Frans_M_Everaerts_Isotachophoresis_378342.pdf

GENERAL EQUATIONS
TABLE 4.2
REDUCED NUMBER OF PARAMETERS, KNOWN PARAMETERS AND EQUATlONS FOR THE
DIFFERENT ZONES IN MOVINGBOUNDARY ELECTROPHORESIS
Zone Parameters and equations
Lea ding Parameters: ifL, PH~, ck, cx,
Known parameters and equations: ck, ci, Ohm’s law, electroneutrality equation
Number of known parameters and equations is equal to the number of parameters
First Parameters: E,, pH,, ci, c$,
Known parameters and equations: Mass balances of B and A,, electroneutrality
equation, Ohm’s law, isotachophoretic condition
Surplus of one equation
Second Parameters: E,, pH,, c fj, ca, I cL2
Known parameters and equations: Mass balances of B, A, and A,, Ohm’s law,
electroneutrality equation
Number of known parameters and equations is equal to the number of parameters
In all other zones, the number of anionic species is increasing. Consequently, the
number of unknown parameters increases, but the number of mass balances also
increases, and the number of unknown parameters and equations and number of
parameters become equal again
Uth Parameters: Eu pHU, cfj, c a t
. . .
Known paramefers and equations.’ Mass balances of B, A,, A,, . . ., AU, Ohm’s law,
electtoneutrality equation
Number of known parameters and equations is equal to the number of parameters
Terminating Parameters: ET pH.,., ck, ci , . . ., ciu
1
Known parameters and e9Uan’onS: cir, . . ., ci, Ohm’s law, electroneutrality
equation
Shortage of one equation
and the pH and the concentration of the counter ions in the terminating zone are
determined by the buffer mass balance of the leading electrolyte zone (the surplus of
one equation). This indicates the problem or calculations with the moving-boundary model.
A surplus of one equation in the first zone determines the pH in the last zone, whereas
the pH in the last zone determines the effective mobilities of the anionic species in that
zone and hence the mass balances of those anionic species which determine the situation
in the first zone. Thus the pH, requires a calculation from the first zone in accordance
with the buffer mass balances, whereas the composition of the first zone is determined
by calculations from the last zone in accordance with the mass balances of the anionic
species.
For nearly all calculations in moving-boundary electrophoresis, simplifications have to
be made in order to avoid this difficulty. A mdel suitable for calculations on strong
electrolytes (for which the mobilities are independent of the pH), neglecting the
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