Diagnosis of used engine oil based on gas phase analysis
A method for determination of the volatile compounds present in new and used petroleum oils was developed. The identification of the new and used oils was based on the abundance of volatile compounds in headspace above the oils. Multivariate analysis based on principal component analysis (PCA), and hierarchal cluster analysis was used to evaluate the degradation compounds found in used engine oil. The gas phase of new and used petroleum oils was analyzed using a time of flight mass spectrometer (TOF MS) and sensor arrays. The samples included used engine oil, up to 35,500 miles. The principal components identified by PCA were volatile constituents of the oils. New and used oils were also differentiated using multivariate analysis of the results from these gas phase detection methods. The identification of the origin of volatile samples in the used oils has been studied by spiking newer oil samples with a complex mixture of volatile compounds. These samples were then analyzed with the sensor array. Results from the spiked samples correlated better with the older, more used oil samples, confirming that the previously identified volatile compounds can be used to classify new and used engine oils. Using chemometrics, the used oils were differentiated into categories using metal oxide semiconductor (MOS) and quartz crystal microbalance (QCM) sensor arrays or mass spectrometry. The QCM sensors were able to better differentiate the new and used oil samples compared to the metal oxides. In the mass spectrometry and sensor array analysis the new oils were clustered into groups and separated by mileages. The older, more used oils were clearly distinguished from the newer oils.