Chromatography

Chromatography

Chromatography is a collective term for a set of analytical techniques used to separate mixtures. Chroma means color and graph means to write or draw. Paper chromatography is an analytical technique used to separate mixtures of chemicals (sometimes colored pigments) using a partitioning method. The paper in this method is called the stationary phase because it does not move and serves as a substrate or surface for the separation. Analytes (substances being analyzed) are separated from each other based on a differential affinity to a solvent. The solvent dissolves and carries the analytes along the matrix of the stationary phase. Since the solvent moves through a wicking action, it is called the mobile phase.
Chromatography_tank

 

The distance that the analyte migrates along the paper related to the total distance that the solvent or mobile phase moves is called the Retention Factor or Rf.

Retention Factor

 

Chromatography Exercise

Are the food colorings used in colored candy the same as the the FD&C approved chemicals?

  1. Obtain a 25 cm square piece of chromatography paper that will fit into the beaker that will serve as the chromatography chamber.
  2. Draw a pencil line across the lower end of the chromatography paper about 2 cm from the bottom.
  3. Draw additional vertical tick marks along this line every 3 cm
  4. Place colored candy in a flask with 2 ml ethanol until the color dissolves into the solution
  5. Using an applicator, create a very small spot on a tick mark and allow to dry
  6. repeat application on the spot to make a very small and dark spot
  7. Continue to spot reference standards along other tick marks. These reference standards are food coloring.
  8. place approximately 1 cm of mobile phase solution (a very polar salt water solution) into the beaker
  9. roll the filter paper into a cylinder and fix with staples
  10. place cylinder into the beaker and cover fro 20 minutes or until the mobile phase reaches 2 cm from the top of the paper.
  11. Mark the final distance of the mobile phase and dry the filter
  12. Measure the distance of each spot from the starting point
  13. Measure the distance from the starting point to the final point that the solvent reached.
  14. Calculate Rf values and tabulate results.