Integrating chemical imaging of cationic trace metal solutes and pH into a single hydrogel layer

Christoph Hoefer, Jakob Santner, Sergey M. Borisov, Walter W. Wenzel, Markus Puschenreiter

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Gel-based, two-dimensional (2D) chemical imaging techniques are versatile methods for investigating biogeochemically active environments at high spatial resolution (sub-mm). State-of-the-art solute imaging techniques, such as diffusive gradients in thin films (DGT) and planar optodes (PO), employ passive solute sampling or sensing. Combining these methods will provide powerful tools for studying the biogeochemistry of biological niches in soils and sediments. In this study we aimed at developing a combined single-layer gel for direct pH imaging using PO and sampling of anionic and cationic solutes by DGT, with subsequent analysis of the bound solutes by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We tested three ultra-thin (<100 μm) polyurethane-based gels, incorporating anion and cation binding materials and the fluorescent pH indicator DCIFODA (2′,7′-dichloro-5(6)-N-octadecyl-carboxamidofluorescein). Results showed that PO-based pH sensing using DCIFODA was impossible in the presence of the anion binding materials due to interferences with DCIFODA protonation. One gel, containing only a cation binding material and DCIFODA, was fully characterized and showed similar performance characteristics as comparable DGT-only gels (applicable pH range: pH 5–8, applicable ionic strength range: 1–20 mmol L-1, cation binding capacity ∼24 μg cm−2). The dynamic range for PO-based pH mapping was between pH 5.5 and 7.5 with t90 response time of ∼60 min. In a case study we demonstrated the gel's suitability for multi-analyte solute imaging and mapped pH gradients and concurrent metal solubility patterns in the rhizosphere of Salix smithiana. pH decreases in the rooted soil were co-localized with elevated solute fluxes of Al3+, Co2+, Cu2+, Fe, Mn2+, Ni2+ and Pb2+, indicating pH-induced metal solubilisation.

Original languageEnglish
Pages (from-to)88-97
Number of pages10
JournalAnalytica Chimica Acta
Volume950
DOIs
Publication statusPublished - 15 Jan 2017

Fingerprint

Hydrogel
trace metal
solute
gel
Gels
Metals
Imaging techniques
Cations
cation
Thin films
Anions
anion
Biogeochemistry
Salix
Sampling
Soils
Inductively coupled plasma mass spectrometry
Polyurethanes
Protonation
metal

Keywords

  • Chemical imaging
  • Diffusive gradients in thin films
  • Fluorescent sensing
  • Laser ablation inductively coupled plasma mass spectrometry
  • Planar optode
  • Rhizosphere

ASJC Scopus subject areas

  • Analytical Chemistry
  • Biochemistry
  • Environmental Chemistry
  • Spectroscopy

Cite this

Integrating chemical imaging of cationic trace metal solutes and pH into a single hydrogel layer. / Hoefer, Christoph; Santner, Jakob; Borisov, Sergey M.; Wenzel, Walter W.; Puschenreiter, Markus.

In: Analytica Chimica Acta, Vol. 950, 15.01.2017, p. 88-97.

Research output: Contribution to journalArticleResearchpeer-review

Hoefer, Christoph ; Santner, Jakob ; Borisov, Sergey M. ; Wenzel, Walter W. ; Puschenreiter, Markus. / Integrating chemical imaging of cationic trace metal solutes and pH into a single hydrogel layer. In: Analytica Chimica Acta. 2017 ; Vol. 950. pp. 88-97.
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