Development and validation of an environmentally friendly attenuated total reflectance in the mid-infrared region method for the determination of ethanol content in used engine lubrication oil

► Method to quantify ethanol content in used lubrication oil is proposed. ► Samples are pretreated in a miniaturized system of extraction. ► NaCl aqueous solution is used as extractant (environmentally friendly). ► Method was validated and considered linear, precise, accurate and sensitive. ► Method can be implemented in routines for quality control of lubricant oils.