Experimental study on the interference of fluorescent tracer

Uranine, Rhodamine and Tinopal are three common tracers used in groundwater tracer tests. As the emission wavelengths of these tracers overlap with each other, interference would occur when more than two kinds of tracers exist in groundwater, resulting in errors in tracer concentrations detected by fluorometer, and further leading to misjudgment of hydrogeological conditions and deviations in parameter calculation. Therefore, in multiple tracer tests, how to select tracers and how to eliminate the interference between tracers are important research issues to improve the application effects of tracer test, such as correctly understanding the hydrogeological conditions and accurately obtaining parameters. This work conducted a number of experiments to investigate the interference relationship among Uranine, Rhodamine and Tinopal in pure water under dark environments. During the experiments, only one kind of tracer was added into a self-designed flow circulation system to control the tracer concentrations in water, meanwhile changes of concentrations of other two kinds of tracers were also detected by fluorometer (GGUN-FL30). Firstly, the results indicate that Uranine has the best performance of anti-interference in laboratory systems, followed by Rhodamine, and Tinopal is most easily interfered by other tracers producing the false impression on increasing detected concentration which obeys a linear law. Moreover, when Rhodamine is used as a tracer, the concentration increment of Uranine and Tinopal changes linearly following the respective equations， ΔCU=0.052CR and ΔCT=0.012CR. When Uranine is used, the concentration increments of Rhodamine and Tinopal obey equations， ΔCR=0.507CU and ΔCT=0.323CU, respectively.This work also analyzed a field binary-tracer test data according to the above laws and then obtained more reasonable test results. The binary-tracer test was conducted in the Dishuiyan karst water system of the Houjia river basin in Xianfeng county, Enshi Prefecture, Hubei Province. During the test, Uranine and Tinopal were respectively put into ponors of two karst depressions at upstream, then both the tracers were detected by the fluorometer (GGUN-FL30) at the outlet of the Dishuiyan underground river. The phenomenon that double peaks appeared in the measured concentration duration curve of Tinopal is hard to explained from the karst development conditions, which may be caused by the interference of Uranine. Thus, the test results were modified by the linear interference law between Uranine and Tinopal obtained from aforementioned laboratory experiments, and then a single peak curve of Tinopal concentration was obtained. At last, it is considered that the development characteristics of karst pipelines analyzed by modified results are more reasonable, and the groundwater velocities calculated are more accurate.The laboratory and field experiments aforementioned suggest Rhodamine should be used together with Tinopal as tracers for field binary-tracer tests, which may produce less interference errors, or to use the linear equations proposed by indoor interference experiments among the tracers to calibrate the detected concentrations.