In this lab, the chemical components of Excedrin and Tylenol, two common, over-the-counter analgesic drugs, were determined by utilizing the technique of thin-layer chromatography, or TLC. The active ingredients of Excedrin were caffeine, acetaminophen, and aspirin with Rf values of 0.11, 0.38, and 0.61, respectively. The lone active ingredient of Tylenol was acetaminophen with an Rf value of 0.39. The elution sequence obtained in the experiment is as follows: ibuprofen (least polar), acetylsalicylic acid, acetaminophen, and caffeine (most polar).
Purpose of Experiment:
The objective of this experiment is to determine the active ingredients contained within a series of over-the-counter painkillers using thin-layer chromatography or TLC.
Introduction and Background:
TLC is a quick and convenient chromatographic method for analyzing a mixture by separating its constituent compounds. Along with determining the number of components in a mixture, TLC can also be of aid in identifying unknown compounds. Separation of compounds is achieved as a partitioning occurs between a mobile phase and a stationary phase. In TLC, the stationary phase is composed of a thin layer of the highly polar silica gel that is deposited on a glass or plastic plate, and the mobile phase consists of a liquid solvent that runs up the plate through capillary action, carrying the solutes, or the chemical compounds that are to be separated and analyzed. The principles of polarity and of intermolecular attractions are of importance in determining how compounds will behave during the separation. While the more polar components of a mixture will stick more strongly to the polar stationary phase and thus, move slower, the least polar components will move the fastest and run higher up the plate. Once separation is achieved, the compounds are then identified by the position of a spot on the plate after development, which enables one to determine the retardation factor, or Rf value, for each compound in the solvent system used. The Rf value is calculated using the following equation: Rf = distance traveled by substancedistance traveled by solvent front
In this experiment, by first developing a plate with the knowns, or standards of analgesic compounds, the Rf values of the unknown compounds contained within various commercial painkillers can be compared with those of the standards for identification purposes.
Chemicals, Equipment and Physical Constants:
* 2 x 400 mL beaker
* 2 x TLC plates & spotting capillaries
* 2 x filter paper
* 2 x watch glass
* Mortar and pestle
* centrifuge & 2 x centrifuge tubes
* UV light & ruler
Compound| MW| mp (°C)| bp (°C)| d (g/mL)| Safety Considerations| Aspirin (Acetylsalicylic acid) (ASA)| 108.16| 135| 140| 1.35| hazardous when breathed in; can cause skin irritation| Acetaminophen (Ace)| 151.16| 169| | 1.293| Harmful if swallowed; skin, eye, and respiratory irritant| Ibuprofen (Ibu)| 206.28| 75-77| | | Harmful if inhaled| Caffeine (Caf)| 194.19| 238| | 1.23| Harmful if swallowed; may affect CNS| Ethyl Acetate| 88.11| 84| 77| 0.8945| Highly flammable| Ethanol| 46.07| -114.1| 78.3| 0.789| Flammable liquid; can cause irritation upon contact with skin| Methylene chloride| 84.93| -96.7| 39.8| 1.3255| Should be handled as a carcinogen with extreme caution| Acetic acid| 60.05| 16.6| 117.9| 1.0492| Corrosive chemical; can irritate the lungs| Iodine (I2, gas)| 253.80| 113-114, but sublimes at room temperature| | | Very toxic if swallowed or inhaled; can be absorbed through skin; wear gloves|
A water bath was preheated to around 60° C. A line was lightly drawn 2 cm from the bottom of two TLC plates. Plate 1 was marked with five points (4 knowns and 1 mixture), and Plate 2 was marked with three points (2 unknowns and 1...