关键词: 化学成像技术, 化学异质性, 原位被动采样, 显色反应, 铁-磷-硫

Abstract: The widespread micro-interfaces in the environment are the gateways of matter cycling and energy exchange, significantly affecting the transfer processes and ecological effects of elements (such as S, Fe, and P). The distribution of elements at the micro-interfaces is highly heterogeneous both spatially and temporally. It is therefore necessary to develop and apply in situ and high-resolution characterization techniques. Diffusive gradient in thin-films (DGT) and diffusive equilibrium in thin-films (DET) techniques are reliable tools for revealing the distribution patterns and biochemical processes of elements and chemicals at the micro-interfaces. Increasing experimental evidences in the last three decades show that the highresolution concentration profiles and bioavailability information of elements and the dynamic process of coupling among multiple elements can be obtained through combination of DGT/DET passive sampling due to diffusion and binding/equilibrium with subsequent high-resolution chemical analysis methods, such as conventional chemical analysis after one-dimensional/two-dimensional gel cutting, laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS), and computer/colorimetric density imaging metrology (CID). Among the above three subsequent analysis methods, CID is the most convenient, rapid and cheap one. The spatial resolution of CID is comparable to that of LA-ICP-MS analysis, reaching tens to hundreds of microns at vertical and horizontal directions. Therefore, there is great potential for popularization and application of CID as a tool for quantification of chemical’s mass captured by DGT/DET. Based on an overview of DGT/DET and CID techniques, we summarized the general guidelines of technology combination, and introduced research and development progresses by category in accordance with the guidelines. In category one, color develops on the functionalized gel of DGT/DET instantaneously as insitu sampling proceeds, where a typical case is sulfide determination by DGT passive sampling with a pale AgI binding gel and CID quantification of the black Ag₂S products on the resulting gel. In category two, staining is needed after insitu sampling to initiate colorimetric reaction on the resulting gel, such as determination of phosphate and chromate by DGT sampling with a zirconium oxide binding gel and CID analysis, and determination of ferrous and alkalinity by combining DET and CID methods. Finally, the development and application trends of technology combination of DGT/DET and CID are prospected.

Key words: chemical imaging technique, chemical heterogeneity, in-situ passive sampling, colorimetric reaction, Fe-P-S.