Regeneration of a PGC column by acid treatment. (A) A standard mixture on a rather new column after about 100 injections of diverse extracts. The pressure had risen from 80 bar to about 160 bar. After this rise to about twice the original pressure, columns often were completely clogged within a few injections..(B) The same mixture after boiling the column in 4 M TFA followed by rinsing with sulfite. (C) The same mixture again on the same column after 7 days and several reductive and oxidative treatments. The original separation characteristics had still not be retained. (D) Analysis on the same column after an additional HCl treatment. Underlined labels indicate nucleotide sugars, whereby UA, G, Gn, F, and R stand for UDP-glucuronic acid, UDP-Glc, UDP-GlcNAc, GDP-Fuc, and ADP-Rib.