Question

Describe capillary electrophoresis. Compare and contrast the method to HPLC. What is order of retention time?

Answer 1

CAPILLARY ELECTROPHORESIS;

Capillary electrophoresis (CE) is a special case of using an electrical field
to separate the components of a mixture. Electrophoresis in a capillary is
differentiated from other forms of electrophoresis in that it is carried out
within the confines of a narrow tube. To understand the behavior of molecules
under the influence of an electrical field inside a capillary it is essential
to understand the phenomena that result from the geometry of a capillary.

Electrophoresis in a Capillary;

*The electrophoretic process in a capillary has all of the features previously
described. In addition, the small diameter of the capillary and its large
aspect ratio (length/width) contribute additional factors.

* the capillaries that are used in CE are circular in cross-section. However, capillary with square cross-sections have been produced. These may offer someadvantages in terms of thermal regulation and detection sensitivity

Comparison of CE and HPLC Methods;

CE (Capillary electrophoresis);

1.Separates ions based on their electrophoretic mobility

2.Electrophoretic mobility depends on the charge of the molecule, the viscosity, and the atom's radius.

3.Detector: diode array UV/Vis
• Background electrolyte/buffer solution:
130 mM NaOH containing 36 mM Na2HPO4
-- must always be fresh
--Sample derivatization is not needed
-- instead: dilution, centrifugation & filtration

HPLC analysis;

1.Chromatography involves a mass transfer process involving adsorption

2.HPLC suffers from peak overlapping

Retention Time;

Retention time is the amount of time a compound spends on the column after it has been injected. If a sample containing several compounds, each compound in the sample will spend a different amount of time on the column according to its chemical composition i.e. each will have a different retention time.

1. Retention times are usually quoted in units of seconds or minutes.

the Factors Affect RT;

Boiling point ,Column temperature,Carrier gas flow-rate,Column length