Page 141 - Applied Pharmacognosy
P. 141
Mobile Phase Selection
Guidelines for Setting Mobile Phase Conditions
❑ If the sample is anionic i.e. acidic:
Reversed phase mode is still an option…. But
❑ Mobile Phase Strength has to be adjusted by changing Eluent
Composition to be either: Phosphate buffer
➢ Acidic buffer solution / acetonitrile. pKa 2.1, 7.2, 12.3
➢ Acidic buffer solution / methanol. • No UV absorption.
• Inexpensive.
➢ The concentration of the buffer • High pH buffering power
salt is often set to 10 mmol/L. in neighborhood of pH 2
to 3 (no preparative use).
Increase retention strength by making the eluent acidic and
suppressing ionization! 140
