TY - JOUR

T1 - Investigation of polynuclear Zr(IV) hydroxide complexes by nanoelectrospray mass-spectrometry combined with XAFS

AU - Walther, Clemens

AU - Rothe, Jörg

AU - Fuss, Markus

AU - Büchner, Sebastian

AU - Koltsov, Sergei

AU - Bergmann, Thorald

N1 - Funding information: The authors acknowledge fruitful and helpful discussions with Marcus Altmaier, Horst Geckeis, Volker Neck, and Bernd Schimmelpfennig. We acknowledge the experimental assistance of Kathy Dardenne and Boris Brendebach. We are grateful for the many comments and suggestions of Enzo Curti, which greatly helped to improve this paper. C.W., M.F., and S.B. acknowledge financial support from the “Programm Nuklear” of the Helmholtz Gemeinschaft Deutscher Forschungszentren (HGF).

PY - 2007/4/5

Y1 - 2007/4/5

N2 - Polynuclear species of zirconium in acidic aqueous solution are investigated by combining X-ray absorption spectroscopy (XAFS) and nanoelectrospray mass spectrometry (ESI-MS). Species distributions are measured between pHC 0 and pHC 3 for [Zr] = 1.5-10 mM. While the monomer remains a minor species, with increasing pH the degree of polymerization increases and the formation of tetramers, pentamers, octamers, and larger polymers is observed. The high resolution of the mass spectrometer permits the unambiguous determination of polynuclear zirconium hydroxide complexes by means of their isotopic patterns. The relative abundances of mononuclear and polynuclear species present simultaneously in solution are measured, even if one of the species contributes only 0.1% of the Zr concentration. For the first time it has been directly observed that the hydrolysis of polynuclear Zr species is a continuous process which leads to charge compensation through the sequential substitution of water molecules by hydroxide ligands until doubly charged polymers dominate at conditions (H+ and Zr concentrations) close to the solubility of Zr(OH)4(am). The invasiveness of the electrospray process was minimized by using very mild declustering conditions, leaving the polynuclear species within a solvent shell of approximately 20 water molecules.

AB - Polynuclear species of zirconium in acidic aqueous solution are investigated by combining X-ray absorption spectroscopy (XAFS) and nanoelectrospray mass spectrometry (ESI-MS). Species distributions are measured between pHC 0 and pHC 3 for [Zr] = 1.5-10 mM. While the monomer remains a minor species, with increasing pH the degree of polymerization increases and the formation of tetramers, pentamers, octamers, and larger polymers is observed. The high resolution of the mass spectrometer permits the unambiguous determination of polynuclear zirconium hydroxide complexes by means of their isotopic patterns. The relative abundances of mononuclear and polynuclear species present simultaneously in solution are measured, even if one of the species contributes only 0.1% of the Zr concentration. For the first time it has been directly observed that the hydrolysis of polynuclear Zr species is a continuous process which leads to charge compensation through the sequential substitution of water molecules by hydroxide ligands until doubly charged polymers dominate at conditions (H+ and Zr concentrations) close to the solubility of Zr(OH)4(am). The invasiveness of the electrospray process was minimized by using very mild declustering conditions, leaving the polynuclear species within a solvent shell of approximately 20 water molecules.

KW - EXAFS

KW - Hydrolysis

KW - Nanoelectrospray

KW - Polymerization

KW - Zirconium

UR - http://www.scopus.com/inward/record.url?scp=34247555920&partnerID=8YFLogxK

U2 - 10.1007/s00216-007-1223-1

DO - 10.1007/s00216-007-1223-1

M3 - Article

AN - SCOPUS:34247555920

VL - 388

SP - 409

EP - 431

JO - Analytical and Bioanalytical Chemistry

JF - Analytical and Bioanalytical Chemistry

SN - 1618-2642

IS - 2

ER -