Machinery Lubrication magazine published by Noria Corporation
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www . machinerylubrication.com | March - April 2021 | 39 www . machinerylubrication.com | March - April 2021 | 39 ML ML mentally problematic. They also have no determinative ASTM-sanctioned FTIR AN methods available. Current direct-read chemo- metric instrumentation serves as a "better than nothing" approach with limitations which are rarely grasped by users. In contrast, this new stoichiometric AN method provides a robust alternative and uses a readily understood Beer's Law cause and effect calibration, oil-type universality and ready validation as well as acid type differentiation. Generic implementation via SpectraGryph® is available, and more substantive details of the methodology are to be presented elsewhere. Its lower cost, higher speed, better accuracy and minimal waste-stream are significant benefits over ASTM titrimetric procedures. Early adopters should consider involving ASTM or ISO to further assess, validate and standardize this methodology to fully define and characterize its benefits, especially its acid differentiation feature. ML References 1. In-Service Oil Analysis Handbook 3rd Edition. Spectro Scien- t i f ic 2017: ht t ps://web.a rc h ive.org /web/2020 0923163612/ https%3A%2F%2Fwww.spectrosci.com%2Fdefault%2Fassets%2F- File%2FSpectroSci_OilAnalysisHandbook_FINAL_2014-08.pdf 2. C. Winterfield and F.R. van de Voort. A new approach to determining the Acid and Base Number AN and BN of used oils. Machinery Lubri- cation. May-June 2015. 3. C. Winterfield and F.R. van de Voort, Quantitative condition moni- toring of in-use oils by FTIR spectroscopy. LUBE Magazine No 127 pp. 24-29 2015. 4. C. Winterfield, and F.R. van de Voort. Automated acid and base number determination of mineral-based lubricants by Fourier trans - form infrared spectroscopy: Commercial laboratory implementation. Journal of Laboratory Automation 1-10 2014 DOI: 10.1177/221 10682 14551825 5. M. Meng, L. Lei, Q. Ye and F.R. van de Voort. Fourier transform infrared (FTIR) spectroscopy as a utilitarian tool for the routine deter - mination of acidity in ester-based oils. Journal of Agricultural and Food Chemistry. 63, 37, 8333-8338. 2015 DOI: 10.1021/acs.jafc.5b02738 6. S p e c t r o s c o p y N i n j a : h t t p s : // w e b . a r c h i v e . o r g / web/20200923165652/https%3A%2F%2Fw w w.ef femm2. de%2Fspectragryph%2Fdown.html 7. van de Voort, F.R. and Viset, M. Generic method for the rapid and accurate determination of Acid Number (AN) in lubricants by FTIR Spectroscopy. Proceedings of the ASTM Symposium Highlighting Standard Guides and Practices that Support the Lubricant Condition Monitoring Industry. (Postponed, December 2020; In Press). About the Authors Michael Viset is a hydrocarbon consultant located in Australia and was instrumental in initiating the development and vetting the manual FTIR AN method and its implementa- tion for onsite analysis at the OK Tedi mine in Papua New Guinea. Dr. Frederik van de Voort is Emeritus Professor at McGill University in Montreal, QC Canada and has been involved in developing quantitative FTIR analytical methods for lubricants and edible oils. Figure 3. Basic analytical protocol used the paired-split sample calibration and analysis 0.5 ml Oil + 2.0 ml Solvent-Diluent 0.5 ml Oil + 2.0 ml Reagent-Diluent Oil Wipe Clean FTIR ~ 1 Drop – Background Scan (I on ) FTIR ~ 1 Drop – Sample Scan (I n ) Differential Absorbance Spectra ( Abs n ) Spectral Processing Stoichiometric Acid Number 0.0035 0.003 0.0025 0.002 0.0015 0.001 0.0005 0 -0.0005 -0.001 -0.0015 -0.002 -0.0025 -0.003 -0.0035 -0.004 -0.0045 -0.005 -0.0055 -0.006 -0.0065 1615 1610 1605 1600 1595 1590 1585 1580 1575 1570 Wavenumbers [/cm] - 1 6 - 1 5 - 1 4 - 1 3 - 1 2 - 1 1 - 1 0 - 9 20 16 12 8 4 0 Peak Area (1602-1581 cm-1) Oleic Acid (mg/ml) in Standard Acidity Total - NaPhenolate Figure 4ab. 2nd derivative spectra of NaPhenolate and its plotted absorbance response to added oleic acid i the calibration standards. Range ~ 0-4 AN, SD < ±0.10 AN.