A rapid method for peroxide value determination in edible oils based on flow analysis with Fourier transform infrared spectroscopic detection

Abstract

The development of an automated, rapid and highly precise method for determination of the peroxide value in edible oils based on a continuous flow system and Fourier transform infrared (FTIR) spectroscopic detection is described. The sample stream was mixed with a solvent mixture consisting of 25% (v/v) toluene in hexanol which contained triphenylphosphine (TPP). The hydroperoxides present in the sample reacted stoichiometrically with TPP to give triphenylphosphine oxide (TPPO) which has a characteristic and intense absorption band at 542 cm⁻¹. A 10% (m/v) TPP solution in the solvent mixture and a 100 cm reaction coil were necessary for complete reaction. FTIR transmission spectra were recorded using a flow cell equipped with CsI windows having an optical pathlength of 100 μm. By using tert-butyl hydroperoxide spiked oil standards and evaluation of the band formed at 542 cm⁻¹ a linear calibration graph covering the range 1–100 PV (peroxide value; mequiv O₂ kg⁻¹ oil) was obtained. The relative standard deviation was 0.23% (n = 11) and the throughput 24 samples h⁻¹. The developed system was also applied to the determination of PV in olive, sunflower and corn oils, showing good agreement with the official reference method of the European Community which is based on titration using organic solvents. The results obtained clearly show that the developed method is superior to the standard wet chemical method, hence suggesting its application in routine analysis and quality control.