Electrophoresis: Overview

Electrophoresis is a powerful analytical separation technique that relies on the differential migration of charged species when subjected to an electric field. The core strength of electrophoresis lies in its ability to separate high-molecular-weight species in complex mixtures. It has found widespread use in biochemistry, molecular biology, and analytical chemistry, allowing the separation of compounds like amino acids, nucleotides, carbohydrates, and proteins with excellent resolution.

There are two main formats for electrophoretic separations: slab electrophoresis and capillary electrophoresis. Slab Electrophoresis uses a gel matrix, such as agarose or polyacrylamide, which acts as a sieve, allowing molecules to move through the pores. Capillary electrophoresis employs a narrow capillary tube filled with a buffer solution, providing high-resolution separation with rapid analysis time and minimal sample requirements. Although slab electrophoresis is widely used in biochemistry and biology to separate high-molecular-mass species, capillary electrophoresis is a more recent development with several advantages.

Capillary electrophoresis is a separation technique used to analyze complex mixtures of analytes based on their differential migration rates in an applied electric field. In this method, a sample is injected into a narrow capillary tube filled with a buffered solution, and an electric field is applied to facilitate separation. The migration rate of the analyte depends on its charge and size. The smaller, more highly charged ions migrate faster than the larger, less charged ones. In capillary electrophoresis, the migration of sample components is influenced by two types of mobility: electrophoretic mobility and electroosmotic mobility. Electrophoretic mobility is the solute's response to the applied electric field, with cations moving toward the negatively charged cathode, anions moving toward the positively charged anode, and neutral species remaining stationary. Electroosmotic mobility occurs when the buffer solution moves through the capillary in response to the electric field, typically toward the cathode.

Under normal conditions, capillary electrophoresis separates cations first, followed by neutral species, and finally, the anions. This separation is based on their respective electrophoretic mobilities and electroosmotic flow velocities. Notably, all separated species are eluted from the same end of the capillary, allowing their detection using quantitative detectors. The detector signals produce an electropherogram resembling a chromatogram but feature narrower peaks.

Capillary electrophoresis is a powerful tool for qualitative and quantitative analysis of complex mixtures. It provides information similar to that obtained from other separation techniques, such as gas chromatography (GC) or high-performance liquid chromatography (HPLC).