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Lube-Tech


trial use with site licenses available to commercial and institutional users, a means for eliminating the constraints and incompatibilities to implementing new methods. The software is intuitive and most operations (measuring areas, peak heights, baseline correct, smooth, take derivatives etc.) are available and sequenced as macros from a list of selectable processes. The final output is a simple comma separated (.csv) file which can be passed on to Excel® and when combined with the macro capability within Excel®


, one can readily calibrate, predict, and


report/print analytical results in lieu of a laboratory information management system (LIMS).


Implementation


SpectraGryph was used to implement AN analysis for an on-site FTIR (Agilent 5500) equipped with a convenient and simple-to-use TumblIR®


(Figure 2) open architecture


accessory. The instrument was destined for on-site use at a remote mining operation in Papua New Guinea for manual CM analysis as well as carrying out deterministic AN analyses of oils in lieu of titration. Titration was not an option and direct-PLS AN determinations were considered inadequate in terms of accuracy or oil-type flexibility. SpectraGryph was bundled with Excel to make a viable AN Analytical Package linked by a coordinating file structure to obtain on-site quantitative AN results. Paired samples were prepared and scanned by FTIR (Figure 3) with SpectraGryph macros run post-spectrally and the .csv file passed onto Excel to calculate and report the results.


Differential Absorbance Spectra (ΔAbsn Spectral Processing )


Stoichiometric Acid Number


FTIR~1 Drop - Background Scan Ion )


Wipe Clean


FTIR~1 Drop - Sample Scan (In )


PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE


No.134 page 4


0.5 ml Oil 1.0 ml Solvent-Diluent Oil


0.5 ml Oil 1.0 ml Reagent-Diluent


Figure 3: Basic analytical protocol used for paired-split sample calibration and analysis.


Calibration


Calibration simply involves the volumetric addition of pure oleic acid to a neutral hydrocarbon matrix (e.g., low viscosity neutral mineral oil or lamp oil), to produce a series of calibration standards covering an effective range of ~0-4 AN. These are split, treated with their respective diluents, scanned and the second derivative of the differential spectra measured for the NaPhenolate and Oleic acid absorptions at 1589 and 1710 cm-1


. The absorptions are related by linear Figure 2: TumblIR® open architecture accessory ideally suited for oil analysis.


regression to the oleic acid concentration expressed as mg Oleic Acid/ml (Figure 4); the calibration precision being < ± 0.10 AN. Samples are analysed in a similar manner, processed via the respective regression equations, and using the known (or assumed) density of the oil, converting the acidity determined into ANTOTAL and ANCOOH, the difference being ANSTRONG.


LUBE MAGAZINE NO.163 JUNE 2021 27


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