We performed centrifugation experiments for a system of replicators, described previously , made from two closely related pentapeptide building blocks, differing only in the nature of the fourth amino-acid residue, which is either a phenylalanine (F; Figure ) or a serine residue (S). Two replicator samples were prepared and characterized by ultra-performance liquid chromatography and mass spectrometry (UPLC-MS): one starting from only building block F, yielding fibers composed of hexameric F6S0, and one starting from an equimolar mixture of both building blocks, yielding hexamer replicators in which F and S were incorporated in a close to statistical ratio (closely matching Pascal's triangle statistics of 1:6:15:20:15:6:1, respectively, for F6S0, F5S1, …, F0S6). These replicator assemblies were then mixed with 5 equivalents (in units of building blocks) of a separately prepared solution of precursors made from an equimolar mixture of F and S and incubated for 5 minutes. The resulting solutions were centrifuged, causing the replicator assemblies to accumulate at the bottom of the vial, together with the precursors bound to them. The composition of the pellets and supernatants were analyzed by UPLC. The pellet of fibers of F6S0 was significantly enriched in Frich precursors (F3S0 and F2S1 trimers; Figure ), while the precursors spun down with the mixed FnS6-n (n=0-6) fibers were considerably more S rich (Figure ). As a control, centrifugation of the precursor solution in the absence of replicator fibers showed almost no sedimentation (Figure ), suggesting that precursor material found in the pellets is there due to binding to the replicator fibers. In conclusion, these experiments demonstrate that replicator assemblies can selectively bind precursors that have a building block composition similar to that of the replicator assembly. Precursor was prepared from 0.20 mM of F and S in equimolar ratio (1:1) and added to 20 mol% of preformed replicator fibers. Libraries were centrifuged for 80 minutes at 15000 rpm and analyzed using UPLC. Error bars represent standard deviation based on 3 repeats. The control experiment without replicator was conducted once.