purification cysteine

[Paul]

We are currently purifying cysteine-MPA (mercapto propionic acid) on C18 preparative reverse phase (Daisogel ODS). We use as mobile phase A : H2O and mobile phase B: TFA 0.1% (No organic solvent). The product was loaded onto the column in a TFA 5% solution. No problems, this process works perfectly but I don't understand why a TFA gradient causes this molecule to elute. If someone know the chemical reason for that...
Thanks
Paul

[Noser222]

Sounds to me like your thought process is right. You are already loading the compound in a much higher concentration of TFA, if 0.1% TFA were really the strong solvent. Is this a published method? How well-retained is cysteine-MPA on this column?