Separation of complex materials can be performed by a number of methods. For large molecules, especially proteins or nucleic acids, one of the methods used is capillary electrophoresis (CE). Separation takes place in a liquid-filled column about 25 to 100 cm in length and 50 to 75 microns in diameter. A high voltage is applied, and the resultant electrical field drives the suspended molecules (ions) toward the detector end of the capillary. Ionic species migrate at differential speeds, which are determined by their mass-to-charge ratio and their interaction with the capillary walls.

Fluorescence detection is sometimes adopted in CE, but in general the method of detection is UV absorbance detection by means of a filtered photodiode. CE instruments can also be coupled to a mass spectrometer, in which case a diode array (linear image sensor) is used to obtain an absorption spectrum of the analyte. In either case, UV hardness of the photodiode or linear image sensor is an important factor to the long-term stability of the detector. As for the source of UV light, a deuterium lamp is an excellent choice because its stability permits the measurement of small changes in optical density.

More information on electrophoretic applications is available on the website of the American Electrophoresis Society.

• R5984 28 mm side-on PMT: sensitivity from 185 nm to 900 nm, plus a wide effective area.
• R3896 28 mm side-on PMT: high-sensitivity multialkali photocathode for measurements from 185 nm to 900 nm.
• S1336-5BQ silicon photodiode: UV to IR sensitivity, low dark current. Designed for precision photometry.
• S3901-1024Q linear image sensor: NMOS sensor with large active area, low power consumption.
• L2D2 deuterium lamps: UV light sources with long life and high output stability.

Please contact us for information on other products which can be used for this application.