ACES (N-(2-Acetamido)-2-aminoethanesulfonic acid) is a zwitterionic buffer. The working pH range of ACES buffer is 6.8-7.2[1][2].
[1]. Melissa D Mertzman, et al. Effect of surfactant concentration and buffer selection on chromatographic figures of merit in chiral microemulsion electrokinetic chromatography. Electrophoresis. 2004 Oct;25(18-19):3247-56. [2]. Rabindra N Roy, et al. Buffer Standards for the Physiological pH of the Zwitterionic Compound, ACES from 5 to 55°C. J Solution Chem. 2009 Apr 1;38(4):471-483.