the experimental results are summarized in table 13 given that upstream protein samples can contain 5 mg ml galactose from cell culture media a sample preparation method was developed to remove the majority of the excess galactose from the media as well as other potentially interfering excipients this clean up alone was not sufficient to remove all process impurities so additional clean up must be performed as part of the capping method preparation two methods of rapid clean up were evaluated dialysis against deionized water and 10 kda centrifugal spin filtering the experiment utilized a buffer exchanged recalpha 1 sample in this experiment a sample was dialyzed against deionized water for 4 hours while another sample was simultaneously cleaned using a 10 kda spin filter both samples were then analyzed by the capping method the conclusion from the experiment was that the 10 kda spin filters were more effective at removing impurities than dialysis and allow for preparation of up to 30 samples at once at a significantly increased turnaround time the chromatograms of both cleanup procedures that involved digestion with reaction c u03b2 galactosidase and u03b1 sialidase are shown in fig3 the spin filtered sample was reconstituted with deionized water and consequently has a lower concentration than the dialyzed sample although trace amounts of galactose may still be present after the clean up all background peaks i e reaction a were subsequently accounted for in the percent capping calculation by subtracting out the contaminate peak area it was also observed that some excipient s from the cell culture supernatants elute shortly after the galactose peak and in some cases appear as a peak shoulder on the galactose peak see fig4 in such cases.