Preparation of solutions
The stock solutions of 10 mg mL−1 of d-AMP, As(V), As(III),
Se(IV), Se(VI) and BrO3
− were prepared in DI water. The d-AMP
solution was stored at −20 ◦C and the latter four solutions were
stored at 4 ◦C until use. A 200 mmol L−1 stock solution of ammonium
carbonate was made by dissolving 3.903 g of ammonium
carbonate in 250 mL of DI water followed by adjustment of pH to
9.2 with 20% ammonium hydroxide. The buffer stock solution was
stored at 4 ◦C. Working buffer solutions of ammonium carbonate
were made from diluting the stock solution to the required concentrations
with DI water and re-adjusting the pH to 9.2 with 10%
ammonium hydroxide solution. All working buffer solutions were
filtered by 0.2 m syringe filters (Fisher Scientific, Ottawa, CA) and
further degassed for 5 min by a sonication (Fisher Scientific, Ottawa,
CA) before use.