No abstract

The development of advanced analytical methods for trace amounts of selenium (Se) ions in wastewater become a matter of great importance in avoiding biological and environmental burdens due to Se pollution. In this study, a simple microanalytical methodology was developed, enabling the rapid and highly efficient extraction, real-time monitoring in situ, and extraction kinetic analysis of Se­(IV) ions. The microscale extraction and analysis was verified by means of fluorescence intensity changes of fluorogenic complex 4,5-benzopiazselenol (BPS) consisting of the coordination of Se­(IV) with 2,3-diaminonaphthalene (DAN). After the optimal BPS formation conditions, including pH, temperature, and Se­(IV)/DAN concentration ratio, were examined, the microscale extraction of BPS was carried out under aqueous and organic two-phase parallel flow regimes in Y-shaped microchannels. The fluorescence intensity profiles of BPS in the organic phase were scanned in situ along the flow direction in the microchannel by a fluorescence microscope. The residence time dependence of the BPS concentrations could be precisely detected in real time. The results show that the developed microsystem has not only a detection limit of a submicromolar level for Se­(IV), which is sufficiently lower than the permeable limit concentration of selenium in wastewater, but also a large apparent extraction rate constant of approximately 0.3 s–1 and a short time to reach equilibrium of approximately 20 s, compared to those of bulk-scale extraction. This would indicate a valuable technique for elucidating microfluidic extraction kinetics and for applying real-time, environmentally friendly monitoring of toxic selenium ions.

We present a resin-packed microchannel that can reduce the radiation exposure risk and secondary radioactive wastes during uranium (U) separation by downscaling the separation using a microchip. Two types of microchips were designed to densely pack the microchannels with resins. The microchannels had almost the same cross-sectional area but different outer circumferences. A satisfactory separation performance could be obtained by arranging more than ca. 10 resins along the depth and width of the microchannels. The resin-packed microchannel is an effective separation technique for determining U concentration via inductively coupled plasma mass spectrometry owing to its ability to avoid the contamination of the equipment by cesium and reduce the matrix effect. The size of the separation site was scaled down to <1/5000 compared to commonly used counterparts. The radiation exposure risk and secondary radioactive wastes can be reduced by 10-and 800-fold, respectively, using the resin-packed microchannel.