Abstract: The primary and/or secondary structure of nucleic acid as well as its content and molecular weight can be analyzed in solutions by light scatter or fluorescence measurements after treatment with 3 or 4 ring aromatic cations which bind to single-stranded nucleic acids by cooperative association and induce their condensation (collapse). Preparative separation of nucleic acids of different types from the mixtures in the solution is also accomplished by the same principle and techniques wherein each condensed acid is removed from solution and the condensation reversed.