Total petroleum hydrocarbons index (TPH) is a typical environmental analysis. It has replaced the infrared spectroscopy method using problematic solvents, i.e. Freons. This gas chromatography analysis (GC) monitors hydrocarbons between n-decane and n-tetracontane. These two hydrocarbons are used as the range marker and injection efficiency control. Aditionally, the GC method has an important advantage – this can show a type of hadrocarbon contamination (e.g. gasoline, naphtha, motor oil) and weathering status (some n-alkanes disappear during their stay in the enviroment).