Diesel exhaust fluid (DEF), alternatively called AUS 32 and marketed as AdBlue is a diesel fuel additive that is stored separately from the car’s fuel tank. To comply with Euro 6 regulations, diesel cars use a Selective Catalytic Reduction (SCR) catalyst to inject AdBlue into the exhaust. When added into the exhaust system, AdBlue reduces the nitrous oxide emissions by breaking down the harmful mono-nitrogen oxides and forming nitrogen and water. Infrared (IR) spectroscopy allows for the visual comparison of a sample against a standard reference sample for confirmation that the material is AdBlue. This application note describes an analytical method for the testing of AdBlue in accordance with ISO method standard 22241-2:2019 (E) using the PerkinElmer Spectrum Two™ FT-IR equipped with a UATR (Universal Attenuated Total Reflectance) accessory.