why is filter paper used in chromatography
mode of separation of paper chromatography is the partition and the basis for
the separation is solubility. As in other chromatographic techniques this also
has a stationary phase as well as a mobile phase. Both phases are liquids. Stationary phase is water that is tightly bound to the paper. Filter papers are
used for this purpose and most common filter paper used is Whatman filter
paper- 98-99% Alpha cellulose. The cellulose paper can well absorb water
molecules. Fiber of cellulose acts as the stationary phase.
Mobile phase is a
solvent- solvent partially miscible in water. Paper chromatography is usually
used for separating amino acids and anions and also testing histamines and antibiotics.
Paper chromatography makes use of paper which acts as a stationary phase. Paper essentially consists of cellulose fibers which are polymers having Б OH functional groups sticking out of the polymer chains. These groups lead to retention and separation of surface absorbed molecules. In practice the separating molecules equilibrate between the layer of adsorbed water and the mobile phase solvent.
Different types of paper have been tried but Whatman No1 and 3 filter papers are found more suitable for analytical work. Chromatography paper is commonly available as 18БX22Б rectangular sheets. Apart from Whatman other popular manufacturers of chromatographic paper are Schleicher and Schull, Macherey Nagel, and Eaton-Dikeman but Whatman appears to be a popular choice. Coarseness of the fibers and packing density of papers decides between speed and resolution.
Fast papers are useful for major applications and when high resolutions are necessary slow papers are preferred In addition to pure cellulose several modified versions are also available to meet the specific separation requirements which include acetylated papers, silicone oil impregnated papers, silica and alumina impregnated papers and papers impregnated with ion exchange materials. Some typical applications of modified papers are
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