Figure 1 : This is the complete working place for a µ-PLC “instrument”. Especially important is the “virtual” TLC chamber:
A chemically stable board with a position detector for adjusting to a precise vertical standing. Three aluminium rods, which allow for an accurate position of the thick glass cover plate (+- 0.1 mm in X and Y). In its center there is a 5 mm hole. In the figure above you see on all four corners under the cover glass small glass plates. They are 1 mm thick, have a size of 5 x 5 mm and keep the cover glass plate in a 1 mm distance above the HPTLC plate under the glass. This forms a virtual thin-layer vapor chamber. It can be flushed by laboratory air pumped through the black aquarium pump. The green plastic tube can be connected with several gas impregnation systems: for keeping the gas dry at a selected level of humidity, or through an impinger which adds formic acid traces, or ammonia traces, or any other volatile material like let say hexadecanol etc. The impinger is kept at a constant low temperature. As the gas flow is constant at about 2 L per minute, the trace concentration in the flowing gas is kept constant impregnating very quickly the 100 x 100 large HPTLC layer inside the virtual chamber. This adds the third and most often important chromatography phase to the µ-PLC system: the gas phase. Suddenly otherwise chemisorbed or tailing substances show perfect chromatography. Or the water content of the stationary phase is at optimum not available ever by a hot air dryer, or a laboratory oven treatment or the many other “tricks” which remain critical as the layer adsorbs or de sorbs very fast when transported through the lab air. When the whole system visible above sits in a plastic container under carbon dioxide, air sensitive substances can be sampled and separated for which otherwise most complex instrumentation would be necessary. Above the glass plate in the figure you see the mobile phase bottle - 1.5 ml volume. The HPTLC plate is position fixed by a piece of tape, which holds the procedure code (what, how, for whom, when, where, by which lab etc). The cover glass plate has a handle - see the aluminium rod right side.