Effects of Free Base Ratio of Amino Group on Plate Number

Same as packing materials for silica based amino columns, the packing material for Asahipak NH2P-50 columns has amino groups which are bonded to weak anion exchange resins.
The amino groups exist in the equilibrium of free type and acid type. (Please refer to the right figure.) The state of the equilibrium(free base ratio) depends on pH and ionic composition of the eluent.
To investigate the effect of free base ratio, NH2P-50 4E columns are equilibrated with ammonium acetate solvents of different pH to prepare columns of different free base ratio. Using the columns, analyses were performed under the same conditions. The result shows that the elution times became shorter and peak shapes became sharper as free base ratio increased.


pH2.848.509.30Plate number
free base ratio
Free base
32 %82 %93 %

Sample : 1. Fructose, 2. Glucose, 3. Sucrose, 4. Maltose

Column       : Shodex Asahipak NH2P-50 4E (4.6 mm I.D. x 250 mm)
Eluent       : CH3CN/H2O=75/25
Flow rate    : 1.0 mL/min
Detector     : RI
Column temp. : 30 °C

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