Hydrocarbon index
The hydrocarbon index (abbreviated also HC index or MKW index) is a sum parameter for mineral oil components in aqueous solutions in analytical chemistry . The hydrocarbon index is defined as the sum of the hexane-extractable organic substances that cannot be absorbed on magnesium silicate and have a boiling range of 175 to 525 ° C, such as heating oil , diesel fuel and lubricating oil .
Methods
In the past, an infrared spectroscopic method was used to determine the content of mineral oil components , in which the solvents carbon tetrachloride or 1,1,2-trichloro-1,2,2-trifluoroethane are used, which have not been used since 2005 for environmental reasons.
Today it is determined using gas chromatography using the hydrocarbon index method . Mineral oil components and substances produced in the petrochemical industry with around ten to forty carbon atoms are recorded. The boiling range must be between 175 ° C and 525 ° C and must not be adsorbed on magnesium silicate . On the basis of a peak pattern recognition, qualitative information on the composition of the mineral oil pollution can also be obtained. Low -boiling hydrocarbons (e.g. motor gasoline ) and high-boiling hydrocarbons (lubricating and gear oils) are not fully recorded. The concentration of the hydrocarbon contamination should be above 0.1 mg / l to ensure a reliable determination.
Both methods are convention methods and not absolute measurements . Therefore the measured values of the two analytical methods are not identical, but mostly comparable. The method can be used for all types of water such as drinking water , water from standing or flowing water , raw wastewater and water from the effluent of sewage treatment plants .