The invention relates to methods for separating or purifying biopolymer conjugated molecules from unconjugated molecules. In particular, methods are described for purifying a PEGylated protein or oligonucleotide from an unPEGylated protein or oligonucleotide, respectively. The methods are quick and efficient separation methods because they do not require gradient chromatography, fractionation of an eluent or analysis of the eluted fractions. Further, the methods increase yield and purity of the biopolymer conjugated molecule.