Effect of bead size in Chelex-based resin hydrogels in DGT on detection of Fe redox species by beam deflection spectroscopy

Hanna Budasheva, Arne Bratkic, Dorota Korte, Mladen Franko

Research output: Unpublished contribution to conferencePoster

Abstract

Background: Iron (Fe) redox speciation in the environments with transitional reductive-oxidative
gradients is the specific “fingerprint” - marker of deposition processes, redox conditions and microbial
metabolism. These processes occur at the submillimetre scale hence the 2-dimensional imaging
of their distribution presents a particular analytical challenge. Diffusive Gradients in Thin-films
(DGT) technique may be used for such imaging using Chelex-based resin gels, as they bind both
Fe redox species. The species in the resins can be detected using photothermal Beam Deflection
Spectroscopy (BDS) as an appropriate highly sensitive method of analysis.
Materials and methods: Combined DGT-BDS enables to achieve 2D information about distribution
of Fe2+ and the total Fe content in the resin hydrogels. However, the maximum spatial resolution
and limit of detection (LOD) of the BDS is controlled by the size of the beads and their density in
the gel. We have investigated the effect of the bead size using two different resins. The typical Chelex-
100 resin (bead size 100 μm) was compared to suspended particulate reagent-iminodiacetate
(SPR-IDA, bead size 0.2 μm) by using BDS as detection method. The results were compared to those
received by UV-Vis spectrometry in the concentration range 0-1000 nmolL-1.
Results: LODs achieved by BDS are 82 nmolL-1 and 39 nmolL-1 for standard Chelex-100 and for SPRIDA,
respectively. By UV-Vis the achieved LODs are 406 nmolL-1 and 169 nmolL-1, respectively. The
maximum spatial resolution was defined by the BDS laser beam width for SPR-IDA gels, showing
that the space between the beads is less than laser beam width. It appears that Chelex-100 beads
distribution in not uniform, even in resin-saturated gels, which interfered with BDS detection.
Conclusions: More than 2 times difference in the values of LODs in both cases confirms that the
smaller size of the resin beads improved BDS detection of Fe redox species. The analysis was faster,
repeatable and more accurate, resulting in lower LOD. This improvement makes the DGT-BDS
technique very promising for the investigation of 2D trace metal distribution and mobilization in
environments with redox gradients at micrometer scales.
Original languageEnglish
Publication statusPublished - 18 Sep 2019
EventDGT Conference 2019 - University of Natural Resources and Life Sciences, Vienna, Austria
Duration: 18 Sep 201920 Sep 2019
https://dgt2019.boku.ac.at/

Conference

ConferenceDGT Conference 2019
Country/TerritoryAustria
CityVienna
Period18/09/1920/09/19
Internet address

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