1. Canultravioletlightbe usedtodistinguishthe substancesfromoneanother?
2. Can iodine be used to distinguish the substances from one another?
3. Can the R f value be used to distinguish one substance from another?
4. Is it important that the sheets be examined under ultraviolet light before the iodine visualization?
5. Why do some substances move along the TLC plate at a rate different from other substances?

Implications and Applications

The analysis of an unknown analgesic drug can be performed by TLC. Specific components of a developed TLC sheet can be identified by the visualization method (under ultraviolet light or in iodine vapor) and from subsequent calculations of the R f values. Crime laboratory technicians often use TLC to determine the presence of controlled substances (e.g., cocaine) in an unknown sample.

The TLC technique is often used by forensic scientists to identify pen inks. For example, the need for differentiating inks arises when people prepare fraudulent documents. A person cheating the government may back-date a record to substantiate a false tax claim. The forensic scientist can determine how many inks or pens were used to prepare a document and the year of manufacture for the inks used.

Lipstick stains on clothing or cigarettes can also give valuable information about the identity of a likely suspect. The dyes that give lipstick its color can be identified by a TLC separation and compared with those used by the friends of the victim.

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