Chromatography Case

Introduction/Background

The purpose of the experiment was to become familiar with the different methods and techniques of chromatography. Chromatography is "a method of finding out which components a gaseous or liquid mixture contains that involves passing it through or over something that absorbs the different components at different rates" (Bing Dictionary). According to the lab manual, "chromatography is the separation of two or more compounds or ions caused by their molecular interactions with two phases-one moving and one stationary" (Weldegirma). There are two phases to chromatography, one being the mobile phase, "which carries the sample through the solid, or liquid" (Weldegirma) and the other phase being the stationary phase (the absorbant), which is the phase that holds the solid or liquid portion of the mobile phase; "The success of the separation depends on the different polarities of the 3 components: the absorbent, the compound, and the solvent" (Weldegirma).

There are four techniques of chromatography: 1. Thin Layer Chromatography (TLC)- A small scale chromatography technique, has a solid (silica gel) for its stationary phase and a liquid for its mobile phase; 2. Column Chromatography (CC) - A large scale chromatography technique, which has a solid (silica gel) stationary phase and a liquid mobile phase; 3. Gas Chromatography (GC)- Involves having a high-boiling liquid as its stationary phase and an inert or inactive gas as its mobile phase; and 4. High Performance Liquid Chromatography (HPLC)- which involves having both its stationary and mobile phase to consist of a liquid. In this particular experiment, only the TLC and CC methods were used.

The TLC method involves using a plastic slip with a coating of silica gel and placing dots (at equal distances of each other so there is no mixing of the compounds) of the compounds along the base line then placing the slip in a jar filled a suitable solvent and closing the lid. The process is complete when the solvent reaches about three-fourths of the slip. Once it reaches that area, the slip is allowed to dry then placed underneath a UV lamp which is used to mark the distance traveled using the retention factor (Rf). The retention factor, or Rf, is "defined as the ratio of the distance traveled by the compound to the distance traveled by the compound to the distance traveled by the solvent" (Weldegirma). For the TLC method, the compound used were aspirin, acetaminophen, caffeine, and ibuprofen; the suitable solvent was made of 95% ethyl acetate and 5% acetic acid (9.5ml:.5ml).

The CC method consisted of 4 parts: preparing the micro-column, extracting the pigment from the spinach leaves, isolating the beta carotene using the CC method, and lastly performing a TLC of the extracted and pure products. In order to perform CC, the column should be wet using petroleum ether. After adding the spinach to the wet column and extracting the first color, you can finish and perform a TLC using the crude sample, pure beta-carotene, and your purified sample. Afterwards, you must calculate the Rf value; your purified and pure values should be about the same.

Experiment Section

Part A-TLC

 Obtain TLC plates

 Using a pencil, lightly draw a line that measures 1cm from the bottom(horizontally) and draw 4 small circles at equal spaces along the line.

 Place a drop of compound per circle ( 4 compounds, 4 circles)- make sure that the drops do not over-lap or touch at any point; For ibuprofen, you will need to use between 10-12 drops, for the other compounds use 3-4 drops. Make sure to label each dot.

 Place under UV lamp to verify that the compounds are present on the silica gel-they should appear as dark pink circles.

 Create the solvent using 9.5ml of ethyl acetate and .5ml of acetic acid and place solvent in solvent jar.

 Place the TLC template with the line at the bottom into the solvent jar and tighten the lid.

 Wait until the solvent is roughly three-fourths of the way up from on the template, remove and let dry.

 Once dry, place underneath UV lamp to locate the compounds; keep in mind that ibuprofen might not be visible.

 Measure the distance the compounds traveled and calculate the Rf value for each compound.

 Obtain another TLC plate.

 Using a pencil, lightly draw a line that measures 1cm from the bottom(horizontally) and draw 4 small circles at equal spaces along the line.

 Place a drop of compound per circle ( 4 compounds, 4 circles)- make sure that the drops do not over-lap or touch at any point; You will replace the ibuprofen with the unknown compound, adding 3-4 drops of each compound. Make sure to label each dot.

 Place underneath the UV to verify the presence of each compound-should appear as dark pink circles.

 Place in the solvent jar.

 Once the solvent is three-fourths of the way up the plate, remove it and let dry.

 Place underneath the UV lamp to locate the compounds.

 Measure the distance traveled by each compound and calculate the Rf value for each, including the unknown.

 Identify the unknown using the data previously obtained

Part B-Column Chromatography

 Prepare the micro-column.

1. Fill the column halfway with silica gel.

2. Add .5cm of sand on top of the silica gel.

 Prepare the crude sample.

1. Obtain 2g of defrosted frozen chopped spinach leaves.

2. Transfer into conical flask.

3. Add 15mL of ethyl acetate.

4. Ground the spinach leaves for 15 minutes.

5. Decant or filter the colored solution.

 Add anhydrous sodium sulfate (Na2SO4) to absorb extra water.

 Remove the solvent by vacuum evaporation.

 Save a few drops of the sample for another part of the experiment.

 Begin the column