Can Acid and Base Numbers of Lubricants be measured using FTIR?
Over the last decades, Fourier Transfer Infrared (FTIR) spectrometers have found their homes in private and commercial lubricant condition monitoring analytical labs. FTIR has been used to reproduce traditional ASTM methods for determining metrics such as moisture, glycol, soot, oxidation, antioxidants, and additive depletion.
Today the advantages of FTIR spectroscopy can be extended to Acid & Base number determination. Specifically the COAT FTIR offers:
- Up to 60 samples per hour, as opposed to 4-6 with legacy methods
- Significantly less sample and solvent volumes (and associated disposal)
- Industry leading reproducibility and accuracy
Advantages of FTIR Spectroscopy
Capabilities, Accuracy, and Speed
FTIR spectroscopy, with a coupled auto-sampler, allows their users to automate the majority of the analytical process. For example, testing for the ASTM soot, oxidation, antioxidants, and wear additive levels do not require any sample preparation, and results can be obtained in seconds.
Combined with an auto-sampler and the right software, FTIR spectrometers like Thermal-Lube’s COAT system can measure up to 120 samples per hour.
Environmentally Green & Economical
The speed and accuracy of FTIR spectroscopy has resulted in users being able to make quick, informed decisions about their lubricant’s remaining life. By knowing exactly when to change your lubricant, you can reduce the waste associated with time based change outs and disposal.
Further, using FTIR only requires a small 10ml sample – almost 25% of the equivalent traditional wet-chemistry ASTM methods.
FTIR Acid and Base Number Challenges
So why hasn’t FTIR spectroscopy been utilized for Acid and Base number until this point? First and foremost, there does not exist a current ASTM approved method of determining these metrics by FTIR.
Second, even the legacy titration methods of determining Acid and Base numbers demonstrate significant variability in results and reproducibility.
Third, the ASTM methods are not necessarially representative of the actual state of the lubricant.
And finally, although several FTIR methods have been developed, none have been able to reproduce the results obtained with ASTM titration methods… Until Now!
FTIR Acid and Base Number Execution
Recently Dr. Van de Voort of McGill University in collaboration with Thermal-Lube developed a mixed-mode method of determining Acid and Base Numbers. This method involves simple sample preparation with the addition of a small amount of solvent to the low sample volume. Within 60 seconds, the FTIR will flush and then pump the sample into the cell, scan the spectra, and produce the appropriate analytical results. What we get is an identical result to traditional titrations with higher reproducibility in a fraction of the time with substantially less lubricant and solvents to dispose of.
If you’d like to learn more about our Acid and Base Number methods, check out our recently published articles in Machinery and Lubrication Magazine here and in The European Lubricants Industry Magazine here.