A high-resolution dialysis technique for rapid determination of dissolved reactive phosphate and ferrous iron in pore water of sediments

Characterization of pore water chemistry necessitates measurements of the chemical components at a high spatial resolution due to the heterogeneous nature of sediments. In this study, a novel high-resolution dialysis technique was developed for rapid sampling of dissolved reactive phosphate (DRP) and ferrous iron (Fe) in pore water at a vertical resolution of 2 mm. This technique employed a mini dialysis device (peeper) with a deployment time of 2 days in sediments for equilibration. Operational procedures following retrieval of the peeper include in situ freezing of the pore water samples through spraying commercial carbon dioxide snow, frozen storage of the pore water samples, and quick analysis of chemicals in pore water samples using 384-well microplate photometric methods. The sample consumption for each parameter can be minimized to 6 μL, which allowed simultaneous determination of DRP and ferrous iron in a peeper device. Laboratory tests showed that the technique was robust enough for the in situ measurements. Field deployment was subsequently performed in three sites of a shallow, eutrophic bay in Lake Taihu of China. Simultaneous determination of DRP and ferrous Fe in all the sites demonstrated a similar behavior of both chemicals in the pore water profiles, verifying the control of P mobilization by Fe in sediments.

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► A dialysis technique was developed by employing a mini peeper to sample pore waters.
► It had a spatial resolution of 2 mm and required a equilibration time of 2 days in sediments.
► Simultaneous measurements of DRP and ferrous iron in pore waters can be performed using it.
► Their coherent behaviors in Lake Taihu supported the control of P mobilization by Fe in sediments.