Hydrazine hydrate (N 2 H 4 •xH 2 O, 98%), potassium nitrate (KNO 3 , 99.99%), potassium monohydrogen phosphate (K 2 HPO 4 , 98%), potassium dihydrogen phosphate (KH 2 PO 4 , 99%) and nitric acid (HNO 3 , 70%) were purchased from Sigma-Aldrich, Dorset, UK, and used as received. An aqueous solution of 1.5 mM hydrazine supported by 0.1 M KNO 3 was prepared, of which the pH was measured to be 9.7. Analogous hydrazine solutions of pH 2.0 and pH 7.0 were prepared via the addition of tiny amounts of HNO 3 to adjust the pH. A phosphate buffer solution (0.1 M PBS, pH 7.0) with 1.5 mM hydrazine was used for further studies. Note that all solutions were prepared using ultrapure water Millipore System Inc., 298 K). A digital sensION TM + PH31 pH meter (HACH, Colorado, USA) was used for pH measurements and calibrated before each measurement. Nitrogen (N 2 , 99.998%) was supplied from BOC,