Capillary electrophoresis
Capillary Electrophoresis is a separation technique by which charged species can be transported inside a channel (capillary) by means of an electric field. Due to the individual differences in radius and electronic charge, each species moves with an individual speed. This makes it possible to sample the species from a blood droplet and to separate the species inside a channel.
The migration velocity, v, of an ion depends on: the electrophoretic mobility, μ [m2V −1s−1], and electric field, E [V/m]:
The electrophoretic mobility, μ, is an individual parameter of each species and is determined by the ion valence, z [-], electron charge, q [C], solution viscosity, η [Nsm−1] and ion radius, r [m]:
By combining the previous two formules it is possible to show that the velocity between individual species can be different while having the same electric field. It is therefore possible to separate these species.
The following graphs show the basic principle of Capillary Electrophoresis. At time t0 the positive ions are located near each other at the location of the positive electrode. Due to the electric field the ions migrate towards the negative electrode. After some time t1 the ions are separated from each other due to the difference in velocity. The smaller and higher valenced ions will have a higher velocity than the large and low valenced ions.
At time t0 positive ions migrate towards the negative electrode.
Duet o difference in velocity the ions are separated from each other inside the channel. This makes it possible to detect the species separately from each other.
By using conductivity detection it is now possible to detect the species at the end of the channel. The moment that a species passes the detection indicates the kind of specie while the change in conductivity is an indication for the amount.
Literature references for Capillary Electrophoresis:
Vrouwe EX, Luttge R, Vermes I, et al.
Microchip capillary electrophoresis for point-of-care analysis of lithium
CLINICAL CHEMISTRY 53 (1): 117-123 JAN 2007
Vrouwe EX, Luttge R, Olthuis W, et al.
Rapid inorganic ion analysis using quantitative microchip capillary electrophoresis
JOURNAL OF CHROMATOGRAPHY A 1102 (1-2): 287-293 JAN 13 2006
Vrouwe EX, Luttge R, Olthuis W, et al.
Microchip analysis of lithium in blood using moving boundary electrophoresis and zone electrophoresis
ELECTROPHORESIS 26 (15): 3032-3042 AUG 2005