Ascites fluid contains, not only your IgG antibody of interest, but also a number of other proteins found in the gut of the animal in which it is produced (in this case, mouse). An antibody in this form is not acceptable for conjugation because the biotinylation reaction targets amino acids on the antibody that would also be found in the other proteins. Your biotin/streptavidin assay would then be detecting, not only the activity of the IgG antibody, but also the activity of all the other proteins you have biotinylated. For biotinylation reactions we recommend only using purified antibodies. You could use our kit to biotinylate a secondary antibody to your Monoclonal Anti-Tyrosine Hydroxylase antibody which would detect antigen binding of the monoclonal. But if you biotinylate the ascites fluid, you will just have a nonspecific binding mess giving falsely high antigen binding results. Our biotinylation kit comes with desalting columns but is not equipped for specific purification of antibodies.