Acetone-d6 was obtained from Sigma-Aldrich (United Kingdom), sodium phosphate monobasic and sodium phosphate dibasic were obtained from BDH Laboratory Supplies (Poole, United Kingdom) and used to prepare a 0.1M pH 7 buffer. Sodium bicarbonate and sodium hydroxide were obtained from Fisher Scientific (United Kingdom) and used to prepare a 0.1M pH 10 buffer.