Lux Amp Series: Is the pH of the mobile phase stable?

1. Yes, if this volatile buffer is in a capped HPLC solvent reservoir, the pH will remain stable
2. The mobile phase is a buffered solution, “a solution that resists changes in pH when acid or alkali is added to it. Buffers typically involve a weak acid or alkali together with one of its salts.” There will be changes in pH when the composition of the mobile phase changes; e.g., Ammonium Bicarbonate will volatilize (reducing the amount in solution) and in turn causing the pH to decrease if the reservoir containing the buffer solution is not capped.  For this reason fresh buffer should be made daily.