Gadolinium nitrate hexahydrate

Zirconium oxychloride octahydrate (ZrOCl∙8H₂O), yttrium oxide (Y₂O₃), gadolinium nitrate hexahydrate and neodymium oxide were purchased from Sigma Aldrich and used as received for nanopowders synthesis of 3 mol % yttria-stabilized zirconia (YSZ), YSZ doped with Nd and YSZ doped with Gd. Chemicals such as HCl, NH₄OH, NaOH used in synthesis and adsorption tests were of analytical grade.
One g/L stock solution of humic acids (Sigma Aldrich, Steinheim, Germany) was prepared by dissolution of HA in the proper volume of double distilled water.

The commercially available contrast agents Dotarem (0.5 mol/L gadoteric acid, ionic macrocyclic Gd-chelate, Guerbet), Gadovist (0.25 mol/L gadobutrol, nonionic macrocyclic Gd-chelate, Bayer) and Primovist (1 mol/L gadoxectic acid, ionic linear Gd-chelate, Bayer) were investigated as well as a 0.5 M Gd³⁺ solution prepared from gadolinium nitrate hexahydrate (99.9 % Sigma-Aldrich). Samples for liquid state ¹H NMR were prepared directly in a 5 mm NMR tube (Wilmad) with a total volume of 500 μL of which 50 μL were D₂O (99.90% & D Euriso-top) to facilitate the use of ²H lock. Samples with concentrations of 10, 20, 30, 40, 50, and 100 mM were prepared of the three commercial contrast agents and Gd³⁺. The required amount was extracted directly from the vial; 50 μL D₂O and an appropriate amount of MiliQ® water was added. Samples were thoroughly mixed before measurement. All series were prepared in duplicates. In addition, 20 mM mixtures of a contrast agent and Gd³⁺ with 0, 5, 10, 50, and 100 mol% Gd³⁺ were prepared by mixing gadolinium nitrate (Gd(NO₃)₃) and the contrast agent in an appropriate amount to probe the detection limit. Irradiation was performed on 10, 20, 30, 40, 50, and 100 mM samples of gadoteric acid (in duplicate), and only on 20 mM samples of gadobutrol and gadoxectic acid (in triplicates), to limit the total number of measurements.