Purification of oligonucleotides has traditionally relied on mobility-based separation methods. However, these are imperfect, biased, and difficult to scale high multiplex. Here, we present a method for simultaneous purification of many oligonucleotides that also normalizes concentrations. The method uses a rationally designed randomer capture probe to enrich for oligos with perfect 5' sequences, based on the observation that synthesis errors are correlated: product molecules with one or more deletions in one region are also more likely to have deletions in other regions. Next-generation sequencing analysis of 64-plex 70 nt purification products show a median 78% purity, a significant improvement over polyacrylamide gel electrophoresis and high pressure liquid chromatography (60% median purity). Additionally, 89% of the oligo products are within a factor of 2 of the median concentration.