Paper chromatography solvent, choice

Preparative, paper-chromatography is frequently used for further fractionation of the resulting mixtures. The high lability of glycosyl esters of nucleoside pyrophosphates seriously limits the choice of solvent systems. Systems used most commonly are neutral or slighdy acidic mixtures of ethanol with ammonium acetate,24,25 or weakly acidic solvents based on 2-methylpropionic acid.26 A solvent system containing morpholinium borate has also been found extremely useful.27... 

The choice of solvents (Table 11.2) and the methods of elution are much the same as for paper chromatography. The procedure must of course be conducted in a closed ehamber to prevent evaporation of the solvent and the technique used is ascending out of necessity. Two dimensional chromatography may also be carried out much in the same way as described for paper chromatography. One of the greatest advantages of TLC is the speed at which the separation is achieved. Generally 10-30 minutes are sufficient. However, with certain compounds about 90 minutes may be required. 

If paper chromatography is to be used successfully in organic analysis, the following factors must be considered carefully method and aim of the work, selection of solvent systems and experimental conditions, and choice of detection methods. In view of this, we shall try in the following paragraphs to give some practical advice. 

Checking the purity. Paper chromatography can also be used for detecting small amounts of impurities in analyzed samples. Success depends on a suitable choice of solvent system and color reaction. For example, all purification procedures can be followed chromatographically by checking the purified compound as well as the concentration of impurities in mother liquors, mixed fractions after column chromatography, etc. The preparation of derivatives can also be followed by this method. 

The separation of interactions by 2D spectroscopy can be compared with 2D chromatography. In a onedimensional thin layer or paper chromatogram, the separation of the constituents by elution with a given solvent is often incomplete. Elution with a second solvent in a perpendicular direction may then achieve full separation. In NMR spectroscopy, the choice of two solvents is replaced by the choice of two suitable (effective) Hamiltonians for the evolution and detection periods which allow unique characterisation of each line. 

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