This International Standard specifies test methods for the analysis of 2-furfural and related furan compounds resulting from the degradation of cellulosic insulation and found in mineral insulating oil samples taken from electrical equipment. 2-furfural and related furan compounds dissolved in mineral oil are analysed by high performance liquid chromatography (HPLC). Prior to HPLC analysis, furan derivatives are extracted from the oil by use of a suitable extraction method such as liquid-liquid extraction (method A) or solid-phase separation on a silica cartridge (method B).