Carbonate buffer (pH 9.5) is prepared by mixing 100 mL of NaHCO3 solution (4.2 g NaHCO3 in 100 mL dW) with 60 mL of Na2CO3 solution (5.3 g Na2CO3 in 100 mL distilled water) and adjusting pH to 9.5. The buffer is then sterilized by 0.2 µm ltration and can be stored at 4°C.