Figure 11 : Start of brush sampling. In figure 10 the PLC analyst realizes, the sampled volume is MUCH too large for an acceptable separation efficiency. Above one sees three spots. One spot - the upper - is made by a single touch of the sample saturated micro brush no. 00. The lower spot right is a double spot. On the left side one sees two partially obverlapped non circular spots made by moving the brush. Under these three sample portions one may see a little circle. This has been made by a fused silica capillary filled with a small volume of red test color which can be focussed but is so polar, that it sticks in the stationary phase with any weaker polar mobile phase. This substance is used for local position signals near the plate center. Reason: this way enough accurate multi sampling, or to guarantee partial overlapping, or to do line or triangle sampling in order to have concentration ranges from low local mass to large sample mass or for an accurate positioning of internal or external calibration solutions. Figure 12 shows how to localize a syringe, a fused silica capillary or a metal/glass capillary filled with about 10 to 30 µl focussing liquid precisely into the plate center. NOTE: the focussing effect needs local precision. In figure 13 you can see what such an accurately positioned focussing makes with the three spots shown in figure 11 above. So click onto the right arrow icon above to reach figure 12 and 13 .
