Method for isolating short-chain nucleic acids

A method for enriching short-chain nucleic acids from a nucleic acid-containing starting material, wherein the nucleic acid-containing starting material comprises short-chain nucleic acids that are less than 1000 bp in length and long-chain nucleic acids that are at least 1000 bp in length, comprising:

• (x) contacting the starting material with a first nucleic acid-binding support material in the presence of at least one chaotropic compound and at least one branched or unbranched alcohol, said alcohol being present at a concentration of ≦25% (v/v);
• and
• (a) contacting said breakthrough or supernatant from step (x) with a second nucleic acid-binding support material in the presence of the at least one chaotropic compound and the at least one alcohol, said alcohol being present at a concentration of from 25% to 40% (v/v),
• wherein the long-chain nucleic acids of the nucleic acid-containing starting material preferably bind to the first nucleic acid-binding support and are thus preferably removed from the breakthrough or supernatant from step (x), and/or the short-chain nucleic acids in the breakthrough or supernatant from step (x) preferably bind to the second nucleic acid-binding support material, thereby short-chain nucleic acids are enriched from the nucleic acid-containing starting material.