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PAPER CHROMATOGRAPHY-notes

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PAPER CHROMATOGRAPHY
• The separation technique known as chromatography was first
used in the early part of the twentieth century. The word
chromatography comes from two Greek words that mean
‘‘colored graph,’’ a good description of the earliest applications
of the technique to separate colored plant pigments.
• All chromatographic methods involve the use of the same
general principle.
• A mixture of dissolved solutes that is to be separated is
passedover a stationary material. The moving phase in which
the solutes are dissolved is called the mobile phase, and
the stationary material is called the stationary phase.
PAPER CHROMATOGRAPHY
• Separation occurs when the dissolved solutes have different affinities
for the mobile and stationary phases. A solute that is strongly
attracted to the stationary phase spends more time attached to
that phase than a solute that is strongly attracted to the mobile
phase.
• As a result, the solute with a stronger affinity(more polar) for the
stationary phase spends less time in the moving mobile phase and
does not move along as rapidly as the solute that is attracted more
strongly to the mobile phase.
• Thus, the solutes move different distances and are separated during
the time the mobile phase is moving through the stationary phase.
PAPER CHROMATOGRAPHY
• The extent of separation of solutes in a chromatogram is expressed
by the Rf value of each solute.
• The Rf (retention factor) value is calculated by dividing the distance
traveled by the mobile phase into the distance traveled by the solute:
PAPER CHROMATOGRAPHY
• The distances used in Equation 1 must be measured from the same
starting point, which is usually the point at which the solute sample
was applied to the paper.
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