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Analytical Chemistry

Common chelator serves as detector for health-relevant metals

EDTA labeled with 13C can distinguish among multiple divalent cations using NMR or MRI

by Jyllian Kemsley
November 14, 2016 | A version of this story appeared in Volume 94, Issue 45

Calcium, magnesium, and zinc are divalent metal ions essential for good health. Other divalent metals, such as cadmium, lead, and arsenic, are toxic. Turning to common metal-chelating agents, researchers have found that they can use nuclear magnetic resonance spectroscopy and magnetic resonance imaging to quantitatively sense and distinguish among all these metals in blood serum (Anal. Chem. 2016, DOI: 10.1021/acs.analchem.6b03546). Gil G. Westmeyer of the Technical University of Munich and colleagues labeled the metal-coordinating carboxyl groups of ethylenediaminetetraacetic acid (EDTA) or ethylene glycol bis(2-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) with 13C. When either of the compounds binds the metals, 13C NMR spectra show well-separated chemical shifts that allow the researchers to distinguish between the metals. For example, they were able to quantitate millimolar concentrations of Ca2+ in human serum in the presence of competing concentrations of Mg2+. The researchers were further able to increase the sensitivity to micromolar concentrations for NMR and MRI by using dynamic nuclear polarization, which involves transferring spin polarization from electrons of a radical to the 13C nuclei to enhance their NMR signals.

13C NMR spectra of labeled EDTA alone and bound to divalent lead, arsenic, cadmium, zinc, magnesium, and calcium.
Credit: Anal. Chem.
NMR shifts for EDTA labeled with 13C (orange dots) enables researchers to distinguish between various divalent cations.


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