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Encyclopedia of Physical Science and Technology En005H-218 June 15, 2001 20:33
Electrophoresis
S. P. Spragg
Birmingham University, England
I. Underlying Theory
II. Free-Solution Electrophoresis
III. Electrophoresis in a Stationary Matrix
IV. Electrophoresis in Oscillating Electric Fields
GLOSSARY F is the product of the particulate coefficient and Avo-
gadro’s number (see Mole).
Chemical potential Ability to do chemical work; analo- Isoelectric point When organic ampholytes (also see
gous to mechanical potentials. Polyampholyte) have two covalently linked basic and
Conductance Inverse of electrical resistance of an ionic acidic ionic groups, the isoelectric point equals the hy-
solution. A specific conductance is defined as the in- drogen ion concentration where the net charge is zero.
3
verse resistance of 1 M of solution under a potential Isotachophoresis A procedure similar in many respects
of1V. to isoelectric focusing, since it separates macroions
Coulomb Unit of electrical charge having dimensions of through differences in charge rather than size (the
ampere seconds. Bringing 1 mol of charges of mag- important property for polyacrylamide gel electro-
nitude ze (e = charge of an election, z = number of phoresis).
charges per particle) up to a potential V requires doing Mobility Normalized velocity of a particle. In elec-
work on the charge equal to zeVN (N = Avogadro’s trophoresis the mobility is the velocity per volt × me-
2
−1
number); here, eN is called the faraday (F), having ter (m sec −1 V ); this is different from the mobility
units of coulombs per mole. coefficients found in diffusion and sedimentation.
Electrochemical equivalence Number of moles of an ion Mole Chemical quantity used to describe a unit contain-
required to carry1Fof charge. ing ∼6.03 × 10 23 molecules or ions; this constant is
Electrodes Conducting units inserted in a solution; neg- called either Avogadro’s or Lochschmidt’s number.
ative electrode is called the cathode, and positive elec- Polyampholyte Polymerized ampholyte in which some
trode is called the anode. A reversible electrode is pro- of the ionizable groups of the monomeric ampholyte
duced by coating the metal with one of its salts, for remain free after polymerization to form a macroion.
example, silver/silver chloride. A protein is a common example and is formed by con-
Frictional coefficients Generally, these are introduced in densation of amino acids (called zwitterions) through
hydrodynamics in order to ascribe a Newtonian friction the terminal carboxyl group of one with the terminal
to particles or molecules. A molar frictional coefficient amino group of the next to form a peptide.
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