An In Situ Analyzer for Two-Dimensional Fe(II) Distribution in Sediment Pore Water Based on Ferrozine Coloration and Computer Imaging Densitometry

A novel integrated analyzer was developed for the in situ determination of two-dimensional (2D) dissolved Fe(II) distributions in sediment pore water. The analyzer utilized gel enrichment and optical imaging techniques. An image probe mainly consisting of a gel holder and portable document scanner was designed to be inserted into sediment. The gel holder exposed to the sediment was made to hold a polyacrylamide gel strip (diffusive gel) and polyacrylamide gel strip impregnated with C18 and coated with ferrozine (concentrating gel). The concentrating gel strip could accumulate the dissolved Fe(II) in pore water and produce a magenta-colored Fe(II)-ferrozine compound on the gel strip in two dimensions. The portable document scanner sealed in a transparent box and stuck onto the back of the gel holder could record gel images from the back of the concentrating gel strip. Gel images with grayscale intensities were acquired and analyzed using ImageJ software, and Fe(II) concentration was determined based on a deployment time related calibration curve established in the laboratory. The measurement accuracy and precision were investigated. The quantitative range reached up to 200 μmol L -1 . The method and analyzer exhibit distinct characteristics of in situ enrichment and measurement; they were successfully applied to determine the 2D Fe(II) distribution in lake and marine sediment pore waters.