MES monohydrateSynonyms: MES, 2-(N-morpholino)ethanesulfonic acid or 4-morpholineethanesulfonic acid monohydrateC₆H₁₃NO₄S · H₂OM_r213.25CAS Number [145224-94-8]EC Number 224-632-3Beilstein Registry Number 6350956RTECS QE3479500MDL Number MFCD00149409PubChem Substance ID 24885996Purity >99.0%pKa 6.1 at 25°CSolutions are stable at 2-8°C for months. Autoclaving is not recommended for any sulfonic acid buffer. When MES solutions are autoclaved, they turn yellow (although pH does not change measurably). The identity of the yellow breakdown product is unknown. When MES solutions are stored at room temperature, they can turn yellow within six months.Useful pH range of MES 5.2 - 7.1MES buffers formulated in Type 1+ ultrapure water, 18.2 megohm resistivity at 25°C, < 5 ppb Total Organic Carbon, <1 Bacteria (CFU/ml), <0.03 Endotoxin (EU/ml). The pH is adjusted using Sodium hydroxide (NaOH). Buffers are sterile filtered using 0.22 micron filters under sterile conditionsCa < 0.005%Cd < 0.0005%Cl < 0.005%Co < 0.0005%Cr < 0.0005%Cu < 0.0005%Fe < 0.0005%K < 0.005%Mg < 0.0005%Mn < 0.0005%Na < 0.005%Ni < 0.0005%Pb < 0.0005%SO₄< 0.005%Zn < 0.0005%