Abstract:
An electrophoretic apparatus comprising: a first electrolyte chamber containing a first electrode; a second electrolyte chamber containing a second electrode; a first sample chamber disposed between the first and second electrolyte chambers and proximate to the first electrolyte chamber; a second sample chamber disposed between the first sample chamber and the second electrolyte; three ion-permeable barriers separating the first electrolyte chamber, the first sample chamber, the second sample chamber, and the second electrolyte chamber, respectively, wherein the ion-permeable barriers impede convective mixing of the contents in each of the respective chambers; a first electrolyte reservoir and a second electrolyte reservoir in fluid communication with the first and second electrolyte chambers, respectively; a first sample reservoir and a second sample reservoir in fluid communication with the first and second sample chambers, respectively; means adapted for communicating a first electrolyte and a second electrolyte between the respective electrolyte chambers and reservoirs; means adapted for communicating a first fluid and a second fluid between the respective sample chambers and reservoirs, wherein at least one of the first and second fluid contains at least a sample, wherein application of an electric potential causes migration of at least one component through at least one of the ion-permeable barriers.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an electrophoresis apparatus and method suitable for electrophoretically altering the original composition of a mixture that contains at least one ampholytic component. 
     When ampholytic compounds, such as amino acids, peptides, oligopeptides, proteins, and the like are present in a solution at a low concentration, their charge-state depends on the pH of their environment. At a certain characteristic pH value, the net charge—and consequently, the electrophoretic mobility—of an ampholytic compound becomes zero. That pH value is called the pI value of the ampholytic compound. When two ampholytic compounds have different pI values, their net charge becomes zero at different pH values. Thus, if a pH gradient is established in an electric field, the two ampholytic species achieve zero net charge at different points of the pH gradient that can result in their separation. Such separations are called isoelectric focusing (IEF) separations. IEF separations have been achieved in (i) artificial pH gradients created from non-amphoteric buffers either at constant or spatially varying temperatures, (ii) natural pH gradients created from carrier ampholytes or from the very components of the mixture to be separated (autofocusing), and (iii) immobilized pH gradients. 
     IEF separations typically rely on anti-convective means to preserve the stability of the pH gradient. The IEF principle has been utilized for both analytical and preparative-scale separation of both simple and complex mixtures of ampholytic components. IEF separations have been obtained in thin-layer format, column-format and in multi-compartment format, in both static and flowing media. In flowing media, separations have been achieved in both straight-through and recycling format. IEF separations often take considerable time because the electrophoretic mobility of each ampholytic species becomes low as they approach the point in the pH gradient where they become isoelectric. 
     Therefore, there is a need for IEF separation schemes and equipment which (i) minimize the distance the components have to migrate electrophoretically to achieve separation, (ii) maximize the electric field strength that brings about the electrophoretic separation without causing detrimental heating effects, (iii) maximize the production rate that can be achieved in unit separation space and time, and (iv) minimize the use of auxiliary agents needed for the electrophoretic separation. 
     The present invention provides an apparatus and method which can electrophoretically alter the original composition of a mixture that contains at least one ampholytic component. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided an electrophoresis apparatus and method which can electrophoretically alter the original composition of a mixture that contains at least one ampholytic component. 
     Further, in accordance with the present invention, there is provided an electrophoresis apparatus and system which (i) minimizes the distance the components have to migrate electrophoretically to achieve separation, (ii) maximizes the electric field strength that brings about the electrophoretic separation without causing detrimental heating effects, (iii) maximizes the production rate that can be achieved in unit separation space and time, and (iv) minimizes the use of auxiliary agents needed for the electrophoretic separation. 
     Still further, in accordance with the present invention, there is provided an electrophoretic apparatus comprising:
         a first electrolyte chamber containing a first electrode;   a second electrolyte chamber containing a second electrode, wherein the second electrolyte chamber is disposed relative to the first electrolyte chamber so that the electrodes are adapted to generate an electric field in an electric field area upon application of a selected electric potential between the electrodes;   a first sample chamber disposed between the first and second electrolyte chambers and proximate to the first electrolyte chamber so as to be at least partially disposed in the electric field area;   a second sample chamber disposed between the first sample chamber and the second electrolyte chamber so as to be at least partially disposed in the electric field area;   a first ion-permeable barrier separating the first and second sample chambers so as to impede convective mixing of the contents in each of the first and second sample chambers;   a second ion-permeable barrier separating the first electrolyte chamber and the first sample chamber so as to impede convective mixing of the contents in each of the first sample chamber and the first electrolyte chamber;   a third ion-permeable barrier separating the second electrolyte chamber and the second sample chamber so as to impede convective mixing of the contents in each of the second sample chamber and the second electrolyte chamber;   a first electrolyte reservoir and a second electrolyte reservoir in fluid communication with the first and second electrolyte chambers, respectively;   a first sample reservoir and a second sample reservoir in fluid communication with the first and second sample chambers, respectively;   means adapted for communicating an associated first electrolyte between the first electrolyte chamber and the first electrolyte reservoir;   means adapted for communicating an associated second electrolyte between the second electrolyte chamber and the second electrolyte reservoir;   means adapted for communicating a first fluid between the first sample chamber and the first sample reservoir; and   means adapted for communicating a second fluid between the second sample chamber and the second sample reservoir, wherein at least one of the first and second fluid contains at least a sample,   wherein application of the selected electric potential causes migration of at least one component through at least one of the ion-permeable barriers.       

     In one preferred form, the first ion-permeable barrier is a membrane having a characteristic average pore size and pore size distribution. In one form, all the ion-permeable barriers are membranes having a characteristic average pore size and pore size distribution. This configuration of the apparatus is suitable for separating compounds on the basis of charge and or size. 
     In another preferred form, the first ion-permeable barrier is an isoelectric membrane having a characteristic pI value. Preferably, the isoelectric membrane has a pI value in a range of about 2 to about 12. 
     In another preferred form, the second and third ion-permeable barriers are membranes having a characteristic average pore size and pore-size distribution. 
     In another preferred form, at least one of the second or third ion-permeable barriers is an isoelectric membrane having a characteristic pI value. Preferably, the at least one isoelectric membrane has a pI value in a range of about 2 to about 12. In another preferred form, both the second and third ion-permeable barriers are isoelectric membranes each having a characteristic pI value. Preferably, the isoelectric membranes have a pI value in a range of about 2 to about 12. When both the second and third ion-permeable barriers are isoelectric membranes, the membranes can have the same or different characteristic pI values. 
     The isoelectric membranes are preferably polyacrylamide-based membranes. It will be appreciated, however, that other isoelectric membranes would also be suitable for the present invention. 
     In another preferred form, the apparatus further comprises means for circulating electrolyte from each of the first and second electrolyte reservoirs through the respective first and second electrolyte chambers forming first and second electrolyte streams in the respective electrolyte chambers; and means for circulating contents from each of the first and second sample reservoirs through the respective first and second sample chambers forming first and second sample streams in the respective sample chambers. 
     Preferably, means for circulating the electrolyte and sample streams are pump arrangements separately controllable for independent movement of the electrolyte streams and the sample streams. 
     The apparatus may further include means for removing and replacing sample in the first or second sample reservoirs. The apparatus may also further include means to maintain temperature of electrolyte and sample solutions. 
     In another preferred form, the separation unit is provided as a cartridge or cassette fluidly connected to the electrolyte reservoirs and the sample reservoirs. In one preferred form, the separation unit is provided as a cartridge or cassette connected to the electrolyte reservoirs and the sample reservoirs. 
     Still further, in accordance with the present invention, there is provided a method for selectively removing at least one component from a selected sample comprising:
         communicating a first electrolyte to a first electrolyte chamber containing a first electrode wherein the first electrolyte chamber is in fluid communication with a first electrolyte reservoir;   communicating a second electrolyte to a second electrolyte chamber containing a second electrode, wherein the second electrolyte chamber is disposed opposite the first electrolyte chamber and wherein the second electrolyte chamber is in fluid communication with a second electrolyte reservoir;   communicating a first fluid to a first sample chamber disposed between the first and second electrolyte chambers and proximate to the first electrolyte chamber, wherein the first sample chamber is in fluid communication with a first sample reservoir;   communicating a second fluid to a second sample chamber disposed between the first sample chamber and the second electrolyte chamber, wherein the second sample chamber is in fluid communication with a second sample reservoir, wherein a first ion-permeable barrier separates the first and second sample chambers, a second ion-permeable barrier separates the first electrolyte chamber and the first sample chamber, and a third ion-permeable barrier separates the second sample chamber and the second electrolyte chamber, wherein the ion-permeable barriers impede convective mixing between the respective chambers, wherein at least one of the first and second fluids contains at least a sample; and   applying a selected electric potential to cause migration of at least one selected component through at least one of the ion-permeable barriers. Preferably, at least one sample component has a pI value.       

     In a preferred form, electrolyte from at least one of the first and second electrolyte reservoirs is circulated through the first or second electrolyte chamber forming a first or second electrolyte stream. 
     The choice of electrolyte in the first and second electrolyte chambers will depend on the compound or compounds to be treated, separated or transferred from a sample chamber to the other sample chamber, or one or both of the electrolyte chambers. Similarly, the choice of the pI of the isoelectric membranes will also depend on the compound or compounds to be treated, separated or transferred from a given sample. 
     Electrolytes such as acetic acid as the anolyte, and triethanol amine as the catholyte, have been found to be suitable for the separation of a number of components from biological samples. Salt such as NaCl may also be added to the electrolyte to assist. It will be appreciated, however, that other electrolytes would also be applicable, depending on the desired separation or treatment. 
     In another preferred form, electrolyte from both the first and second electrolyte reservoirs is circulated through the first and second electrolyte chambers forming first and second electrolyte streams. 
     In another preferred form, the contents of the first or second sample reservoir is circulated through the first or second sample chamber forming a first or second sample stream through the first or second sample chamber. In another preferred form, sample or liquid in the first or second sample reservoir is removed and replaced with fresh sample or liquid. 
     Preferably, substantially all transbarrier migration occurs upon the application of the electric potential. In another preferred form, the application of the electric potential is maintained until at least one desired component reaches a desired purity in at least one of the first and second sample chamber or in the first or second sample reservoirs. 
     Still further, in accordance with the present invention, there is provided an electrophoretic separation unit comprising:
         a first electrolyte chamber containing a first electrode;   a second electrolyte chamber containing a second electrode, wherein the second electrolyte chamber is disposed relative to the first electrolyte chamber so that the electrodes are adapted to generate an electric field in an electric field area upon application of a selected electric potential between the electrodes;   a first sample chamber disposed between the first and second electrolyte chambers and proximate to the first electrolyte chamber so as to be at least partially disposed in the electric field area;   a second sample chamber disposed between the first sample chamber and the second electrolyte chamber so as to be at least partially disposed in the electric field area;   an isoelectric barrier separating the first and second sample chambers so as to impede convective mixing of the contents in each of the first and second sample chambers;   a first ion-permeable barrier separating the first electrolyte chamber and the first sample chamber so as to impede convective mixing of the contents in each of the first sample chamber and the first electrolyte chamber;   a second ion-permeable barrier separating the second electrolyte chamber and the second sample chamber so as to impede convective mixing of the contents in each of the second sample chamber and second electrolyte chamber;   means adapted for communicating an associated first electrolyte to the first electrolyte chamber;   means adapted for communicating an associated second electrolyte to the second electrolyte chamber;   means adapted for communicating a first fluid to the first sample chamber; and   means adapted for communicating a second fluid to the second sample chamber, wherein at least one of the first and second fluids contains at least a sample;   wherein application of the selected electric potential causes migration of at least one component through at least one of the ion-permeable barriers.       

     Still further, in accordance with the present invention, there is provided a method for selectively altering the concentration of a selected sample:
         communicating a first electrolyte to a first electrolyte chamber containing a first electrode;   communicating a second electrolyte to a second electrolyte chamber containing a second electrode;   communicating a first fluid to a first sample chamber disposed between the first and second electrolyte chambers and proximate to the first electrolyte chamber;   communicating a second fluid to a second sample chamber disposed between the first sample chamber and the second electrolyte chamber, wherein an isoelectric barrier separates the first and second sample chambers, a first ion-permeable barrier separates the first electrolyte chamber and the first sample chamber, and a second ion-permeable barrier separates the second sample chamber and the second electrolyte chamber, wherein the barriers impede convective mixing between the respective chambers, wherein at least one of the first and second fluids contains a sample; and   applying a selected electric potential to cause migration of at least one selected component through at least one of the barriers.       

     An advantage of the present invention is that the apparatus and method have scale-up capabilities, increased separation speed, lower cost of operation, lower power requirements, and increased ease of use. 
     Yet another advantage of the present invention is that the apparatus and method have improved yields of the separated component, and improved purity of the separated component. 
     These and other advantages will be apparent to one skilled in the art upon reading and understanding the specification. 
     Throughout this specification, unless the context requires otherwise, the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. 
     Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia before the priority date of each claim of this application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a separation unit for use in the present invention. 
         FIG. 2  is a schematic diagram of an apparatus according to the present invention utilizing the separation unit of FIG.  1 . 
         FIG. 3  is an exploded view of a cartridge which may be used with the separation unit of FIG.  1 . 
         FIG. 4A  is a plan view of a grid element which may be incorporated as a component of a cartridge of a separation unit. 
         FIG. 4B  is a reverse plan view of the grid element of FIG.  4 A. 
         FIG. 5  is a cross-sectional view on the lines X—X of FIG.  4 A. 
         FIG. 6  is a cross-sectional view on the lines XI—XI of FIG.  4 A. 
         FIG. 7  is a cross-sectional view on the lines XII—XII of FIG.  4 A. 
         FIG. 8  is a plan view of an alternative embodiment of a grid element which may be incorporated as a component of a cartridge of a separation unit. 
         FIG. 9  shows an apparatus utilizing the separation unit of FIG.  1 . 
         FIG. 10  shows the image, at 280 nm, of the protein bands separated by the iCE280 full-column-imaging capillary isoelectric focusing instrument, from a chicken egg-white sample, used as the starting material for the electrophoretic separation experiments described in Examples 1 to 3. The peaks labeled pI 3.52 and pI 9.61 correspond to dansyl phenylalanine and terbutaline, respectively, used as isoelectric point markers. The egg-white sample was diluted 1:25 with deionized water and filtered prior to analysis. Analysis conditions: instrument: iCE280 full-column imaging capillary IEF system, separation capillary: 5 cm long, 100 micrometer I.D. fused silica, focusing medium: 8% carrier ampholytes for pH 3-10 in aqueous 0.1% methylcellulose solution, focusing time: 5 minutes, applied potential: 3,000 V. 
         FIG. 11  shows the image, at 280 nm, of the protein bands separated by the iCE280 full-column-imaging capillary isoelectric focusing instrument, from aliquots collected at the end of the experiment from the first sample reservoir (bottom panel) and second sample reservoir (top panel) of the electrophoretic apparatus disclosed here and described in Example 1. Separation conditions: anolyte: 60 mL of 80 mM acetic acid, pH=2.9, catholyte: 60 mL 8 mM triethanol amine, pH=9.9, sample: 60 mL aqueous egg-white sample diluted 1:25 in deionized water, separation time: 15 minutes, applied potential: 250 V, first ion-permeable barrier between the first electrolyte chamber and the first sample chamber: pI=4.0 isoelectric membrane, second ion-permeable barrier between the first sample chamber and the second sample chamber: pI=5.0 isoelectric membrane, third ion-permeable barrier between the second sample chamber and the second electrolyte chamber: pI=7.0 isoelectric membrane. The peaks labeled pI 3.52 and pI 9.61 correspond to dansyl phenylalanine and terbutaline, respectively, used as isoelectric point markers. Analysis conditions: instrument: iCE280 full-column imaging IEF system, capillary: 5 cm long, 100 micrometer I.D. fused silica, focusing medium: 8% carrier ampholytes for pH 3-10 in aqueous 0.1% methylcellulose solution, focusing time: 5 minutes, applied potential: 3,000 V. 
         FIG. 12  shows the image, at 280 nm, of the protein bands separated by the iCE280 full-column-imaging capillary isoelectric focusing instrument, from aliquots collected at the end of the experiment described in Example 2 from the first sample reservoir (bottom panel) and the second sample reservoir (top panel) of the electrophoretic apparatus disclosed here. Separation conditions: anolyte: 60 mL 2 mM acetic acid, catholyte: 60 mL 8 mM triethanol amine, sample: 60 mL aqueous egg-white sample diluted 1:25 in distilled water, separation time: 15 minutes, applied potential: 250 V, first ion-permeable barrier between the first electrolyte chamber and the first sample chamber: polyacrylamide membrane with a nominal molecular mass cut-off of 5,000 dalton, second ion-permeable barrier between the first sample chamber and the second sample chamber: pI=5.0 isoelectric membrane, third ion-permeable barrier between the second sample chamber and the second electrolyte chamber: polyacrylamide membrane with a nominal molecular mass cut-off of 5,000 dalton. The peaks labeled pI 3.52 and pI 9.61 correspond to dansyl phenylalanine and terbutaline, respectively, used as isoelectric point markers. Analysis conditions: instrument: iCE280 full-column imaging IEF system, capillary: 5 cm long, 100 micrometer I.D. fused silica, focusing medium: 8% carrier ampholytes for pH 3-10 in aqueous 0.1% methylcellulose solution, focusing time: 5 minutes, applied potential: 3,000 V. 
         FIG. 13  shows the image, at 280 nm, of the protein bands separated by the iCE280 full-column-imaging capillary isoelectric focusing instrument, from aliquots collected at the end of the experiment described in Example 3 from the first sample reservoir (bottom panel) and the second sample reservoir (top panel) of the electrophoretic apparatus disclosed here. Separation conditions: anolyte: 60 mL 2 mM acetic acid, catholyte: 60 mL 8 mM triethanol amine, sample: 60 mL aqueous egg-white sample diluted 1:25 in deionized water, separation time: 15 minutes, applied potential: 250 V, first ion-permeable barrier between the first electrolyte chamber and the first sample chamber: polyacrylamide membrane with a nominal molecular mass cut-off of 1,000,000 dalton, second ion-permeable barrier between the first sample chamber and the second sample chamber: pI=5.0 isoelectric membrane, third ion-permeable barrier between the second sample chamber and the second electrolyte chamber: polyacrylamide membrane with a nominal molecular mass cut-off of 1,000,000 dalton. The peak labeled pI 3.52 corresponds to dansyl phenylalanine, used as isoelectric point marker. Analysis conditions: instrument: iCE280 full-column imaging IEF system, capillary: 5 cm long, 100 micrometer I.D. fused silica, focusing medium: 8% carrier ampholytes for pH 3-10 in aqueous 0.1% methylcellulose solution, focusing time: 5 minutes, applied potential: 3,000 V. 
         FIG. 14  shows the image of an SDS-PAGE gel used to analyze the protein bands present in the aliquots collected from the first and second sample reservoirs of the electrophoretic apparatus disclosed here and described in Example 4 during the isolation of IgG from human plasma. Molecular weight markers (Sigma, St. Louis, Mo., USA) were applied onto Lane 1, a pharmaceutical-grade IgG preparation used as reference material onto Lane 2. Samples taken at 0, 10, 20, and 40 minutes respectively from the first sample reservoir were applied onto Lanes 3, 4, 5, and 6. Samples taken at 0, 10, 20, and 40 minutes respectively from the second sample reservoir were applied onto Lanes 7, 8, 9, and 10. Separation conditions: anolyte: 2 L 2 mM 5-aminocaproic acid adjusted to pH 4.8 with HCl, also containing 5 mM NaCl, catholyte: 2 L 2 mM MOPSO adjusted to pH 6.8 with NaOH, also containing 5 mM NaCl, sample: 10 mL human plasma sample diluted 1 to 3 with deionized water, separation time: 40 minutes, applied potential: 250 V, first ion-permeable barrier between the first electrolyte chamber and the first sample chamber: polyacrylamide membrane with a nominal molecular mass cut-off of 150,000 dalton, second ion-permeable barrier between the first sample chamber and the second sample chamber: pI=5.8 isoelectric membrane, third ion-permeable barrier between the second sample chamber and the second electrolyte chamber: polyacrylamide membrane with a nominal molecular mass cut-off of 150,000 dalton. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Before describing the preferred embodiments in detail, the principal of operation of the apparatus will first be described. An electric field or potential applied to ions in solution will cause the ions to move toward one of the electrodes. If the ion has a positive charge, it will move toward the negative electrode (cathode). Conversely, a negatively-charged ion will move toward the positive electrode (anode). 
     In the apparatus of the present invention, ion-permeable barriers that substantially prevent convective mixing between the adjacent chambers of the apparatus or unit are placed in an electric field and components of the sample are selectively transported through the barriers. The particular ion-permeable barriers used will vary for different applications and generally have characteristic average pore sizes and pore size distributions and/or isoelectric points allowing or substantially preventing passage of different components. 
     Having outlined some of the principles of operation of an apparatus in accordance with the present invention, an apparatus itself will be described. 
     Referring to  FIG. 1 , a schematic representation of separation unit  2  is shown for the purpose of illustrating the general functionality of a separation device utilizing the technology of the present invention. Separation unit  2  comprises first electrolyte inlet  4 , and second electrolyte inlet  6 , first sample inlet  8 , and second sample inlet  10 , first electrolyte outlet  12 , and second electrolyte outlet  14 , and first sample outlet  16  and second sample outlet  18 . Between first electrolyte inlet  4  and first outlet  12  is first electrolyte chamber  22 . Likewise, between second electrolyte inlet  6  and second electrolyte outlet  14  is second electrolyte chamber  24 . First sample and second sample inlets and outlets also have connecting chambers. First sample chamber  26  running adjacent to first electrolyte chamber  22  connects first sample inlet  8  to first sample outlet  16 . Similarly, second sample chamber  28  running adjacent to second electrolyte chamber  24  connects second sample inlet  10  to second sample outlet  18 . Ion-permeable barriers  30  and  32  separate electrolyte chambers  22  and  24  from first sample and second sample chambers  26  and  28 , respectively. Between first sample and second sample chambers  26  and  28  is ion-permeable barrier  34 . In one embodiment, when in use, first and second electrolyte  36  and  38  occupy first and second electrolyte chambers  22  and  24 . It should be understood that during operation, first and second electrolyte  36  and  38 , as well as first and second sample  56  and  66  may be stagnant in, or flow through, the respective chambers. 
     A schematic diagram of an apparatus utilizing separation unit  2  of  FIG. 1  is shown in  FIG. 2  for the purpose of illustrating the general functionality of an apparatus utilizing the technology of the present invention. In this purely illustrative example, four chambers (first electrolyte chamber  22 , second electrolyte chamber  24 , first sample chamber  26 , and second sample chamber  28 ) are connected to four flow circuits. First electrolyte flow circuit  40  comprises first electrolyte reservoir  42 , electrolyte tubing  44 , and electrolyte pump  46 . Second electrolyte flow circuit  41  comprises second electrolyte reservoir  43 , electrolyte tubing  45 , and electrolyte pump  47 . In the configuration shown in  FIG. 2 , electrolyte flow circuits  40  and  41  are running independently from each other so that the composition, temperature, flow rate and volume of first electrolyte  36  and second electrolyte  38  can be suitably adjusted independently of one another. 
     In the embodiment shown, first electrolyte  36  flows from first electrolyte reservoir  42  through tubing  44  to pump  46  to first electrolyte chamber  22 . Second electrolyte  24  flows from second electrolyte reservoir  43  through tubing  45  to pump  47  to second electrolyte chamber  24 . First electrolyte  36  flows through inlet  4  and second electrolyte  38  flows through inlet  6 . First electrolyte  36  exits separation unit  2  through outlet  12  and second electrolyte  38  exits separation unit  2  through outlet  14 . After exiting separation unit  2 , electrolytes  36  and  38  flow through tubing  44  and  45  back into respective electrolyte reservoirs  42  and  43 . In one embodiment, electrolytes  36  and  38  are held stagnant in electrolyte chambers  22  and  24  during separation. Electrolytes  36  and  38  can also act as a cooling medium and help prevent a build up of gases generated during electrophoresis. 
     First sample flow circuit  48  contains first sample reservoir  50 , tubing  52  and pump  54 . First sample  56  flows from first sample reservoir  50  through tubing  52  to pump  54 , then through inlet  8  into first sample chamber  26 . In one embodiment, the flow directions of first sample  56  and electrolytes  36  and  38  in first sample chamber  26  are opposite. First sample  56  exits separation unit  2  at outlet  16  and flows through tubing  52 , then heat exchanger  68  that passes through second electrolyte reservoir  43  before returning to first sample reservoir  50  through tubing  52 . In an alternative embodiment, heat exchanger  68  passes through first electrolyte reservoir  42 . In another embodiment, the flow directions of first sample  56  and electrolytes  36  and  38  in first sample chamber  26  are the same. 
     In addition to components of interest, first sample  56  may contain any suitable electrolyte or additive known in the art as demanded by the procedure, application, or separation being performed to substantially prevent or cause migration of selected components through the ion-permeable barriers. In a preferred embodiment, sample from which constituents are to be removed is placed into first sample reservoir  50 . However, it is understood that in an alternative embodiment, sample from which constituents are to be removed is placed into second sample reservoir  60 . 
     Similarly, second sample flow circuit  58  contains second sample reservoir  60 , tubing  62  and pump  64 . Second sample  66  flows from second sample reservoir  60  through tubing  62  to pump  64 , then through inlet  10  into second sample chamber  28 . In one embodiment, the flow directions of second sample  66  and electrolytes  36  and  38  in second sample chamber  28  are opposite. Second sample  66  exits separation unit  2  at outlet  18  and flows through tubing  62 , then heat exchanger  70  that passes through second electrolyte reservoir  43  before returning to second sample reservoir  60  through tubing  62 . In an alternative embodiment, heat exchanger  70  passes through first electrolyte reservoir  43 . 
     Second sample  66  may contain any suitable electrolyte or additive known in the art as demanded by the procedure, application, or separation being performed to substantially prevent or cause migration of selected components through the ion-permeable barriers. In a preferred embodiment, sample from which constituents are to be removed is placed into second sample reservoir  60 . However, it is understood that in an alternative embodiment, sample from which constituents are to be removed is placed into first sample reservoir  50 . 
     Individually adjustable flow rates of first sample, second sample, first electrolyte and second electrolyte, when employed, can have a significant influence on the separation. Flow rates ranging from zero through several milliliters per minute to several liters per minute are suitable depending on the configuration of the apparatus and the composition, amount and volume of sample processed. In a laboratory scale instrument, individually adjustable flow rates ranging from about 0 mL/minute to about 50,000 mL/minute are used, with the preferred flow rates in the 0 mL/min to about 1,000 mL/minute range. However, higher flow rates are also possible, depending on the pumping means and size of the apparatus. Selection of the individually adjustable flow rates is dependent on the process, the component or components to be transferred, efficiency of transfer, and coupling of the process with other, preceding or following processes. 
     Preferably, all tubing  44 ,  52 , and  62  is peristaltic tubing that is autoclavable, chemically resistant, and biologically inert. One such tubing is Masterflex® C-FLEX® 50 A tubing. Also, pumps  46 ,  47 ,  54  and  64  are preferably peristaltic pumps. In the presently preferred embodiment, heat exchangers  68  and  70  are constructed from stainless steel, although other materials known in the art are suitably used. Preferably, heat exchangers  68  and  70  are autoclavable, chemically resistant, biologically inert and capable of facilitating heat exchange. 
     Furthermore, it is preferable that first sample flow circuit  48 , second sample flow circuit  58 , first electrolyte flow circuit  40  and second electrolyte flow circuit  41  are completely enclosed to prevent contamination or cross-contamination. In a preferred embodiment, reservoirs  42 ,  43 ,  50 , and  60 , are completely and individually enclosed from the rest of the apparatus. 
     The separation unit further comprises electrodes  88   a  and  88   b.  Preferably, the respective electrodes are located in the first and second electrolyte chambers and are separated from the first and second sample chambers by ion-permeable barriers. 
     Electrodes  88   a  and  88   b  are suitably standard electrodes or preferably are formed from platinum coated titanium expanded mesh, providing favorable mechanical properties, even distribution of the electric field, long service life and cost efficiency. Electrodes  88   a  and  88   b  are preferably located relatively close to ion-permeable barriers  30  and  32  providing better utilization of the applied potential and diminished heat generation. A distance of about 0.1 to 6 mm has been found to be suitable for a laboratory scale apparatus. For scaled-up versions, the distance will depend on the number and type of ion-permeable barriers, and the size and volume of the electrolyte and sample chambers. Preferred distances would be in the order of about 0.1 mm to about 10 mm. 
     Separation unit  2  also preferably comprises electrode connectors  78  that are used for connecting separation unit  2  to power supply  72 . Preferably, power supply  72  is external to separation unit  2 , however, separation unit  2  is configurable to accept internal power supply  72 . Electrode connectors  78  are preferably autoclavable. 
     Separation is achieved when an electric potential is applied to separation unit  2 . Selection of the electric field strength varies depending on the separation. Typically, the electric field strength varies between 1 V/cm to about 5,000 V/cm, preferably between 10 V/cm to 2,000 V/cm and leads to currents of up to about 1 A. It is preferable to maintain the total power consumption of the unit at the minimum, commensurable with the desired separation and production rate. 
     In one embodiment, the applied electric potential is periodically stopped and reversed to cause movement of components that have entered the ion-permeable barriers back into at least one of the fluid streams, while substantially not causing re-entry of any components that have entered other fluid streams. In another embodiment, a resting period is utilized. Resting (a period during which fluid flows are maintained but no electric potential is applied) is an optional step that suitably replaces or is included after an optional reversal of the electric potential. Resting is often used for protein-containing samples as an alternative to reversing the potential. 
     Separation unit  2  is suitably cooled by various methods known in the art such as ice bricks or cooling coils (external apparatus) placed in one or both electrolyte reservoirs  42  and  43 , or any other suitable means capable of controlling the temperature of electrolytes  36  and  38 . Because both first sample flow circuit  48  and second sample flow circuit  58  pass through either electrolyte reservoir  42  or  43 , heat is exchanged between first and second samples and one or both of first and second electrolytes. Heat exchange tends to maintain the temperature in first sample  56  and second sample  66  at the preferred, usually low levels. 
     In another form, there is provided an electrophoresis unit that comprises four chambers (first electrolyte chamber  22 , second electrolyte chamber  24 , first sample chamber  26 , and second sample chamber  28 ). Ion-permeable barriers  30  and  32  separate electrolyte chambers  22  and  24  from first sample and second sample chambers  26  and  28 , respectively. Between first sample and second sample chambers  26  and  28  is ion-permeable barrier  34 . Electrodes are housed in the first and second electrolyte chambers and sample and/or fluid is placed into first sample chamber  26  and second sample chamber  28 . In use, an electric potential is applied between the electrodes and one or more components in the first sample chamber  26  or second sample chamber  28  are caused to move to the other sample chamber or to one of the electrolyte chambers. 
       FIG. 3  is an exploded view of cartridge  100  which is preferably a modular component of separation unit  2 . When configured as a modular unit, cartridge  100  preferably comprises housing  102  for holding in place or encasing the component parts of cartridge  100 . In a presently preferred embodiment, cartridge  100  is generally elongated and has side walls  104  which are generally parallel to one another and the longitudinal axis A of cartridge  100 . The cartridge is suitably generally octagonal, hexagonal, or ovular. In an octagonal configuration, cartridge  100  has three end walls  106  on each side of side walls  104  forming an octagon. However, two end walls on each side  106  are suitably used to form a hexagon, or one curved end wall  106  on each side is suitably used to form a generally ovular shape. Furthermore, end walls  106  are suitably either straight or generally curved. 
     Extending around the base of side walls  104  and end walls  106  is a small flange  108  that is generally perpendicular to side walls  104  and end walls  106  and projects inward toward the center of cartridge  100 . Along the exterior of either side walls  104  or end walls  106  is preferably a handle  110  to facilitate placement of cartridge  100  into separation unit  2 . Flange  108  is preferably configured to interact with lower gasket  112 . In a preferred embodiment, lower gasket  112  is generally planar and configured to fit inside walls  104  and  106  of cartridge  100 . In a presently preferred embodiment, lower gasket  112  is made from silicon rubber. Lower gasket  112  may be configured so that it has an aperture  114  extending in an elongated manner through the center of lower gasket  112 . Also extending through and adjacent each end of lower gasket  112  are alignment holes  116 . In a preferred embodiment, alignment holes  116  are circular, forming generally cylindrical channels through lower gasket  112 . However, it is also contemplated that alignment holes  116  are suitably triangular, square, rectangular, hexagonal, octagonal, or similarly shaped. 
     Above lower gasket  112  is a generally planar lower ion-permeable barrier  32 . The external shape of ion-permeable barrier  32  is generally the same as that of lower gasket  112  and the interior of cartridge  100  so that ion-permeable barrier  32  is configured to fit inside cartridge  100 . Like lower gasket  112 , ion-permeable barrier  32  preferably has two alignment holes of the same location and configuration as alignment holes  116  in lower gasket  112 . Ion-permeable barrier  32  substantially prevents convective mixing of the contents of first electrolyte chamber  22  and first sample chamber  26 , while permits selective trans-barrier transport of selected constituents upon application of the electric potential. 
     In one embodiment, ion-permeable barrier  32  is formed from a membrane with a characteristic average pore size and pore-size distribution. The average pore size and pore size distribution of the membrane is selected to facilitate trans-membrane transport of certain constituents, while substantially preventing trans-membrane transport of other constituents. 
     In another embodiment, ion-permeable barrier  32  is an isoelectric ion-permeable barrier, such as an isoelectric membrane that substantially prevents convective mixing of the contents of first electrolyte chamber  22  and first sample chamber  26 , while permits selective trans-barrier transport of selected constituents upon application of the electric potential. Suitable isoelectric membranes can be produced by copolymerizing acrylamide, N,N′-methylene bisacrylamide and appropriate acrylamido derivatives of weak electrolytes yielding isoelectric membranes with pI values in the 2 to 12 range, and average pore sizes that either facilitate or substantially prevent trans-membrane transport of components of selected sizes. 
     Above lower ion-permeable barrier  32  is lower grid element  118  that is generally planar and also shaped like lower gasket  112  and the interior of cartridge  100  so that lower grid element  118  is configured to fit inside cartridge  100 . One of the functions of lower grid element  118  is to separate lower ion-permeable barrier  32  from ion-permeable barrier  34 . Another function of lower grid element  118  is to provide a flow path for first sample  56 . Like lower ion-permeable barrier  32  and lower gasket  112 , lower grid element  118  suitably also has alignment holes  116 . 
     Above lower grid element  118  is generally planar ion-permeable barrier  34 . The external shape of ion-permeable barrier  34  is generally the same as that of lower gasket  112  and the interior of cartridge  100  so that ion-permeable barrier  34  is configured to fit inside cartridge  100 . Ion-permeable barrier  34  substantially prevents convective mixing of the contents of first sample chamber  26  and second sample chamber  28 , while permits selective trans-barrier transport of selected constituents upon application of the electric potential. 
     In one embodiment, ion-permeable barrier  34  is formed from a membrane with a characteristic average pore size and pore-size distribution. The average pore size and pore size distribution of the membrane is selected to facilitate trans-membrane transport of certain constituents, while substantially preventing trans-membrane transport of other constituents. 
     In another embodiment, ion-permeable barrier  34  is an isoelectric ion-permeable barrier, such as an isoelectric membrane that substantially prevents convective mixing of the contents of first sample chamber  26  and second sample chamber  28 , while permits selective trans-barrier transport of selected constituents upon application of the electric potential. Suitable isoelectric membranes can be produced by copolymerizing acrylamide, N,N′-methylene bisacrylamide and appropriate acrylamido derivatives of weak electrolytes yielding isoelectric membranes with pI values in the 2 to 12 range, and average pore sizes that either facilitate or substantially prevent trans-membrane transport of components of selected sizes. 
     Above ion-permeable barrier  34  are three upper components: upper grid element  120 , upper ion-permeable barrier  38 , and upper gasket  124 . These three components are placed so that upper grid element  120  is immediately above ion-permeable barrier  34 , ion-permeable barrier  38  is immediately above upper grid element  120 , and upper gasket  124  is immediately above ion-permeable barrier  38 . The configuration of the three upper components suitably mirrors that of the lower three components. 
     Components below ion-permeable barrier  34  having alignment holes  116  may be connected together with a fastener, which is any type of connector configured to interact with alignment holes  116  and facilitate through flow of first sample  56 . Similarly, components above ion-permeable barrier  34  having alignment holes  116  may be connected together with a fastener, which is any type of connector configured to interact with alignment holes  116  and facilitate through flow of second sample  66 . 
     Components of cartridge  100  are suitably held in cartridge  100  by clip  126 . Clip  126  is suitably snap fitted or glued around the top of walls  104  and  106  of cartridge  100 . 
     Ion-permeable barrier  38  substantially prevents convective mixing of the contents of second electrolyte chamber  24  and second sample chamber  28 , while permits selective trans-barrier transport of selected constituents upon application of the electric potential. 
     In one embodiment, ion-permeable barrier  38  is formed from a membrane with a characteristic average pore size and pore-size distribution. The average pore size and pore size distribution of the membrane is selected to facilitate trans-membrane transport of certain constituents, while substantially preventing trans-membrane transport of other constituents. 
     In another embodiment, ion-permeable barrier  38  is an isoelectric ion-permeable barrier, such as an isoelectric membrane that substantially prevents convective mixing of the contents of second electrolyte chamber  24  and second sample chamber  28 , while permits selective trans-barrier transport of selected constituents upon application of the electric potential. Suitable isoelectric membranes can be produced by copolymerizing acrylamide, N,N′-methylene bisacrylamide and appropriate acrylamido derivatives of weak electrolytes yielding isoelectric membranes with pI values in the 2 to 12 range, and average pore sizes that facilitate or substantially prevent trans-membrane transport of components of selected sizes. 
     Preferred grid elements  118  and  120  are shown in more detail in  FIGS. 4  to  7 .  FIG. 4A  shows a plan view of a preferred grid element which is incorporated as a component of cartridge  100  for separation unit  2 . An elongate rectangular cut-out portion  128  which incorporates lattice  131  is defined in the center of the grid element. At each end of the grid element, an alignment hole  116  is suitably provided for alignment with the other components of cartridge  100 . Preferably, a triangular channel area  130  having sides and a base, extends and diverges from each alignment hole  116  to cut-out portion  128 . Upstanding ribs  132 ,  134 , and  136  (best shown in  FIGS. 6 and 7 ) are defined in channel area  130 . Liquid flowing through hole  116  thus passes along triangular channel area  130  between ribs  132 ,  134 , and  136  and into lattice  131 . Ribs  132 ,  134 , and  136  direct the flow of liquid from hole  116  so that they help ensure that liquid is evenly distributed along the cross-section of lattice  131 . Ribs  132 ,  134 , and  136  also provide support to ion-permeable barrier  34  disposed above or below the grid element. 
     Lattice  131  comprises a first array of spaced parallel members  138  extending at an angle to the longitudinal axis of the grid disposed above and integrally formed with a second lower set of spaced parallel members  140  extending at approximately twice the angle of the first array of parallel members  138  to the longitudinal axis of the grid. In the presently preferred embodiment, the first array of parallel members  138  extend at approximately a 45 degree angle from the longitudinal axis and the second array of parallel members  140  extend at approximately 90 degrees to the first array of parallel members  138 , however, other angles are also suitably used. 
     Referring to  FIG. 4B , the reverse side of the grid element is illustrated. The reverse side is suitably relatively smooth and flat aside from cut-out area  128  and alignment holes  116 . The smooth, flat surface tends to ensure sealing between ion-permeable barriers  32  and grid element  118 , and ion-permeable barrier  38  and grid element  120 , respectively. 
     Referring to  FIG. 5 , the upper and lower surfaces of first and second parallel members  138  and  140  are preferably rounded. When parallel members  138  and  140  are rounded, the absence of any sharp edges help prevent damage to ion-permeable barrier  34  and provide extra support. Lattice  131  evenly distributes the flow of liquid over the surface of ion-permeable barrier  34 . The use of a first set of members  138  disposed above a second set of members  140  tends to ensure that the liquid in a stream is forced to move up and down, changing direction frequently, which helps to encourage mixing of the liquid and tends to inhibit static flow zones. 
     The thickness of the grid element is preferably relatively small. In one presently preferred embodiment, exterior areas  144  of the element are 0.8 mm thick. Sealing ridge  142  (also shown in  FIGS. 4A and 4B ) extends around the periphery of lattice  131  to improve sealing. Ridge  142  is preferably approximately 1.2 mm thick measured from one side of the grid element to the other. The distance between the opposite peaks of lattice elements  138  and  140  measured from one side of the grid to the other is preferably approximately 1 mm. The relatively small thickness of the grid provides several advantages. First, it results in a more even distribution of liquid over ion-permeable barrier  34  and assists in inhibiting its fouling by macromolecules. 
     Also, the volume of liquid required is decreased by the use of a relatively thin grid which enables relatively small sample volumes to be used for laboratory-scale separations, a significant advantage over prior art separation devices. 
     Finally, if the electric field strength is maintained constant, the use of a relatively thinner grid element enables less electrical power to be deposited into the liquid. If less heat is transferred into the liquid, the temperature of the liquid remains lower. This is advantageous, since high temperatures may destroy both the sample and the desired product. 
       FIG. 8  illustrates grid element  144  for an alternative embodiment of the present invention. Grid element  144  utilizes an ion-permeable barrier having a much larger surface area than that of grid elements  118  and  120 . The principal operation of grid element  144  is suitably generally the same as that of the smaller grid elements although holes  146  through which first sample  56  or second sample  66  are fed are located in two opposite corners of grid  144  and there are many more channels  148  feeding streams from holes  146  to central portion  150  of grid  144 . The cartridge, cartridge casing, and other components are increased in size and shape so as to match that of grid  144 . 
       FIG. 9  is a diagram of a presently preferred embodiment of a separation apparatus  200  for use in accordance with the present invention. The separation apparatus comprises separation unit  2  configured to accept cartridge  100  and clamp  86 . Clamp  86  is used to fix separation unit  2  in place once a component cartridge is placed into separation unit  2 . In the presently preferred embodiment, clamp  86  is constructed from aluminum and is preferably anodized. Clamp  86  is preferably a simple screw clamp unit so that a screw-operated knob may be used to open and close clamp  86 . The separation apparatus shows first sample reservoir  50 , second sample reservoir  60 , and first and second electrolyte reservoirs  42  and  43  in electrolyte compartment  202 . 
     In order that the present invention may be more clearly understood, examples of separation methodology are described with reference to the preferred forms of the separation technology as described. 
     EXAMPLE 1 
     An apparatus according to the present invention, shown in  FIG. 9 , was used to separate the proteins present in chicken egg-white into two fractions. An electrophoresis separation cartridge, shown in  FIGS. 3  to  7 , was adapted to be used in the apparatus. The first ion-permeable barrier placed between the first electrolyte chamber and the first sample chamber was a pI=4.0 isoelectric membrane prepared from Immobiline chemicals (Pharmacia, Sweden), acrylamide and N-N′-methylene bis-acrylamide. The second ion-permeable barrier placed between the first sample chamber and the second sample chamber was a pI=5.0 isoelectric membrane prepared from Immobiline chemicals (Pharmacia, Sweden), acrylamide and N-N′-methylene bis-acrylamide. The third ion-permeable barrier placed between the second sample chamber and the second electrolyte chamber was a pI=7.0 isoelectric membrane prepared from Immobiline chemicals (Pharmacia, Sweden), acrylamide and N-N′-methylene bis-acrylamide. 
     The first electrolyte reservoir was filled with 60 mL of an 80 mM acetic acid solution, pH 2.9. The second electrolyte reservoir was filled with 60 mL of an 8 mM triethanol amine solution, pH 9.9. The first and second sample reservoirs were filled with 30 mL each of a filtered chicken egg-white solution, diluted with deionized water at a rate of 1 to 25. The anode was placed into the first electrolyte chamber, the cathode into the second electrolyte chamber. The applied potential was 250 V, the separation time was 15 minutes. Aliquots were taken for analysis from the sample reservoirs before separation and at the end of the separation. 
     Full-column-imaging capillary isoelectric focusing on an iCE280 instrument (Convergent Bioscience, Toronto, Canada) was used to analyze the egg-white samples. The fused silica separation capillary was 5 cm long, its internal diameter was 100 micrometer. The focusing medium contained 8% carrier ampholytes to cover the pH 3-10 range, in an aqueous, 0.1% methylcellulose solution. Seventy-five microliter of the sample to be analyzed was mixed with 150 microliter of the focusing medium, filled into the capillary and focused for 5 minutes at 3,000 V. Dansyl phenylalanine (pI=3.52) and terbutaline (pI=9.61) were used as pI markers. 
       FIG. 10  shows the results for the egg-white feed sample. The peaks between pixels  650  and  850  correspond to ovalbumin isoforms, those between pixels  1250  and  1350  correspond to ovotransferrin isoforms. 
     As a result of the electrophoretic separation, proteins with pI values lower than 5.0, such as ovalbumin (pI=4.7), accumulated in the first sample reservoir, on the anodic side of the pI=5.0 isoelectric membrane (bottom panel in FIG.  11 ). Proteins with pI values greater than 5.0, such as ovotransferrin (pI=6.1) accumulated in the second sample reservoir, on the cathodic side of the isoelectric membrane (top panel in FIG.  11 ). 
     EXAMPLE 2 
     The same apparatus as in Example 1 was used to separate the proteins present in chicken egg-white into two fractions. An electrophoresis separation cartridge, shown in  FIGS. 3  to  7 , was adapted to be used in the apparatus. The first ion-permeable barrier placed between the first electrolyte chamber and the first sample chamber was a polyacrylamide membrane with a nominal molecular mass cut-off of 5,000 dalton. The ion-permeable barrier between the first sample chamber and the second sample chamber was a pI 5.0 isoelectric membrane prepared from Immobiline chemicals (Pharmacia, Sweden), acrylamide and N-N′-methylene bis-acrylamide as in Example 1. The third ion-permeable barrier placed between the second sample chamber and the second electrolyte chamber was a polyacrylamide membrane with a nominal molecular mass cut-off of 5,000 dalton. 
     The first electrolyte reservoir was filled with 60 mL of a 2 mM acetic acid solution, pH 3.8. The second electrolyte reservoir was filled with 60 mL of an 8 mM triethanol amine solution, pH 9.9. The first and second sample reservoirs were filled with 30 mL each of a filtered chicken egg-white solution, diluted with deionized water at a rate of 1 to 25. The anode was placed into the first electrolyte chamber, the cathode into the second electrolyte chamber. The applied potential was 250 V, the separation time was 15 minutes. Aliquots were taken for analysis from the sample reservoirs at the end of the separation. 
     Full-column-imaging capillary isoelectric focusing on an iCE280 instrument (Convergent Bioscience, Toronto, Canada) was used to analyze the egg-white samples. The fused silica separation capillary was 5 cm long, its internal diameter was 100 micrometer. The focusing medium contained 8% carrier ampholytes to cover the pH 3-10 range, in an aqueous, 0.1% methylcellulose solution. Seventy-five microliter of the sample to be analyzed was mixed with 150 microliter of the focusing medium, filled into the capillary and focused for 5 minutes at 3,000 V. Dansyl phenylalanine (pI=3.52) and terbutaline (pI=9.61) were used as pI markers. 
     As a result of the electrophoretic separation, proteins with pI values lower than 5.0, such as ovalbumin (pI=4.7), accumulated in the first sample reservoir, on the anodic side of the pI=5.0 isoelectric membrane (bottom panel in FIG.  12 ). Proteins with pI values greater than 5.0, such as ovotransferrin (pI=6.1) accumulated in the second sample reservoir, on the cathodic side of the pI=5.0 isoelectric membrane (top panel in FIG.  12 ). Neither ovalbumin nor ovotransferrin were lost into the first or second electrolyte chambers despite the fact that the first and third ion-permeable barriers were not isoelectric membranes as in Example 1. At the end of the separation, the solution pH in the first and second sample reservoirs was 4.7 and 6.7, respectively. 
     EXAMPLE 3 
     The same apparatus as in Example 1 was used to separate the proteins present in chicken egg-white into two fractions. The first ion-permeable barrier placed between the first electrolyte chamber and the first sample chamber was a polyacrylamide membrane with a nominal molecular mass cut-off of 1,000,000 dalton. The ion-permeable barrier between the first sample chamber and the second sample chamber was a pI 5.0 isoelectric membrane prepared from Immobiline chemicals (Pharmacia, Sweden), acrylamide and N-N′-methylene bis-acrylamide as in Example 1. The third ion-permeable barrier placed between the second sample chamber and the second electrolyte chamber was a polyacrylamide membrane with a nominal molecular mass cut-off of 1,000,000 dalton. 
     The first electrolyte reservoir was filled with 60 mL of a 2 mM acetic acid solution, pH 3.8. The second electrolyte reservoir was filled with 60 mL of an 8 mM triethanol amine solution, pH 9.9. The first and second sample reservoirs were filled with 30 mL each of a filtered chicken egg-white solution, diluted with deionized water at a rate of 1 to 25. The anode was placed into the first electrolyte chamber, the cathode into the second electrolyte chamber. The applied potential was 250 V, the separation time was 15 minutes. Aliquots were taken for analysis from the sample reservoirs at the end of the separation, and analyzed by full-column-imaging capillary isoelectric focusing on an iCE280 instrument. 
     As a result of the electrophoretic separation, proteins with pI values lower than 5.0, such as ovalbumin (pI=4.7), accumulated in the first sample reservoir, on the anodic side of the pI=5.0 isoelectric membrane (bottom panel in FIG.  13 ). Proteins with pI values greater than 5.0, such as ovotransferrin (pI=6.1) accumulated in the second sample reservoir, on the cathodic side of the pI=5.0 isoelectric membrane (top panel of FIG.  13 ). Neither ovalbumin nor ovotransferrin were lost into the first or second electrolyte chambers despite the fact that the average pore size of the first and third ion-permeable barriers was large enough to permit their passage through these barriers. At the end of the separation, the solution pH in the first and second sample reservoirs was 4.7 and 6.2, respectively. 
     EXAMPLE 4 
     The same apparatus as in Example 1 was used to purify immunoglobulin G (IgG) from human plasma. The first ion-permeable barrier placed between the first electrolyte chamber and the first sample chamber was a polyacrylamide membrane with a nominal molecular mass cut-off of 150,000 dalton. The ion-permeable barrier between the first sample chamber and the second sample chamber was a pI 5.8 isoelectric membrane prepared from Immobiline chemicals (Pharmacia, Sweden), acrylamide and N-N′-methylene bis-acrylamide. The third ion-permeable barrier placed between the second sample chamber and the second electrolyte chamber was a polyacrylamide membrane with a nominal molecular mass cut-off of 150,000 dalton. 
     The first electrolyte reservoir was filled with 2 L of a 2 mM 5-amino caproic acid solution that also contained 5 mM NaCl, its pH was adjusted to 4.8 with HCl. The second electrolyte reservoir was filled with 2 L of a 2 mM MOPSO solution that also contained 5 mM NaCl, its pH was adjusted to 6.8 with NaOH. The anode was placed into the first electrolyte chamber, the cathode into the second electrolyte chamber. The applied potential was 250 V. Initially, both sample reservoirs were filled with deionized water. Potential was applied for 2 minutes to remove any unpolymerized material from the membranes. After 2 minutes, all reservoirs were emptied, the electrolyte reservoirs were refilled with fresh electrolytes, the sample reservoirs were filled with 15 mL each of human plasma diluted 1 to 3 with deionized water. Potential was applied for 40 minutes. Aliquots were taken for analysis from the sample reservoir chambers at 0, 10, 20, and 40 minutes, respectively. 
       FIG. 14  shows the image of an SDS-PAGE gel used to analyze the protein bands present in the aliquots collected from the first and second sample reservoirs of the electrophoretic apparatus during the isolation of IgG from human plasma. Molecular weight markers (Sigma, St. Louis, Mo., USA) were applied onto Lane 1, a pharmaceutical-grade IgG preparation used as reference material onto Lane 2. Samples taken at 0, 10, 20, and 40 minutes respectively from the first sample reservoir were applied onto Lanes 3, 4, 5, and 6. Samples taken at 0, 10, 20, and 40 minutes respectively from the second sample reservoir were applied onto Lanes 7, 8, 9, and 10. IgG was purified within 40 minutes. 
     These examples indicate that remarkably rapid separation of ampholytic components can be achieved using the apparatus and method disclosed here. The high production rates are attributed to the short electrophoretic migration distances, high electric field strength and good heat dissipation characteristics of the system. 
     The invention has been described herein by way of example only. It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. Other features and aspects of this invention will be appreciated by those skilled in the art upon reading and comprehending this disclosure. Such features, aspects, and expected variations and modifications of the reported results and examples are clearly within the scope of the invention where the invention is limited solely by the scope of the following claims.