CE Systems Components

CE Systems Components

Home > Amplified DNA Product Separation > Capillary Electrophoresis > Principles > CE Systems Componenets

The most commonly used capillary electrophoresis units are manufactured by Applied Biosystems. All Applied Biosystems CE instruments operate similarly. The two most common models used in forensic science are the ABI 310 and the ABI 3100. This section focuses on the ABI Prism^® 310 Genetic Analyzer instrument. Other CE instruments used in forensic DNA laboratories are listed at the end of this module.

ABI Prism 310 Genetic Analyzer - Inside View. Shows pump block, detection regio, gel block region, and autosampler region.

Autosampler Region
Component	Purpose
Autosampler	Holds the sample tray and tubes and presents them to the capillary for injection
Cathode Electrode	Provides a negative pole for electrical current and is composed of platinum

Autosampler region. Shows cathode, autosampler, and tray.

Gel Block Region
Component	Purpose
Syringe	Stores the polymer between runs and generates the necessary force to fill the capillary with polymer
Anode Electrode	Provides a positive electrical current and is composed of platinum
Anode Buffer Reservoir	Contains buffer required for electrophoresis
Syringe Drive	Provides positive pressure to the syringe
Waste Vial	Collects waste

Gel block Region. Shows syringe drive, syringe, anode, anode buffer reserve, and waste vile.

Ions migrate through the capillary during electrophoresis. Positive ions will gather at the cathode and negatively charged ions will gather at the anode. The movement of ions creates an imbalance called buffer depletion. Buffer depletion can impair separation of DNA fragments due to a reduction in current. It is important to replenish or replace the buffer regularly to compensate for buffer depletion.

Detection Region
Component	Purpose
Charge-Coupled Device (CCD)	Detects fluorescence after the laser excites the dyes in the sample. The CCD camera is located behind the detector window.
Heat Plate	Heats the capillary during electrophoresis
Capillary	Where separation occurs. The capillary is a hollow fused silica tube with an internal diameter of 50-100 µm and 25-75cm in length. There is an outer polyimide coating that provides physical strength while allowing a degree of flexing of the silica tube. The capillary is filled with polymer and is transparent to ultraviolet and visible light. The capillary itself can be used as the detector cell when fluorescence detection is used. Before each injection, the capillary is filled with a new aliquot of a viscous polymer solution.
Detection Cell Window	Where dye tagged product is detected. The detection cell window is produced by burning the polyimide outer coating off the capillary. This cleared area is directly in the line of the laser beam to detector path, allowing the DNA fragments to be visualized as they pass by. Note: The detection cell window makes the capillary fragile in this area.

Detection Region graphic. Shows heat plate, capillary and detector window.

Computer
Component	Purpose
Computer	Controls the operation of the instrument. The instrument settings are defined in method files in the computer. These settings consist of run temperature, voltage, injection parameters, rinse cycles, and sample positions.

< Previous Page :: Next Page >