Figure 10 : Micro brush sampling - brush code number - repeatability - volume The first row shows 5 repetitions made by brush no. 1. The fifth spot has been focussed to a circle using methanole. The second row is made by brush no. 3, the third by no. 5, the forth by no. 6, the fifth with the smallest brush nr 00. This micro brush is also seen in the figure above as the left one of two. The last row has been sampled with a 20 µl glass pipette. The repeatability standard deviation values reach +- 1.5 % in the best case (largest size) and around +- 4 % by the smallest brush no. 00. The following table informs about the sampled volume as function of the brush no.
On 0.2 mm thick HPTLC plates a standard mobile phase like hexane produces a circular wet area of 90 mm diameter if covered by a cover glass plate in 1 mm distance. This causes a virtual TLC chamber. There are no measurable vapor phase losses if the plates and thus the virtual chamber are in precise vertical position.
