Linear Formula: HCHO, Molecular Weight: 30.03, ACS reagent, 37 wt. % in H2O, contains 10-15% Methanol as stabilizer (to prevent polymerization), Synonym: Formalin. Formaldehyde solution has been used as a fixing agent to fix cells during immunofluorescence imaging and for cross-linking cells during chromatin immunoprecipitation (ChIP) assay. Formaldehyde solution has been used for cross-linking/fixing of cells in ChIP (chromatin immunoprecipitation) assay. It has been used for fixing of cells for imaging.