Citation: Holland, T.; Karunanithy, R.; Mandrell, C.; Abdul-Munaim, A.M.; Watson, D.G.; Sivakumar, P. Observation of a Signal Suppressing Effect in a Binary Mixture of Glycol-Water Contamination in Engine Oil with Fourier-Transform Infrared Spectroscopy. Standards 2022, 2, 474–483. https://doi.org/ 10.3390/standards2040032 Academic Editor: El ˙ zbieta Macioszek Received: 22 September 2022 Accepted: 14 October 2022 Published: 1 November 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Article Observation of a Signal Suppressing Effect in a Binary Mixture of Glycol-Water Contamination in Engine Oil with Fourier-Transform Infrared Spectroscopy Torrey Holland 1,2 , Robinson Karunanithy 1 , Christopher Mandrell 1 , Ali Mazin Abdul-Munaim 3 , Dennis G. Watson 4 and Poopalasingam Sivakumar 1, * 1 Department of Physics, Southern Illinois University Carbondale, 1245 Lincoln Dr, Neckers 483-A, Carbondale, IL 62901, USA 2 Department of Life and Physical Science, John A. Logan College, 700 Logan College Dr, Carterville, IL 62918, USA 3 Department of Agricultural Machines and Equipment, College of Agricultural Engineering Sciences, University of Baghdad, Baghdad 10071, Iraq 4 Department of Plant, Soil and Agricultural Systems, Southern Illinois University, Carbondale, IL 62901, USA * Correspondence: psivakumar@siu.edu; Tel.: +1-618-453-2272 Abstract: An in-depth experimental study of the matrix effect of antifreeze (ethylene glycol) and water contamination of engine oil through FT-IR spectroscopy. With a comparison of the percent by volume concentration of contaminated fresh 15W-40 engine oil, there appeared to be a noticeable reduction in the O–H stretching signal in the infrared spectrum when ethylene glycol based antifreeze was included as a contaminant. The contaminants of distilled water, a 50/50 mixture of water and commercial ethylene glycol antifreeze, and straight ethylene glycol antifreeze were compared and a signal reduction in the O–H stretch was clearly evident when glycol was present. Doubling the volume of the 50/50 mixture as compared to water alone still resulted in a weaker O–H stretching signal. The possibility that this signal reduction was due to the larger ethylene glycol molecule having fewer O–H bonds in a given sample size was eliminated by comparing samples with the same number of O–H bonds per unit volume. The strong hydrogen bonding between that of water and glycol appeared to reduce the O–H stretching signal, even after comparing the different sample types at concentrations with the same number of O–H bonds per unit volume. Tukey’s highly significant difference was used to show that samples of the 50/50 mixture and straight glycol were not reliably distinguishable from one another when comparing the same number of O–H bonds per unit volume but readily distinguishable from that of water as the lone contaminant. Keywords: infrared spectroscopy; sonication; emulsion; glycol; antifreeze contamination; matrix effect; engine’s lubrication oil 1. Introduction Contamination of engine oil by glycol can yield severe damage to engine components within a short period [1]. While a reasonable threshold limit exists for small amounts of other harmful engine oil contamination, such as water, dirt, soot, fuel contamination, etc., in engine oil [2,3], differing sources have more caution against glycol contamination. Sources have suggested anywhere from a cautionary 200 ppm contaminate level [4], a maximum allowable value of 100 ppm [5], or having no safe limit of glycol contamination in engine lubricating oil at all [6]. Glycol-based engine coolants or antifreeze can contaminate engine oil through faulty engine seals, head gaskets, a cracked engine block, cracked cylinder heads, a defective water pump seal, or head bolts that have been improperly torqued [1,7]. When engine coolant is exposed to the engine’s lubricating oil under the high heat of a running engine, the glycol Standards 2022, 2, 474–483. https://doi.org/10.3390/standards2040032 https://www.mdpi.com/journal/standards