To check aged degradation of insulating oil, degradation product in insulating oil is often measured. Furfural is one of a degradation product of cellulose composing insulating paper in insulating oil. Furfural is stably dissolved in oil and distinction of degraded state of oil can be confirmed by measuring the concentration of furfural.
In this technical note, we introduce a HPLC method and two sample preparation methods (liquid-liquid extraction and solid phase extraction with silica gel column) for monitoring furfural in insulating oil.