Residual Counter-Ion Determination

Due to their chemical properties lyophilized peptides may still contain counter ions on protonated amino functions (N-terminus, Arg, His, Lys, etc.). These counter ions result from acids being used in the workup or purification of the peptides and are not considered an impurity. However, they reduce the actual peptide content by 5 to 25% depending on the peptide sequence. In order to determine the exact net-amount of a lyophilized peptide sample, the amount of residual counter-ions needs to be analyzed. Furthermore, when TFA (trifluoroacetic acid) is being used during peptide synthesis and purification, potential cytotoxicity needs to be considered for some applications. Then, TFA can be removed by anion exchange using chloride (HCL) or acetate (HOAc). To assess whether the anion exchange was successful it is possible to determine residual TFA amounts. Gas chromatography is being used to determine residual counter-ion amounts.

Material requisition: 1.5 mg/sample

Time needed: 2 weeks

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