Study on the stability of colored fluorescent tracers in highly sulfated reservoir waters

Abstract

The article presents the issues related to the determination of colored fluorescent tracers such as fluorescein, eosin yellowish, rhodamine B and uranine in reservoir waters by spectrophotometric method. For this purpose, the influence of the pH of the solution on the absorption spectra of the tested tracers was checked. Test results show that fluorescein, rhodamine B and uranine are sensitive to changes in the buffer pH, therefore it is advisable to use stable tracer solutions as well as to control and possibly correct pH in further tests. As part of the study, calibration curves of fluorescein, eosin yellowish, rhodamine B and uranine in distilled water, reservoir water A4 and highly sulfated reservoir waters A5 and A6 were plotted and the analytical methods were validated. Analytical validation included determination of linearity, standard deviation and relative standard deviation of the tested tracers solutions. High values of the regression parameters (0.9927–0.9998) of the analyzed tracers prove a good linear fit, while low values of standard deviation and relative standard deviation prove its repeatability and precision. Particular attention was paid to testing the stability of colored fluorescent tracers in highly sulfated reservoir waters. For this purpose, solutions of the tested tracers were prepared at concentrations of 10 mg/dm3 in distilled water, A4 reservoir water and highly sulfated A5 and A6 reservoir waters. Measurements of the tested tracers in the prepared solutions were performed every 2 days over the period of 1 month. The test results show that fluorescein, eosin yellowish, rhodamine B and uranine solutions are stable in the distilled water and A4 reservoir water, while they degrade in the A5 and A6 reservoir waters. Fluorescein and uranine turned out to be the most sensitive, as they degraded completely in the A6 reservoir water after 20 (fluorescein) and 22 (uranine) days. Yellowish eosin and rhodamine B turned out to be slightly more stable in highly sulfated reservoir waters, as they degraded completely in the A6 reservoir water after 24 days.