Determination of viscosity index in lubricant oils by infrared spectroscopy and PLSR

In order to ensure the quality of the lubricants, the productive sector and the regulatory agencies require a robust and accurate method to monitor the quality parameters of the lubricant oils. Multivariate methods based on infrared spectroscopy have been proposed as an alternative for quality control analysis of lubricants. However, to the best of our knowledge, no studies or methods were reported covering a significant number of samples of different manufacturers or oil brands that prove their performance and robustness for routine analysis in quality control monitoring by regulatory agencies. Therefore, the present paper describes the development and validation of a method for determination of the viscosity index (VI) of lubricant oils that could be applied for 81 different producers/brands. The 1085 samples used for development and validation were collected from all regions of Brazil by the monitoring program of the National Agency of Petroleum of the Brazil, so that the dataset is representative of the variation in most of the lubricant market in Brazil. The results indicate that the method can be applied for VI determination taking into account the variation in a high number of lubricant producers/brands, different kinds of lubricating oils, regarding the origin of the base oils (mineral or synthetic) and the API and SAE classifications. The method was also simpler than the reference method, fast, required a lower amount of sample and produced fewer chemical residuals.