Before the analysis, the sample is shaken by hand for 30 s after a break of minimum 5 hours. Afterwards 50 ml sample and 50 ml filtered heptane are slowly mixed together. A new, dried membrane with a pore size of 0,45 µ is weighed.
The oil solvent mixture is filtered under a vacuum (710 mbar). When all visible liquid is gone, the membrane is dried for 3 hours at 80 °C. Afterwards it is weighed again to calculate the increase of weight due to the formation of residues in percent.
The color of the residues on the patch is analyzed with the colorimeter. A light source which consists of three LEDs emits light within the spectral region onto the membrane. The residues on the membrane reflect or absorb the light completely or partly. A sensor detects the intensity of the reflected light at different light wave spectra. The electronics analyses the difference between the sent and the reflected light. The differences in reflection and the color intensity at the different spectral regions make the calculation of the MPC index possible.