This test method covers monitoring phenol antioxidant additives in in-service petroleum and hydrocarbon-based lubricants such as various types of engine oils, hydraulic oils, and other lubricants that are formulated for protection against oxidation. Typical phenol antioxidant additives include sterically hindered, alkyl-substituted phenols such as 2,4,6-Tri-tert-butylphenol (2,4,6-TTBP), 2,6-Di-tert-butylphenol (2,6-DTBP), or 2,6-Di-tert-butyl-p-cresol.
This test method uses Fourier transform infrared (FTIR) spectrometry for monitoring of phenol antioxidant additive depletion in in-service petroleum and hydrocarbon-based lubricants as a result of normal oil aging. Monitoring the phenol antioxidant in in-service lubricants can indicate severe operating conditions before a degradation of the base oil itself. This test method is designed as a fast, simple spectroscopic check for monitoring of phenol antioxidant additives in in-service petroleum and hydrocarbon-based lubricants with the objective of helping diagnose the operational condition of the machine based on measuring the level of phenolic compounds in the oil.
Acquisition of FT-IR spectral data for measuring phenol antioxidant additives in in-service oil and lubricant samples is described in Practice D7418. In this test method, measurement and data interpretation parameters for phenol antioxidant additives using both direct trend analysis and differential (spectral subtraction) trend analysis are presented.