“…However, due to the very low aqueous solubility of Hf and even Hf · HCl, the addition of a cosolvent was required. N ‐Methyl‐2‐pyrrolidone (NMP) was chosen because it has been reported to be an effective cosolvent for several poorly water soluble drugs8 and, in comparison with other solvents was the most efficient in maintaining solubility of Hf · HCl in aqueous solution. Buffer solutions (20 mM, ionic strength adjusted to 0.1 M with sodium chloride) of pH values ranging from 2 to 10 were prepared using either phosphate, acetate, TRIS, or carbonate buffer salts and adjusted to the required pH using 1 N sodium hydroxide or hydrochloric acid.…”