What is the function of chloroform in RNA extraction?

Chloroform is one important reagent for RNA purification with guanidinium thiocyanate-phenol-chloroform extraction method. It is used to promote phase separation so that RNA is isolated from DNA and proteins in a biological sample.

Phenol and guanidinium isothiocyanate are first used to solubilize biological materials and denature proteins. After solubilization, the addition of chloroform causes phase separation, where protein stays in the bottom organic phase, DNA resolves as the interface, and RNA is extracted to the top aqueous phase. Hence, RNA is purified from the sample.