Chemistry Reference
In-Depth Information
18. Thin Layer Chromatography
Topic
Over-the-counter analgesics can be characterized using thin layer
chromatography.
Introduction
Pain relievers, or
analgesics
, come in many different varieties.
Pharmaceutical companies spend millions of dollars each year on
advertisements claiming that their brands of pain relievers are the
best and most effective. Most types of analgesics contain different
combinations of just a few common compounds. Some of the most
widely used compounds in pain relievers include aspirin, acetaminophen,
and ibuprofen. These compounds, some of which are shown in Figure 1,
are often combined with caffeine, a mild stimulant that counteracts the
sedative effects of the pain reliever.
In the laboratory, the components of an over-the-counter pain reliever
can be determined using
thin layer chromatography
(TLC), a technique
that separates compounds based on their size or polarity. Compounds
are placed in small spots on a plate coated with a substance such as
silica or alumina gel. The plate is placed in a container with
solvent
that
dissolves the spotted solution and carries it up the chromatography
plate as it moves upward. Different components of the solution will “fall
out” of solution as the solvent moves up the plate. The distance that
the substance travels varies based on the chemical composition of that
substance. For this reason, TLC can be used to identify the components
of an over-the-counter analgesic tablet if compared to known solutions.
In this experiment, you will perform thin layer chromatography on four
known solutions and two unknown solutions made from over-the-counter
analgesic tablets. You will then compare the results and determine which
compounds are present in the unknown tablets.
