Fig. 4.

Liquid chromatography methods. a Reversed-phase ion-pairing chromatography; the lipophilic stationary phase retains the RNA thanks to a lipophilic cation-pairing agent (tetrabutylammonium is depicted). b Ion-exchange chromatography; a positively charged stationary phase interacts and retains the negatively charged RNA molecules. c Affinity chromatography; a polyuridine (poly(U)) functionalized stationary phase selectively interacts with polyadenosine (poly(A)) tails of messenger RNAs (mRNA). d Size-exclusion chromatography; large RNAs are eluted through the porous medium of the stationary phase with short retention times, and smaller RNAs are absorbed into the porous medium, resulting in longer retention times