Because the chromate has a relatively intensive yellow color, by taking a picture of the microchip, a densitogram of each microcolumn can be created by means of a densitometric software (e.g. CP Atlas 2.0, freeware thin layer chromatogram evaluation software) [29]. The densitograms, that is the plots of intensity (RGB values) of colors per pixels of the picture of the microcolumn, are shown in Fig. 4c.