Chromatography Lab

Chromatography The separation of components of a mixture. Paper Chromatography consists of placing a spot of color from something like a marking pen onto a piece of paper. (Use a pencil to mark the spot where the pen colors go at the beginning of the experiment so you know where the sample began. This location is called the origin.

The bottom of the paper is carefully immersed in water but be careful to not let the water go above the spot when you initially put the paper in the water or the colors will run in every direction. You want the water to move slowly up the paper through the spot.

As the water makes it way up the paper by capillary action, it will dissolve any water soluble components of the inks. More soluble components will move further up the paper and less soluble components will remain behind.

The two opposing forces at work are the solubility of the ink component in water and the attraction the ink components have for the paper. If the solubility in water is sufficient then the ink component will travel further up the paper. If the solubility is low, then the attraction for the paper will remain a greater force of attraction and the component will remain behind on the paper.

Retention factor is a measure of the average distance traveled by each component. You can measure the retention factor by measuring the distance the center of each color spot traveled from the origin (the original pencil mark.) Then divide the distance traveled by each spot by the distance traveled by the solvent front (the water level at its furthest point from the origin.) The fraction you get is called the retention factor.

Place spot in pencil about 2 cm from the bottom of a piece of chromatography paper equidistant from both sides. Apply a marker onto this spot and let the ink soak into the paper until the spot of ink is about 3-4 mm in diameter.

Roll the opposite end of the paper around a pencil or pen and paperclip the paper in place. Place the bottom of the paper in a large beaker containing just enough tap water to go about half way to the spot. Do not allow the water to touch the spot before it gets a chance to soak into the paper.

Let the water wick up the paper until it gets about ¾ - 4/5 of the way to the very top. Pull out the paper and let it rest on a paper towel. Before the water dries too much but after the water level ceases to rise up the paper (it will continue to wick into the paper after it is removed from the beaker) draw a pencil line across the top of the paper at the water level. You will use the distance from the origin to this location as the distance traveled by the solvent (water in this case).

Carefully draw circles around each color component. This may be tricky as the colors might overlap. Some may be very difficult to determine where the circle begins and ends. Do the best you can. Place a pencil spot in the center of each spot. You will use the distance from the origin to this location to calculate the distance traveled by the spot. (Since the color spot is larger than a single point, the spot in the center will give you the average distance traveled by this spot.)

Calculate the retention factor of each colored spot you can locate. In your conclusion, report the retention factor of each spot for each of two pens used. Be careful to organize the conclusion so it is clear which spots belong to which pens. Use a different paragraph for each pen.

Discuss the relevance of the data. – What do the different retention factors tell us about each pen component? – Which colored components are more soluble than others? – There is no significant error analysis for this experiment.

Research chromatography and write one paragraph on its use in science, medicine, forensics etc. Be sure to include your references. Type and double space please.