Abstract
In order to evaluate the applicability of sodium fluorescein as geothermal tracer, in addition to the effect of pH on the fluorescence intensity of sodium fluorescein, the time dependence and the effects of dissolved ions on fluorescence intensity were examined. The fluorescence intensity decreased with decreasing pH when the pH of samples was lower than 9. On the other hand, the intensity was showed stable value when the pH was higher than 9. Therefore, for the samples without dissolved particular chemicals, the fluorescein concentration can be certainly measured when the pH of samples is adjusted to over 9 before measured using a fluorescence spectrophotometer. The fluorescein in the transparent and the brown glass bottles were easily decomposed under lights of . fluorescent lamps. On the other hand, the fluorescein in the bottle covered with aluminum foil was hardly decomposed during 1 month. As a result of examining the effects of dissolved ions on the fluorescence intensity, the effects of potassium, calcium, chloride, sulfuric acid or carbonate ion hardly could be observed. On aluminum ion, it was proven that the fluorescence intensity was not almost affected in the aluminum ion concentration of the degree that is also included for general geothermal brine (about 1 mg/l). Though the magnesium ion affects fluorescence intensity, adjusting pH over 12 could ease the effect. As the ferrous ion concentration is high, the accurate measurement becomes very much the difficulty since the fluorescence intensity seems to lower by the adsorption of the fluorescein on hydroxide as similar form of colloidal.Keywords : sodium fluorescein, fluorescent tracer, fluorescence intensity, peak wavelength, pH effect, salt effect
