Epc. Lai et Rs. Vucic, KINETIC-STUDY OF THE DEGRADATION OF LUBRICATING MOTOR OIL BY LIQUID-CHROMATOGRAPHY AND PHOTOACOUSTIC SPECTROMETRY, Fresenius' journal of analytical chemistry, 347(10-11), 1993, pp. 417-422
Lubricating motor oil samples were collected throughout one oil change
period of 5000 km and analyzed for saturate, aromatic, polynuclear ar
omatic hydrocarbon (PAH) and polar species using normal-phase high-per
formance liquid chromatography (HPLC) with ultraviolet light absorptio
n and refractive index detections. The oil samples were also analyzed
using a new photoacoustic spectrometry (PAS) method. Fair correlation
was established between the HPLC method and the PAS method for determi
ning aromatic concentration. Moreover, the PAS method offers shorter a
nalysis time, comparable reproducibility, and improvement in detection
sensitivity over the HPLC method. The analyses data obtained were use
d to study the degradation kinetics of the motor oil against mileage.
The aromatic species were found to increase in concentration with pseu
do zeroth-order kinetics, the PAH species rose from zero to some highe
r amount, whereas the saturate and the polar species remained essentia
lly constant over the mileage period.