What counterions are present in the peptides?
Normally, the peptides are supplied with trifluoroacetate counterions. Upon request, the peptides can also be supplied in acetate counterions. However, since there is no purification step, it cannot be guaranteed that the peptide is free of trifluoroacetate counterions. If the peptide set had been supplied in trifluoroacetate, most of the trifuloroacetate counterions can be exchanged to acetate counterions by resuspending the peptides in 200 ml of neat HOAc, followed by re-lyophilization. This procedure is repeated one more time. Finally, the peptides are re-dissolved in 50% acetic acid in water and then re-lyophilized. The residual trifluoroacetate concentration is usually too low to be a factor in most research applications.
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