Answer the questions –- Print

1) If dye A is organic in nature , then it will be more solublein non-polar isopropanol than any polar solvent .So it will migratelarger distance in solvent with more isopropanol.

2) TLC can be used to help identify unknown compounds. Explainhow this might be accomplished using the dyes as an example.

TLC or thin layer chromatography, has a thin layer of solidadsorbent like SiO2(silica ) or alumina (Al2O3) applied on glass orplastic,called the stationary phase.A solvent generally non-polaris allowed to flow through the stationary phase(the mobile phase),carrying the components of the mixture with it.Mostly, non –polarcomponents of the mixture is separated by the non-polar mobilephase and the polar components are adsorbed by the polar stationaryphase.

A small amount of the mixture to be analyzed is put near thebottom of the TLC and then the plate d in placed in the solven.Theeluent or the solvent slowly rises up the plate by capillaryaction.

As the solvent moves past the mixture an equilibrium isestablished for each component of the mixture with its moleculesadsorbed on the solid adsorbent and the molecules which are insolution.

As the components differ in solubility in the solvent ,somecomponents will move farther up the plate than others.

The plate is removed from the developing chamber, dried, and thecomponents of the mixture are separated.

3) a. Retention factor =It is the ratio of the distance migratedby the sample to be analysed to the distance moved by thesolvent.

b. Resolution=The resolution of a elution in HPLC is thedifference in retention times between two given peaks, divided bythe combined widths of the peaks.

RS=2[(tR)B−(tR)A]/WB+WA

Where B has longer retention time, tR and W is the elution peakwidth .If the resolution is greater than one, the peaks can bedifferentiated.

c. Diffusion =Fluid or solvent travels from the region of highconcentration of solute dissolved in it to the region of lowconcentration spontaneously.This process is called diffusion.

d. Plate=Glass or plastic or metal surface used forchromatography, where solid adsorbent is applied for running aneluent or solvent.The mixture to be separated is placed at thebottom of the plate.

e. Plate height =

The chromatographic column is divided into discrete sectionscalled theoretical plates. There exists an equilibrium partitioningof the solute between the stationary phase and the mobile phase inthese plates.The column efficiency in defined terms of the numberof theoretical plates, N and plate height.

               N = L / H

Where, L is the total length of the column and H is the heightof each theoretical plate. Smaller theoretical plates defines moreColumn efficiency.

f. Longitudinal diffusion =

It is well-known that molecules disperse due to the diffusion.The longitudinal diffusion is the diffusion along the column longeror longitudinal axis .This leads to the band broadening of thechromatographic zone.

g. Adsorption chromatography =

Adsorption chromatography is the chromatography in which amobile solvent or gaseous phase is adsorbed on a stationary solidphase. The equilibrium between the mobile and stationary phaseaccounts for the separation of different solutes , as the solute isdistributed between the phases based on their affinity for solidphase or solubility in the mobile solvent.

h. Partition chromatography=

Partition Chromatography is based on a thin film formed on thesurface of a solid support by a liquid stationary phase. Solute isdistributed between the mobile phase and the stationary liquid. Egcolumn chromatography