Influence of Sample Mixing Techniques on Engine Oil Contamination Analysis by Infrared Spectroscopy

Torrey Holland,Dennis G Watson,Ali Mazin Abdul-Munaim,Poopalasingam Sivakumar

doi:10.3390/lubricants7010004

Torrey Holland, Dennis G Watson + Show 2 more

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https://doi.org/10.3390/lubricants7010004

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Abstract

For the most reliable and reproducible results for calibration or general testing purposes of two immiscible liquids, such as water in engine oil, good emulsification is vital. This study explores the impact of emulsion quality on the Fourier transform infrared (FT-IR) spectroscopy calibration standards for measuring water contamination in used or in-service engine oil, in an attempt to strengthen the specific guidelines of ASTM International standards for sample preparation. By using different emulsification techniques and readily available laboratory equipment, this work is an attempt to establish the ideal sample preparation technique for reliability, repeatability, and reproducibility for FT-IR analysis while still considering the ease and efficiency of the technique. This study demonstrates that a stable emulsion within a sample, which depends heavily upon the method, provides a reliably consistent homogenous sample for quantification purposes with FT-IR analysis. Analysis of variance (ANOVA) modeling and limit of detection calculations demonstrate the stability of the emulsion. The results reveal that setting a mixing time for a calibration standard depends on the emulsification process. Inserting a probe directly into a sample (direct sonication) allows for a rapid, stable emulsion with high reproducibility. Indirect sonication produces relatively non-miscible liquids of different densities. The pan-shaker produces a reasonably stable emulsion, but without the long-term stability or quick production time of direct sonication. Reaction time plays a critical role in the rotary mixing method, which leads to a slow development of emulsification.

Highlights

To counter the adverse effects of water contamination on the lubricity in an engine, many analytical methods have been employed to test for contamination to avoid more costly repairs and increased downtime
The techniques utilized in this study to form emulsions are the rotary (ROT) method, bath sonication only (BSO), bath sonication followed by a rotary (BSR), pan-shaker (PSH) method, and direct probe sonication (DPS)
Fourier transform infrared (FT-IR) results of bath sonication only (BSO) and bath sonication followed by a rotary (BSR) mixing were compared with 0%, 0.5%, and 1% water contaminated engine oil, as shown in Figures 2 and 3

Summary

Introduction

To counter the adverse effects of water contamination on the lubricity in an engine, many analytical methods have been employed to test for contamination to avoid more costly repairs and increased downtime. When it comes to analyzing water contamination of used or in-service engine oil, FT-IR analysis stands apart from other commonly employed techniques because it can measure dissolved, free, and emulsified water, and correlates well with the Karl Fischer method [1,2,3]. A thoroughly emulsified sample is inherently more stable, homogeneous, and representative of the whole, yielding better reproducibility and reliability in results by reducing the variability in IR measurements that arises due to light scattering in samples with larger water droplet sizes [7,10]

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