Marking the plate - With a pencil, make two small notches into the adsorbent about 2 cm from the bottom of the plate. The notches should be on the edges of the plate, and each notch should be the same distance up from the bottom of the plate. The notches must be farther from the bottom of the plate than the depth of the solvent in the jar.
Preparing a capillary tube - (As always, wear safety glasses.
Remember: hot glass looks like cool glass.) Take a capillary tube and gently
heat the middle of the tube in the flame of a gas burner. When the glass
gets soft, quickly pull the two ends of the capillary apart. The tube
should be very thin where the glass was soft. Now bring the two ends
together until the tube breaks in the middle. You now have two
narrow-tipped capillaries to use.
Spotting a sample - Touch the narrow tip of the drawn-out capillary tube to the liquid sample and draw up about 5 mm of solution. If you draw up too much solution, touch the tip of the capillary tube to a piece of clean filter paper. To spot the sample, gently, without disturbing the surface of the adsorbent, touch the capillary tube to the plate between the two notches and no closer than 2 mm to any edge. Make sure the spots are no more than about 3 mm in diameter.
Re-spotting a sample - After the first spot dries, spot the sample again directly over the top of the original spot. The second spot should not grow larger in diameter than the first spot.
