peptide biotinylation question

[Student]

I need to biotinylate two 10-amino acid peptides with NHS-X-Biotin. My
problem is this: how can I effectively remove all the unreacted free biotin
ester after the biotinylation reaction? I can't use the normal desalting
methods because the biotinylated peptide is still too small.

Some people suggested using dialysis but are there any dialysis membranes
that have such a small limit? If so, can someone suggest a place where I can
get it in the UK?

Any other suggestions will be appreciated. Thanks.