Quantitative Separation of Unknown Organic-Metal Complexes by Liquid Chromatography-Inductively Coupled Plasma-Mass Spectrometry

Christian Dewey, Daniel I. Kaplan, Scott Fendorf, Rene M. Boiteau

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

Dissolved organic matter (DOM) is widely recognized to control the solubility and reactivity of trace metals in the environment. However, the mechanisms that govern metal-DOM complexation remain elusive, primarily due to the analytical challenge of fractionating and quantifying metal-organic species within the complex mixture of organic compounds that comprise DOM. Here, we describe a quantitative method for fractionation and element-specific detection of organic-metal complexes using liquid chromatography with online inductively coupled plasma mass spectrometry (LC-ICP-MS). The method implements a post-column compensation gradient to stabilize ICP-MS elemental response across the LC solvent gradient, thereby overcoming a major barrier to achieving quantitative accuracy with LC-ICP-MS. With external calibration and internal standard correction, the method yields concentrations of organic-metal complexes that were consistently within 6% of their true values, regardless of the complex's elution time. We used the method to evaluate the effects of four stationary phases (C18, phenyl, amide, and pentafluoroylphenyl propyl) on the recovery and separation of environmentally relevant trace metals (Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb) in Suwannee River Fulvic Acid and Suwannee River Natural Organic Matter. The C18, amide, and phenyl phases generally yielded optimal metal recoveries (>75% for all metals except Pb), with the phenyl phase separating polar species to a greater extent than C18 or amide. We also fractionated organic-bound Fe, Cu, and Ni in oxidized and reduced soils, revealing divergent metal-DOM speciation across soil redox environments. By enabling quantitative fractionation of DOM-bound metals, our method offers a means for advancing a mechanistic understanding of metal-organic complexation throughout the environment.

Original languageEnglish (US)
Pages (from-to)7960-7967
Number of pages8
JournalAnalytical Chemistry
Volume95
Issue number20
DOIs
StatePublished - May 23 2023
Externally publishedYes

Bibliographical note

Funding Information:
We thank Chris Russo (Oregon State University) for his technical assistance. This work was supported by the U.S. Department of Energy (DOE) (Project Award Numbers DE-SC0020205, DE-AC02-06CH11357, and DE-EM0005228) and the National Science Foundation (CHE-2108340, OCE-1829761).

Publisher Copyright:
© 2023 American Chemical Society. All rights reserved.

PubMed: MeSH publication types

  • Journal Article

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