Frans_M_Everaerts_Isotachophoresis_378342.pdf

MATHEMATICAL MODEL FOR THE STEADY STATE 59
EL rEAL = EvfiAv (4.28)
where fi and fiA are the effective mobilities of the leading ion in the leading zone and
AL . 1.I
the sample ions A, in the Vth zone, respectively.
(4.29)*
For all other ionic species, a similar expression for the effective mobilities can be derived.
The isotachophoretic condition is the essential difference between isotachophoresis and
other electrophoretic methods.
4.3- 2.3. Mass balance of the buffer
The movements of the zone boundaries LV and VW per unit of time are equal (AX;
see Fig.4.8):
AX=ELfiAL=E V fi Ay =E W fi AW
A buffer ion Pin the Vth zone (at t=O) can just reach the zone boundary VW at t= 1 if
the distance over which it moves during one unit of time is
B2X = Ev%v
and a buffer ion Q (at t=O) can just reach the zone boundary LV if
(4.30)
(4.3 1 )
B1X = ELMB. (4.32)
This means that the amounts of the buffer that pass the zone boundaries LV and VW are
the amounts of the buffer present in the volumes A, and A2 at time t=O. The amounts
of the buffer entering and leaving a zone must be equal in the steady state, and therefore
OAIC&= O A ~ V C ~
or
O(AX+BlX) cr = O(AX+B2X) 4
BL
V
*Compare with eqn. 4.16.
(4.33)