In paper chromotgraphy, what is the effect of the ammonia, dimethylglyoxime and

Question

In paper chromotgraphy, what is the effect of the ammonia, dimethylglyoxime and oxine that leads to some of the colourless spots becoming visible?

Note: In this experiment, paper chromatography is used to identify the cations: Zn2+, Co2+, Cu2+, Cd2+ , Fe3+, and Ni2+ in two unknown solutions and a mixture. Filter paper (Whatman #1) serves as the stationary phase, and the mobile phase consists of a mixture of acetone and 6 M hydrochloric acid. A single spot of the mixture to be analyzed is applied near one edge of a sheet of filter paper. A spot of solution containing each of the cations that might be in the unknown mixture is also placed near the edge of the same sheet for comparison. The treated strip is then placed in a covered jar or beaker (which acts as a developing chamber) containing a shallow layer of the solvent mixture (see Figure 3). Since filter paper is very permeable to the solvent, the solvent begins to rise up the strip by capillary action. The various spots on the developed chromatogram will be highlighted by treatment with several chemical reagents to enhance their color. The reagents to be used are ammonia, dimethylglyoxime (DMG), and 8–hydroxyquinoline (oxine).

Explanation / Answer

Solution :-

In the paper chromatography when the TCL plate is placed in the solvent then the metal cation spots run along the solvent but these spots are colorless therefore to observe the spots when we use the different chemical reagents such as ammonia, dimethylglyoxime and oxine then these reagents forms complexes with the metal cations and these complexes have specific color so that the invisible spot shows the color for the specific complex.

Therefore the using the ammonia, dimethylglyoxime and oxine reagents we can observe the colors to the invisible spots because of the formation of the metal ion complexes with these reagents.

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