on a solution of 10 mu M FL and 336 mu M tetrabutylammonium hydroxide in 1:1 (v/v) DMT/DMF has been developed for the determination of O-2 and CO2, Their responses are reversible and independent. This solution can be used for future development of a single fiber-optic-based O-2/CO2 sensor.