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Probing uranyl(VI) speciation in the presence of amidoxime ligands using electrospray ionization mass spectrometry
Author(s) -
Mustapha Adetayo M.,
Pasilis Sofie P.
Publication year - 2013
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.6672
Subject(s) - chemistry , uranyl , genetic algorithm , electrospray ionization , electrospray mass spectrometry , mass spectrometry , extractive electrospray ionization , electrospray , chromatography , sample preparation in mass spectrometry , organic chemistry , ion , evolutionary biology , biology
RATIONALE Extraction processes using poly(acrylamidoxime) resins are being developed to extract uranium from seawater. The main complexing agents in these resins are thought to be 2,6‐dihydroxyiminopiperidine (DHIP) and N 1 , N 5 ‐dihydroxypentanediimidamide (DHPD), which form strong complexes with uranyl(VI) at the pH of seawater. It is important to understand uranyl(VI) speciation in the presence of these and similar amidoxime ligands to understand factors affecting uranyl(VI) adsorption to the poly(acrylamidoxime) resins. METHODS Experiments were carried out in positive ion mode on a quadrupole ion trap mass spectrometer equipped with an electrospray ionization source. The ligands investigated were DHIP, DHPD, and N 1 , N 2 ‐dihydroxyethanediimidamide (DHED). DHED and DHPD differ only in the number of carbons separating the oxime groups. The effects on the mass spectra of changes in uranyl(VI):ligand ratio, pH, and ligand type were examined. RESULTS DHIP binds uranyl(VI) more effectively than DHPD or DHED in the pH range investigated, forming ions derived from solution‐phase species with uranyl(VI):DHIP stoichiometries of 1:1, 1:2, and 2:3. The 2:3 uranyl(VI):DHIP complex appears to be a previously undescribed solution species. Ions related to uranyl(VI):DHPD complexes were detected in very low abundance. DHED is a more effective complexing agent for uranyl(VI) than DHPD, forming ions having uranyl(VI):DHED stoichiometries of 1:1, 1:2, 1:3, and 2:3. CONCLUSIONS This study presents a first look at the solution chemistry of uranyl(VI)–amidoxime complexes using electrospray ionization mass spectrometry. The appearance of previously undescribed solution species suggests that the uranyl–amidoxime system is a rich and relatively complex one, requiring a more in‐depth investigation. Copyright © 2013 John Wiley & Sons, Ltd.