Abstract:
An automated capillary zone electrophoretic system is disclosed. The system employs a capillary cartridge having a plurality of capillary tubes. The cartridge has a first array of capillary ends projecting from one side of a plate. The first array of capillary ends are spaced apart in substantially the same manner as the wells of a microtitre tray of standard size. This allows one to simultaneously perform capillary electrophoresis on samples present in each of the wells of the tray. The system includes a stacked, dual carrousel arrangement to eliminate cross-contamination resulting from reuse of the same buffer tray on consecutive executions from electrophoresis. The system also has a container connected to the detection end of the capillaries. The container is provided with valving which facilitate cleaning the capillaries, loading buffer into the capillaries, introducing samples to be electrophoresced into the capillaries, and performing capillary zone electrophoresis on the thus introduced samples.

Description:
TECHNICAL FIELD 
     This invention relates to an automated apparatus for performing multiplexed Capillary Electrophoresis. It is especially useful in an automated Capillary Zone Electrophoresis (CZE) system for loading samples into a plurality of capillaries from wells of commercially available, microtitre trays of standard size. 
     BACKGROUND 
     The contents of commonly-owned U.S. patent application Ser. No. 09/105,988, which issued as U.S. Pat. No. 6,027,627 and also was published as WO 99/00664 are incorporated by reference to the extent necessary to understand the present invention. This reference discloses an automated apparatus for capillary electrophoresis. 
     FIG. 1 illustrates a prior art automated electrophoretic apparatus discussed in the above-referenced patent application for capillary electrophoresis. The apparatus includes a light source  452 , a processor/controller  404 , a dual carrousel arrangement having an upper carrousel  601  and a lower carrousel  602  which are aligned and spaced apart along a common axis and operated by a rotor  604 , a DC motor  605  having a movable member  603  to move a tray  214  place on one of the carrousels along a common axis toward or away from an array of capillary ends belonging to a capillary cartridge  300 , a detector  408  for detecting, at a window region  130  of the capillaries, the fluorescence emitted by samples migrating along the capillaries, and a computer monitor  406  to view the results of the migration. An electrophoretic medium, such as a gel, can be introduced into the capillaries via a conduit  606  in preparation for an electrophoretic run. 
     FIG. 2 illustrates a prior art plumbing system in accordance with the above-identified reference, for performing capillary electrophoresis using the device of FIG.  1 . In particular, FIG. 2 shows the integration of a gel syringe  804   5  and an HPLC wash solvent system  807  into the solvent/gel delivery module. A solvent manifold  850  connects three inlets from the feeder tubes  806  of the solvent containers  801 ,  802 ,  803  to an outlet. Feeder tubes  806  from the solvent containers  801 ,  802 ,  803  are connected to the inlets of the solvent manifold  850  by tubing  860 . The controller  404  pictured in FIG. 1 controls the solvent manifold  850  to select solvent from one of the three solvent containers  801 ,  802 ,  803 . The inlet of the HPLC pump  807  is connected to the outlet of the solvent manifold  850  by tubing  861  and the outlet of the HPLC pump  807  is connected to an inlet of a valve manifold  851  by tubing  862 . 
     The valve manifold  851  connects two inlets and an outlet. One inlet of the valve manifold  851  is connected to the gel syringe  804  by tubing  863  and the other inlet of the valve manifold  851  is connected to the outlet of the HPLC pump  807 . The outlet of the valve manifold  851  is connected to the solvent/gel input port  606  by tubing  864 . The controller  404  pictured in FIG. 11 causes the valve manifold  851  to select either the inlet connected to the gel syringe  804  or the inlet connected to the HPLC pump  807 . In this manner, gel and solvents are delivered to the capillary cartridge  909  in preparation for capillary gel electrophoresis of samples in microtitre tray  852 . 
     In the preferred embodiment, the tubing connecting the feeder tubes  806  of the solvent containers  801 ,  802 ,  803  to the inlets of the solvent manifold  850  is standard teflon tubing with a diameter of ⅛ inches. The tubing  861  connecting the outlet of the solvent manifold  850  to the inlet of the HPLC pump  807  is PEEK tubing with a diameter of {fraction (1/16)} inches. The tubing  861  connecting the outlet of the solvent manifold  850  to the inlet of the HPLC pump  807 , the tubing  862  connecting the outlet of the HPLC pump  807  to an inlet of the valve manifold  851 , the tubing  863  connecting the gel syringe  804  to an inlet of the valve manifold  851  and the tubing  864  connecting the outlet of the valve manifold  851  to the solvent/gel input port are PEEK tubing with a diameter of {fraction (1/16)} inches. 
     FIG. 3 illustrates a preferred embodiment of capillary cartridge  1180  in accordance with the above-identified application. In this embodiment, the capillary tubes run from their first ends  1188  disposed in an electrode/capillary array  1181 . The capillary tubes then run inside multilumen tubing  1183 . The multilumen tubing is taught in detail in U.S. patent application Ser. No. 08/866,308, which is incorporated by reference herein. The multilumen tubing  1183  is held firmly in place by tubing holders  1185 . The capillary tubes, without the protection the multilumen tubing, pass through an optical detection region  1187 . Beyond the optical detection region  1187 , the capillary tubes have a common termination and are bundled together and cemented into a high pressure T-shaped fitting  1182  made from electrically conductive material, which, during electrophoresis, is connected to electrical ground. 
     The tubing holders  1185  and the T-fitting  1182  are fixed to a cartridge base  1186 . The cartridge base  1186  is made from polycarbonate plastic for its dielectric characteristic. The base  1186  in turn is removably attached to a shuttle  1179  which includes a set of rail couplings  1184  protruding from its bottom. These rail couplings  1184  are arranged so that they fit on to a railing system (not shown in FIG. 18) of the apparatus in FIG.  1 . The railing system allows the shuttle  1184  to move between an in position and out position. The base  1186  is detached from the shuttle  1179  so that the cartridge  1180  is disposed (or cleaned) and a new (or cleaned) capillary cartridge is attached when the shuttle  1179  is in its out position. The combination of the railing system and the shuttle  1179  allows the newly attached capillary cartridge to be repeatedly located at the same position as that of the disposed capillary cartridge in relation to a camera and a laser (not shown in FIG. 3) when the shuttle  1179  is in its in position. In a preferred embodiment, the shuttle  1179  extends the length of the base  1186  with an opening to accommodate the electrode/capillary array  1181 ; the shuttle  1179  is attached to the base  1186  by a plurality of removable fasteners  1178 . 
     The prior art plumbing system of FIG.  2  and T-fitting of FIG. 3 are best suited for capillary gel electrophoresis. In capillary gel electrophoresis, the gel is fairly viscous, on the order of 50,000 centi-poise. This requires a system which can create pressure sufficient to load gel into the capillaries in preparation for a capillary electrophoresis run, and sufficient to expel the gel from the capillaries during reconditioning. 
     In contrast to the gels that are used in capillary gel electrophoresis, buffers are used to load the capillaries in capillary zone electrophoresis (CZE). These buffers have a viscosity on the order of that of water, i.e., about 1 centi-poise. While the low viscosity of buffers has the advantage of not needing high pressure to load and unload the electrophoretic medium, CZE with buffers does have the disadvantage of capillary siphoning. Capillary siphoning is characterized by the buffer solution at one end of the capillaries being completely drawn into the capillaries, thereby depleting the buffer at that one end. Like siphoning of any tubing, this problem occurs when the two ends of the capillaries terminate at different heights. The obvious solution to this problem is to ensure that opposite ends of the capillaries are maintained at the same level. This, however, is less than an ideal solution. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an automated parallel capillary zone electrophoresis (CZE) system. The CZE system of the present invention is realized by modifying the prior art capillary gel electrophoresis (CGE) system of the above-reference prior art. More particularly, the present invention is principally realized by modifying the plumbing at the ends of the capillaries towards which samples in the capillaries migrate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a prior art automated capillary electrophoresis system suitable for capillary gel electrophoresis; 
     FIG. 2 illustrates a prior art plumbing system for the electrophoresis system of FIG. 1; 
     FIG. 3 is a side view of a prior art capillary cartridge for use with the electrophoresis system of FIGS. 1 and 2; and 
     FIG. 4 a  shows a preferred embodiment of the present invention for performing capillary zone electrophoresis; 
     FIG. 4 b  shows a sequence of valve settings for the embodiment of FIG. 4 a;    
     FIG. 5 shows a second embodiment of a system in accordance with the present invention; 
     FIGS. 6 a  &amp;  6   b  show two versions of a third embodiment of a system in accordance with the present invention; 
     FIG. 7 shows intensity images comprising fluorescence data from experimental samples in 96 capillaries simultaneously migrating; and 
     FIGS. 8 a ,  8   b  &amp;  8   c  shows intensity plots for experimental samples migrating in three of the 96 capillaries. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The contents of commonly-owned, aforementioned U.S. patent application Ser. No. 09/105,988, which issued as U.S. Pat. No. 6,027,627 and also was published as WO 99/00664, are incorporated by reference to the extent necessary to understand the present invention. 
     FIG. 4 a  shows a buffer cell  100  connected to a capillary cartridge  102  via a pressure fitting  104  not unlike that shown in FIG.  3 . Indeed, capillary cartridge  102  is similar in structure to the capillary cartridge  1180  of FIG. 3, except that capillary cartridge  102  does not include the T-fitting  1182 . In the present invention, the buffer cell  100  and its associated hardware shown in FIG. 4a replace the prior art T-fitting  1182  of FIG.  3  and some of the prior art plumbing system seen in FIG.  2 . 
     The buffer cell  100  has a interior cavity  106  which is which preferably is sealed from the exterior, except for openings discussed below. In the preferred embodiment, the cell is formed from an acrylic plastic, which is an electrical insulating material. Inner walls of the cell are shaped and sized to provide an interior cavity  106  into which a buffer or other liquid  112  may be introduced. In the preferred embodiment, the container has a capacity of about 100 ml, by volume. 
     A high voltage electrode  110  connected to a power supply (not shown) is in contact with the liquid  112  in the cell  100 . for the purpose of applying a predetermined potential to the liquid in the container, and thereby also to the first, cell ends  107  of the capillaries which are in communication with the liquid  112 . During CZE, the high voltage electrode  110  is held at ground, while a non-zero voltage is applied to the second, sample ends  108  of the capillaries, with the polarity of the voltage being determined by the charge-type of the samples being separated. The magnitude of the applied voltage is on the order of 10-15 kV, not unlike that used in capillary gel electrophoresis. 
     A plurality of conduits communicate with the cavity  106  via corresponding valves. In the preferred embodiment, the valves are solenoid valves or the like, which can be controlled by computer, much as discussed in the above-identified U.S. application Ser. No. 09/105,888. In FIG. 4 a , each of the five conduits connected to the cell  100 , whether it is an inlet or an outlet, or serves as both, is shown to have a separate valve. It is understood, however, that one or more of these valves may be internal to equipment connected to the corresponding conduit, rather than being a discrete valve. 
     Drain outlet  114  and drain valve  116  allow a liquid in the cavity  106  to exit the cell  100  into a waste container (not shown). Air conduit  118  and gas (air) release valve  120  provide a path from the interior of the cavity  106  to the atmosphere when air valve release  120  is open. Pump inlet  122  and pump valve  124  provide a path for buffers, solvents and other liquids in containers, such as those indicated by  801 ,  802  and  803 , to enter the cell  100  via one or manifolds  850 , under assistance of an HPLC pump  807 , or the like. Pressure conduit  126  and pressure valve  128  connect a syringe  130  or other pressure applicator to the cavity  106  at a point above the level of liquid  112  therein. Finally, overflow outlet  132  and overflow valve  134  cooperate to provide a passage from the interior of the cavity  106  to a waste container, so as to ensure that the cell  100  does not overfill. While the various valves  116 ,  120 ,  124 ,  128  and  134  are shown to be distinct devices, it should be kept in mind that one or more of these valve may be an integral part of another device. For instance, pump valve  124  may be integrally formed as part of HPLC pump  807 , and pressure valve  128  may be replaced by precisely controlling the syringe&#39;s piston  136  by a stepper motor, or the like, under the direction of a controller. 
     FIG. 4 a  depicts the valve positions for performing steps associated with preparing and conducting electrophoresis on the samples in the capillary tubes of the capillary cartridge  102 . 
     When the cell  100  is to be drained, the pressure valve  128  and the pump valve  124  are closed, and the drain valve  116  and at least one, if not both, of the air valve  120  and the overflow valve  134  are opened. This allows the liquid in the cell to drain via drain conduit  114 . 
     Once the cell  100  has been completely drained, it may be partially filled with a liquid. For this, the drain valve  116  and the pressure valve  128  are closed, and the pump valve  124  and at least one, if not both, of the air valve  120  and overflow valve  134  open. The pump  807  is then operated to introduce a selected one of the liquids in containers  801 ,  802 ,  803  into the cell  100 . Because the pump introduces liquid into the reservoir and, because at least one of the air valve  120  and the overflow valve  132  is open, the liquid is not forced into the capillaries. However, the pump is controlled to turn off when the liquid reaches a predetermined level within the cell. 
     When the capillaries are to be cleaned, a cleaning solution, or the like, present in one or more of the containers  801 ,  802 ,  803 , is forced into the cell  100 , into the cell ends  107  of the capillary tubes, and out the sample ends  108  of the capillary tubes. For this, only the pump valve  124  is open while all the other valves are closed. Under such conditions, when the HPLC pump  807  operates, it forces liquid into the cell  106 , increasing the pressure therein. The increased pressure forces the cleaning solution into the cell ends  107 , through the capillary tubes and out the sample ends  108 . Once cleaning solution has been forced through, the pump valve may be closed, and the cell  100  drained, as discussed above. 
     After cleaning, the cell can be filled with buffer to a predetermined level by selecting the appropriate container  801 ,  802 ,  803  with the manifold  850 , and operating the pump  807  with the drain valve  116  and the pressure valve  128  closed, and the pump valve  124  and at least one, if not both, of the air valve  120  and overflow valve  134  open. The predetermine level of buffer should exceed the level of the bundle of capillary cell ends  107 . 
     Once the level of the buffer has exceeded the level of the capillary cell ends  107 , buffer may be loaded into the capillaries. For this, the only the pump valve  124  is left open, and all other valves are closed. The buffer enters the capillary cell ends  107 , thereby forcing any material within the capillary tubes out the capillary sample ends  108  into a waste container (not shown), and loading the capillary tubes with buffer. At this point, the cell  100  is filled with buffer to just below the level of the overflow conduit  132 , yet above the level of the capillary cell ends. In the preferred embodiment, the overflow conduit  132  is at about the 60% fill level and so the cell  100 , having a capacity of 100 ml, contains approximately 60 ml of buffer. 
     It should be evident that filling the capillaries with buffer is similar to the procedure for cleaning the capillaries, except that buffer, rather than a cleaning solvent, is used. As discussed above, this is controlled by operating the manifold  850  connected to the containers  80 ,  802  and  803  holding buffers, cleaning solutions and other liquids. It should be noted, however, that buffer itself can be used to clean the capillaries 
     To introduce a sample into the sample ends  108  of the capillaries, the sample ends  108  are first dipped into wells of a microtitre tray of standard size, such as those having a rectangular array of 8 rows of 12 wells, or those having 16 rows of 24 wells. The wells contain the samples to be electrophoresced. 
     The samples can be introduced into the sample ends  108  of the capillaries in one of two ways. One way is electro-kinetic injection wherein a voltage differential is applied between the sample ends and the cell ends of the capillaries so as to cause a portion of the sample to enter the sample ends. During electro-kinetic injection, the air valve  120  is kept open keep the reservoir  100  at atmospheric pressure, equilibrated with the cell ends  107  of the capillary. By applying a high voltage differential, the electro-osmotic flow causes sample enter the capillary sample ends  108 . Once the sample has been introduced into the sample ends from the wells of the microtitre tray, the sample tray is replaced a buffer tray and electrophoretic separation can take place in the capillaries under high voltage. 
     A second way in which to load samples into the sample ends  108  of the capillaries is by hydrodynamic injection. First, air valve  120  is opened and all other valves are closed to equilibrate both ends of the capillaries with atmospheric pressure. After equilibration, the air valve  120  is also closed, and so no valves are left open. At this point, the plunger  136  of the syringe  130  is pulled back by a predetermined volume. This causes the air above the liquid level in the cell to expand into a slightly greater volume and thereby create a vacuum, or negative pressure. At this point, the pressure valve  128  is opened, thereby applying this negative pressure to the surface of the buffer  112  in the cell  100 . Due to the negative pressure, a small amount of sample (or other substance in each of the wells of the microtitre tray) is sucked in at each of the capillary sample ends. 
     However, because air expands to fill the volume, there is a slight time lag between opening the pressure valve  128  and the uptake of sample. After the sample is allowed to enter due to the negative pressure for a predetermined period of time, typically on the order of a few seconds, the air valve  120  is opened, thereby stopping the injection process. Experiments have shown that hydrodynamic injection produces more reproducible results, and more even sample injection into the capillaries. This is because the volume into which the air expands does not immediately cause an instantaneous, corresponding intake of sample at the capillary sample ends, when the pressure valve  126  is opened. Instead, a fairly even uptake into each of the capillary sample results. 
     The pulling volume of the syringe controls the degree of negative pressure or vacuum. In the preferred embodiment, the plunger is pulled back by an amount sufficient to displace about 2 ml. In a 100 ml container having 60 ml of buffer therein, there is about 40 ml of air. When the plunger is pulled back by 2 ml, a negative pressure (relative to atmospheric) of 2.0 ml/40.0 ml=0.05 atm (or about 0.7 psi) is generated. Assuming a syringe precision of 0.1 ml and a container volume of 100 ml, the precision of the negative pressure can be controlled to about 0.001 atm. 
     Once the sample has been introduced into the capillary sample ends, the sample tray is preferably replaced by a buffer tray in preparation for electrophoresis. Replacing the sample trays with buffer trays helps ensure than excess sample is not taken into the capillary tubes, and also ensures that both ends of the capillary tubes are inserted into buffer. Using a device in accordance with the present invention, electrophoresis can take place in either a static mode, or a dynamic mode. 
     In the static mode, the pump  807  is not operational and only the air valve  120 , or the overflow valve  134 , or both, are open, with the remaining valves closed. Under these conditions, the buffer in the cell  112  is substantially stagnant during electrophoresis. 
     In the dynamic mode, the pressure valve  128  is closed, and all other valves are open, and the pump is operational, with buffer continuously being pumped into the cell through the pump inlet  122  and exiting the cell via drain outlet  114 . This ensures that fresh buffer bathes the capillary cell ends during electrophoresis while older buffer drains from the cell. Samples which have completed migrating from the sample end all the way to the cell end are also drained through drain outlet  114  and drain valve  116 . At the same time, since air conduit  118  and air valve  120  are open, the atmospheric pressure at both ends of the capillaries is equalized, thereby counteracting the siphoning effect, especially when the capillary ends are at the same height. 
     The dynamic mode, in which there is continuous flushing of the cell  100 , provides several advantages. First, continuously providing fresh buffer solution to the capillary cell ends removes charge depletion during electrophoresis. Charge depletion happens when anion and cation layers build up around the electrode, thereby resulting in a voltage drop between these layers which, in turn, reduces the voltage drop across the capillary tubes for separation. Flowing buffer helps retard the formation of such layers so that sample separation is more reproducible from run to run. 
     A second advantage to constant flushing is that it assists in removing fluids and contaminants introduced into the cell by electro-osmotic flow (EOF) during electrophoresis. EOF is a continuous pumping process which brings small amounts of sample-laden buffer into the cell. This can cause a change in buffer conductivity during electrophoresis. Constant flushing helps mitigate the problem of a solute-imbalance. Sensors and feedback control systems connected to the pump and to the pump and drain valves can ensure that the liquid level in the cell is maintained at a predetermined level. 
     A third advantage to continuous flushing is that it reduces the time spent cleaning the capillary tubes between runs. Because fresh buffer is constantly being introduced into the cell in the dynamic mode, one need spend as much time rinsing out the cell, upon conclusion of each run. 
     A fourth advantage to continuous flushing is that it removes air bubbles which otherwise collect around the capillary cell ends  107  during electrophoresis. Such removal is believed to be brought about by the buffer flowing past this area. 
     In one example of continuous flushing using capillaries with an inner diameter of 50 μm, a voltage differential of 10 kV across the capillary ends and borate buffer at a pH of 10.5, EOF speed is about 12 cm/min. This causes the liquid volume of the cell to increase at the rate of about 53 μ/min. If a drain is provided, the buffer must be replenished, as needed. In the preferred embodiment, only about 1 ml/min of fresh buffer is introduced into the cell while the drain valve is opened during electrophoresis. 
     Despite the above-stated advantages, it should be kept in mind that continuous flushing, though preferable, is not an absolute requirement in the present invention. Indeed, the primary requirements for carrying out CZE in accordance with the present invention are that a cell be provided, the cell having a liquid therein with the capillary cell ends terminating in said liquid, and that some mechanism be provided for creating a vacuum, or suction effect, at the capillary cell ends so as to draw samples into capillary sample ends. 
     FIG. 5 presents another embodiment in accordance with the present invention. In the embodiment of FIG. 5, a sealed, or at least sealable, cell  100  partially filled with a liquid  112  is provided. The capillary cell ends  107  terminate in this liquid  112 . An air syringe  130  and an HPLC pump  807  are also provided. When the syringe plunger  136  is pulled in the direction shown by the arrow Al, sample is introduced into the capillary sample ends  108 , as depicted by arrow A 2 . As discussed above with reference to FIG. 4 a , conduits for drain, air release and overflow may also be provided. To clean the cell in this embodiment, one simply restrains the syringe plunger and runs the pump to flush out the liquid in the cell and in the capillary tubes via the capillary second ends. 
     FIG. 6 a  presents yet another embodiment in accordance with the present invention. In this embodiment, which is similar to embodiment of FIG. 5, the entire cell and the syringe are filled with liquid and no air (or other gas) is used. Unlike air, liquid is incompressible, and so there is neither a time delay nor a variation in volume, between pulling the syringe plunger and the introduction of samples into the capillary sample ends. This means that the syringe must be much more precisely controlled in the embodiment of FIG. 6 a  than in the embodiment of FIG.  5 . For this, a micro-syringes operated by high-precision stepper motors, or the like, is used to ensure that only a small quantity of sample, about 0.1 μl or so, per capillary, is introduced into each of the capillary second ends. To clean the cell and the capillary tubes in the embodiment of FIG. 6 a , one may either push on the syringe plunger or run the pump; either one forces buffer into the cell and out through the capillary sample ends. 
     FIG. 6 a  presents still another embodiment in accordance with the present invention. In this embodiment, the syringe is replaced by a narrow-diameter drain outlet  140  controlled by a valve  142  situated at a vertical position lower than that of the capillary sample ends  108 . In this embodiment, gravity is used to cause a negative pressure. With the pump off, when the valve  142  is opened, liquid drains through the conduit  140  as indicated by arrow A 3 . This siphons liquid into the capillary sample ends, as indicated by arrow A 4 . 
     In the embodiments of FIGS. 5,  6   a  and  6   b , discrete valves between the pump and the cell are not shown; it is understood, however, that such valves may be integral with the pump. Similarly, no such valves are shown between the syringe and the cell. As explained above, the syringe plunger may be restrained and controlled by a motor so as to exert sufficient force in the appropriate direction, as dictated by a microprocessor or other controller. Also, with regard to the embodiments of FIGS. 6 a  and  6   b , it is noted that since only a very minute quantity of liquid is introduced from the capillary tubes into the cell, there is no appreciable increase in pressure within the cell, which is substantially able to accommodate the added amount. 
     Experimental Example 
     In an experimental set-up, capillary zone electrophoresis was carried out simultaneously in 96 capillaries using a device substantially arranged as shown in FIG. 4 a . About 60 ml of buffer was introduced into a 100 ml cell. The buffer used was a 10 mM borate solution in de-ionized water, adjusted to a pH 10.5 with NaOH. The viscosity of the buffer was almost the same as that of water. 
     Ninety-six capillaries, each having a length of about 50 cm, and ID of 50 μm and an 150 OD μm, available from Polymcro Technology of Phoenix, AZ were used. A window region was burned into each capillary using a hot wire at a point approximately 10 cm from one end of the capillaries, thereby providing an effective migration distance of about 40 cm from the sample end to the window region at which sample detection would take place. The capillaries were arranged substantially parallel to one another in a ribbon-like arrangement. More specifically, for most of their length from the sample ends to the window, the capillaries were spaced apart from one another by about 150 μm and, at the window region, were spaced apart by about 300 μm. Beyond the window region, the cell ends of the 96 capillaries were bound together as a bundle with Torr Seal, available from Varian Vacuum Products of Lexington, Mass. This bundle was connected to the cell shown in FIG. 4 a  with a Swagelock fitting, with the capillaries being in communication with the buffer. Meanwhile, the sample ends of the capillaries formed a two-dimensional array with a spacing corresponding to that of the wells of an 8×12 microtitre tray of standard size. 
     A 3 μl sample was introduced into each of the wells of an 8×12 microtitre tray. The sample comprised a protein cluster separated from among a multitude of such clusters in a protein mixture extracted from bacteria. The proteins were labeled with fluorescein dye, which has its absorption maximum at 495 nm. The sample ends of the capillaries were inserted into corresponding wells of the microtitre tray, in contact with the sample therein. Samples in each of the 96 wells were then hydrodynamically injected into the sample ends of the capillaries. This was performed by creating a vacuum by pulling on the syringe plunger to displace a 3 ml volume with all valves closed, and holding the plunger in place. At this point, the pressure valve was opened, thereby causing a negative pressure at the air-buffer interface on the surface of the buffer in the cell. The pressure valve was opened for about 20 seconds, permitting sufficient time for sample to be sucked into each of the capillary sample ends. At this point, the air valve was opened to alleviate the negative pressure and stop further hydrodynamic injection of sample. 
     Next, the microtitre tray containing samples was replaced with a microtitre tray containing buffer, in preparation for electrophoresis. A voltage differential of 10 kV was applied for about 10 minutes across the 50 cm-long capillaries, thereby providing an electric field of 200 v/cm and causing the samples to migrate under electro-osmotic flow, along with the buffer. An all-line Argon-ion laser, available from Spectra-Physics of Mountain View, Calif., and having an emissions peak not far from 495 nm, was used to illuminate the capillaries substantially at right angles thereto at the window region during electrophoresis. A CCD camera, available from PixelView of Beaverton, Oregon, was used to detect the fluorescence of the samples as they passed through the window region of the capillaries. The camera was set up substantially as disclosed in co-owned allowed U.S. application Ser. No. 09/084,236, also published as WO 99/32877. 
     FIG. 7 shows the fluorescence intensities at 530±8 nm, as a function of time, of the samples in the 96 capillaries, In FIG. 7, the abscissa (x-axis) represents the capillary number while the ordinate (y-axis) represents time. The darker the spot, the higher the intensity. 
     FIGS. 8 a ,  8   b  and  8   c  show plots of relative intensities for edge and center capillaries (capillary nos.  1 ,  48  and  96 ) in the array, as a function of time. In FIG. 8, the abscissa (x-axis) represents time, while the ordinate (y-axis) represents the intensity. As seen in FIG. 8, the intensity contours are substantially the same, exhibiting similar peaks from each capillary, albeit at slightly different migration times for each capillary. 
     As seen in this experimental example, CZE can be used to separate proteins in a buffer having a predetermined pH. For example, CZE can be used for human growth hormone separation, Ca++ binding protein separation, and recombinant human erythroprotein protein separation, among others. The separation mechanism in CZE is based on the ratio of the net charge to the size of the proteins. The net charge can be of either polarity, depending on the buffer pH and the protein&#39;s structure. Electro-osmotic flow of the buffer in the capillaries sweeps neutral molecules, as well as charged proteins, toward the detection window. The buffer preferably has a viscosity about the same as that of water. 
     The present invention may also be used in other capillary electrophoresis settings in which the separation media has low viscosity, on the order of 1-150, and more preferably on the order of 1-50, centipoise. At these viscosities, the separation media can be pumped into the capillaries under pressure without damage to the capillaries or other components of the system, and the samples injected hydrodynamically. A number of these other approaches and applications are now discussed. 
     Sodium Dodecyl Sulfate(SDS)-type Capillary Gel(CGE)/NGE (Non-Gel)Electrophoresis. In this approach, the proteins are bound with the surfactant SDS to form negatively charged aggregates. A polymer-based sieving matrix, such as polyethylene oxide(PEO), preferably kept at a low pH to extend the lifetime of the capillaries, is used as the separation medium. Applications for this include peptide mapping, molecular weight estimation, protein quantization and protein stability analysis. In some cases, CGE with a low-viscosity separation media, such as polyvinylpyrrolidone (PVP), which has a viscosity of 1-25 centipoise when in a weight percentage of 0.1-5%, can be used for DNA separation, as reported in Gao &amp; Yeung, Anal. Chem., 1998, v. 70, pp. 1382-1388. 
     Capillary Iso-Electric Focusing (CIEF), in which the proteins are separated according to their unique iso-electric points in a separation medium having a viscosity similar to that of water, may also be performed using the device and method of the present invention. 
     Affinity Capillary Electrophoresis (ACE) in which proteins are separated on the basis of specific bonding to other molecules in a separation medium having a viscosity of about 5-50 centipoise may also be performed using the device and method of the present invention. 
     Micellular Electrokinetic Capillary Chromotography (MEKC),in which compounds are separated based on their hydro-phobicity in a separation medium having a viscosity of about 5-50 centipoise may also be performed using the device and method of the present invention. Such an approach would be espcially useful in separating non-charged species. 
     Capillary Isotachphoresis (CITP), which is used for incapillary protein pre-concentration, immediately preceding CZE, may be performed using the device and method of the present invention. 
     While the above invention has been described with reference to certain preferred embodiments, examples and suggested applications, it should be kept in mind that the scope of the present invention is not limited to these. One skilled in the art may find variations of these preferred embodiments which, nevertheless, fall within the spirit of the present invention, whose scope is defined by the claims set forth below.