Mid-IR Spectroscopy Method Validation for TBN Determination of Fresh Marine Oils

The standard test method to determine the total base number (TBN) in fresh marine oil is through the potentiometric perchloric acid titration or ASTM D2896. Sample solvent and titrant solutions are being utilized in ASTM D2896, composed of chlorobenzene, glacial acetic acid and perchloric acid.

This method is already established in analyzing fresh petroleum products. However, the use of hazardous chemicals and generation of hazardous wastes pose risks in the safety of the chemists using them. In addition, frequent interruptions due to reagent unavailability and delayed scheduled equipment services have been part of the challenges that laboratories are facing nowadays. This required the validation of alternative methods for TBN determination of fresh marine oils.

In this study, the FTIR method was evaluated as a feasible alternative because of its non-destructive, reagent-free, and direct type of analysis. The fresh marine oils that were used are those with active components of phenates and salicylates and have TBN of 10 to 70 mg/kg. The method validation includes assessment of its blank, selectivity, working range, LOB, LOD, LOQ, trueness and bias, and precision. At increasing TBN concentrations of fresh marine oils, the response of the FTIR method is directly related with the response of ASTM D2896. The repeatability of the FTIR method is 3.7% and 2.5% of the means for phenates and phenates-salicylates, respectively. The result of this study presents that the FTIR method can be an analytical technique and an easy plug-and-play program.