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

When the substances being chromatographed are colorless, faintly colored or very low in concentration, various techniques may be used to make the spots clearly visible.

In this experiment, visualization will be effected by spraying the chromatograms with reagents like ammonia dimethylglyoxime and oxine which react with the components sought to produce colored complexes.

for detection of Group IIIB elements :Co+2,Ni+2,ZN+2

and Group IIIA, Fe+3,Cr+3

Spray reagent like ammonia is used until yellow, green or brown spots are clearly visible

Fluorescent reagents may also be used to provide a fluorescent background when viewed under ultraviolet (u.v.) light, with spots being visible as dark areas where fluorescence quenching occurs.

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