Abstract: The molecular composition of lube base oil was characterized by gas chromatography/field ionization time-of-flight mass spectrometry (GC/FI TOF MS). The carbon number distribution of alkanes and 1-6 rings naphthenes in base oils could be obtained simply and quickly by qualitative analysis based on accurate relative molecular mass and mass spectrum quantitative analysis. Based on the molecular composition data of the base oil, the Kennard-Stone design method was used to divide the sample set into a calibration set and a verification set. A model for predicting viscosity and viscosity index was established based on the partial least squares method (PLS). The standard deviations of the model calibration value and prediction value based on molecular composition data were less than 2.0 mm²/s for viscosity and 2 for viscosity index,respectively,and the correlation coefficient(R) was greater than 0.99. The model has good applicability and high accuracy for the prediction of base oil viscosity and viscosity index, and it has certain practical value.

Key words: lube base oil, GC/FI TOF MS, molecular composition, viscosity