Tracer-grade rhodamine WT: Structure of constituent isomers and their sorption behavior
Tracer-grade rhodamine WT: Structure of constituent isomers and their sorption behavior
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DOI：
10.1021/es010880x
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发表时间：
2001-10-15
影响因子：
11.4
通讯作者：
Francisco, AB
中科院分区：
文献类型：
--
作者：
Vasudevan, D;Fimmen, RL;Francisco, AB
罗丹明WT（RWT）是一种荧光染料，常被用作含水层表征中的保守示踪剂和污染物归宿和迁移的替代或吸附示踪剂。采用RWT的定量示踪被示踪剂级混合物中两种主要荧光成分的存在所混淆。在这里，我们已经证实，这两种成分是RWT的异构体，阐明了它们的分子结构和它们在示踪剂级混合物中的质量分布百分比，并研究了它们在土壤固体上的单独吸附行为。能量最小化的几何结构的Meta异构体表明，它具有更大的潜力（i）从本体溶液的疏水排斥，（ii）静电吸引的固相，和（iii）表面络合与表面结合的Al和Fe离子相比，帕拉异构体。因此，Meta异构体始终在较高程度上吸附到所检查的矿物相上。帕拉异构体有潜力成为一个近保守的示踪剂，和Meta异构体有潜力成为一个非保守的示踪剂。为了便于RWT用作保守示踪剂和比较不同地点的示踪剂试验，我们建议修改RWT生产工艺，以生产100%的帕拉异构体。另外，适当设计的测试与示踪剂级RWT有可能同时估计水力参数和污染物的命运和运输。
Rhodamine WT (RWT), a fluorescent xanthene dye, is often used as a conservative tracer in aquifer characterization and as a surrogate or sorbing tracer for contaminant fate and transport. Quantitative tracing employing RWT is confounded by the presence of two major fluorescent constituents in the tracer-grade mixture. Here, we have confirmed that the two constituents are isomers of RWT, elucidated their molecular structures and their percent mass distribution in the tracer-grade mixture, and examined their individual sorption behavior onto soil solids. The energy-minimized geometry of the meta isomer indicates that it possesses a greater potential for (i) hydrophobic exclusion from bulk solution, (ii) electrostatic attraction to the solid phase, and (iii) surface complexation with surface-bound Al and Fe ions as compared with the para isomer. Hence, the meta isomer consistently sorbs to a higher extent onto the mineral phases examined. The para isomer has the potential to be a nearly conservative tracer, and the meta isomer has the potential to be a nonconservative tracer. To facilitate RWT use as a conservative tracer and comparison of tracer tests at different locations, we recommend modification of the RWT manufacturing process toward production of 100% of the para isomer. Alternatively, appropriately designed tests with tracer-grade RWT have the potential for simultaneous estimation of hydraulic parameters and contaminant fate and transport.