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Ultratrace Metal Speciation Analysis by Coupling of Sector-Field ICP-MS to High-Resolution Size Exclusion and Reversed-Phase Liquid Chromatography
journal contribution
posted on 2019-08-15, 18:36 authored by Hendrik Küpper, Syed Nadeem Hussain Bokhari, Noelia Jaime-Pérez, Lyudmila Lyubenova, Nermeen Ashraf, Elisa AndresenTechniques
for metal speciation analysis with subnanomolar (ppt)
detection limits in complex matrices, with simultaneous quantification
of matrix elements, have become a necessity for investigating targets
of trace metal binding to macromolecules and pigments at environmentally
relevant concentrations. In this work we optimized the analysis of
such metal binding in a custom-built HPLC-ICP-MS system. Key elements
of the optimization were the choice of components for the metal-free
HPLC-DAD system and sector-field ICP-MS detection (ICF-sfMS) with
desolvating injection and optimization of sample handling. Protein
analysis was done using ammonium bicarbonate buffer and size exclusion
chromatography (SEC-ICP-sfMS), with possible addition of anion exchange
chromatography. Detection of metal exchange in pigments (chlorophylls
and bacteriochlorophylls) was based on reversed-phase chromatography
with a methanol-acetone gradient and coupling to the ICP-sfMS via
a dedicated organic matrix interface (RPC-ICP-sfMS). The resulting
HPLC-DAD-ICP-sfMS system has detection limits in the picomolar range
in protein buffer, limited by the maximal achievable purity of buffers/solvents
and not by system sensitivity. Tests for method optimization showed
that sonication, meant to increase protein solubilization, leads to
artifacts of metal loss from metalloproteins. Examples for Cd binding
to soybean proteins and chlorophyll, Cr binding to Arabidopsis
thaliana proteins, La binding to Desmodesmus quadricauda proteins, and Cu binding to Rhodospirillum rubrum proteins and pigments are shown. These application examples demonstrate
that the system is sensitive enough to detect binding of metals to
proteins and pigments at background concentration levels of typical
nutrient solutions made from analytical grade chemicals, equivalent
to ultratrace metal concentrations in nonpolluted environments.
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Keywords
detection limitsbackground concentration levelsHigh-Resolution Size ExclusionpigmentUltratrace Metal Speciation AnalysisRhodospirillum rubrum proteinsArabidopsis thaliana proteinssector-field ICP-MS detectionsize exclusion chromatographyDesmodesmus quadricauda proteinsultratrace metal concentrationsincrease protein solubilizationoptimizationmetal-free HPLC-DAD systemHPLC-ICP-MSanion exchange chromatographymetal speciation analysistrace metal bindingReversed-Phase Liquid Chromatography Techniquesammonium bicarbonate buffer
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