Analytical method for determining the sulfur content of EP (extreme pressure) additives in lubricating oils

Sulfur-containing organic compounds are important Extreme Pressure (EP) additives used in lubricants and are typically produced by the sulfurization of unsaturated organic compounds. The two most widely applied sulfurization routes-dark and light-result in products with markedly different properties. Dark sulfurization yields less stable additives with unpleasant odour, whereas light sulfurization technologies produce brighter and more stable products with superior performance, albeit at higher production costs. In response to increasing sustainability requirements, sulfurized vegetable oils have gained increasing attention as EP additives due to their renewable origin and biodegradability. Accurate determination of sulfur content is essential for the development, optimization, and quality control of EP additives. Various analytical methods are available for sulfur determination in the oil industry; however, many of them require expensive instrumentation or complex sample preparation. In this work, a UV-VIS spectrophotometry-based method was developed and evaluated for the determination of sulfur content in sulfur-containing EP additives. The method was validated by comparison with standard methods (ASTM D 6481 and ASTM D 5185), showing good agreement at 312 nm. • This method applies UV-VIS spectrophotometry to determine the sulfur content of EP additives. • This method offers a rapid and cost-effective alternative to widely used methods for the determination of sulfur content in industrial EP additives and lubricating oils.