About 0.5 g oil sample
were initially homogenised with iso-octane, until a total volume
of 25 ml was obtained. From the solution, 5 ml were taken and reacted
with 1 ml of p-anisidine solution (mixture of p-anisidine and
glacial acetic acid). Measurement of AnV was performed spectrophotometrically
at a wavelength of 350 nm using a Cecil 1000 Series
spectrophotometer (Cecil Instruments Ltd, Cambridge, UK).