Thin layer chromatography (tlc).

Submerge the tip of a micro pipet into the dilute solution to be analyzed. A small amount of liquid will be drawn up into the pipet by capillary action. Then touch the tip to the tlc plate at the previously made pencil mark as shown in the next photo. Capillary action will cause a small amount of liquid to be drawn down onto the tlc plate. The spotting solvent will evaporate and a small spot of sample will remain.

After spotting is complete, the plate should be examined under the ultraviolet (uv) lamp to ensure that the spots are not too big or too small. The plate is then placed into the development bottle and allowed to develop as shown in the next photo. Care should be taken to ensure that the spots are above the level of the solvent, that the tlc plate stands straight, and that the filter paper in the bottle does not touch the edge of the plate. It is also best if the plate rests at the center of the bottom of the bottle. Otherwise the solvent meniscus near the edge of the bottom of the bottle may cause solvent to flow up the plate unevenly.

After the solvent has run almost to the top of the plate, remove the plate, mark the solvent front, and allow the solvent to evaporate, preferably in the hood.

The spots are then visualized, first with uv light as shown in the next photo, and then with iodine. The spots are marked with a pencil. The uv lamp must be held close to the plate for visualization to be effective.

Rf values are then calculated from the positions of the spots, the starting point and the final solvent front.

If a pen instead of a pencil is used to mark the starting line, the ink will be separated into its components as shown in the next photo (black felt-tipped marker used). It's pretty but not helpful to your analysis. This demonstration can be done at home using a piece of coffee filter, various pens of different colors and makes or food coloring, a small bottle, and a common solvent such as 2-propanol (aka rubbing alcohol. Caution; flammable, toxic). Using filter paper for chromatography is known as paper chromatography.