MOPS and MES are buffers used in biology and biochemistry. They consist of a morpholine ring and propanesulfonic acid. Both molecules are zwitter-ionic and very polar. No retention can be achieved on reversed-phase columns. MOPS and MES are analyzed in HILIC mode on a Primesep N HPLC column. Other biological buffers can be analyzed with this general method. Biological buffers are not UV active and can be monitored by ELSD, CAD or LC/MS.