Vernier Software and Technology
Vernier Software & Technology

Identifying an Unknown Analgesic by Melting Temperature and Thin-Layer Chromatography


Thin-layer chromatography (TLC) is an important technique in organic chemistry. TLC uses the different affinities a compound has for the mobile and stationary phases to achieve separation of mixtures of organic compounds. TLC can also be used to identify compounds by comparison with known samples, check the relative purity of a compound, and monitor the progress of a reaction.

In thin-layer chromatography, the stationary phase is the adsorbent (usually silica or alumina) coated on a sheet of glass, metal, or plastic. The sample is applied as a spot near the bottom of the plate. The TLC plate is then placed in a developing chamber containing a shallow layer of solvent where the mobile phase (solvent) slowly rises by capillary action.

Under a given set of conditions, a specific compound will travel a fixed unique distance relative to the solvent front. Different compounds generally move at different rates. As a result, if the sample is a mixture of compounds it will separate into a series of spots at varying distances up the plate. If the sample is pure, then only one spot will result. A UV light source is used to visualize the spots on the TLC plate. Under UV light, the chemical deposits will appear as dark spots against a bright background.

TLC separation results are expressed in terms of Rf (retention factor) values. The Rf is a ratio calculated by dividing the distance traveled by the sample by the distance traveled by the solvent at the end of the experiment.

In this experiment, TLC and melting temperature will be used to identify the active ingredients in an unknown over-the-counter medicine tablet. The tablet you will test contains one or more of the following: acetylsalicylic acid (aspirin), acetaminophen (the active ingredient in Tylenol®), caffeine (ingredient in Excedrin®), and/or ibuprofen (the active ingredient in Advil®).


In this experiment, you will

  • Calculated the Rf values of acetylsalicylic acid, acetaminophen, caffeine, and ibuprofen.
  • Determine the melting temperature of each of these analgesics.
  • Identify the solvent system for good separation.
  • Use TLC and melting temperature to identify your unknown analgesic.

Sensors and Equipment

This experiment features the following Vernier sensors and equipment.

Additional Requirements

You may also need an interface and software for data collection. What do I need for data collection?

Organic Chemistry with Vernier

See other experiments from the lab book.

1Determining Melting Temperature
2Recrystallization of Benzoic Acid and Aspirin
3Determination of a Boiling Point: Simple and Fractional Distillation
4Identifying an Unknown Analgesic by Melting Temperature and Thin-Layer Chromatography
5Separation of Organic Compounds by Acid-Base Extraction Techniques
6Understanding Polarimetry
7Identification of Organic Unknowns Using Polarimetry
8Investigating Gas Chromatography
9Fractional Distillation of Esters
10Understanding Intermolecular Forces Using a Gas Chromatograph: Enthalpy of Vaporization
11Investigating Thermodynamic Relationships of Substituted Hydrocarbons
12Extraction of Spinach Pigments and Analysis by Electronic Absorption Spectroscopy
13SN1: Synthesis of t-butyl chloride
14SN2: Synthesis of 1-bromobutane
15Observing the Reaction Kinetics of Sucrose with Polarimetry
16The Synthesis and Analysis of Aspirin
17Isolation and Epoxidation of a Natural Product: Limonene
18Synthesizing Ethyl Acetate by Fisher Esterification
19Synthesis of Dibenzalacetone by Aldol Condensation
20The Diels-Alder Reaction of Anthracene with Maleic Anhydride
21Friedel-Crafts Acylation of Ferrocene
22Grignard Formation of Crystal Violet
23Synthesis of Fluorescein
24Synthesis of Methyl Orange and Its Application to Textiles
25Analysis of Natural Products
26Using a Gas Chromatograph: Identifying an Unknown Compound

Experiment 4 from Organic Chemistry with Vernier Lab Book

<i>Organic Chemistry with Vernier</i> book cover

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