Sample injector for high pressure liquid chromatography

Abstract

Apparatus and method for driving a sample, having a well-defined volume, under pressure into a chromatography column. A conventional high pressure sampling valve is replaced by a sample injector composed of a pair of injector components connected in series to a common junction. The injector components are constructed so as to provide for electroosmotic flow of a sample into the junction. At an appropriate time, a pressure pulse from a high pressure source, that can be an electrokinetic pump, connected to the common junction, drives a portion of the sample, whose size is determined by the dead volume of the common junction, into the chromatographic column for subsequent separation and analysis. The apparatus can be fabricated on a substrate for microanalytical applications.

We claim:  
     
         1 . An apparatus for injecting a sample into a chromatographic column, comprising: 
 a source of high pressure joined at a common junction to the inlet of the chromatographic column; and    a sample injector joined to the common junction, said sample injector comprising at least two elements combined in a series arrangement and connected to a common power supply, wherein each element comprises a container having an inlet end and an outlet end, the container filled with a dielectric material forming a porous bed therein.    
     
     
         2 . The apparatus of    claim 1   , wherein said high pressure source comprises an electrokinetic pump.  
     
     
         3 . The apparatus of    claim 1   , wherein the porous dielectric material is comprised of a nonporous and uncoated material.  
     
     
         4 . The apparatus of    claim 3   , wherein the dielectric material includes a glass, ceramic, or polymer material.  
     
     
         5 . The apparatus of    claim 4   , wherein the dielectric material is silica beads.  
     
     
         6 . The apparatus of    claim 1   , wherein the porous bed has a pore size in the range of about 25 to 300 nm.  
     
     
         7 . The apparatus of    claim 1   , further including at least one salt bridge disposed between the electrodes of the power supply and the elements of said sample injector.  
     
     
         8 . A method of injecting a sample into a chromatography column for chromatographic analysis, comprising the steps of: 
 providing a flow of a running buffer to the chromatography column;    shutting off the flow of running buffer;    applying a voltage to a sample injector having a common junction with the chromatography column to cause a sample to flow into the common junction; and    starting the flow of running buffer to apply a pressure to drive the sample contained in the common junction into and through the chromatography column.    
     
     
         9 . An apparatus for the high pressure injection of a sample into a chromatography column, comprising: 
 a substrate fabricated to define a microchannel system disposed thereon, the microchannel system comprising, in combination, 
 a source of high pressure joined at a common junction to the inlet of the chromatography column; and  
 a sample injector joined to the to the common junction, said sample injector comprising at least two elements combined in a series arrangement and connected to a common power supply, wherein each element comprises a container having an inlet end and an outlet end, the container filled with a dielectric material forming a porous bed therein.  
   
     
     
         10 . The apparatus of    claim 9   , wherein the source of high pressure is an electrokinetic pump.  
     
     
         11 . The apparatus of    claim 9   , further including at least one salt bridge disposed between the electrodes of the power supply and the elements of said sample injector.  
     
     
         12 . The apparatus of    claim 9   , wherein the dielectric material comprising the porous bed is produced by lithographic etching.