Question

So I have a lab practical coming up; how do I know when to take an IR spec versus making a TLC chamber?

Follow up question: Can someone walk me through the interpretation of a TLC chamber?

Answer 1

1) IR spectrum is taken to identify the compound on the basis of the specific wavelengths infra-red radiation absorbed by the functional groups present in the compound.

The spectrum of a mixture of compound is not as clear as the spectrum of a pure compound.So often IR spectrum is taken to check the purity of compound separated by physical methods like fractional distillation, chromatography and other.

The IR spectrum of pure compound (or expected compound ) from the separation is compared with the IR spectrum of the compound you obtained by TLC,.If the peaks of absoroption in the two overlaps with each other ,then it is taken that the separated compound is pure.

2) Interpretation of TLC=

TLC is used for separation and identification of compounds in a mixture of compounds.Identification is done by comparing the Rf value of the separated compound with the Rf of known compounds.

A TLC plate may be sheet of glass or metal coated with a thin layer of a solid adsorbent material like silica /alumina (the stationary phase).

Only a small amount of the mixture of compounds (meant to be analyzed) is spotted near to the bottom of this plate at the base line.

The TLC plate is to be placed in a solvent or the eluent (mobile phase). As the eluent rises up the TLC plate by capillary action, the spotted compounds in the mixture rises along with it at different rates (based on their absorption on the solid adsorbent).

Some components of the mixture travels faster and reaches the top position ,while other may reach only up to a certain level.We remove the plate from the developing chamber as soon as the eluent reaches near the top of the plate.The plate is then dried and the separated components are studied.

Rf (retardation factor) value for each compound is calculated and compared with Rf of known compounds for identification.

Rf=distance travelled by the compound/distance travelled by solvent

Both the tools of IR and TLC helps in efficient separation and identification of compounds in a mixture