Fourier Transform Infrared Spectroscopy (FT-IR) was used to differentiate recycled cooking oil in this research. Results showed that, the recycling cooking oil had characteristic absorption peak at the wave number of 1711 cm-1, which was different from fresh edible vegetable oil. For the illegal cooking oil mixed with recycled cooking oil, the detection limit is 10%. GC-MS analysis showed that the characteristic peak of the recycled cooking oil samples represented carboxylic acid.
