Adblue is used as a consumable in selective catalytic reduction in order to lower NOx concentration in the diesel exhaust emissions from diesel engines. It is an aqueous urea solution made with 32.5% urea and 67.5%. Or at least it should be. Poor fluid handling practices mean that contamination is common.
Elemental Analysis, Appearance Check, Urea Content, Density, Refractive Index and Hydrocarbon Content Measurements are used to check Adblue condition and contamination levels.