Abstract: Method and apparatus for controlling precisely the composition and delivery of liquid at sub-.mu.L/min flow rate. One embodiment of such a delivery system is an electro-osmotically driven gradient flow delivery system that generates dynamic gradient flows with sub-.mu.L/min flow rates by merging a plurality of electro-osmotic flows. These flows are delivered by a plurality of delivery arms attached to a mixing connector, where they mix and then flow into a receiving means, preferably a column. Each inlet of the plurality of delivery arms is placed in a corresponding solution reservoir. A plurality of independent programmable high-voltage power supplies is used to apply a voltage program to each of the plurality of solution reservoirs to regulate the electro-osmotic flow in each delivery arm. The electro-osmotic flow rates in the delivery arms are changed with time according to each voltage program to deliver the required gradient profile to the column.

Abstract: In many separation techniques, such as field flow fractionation, liquid chromatography and electro-phoresis, chemical species form bands that migrate at different velocities. If the data-digitization rate and excitation intensity are both set to be optimal for the fastest migrating band, to compensate for different band velocities, both the data-digitization rate and the excitation intensity are decreased as a function of time by a factor equal to the migration time of the fastest migrating band to the separation time.

Abstract: End-column detectors are provided in which either a sensing microelectrode or optical fiber is placed at the end of the separation capillary. Additionally, an alignment apparatus is provided to facilitate the manual or automated positioning of either type of sensing device relative to the end of the separation capillary. The invention provides detectors that are sensitive, reliable, and easy to construct and to operate.

Abstract: An electrophoretic or chromatographic separation capillary containing a fluid or gel defines a bore therein through which a sample migrates and separates into components. The tube has a side wall defining a passage therein. A substance is introduced into the capillary through the pasage by means of gravity, pressure or electroosmosis. The substance introduced changes the electroosmotic flow rate of the fluid in the capillary tube. The electroosmotic flow rate of the fluid in the capillary tube can be monitored by introducing a compound through the passage and detecting the concentration of the compound. Information on the flow rate can be used in a feedback action to control the flow rate, such as to keep it constant.

Abstract: A voltage alternating between a high value and a low value is applied across a separation capillary in an electrophoretic system and electrochemical detection is performed only during time periods when a low voltage or no voltage is applied to the tube to improve the sensitivity of detection.

Abstract: An electrophoretic or chromatographic separation capillary containing a fluid defines a bore therein through which a sample travels and separates into components. The tube has a side wall defining a through hole therein which is surrounded by a medium including a substance. The substance is introduced into the capillary through the hole by means of gravity, pressure or electroosmosis. The substance introduced may be used to label sample components to enhance detection, or to enhance separation of sample components.