Figure 22 : the wick of the mobile phase bottle sits on the stationary phase surface only as strong as caused by the weight of bottle, PTFE tube, wick and the 1..1.5 ml liquid inside. Thus the 5 mm PTFE tube must be movable up/down without mechanical restriction. Thus the accuracy of the i.d. of the cover glass hole and the outer diameter of the PTFE tube allow only + 0.05 mm tolerance. More would cause too strong deviations from the center position and a too slate angle of the wick.