Converting a pump for use in supercritical fluid chromatography

Abstract

A method and apparatus for converting a pump for use in a flow stream containing a mixture of highly compressed gas, compressible liquid or supercritical fluid wherein the pump delivers a compressible fluid against a back-pressure regulator which in turn delivers a controllable flow rate downstream of the regulator without performing variable compressibility compensation adjustments on the pump. By using a pressurized source of compressible fluid combined with isocratic conditions, the delivery pressure from the pump is controlled at a rate higher than the downstream gradient with the back-pressure regulator, and an inexpensive pump may be used in place of specialized, expensive pumps and compressibility compensation systems for use in stems operating at or near supercritical fluid levels of compressible fluids. Significant capital and operating laboratory costs are saved through a simpler and cheaper system for accurately delivering compressible fluids into mobile phase flow streams.

What is claimed:  
     
         1 . A method for converting a pump for use in a combined flow stream containing a mixture of highly compressed gas, compressible liquid or supercritical fluid; and a relatively incompressible liquid, comprising: 
 controlling pressure, of a first flow stream containing a highly compressed gas, compressible liquid, or supercritical fluid, by maintaining an elevated pressure rate after said outlet of said pump but prior to joining a second flow stream of a relatively incompressible liquid;    pumping of said first flow stream consisting of a pure fluid resulting in delivery of a controllable flow rate of said first flow stream at a constant compressibility compensation without the need for dynamically compensating said pump for compressibility changes in said first flow stream.    
     
     
         2 . The method of  claim 1 , wherein: 
 said maintenance of an elevated pressure rate after said outlet of said pump being accomplished by delivering said fluid first flow stream from said pump against a back pressure regulator valve installed in said first flow stream downstream of said pump and upstream to the joining of said first flow stream with said second fluid flow stream containing a relatively incompressible liquid.    
     
     
         3 . The method of  claim 1 , further comprising: 
 pumping said first fluid flow stream against a fixed elevated pressure provides a reproducible flow source to a supercritical fluid system.    
     
     
         4 . The method of  claim 1 , wherein: 
 delivering said first fluid flow stream against a fixed elevated pressure provides an accurate flow source to a supercritical fluid system.    
     
     
         5 . The method of  claim 1 , wherein: 
 said pump rate is controllable with variable flow rates when pumping against said elevated pressure in said first fluid flow stream.    
     
     
         6 . The method of  claim 1 , wherein: 
 said method is operated under approximate isocratic conditions.    
     
     
         7 . The method of  claim 1 , wherein: 
 the mass flowrate of said first flow stream after said back-pressure regulator is determinable by calibration.    
     
     
         8 . A method for converting a pump for use in a combined flow stream containing a mixture of highly compressed gas, compressible liquid or supercritical fluid; and a relatively incompressible liquid, comprising: 
 controlling inlet pressure to a pump of a first flow stream of a highly compressed gas, compressible liquid or supercritical fluid;    controlling temperature of said first flow stream;    pumping of said first flow stream, consisting of a pure fluid, against an elevated pressure rate resulting in delivery of a controllable flow rate of said first flow stream at a constant compressibility compensation without the need for dynamically compensating said pump for compressibility changes in said first flow stream.    
     
     
         9 . The method of  claim 8 , wherein: 
 said pump is operated at variable flow rates when pumping against said elevated pressure in said first fluid flow stream.    
     
     
         10 . The method of  claim 8 , further comprising: 
 delivering said first fluid flow stream against said elevated pressure produces a reproducible flow source to a supercritical fluid system.    
     
     
         11 . The method of  claim 8 , wherein: 
 said elevated pressure after said outlet of said pump is accomplished by delivering said first fluid flow stream from said pump against a back pressure regulator valve installed in said flow stream downstream of said pump and upstream from the joining of said first flow stream with said second fluid flow stream.    
     
     
         12 . The method of  claim 8 , wherein: 
 delivering said first fluid flow stream against a fixed elevated pressure provides a reproducible flow source to a supercritical fluid system.    
     
     
         13 . The method of  claim 8 , wherein: 
 said method is operated under approximate isocratic conditions.    
     
     
         14 . The method of  claim 8 , wherein: 
 the flowrate of said first flow stream after said elevated pressure is determinable by calibration.    
     
     
         15 . An apparatus for converting a pump for use in a combined flow stream containing a mixture of highly compressed gas, compressible liquid or supercritical fluid; and a relatively incompressible liquid, comprising: 
 means for controlling pressure of a first flow stream containing a highly compressed gas, compressible liquid, or supercritical fluid, by maintaining an elevated pressure rate after said outlet of said pump but prior to joining a second flow stream of a relatively incompressible liquid;    means for pumping of said first flow stream consisting of a pure fluid resulting in delivery of a controllable flow rate of said first flow stream at a constant compressibility compensation without the need for dynamically compensating said pump for compressibility changes in said first flow stream.    
     
     
         16 . The apparatus of  claim 15 , wherein: 
 said maintenance of an elevated pressure rate after said outlet of said pump being accomplished by means for delivering said fluid first flow stream from said pump against a back pressure regulator valve installed in said first flow stream downstream of said pump and upstream to the joining of said first flow stream with said second fluid flow stream containing a relatively incompressible liquid.    
     
     
         17 . The apparatus of  claim 15 , wherein: 
 means for pumping said first fluid flow stream against a fixed elevated pressure provides a reproducible flow source to a supercritical fluid system.    
     
     
         18 . The apparatus of  claim 15 , wherein: 
 said apparatus is operated under approximate isocratic conditions.    
     
     
         19 . The apparatus of  claim 15 , wherein: 
 the mass flowrate of said first flowstream after said back-pressure regulator is determinable by calibration.    
     
     
         20 . An apparatus for converting a pump for use in a combined flow stream containing a mixture of highly compressed gas, compressible liquid or supercritical fluid; and a relatively incompressible liquid, comprising: 
 a pressurized first flow stream source of a pure fluid of compressed gas, compressible liquid or supercritical fluid; and    a pump to deliver said flow stream to a column after mixing with a second flow stream containing a relatively incompressible liquid; and    a back-pressure regulator device installed downstream of said pump and set to deliver said first flow stream at a pressure above any point in the gradient downstream of said back-pressure device; and    wherein the flow rate of said pump is controllable while delivers said first flow stream at a fixed pressure through said back-pressure regulator without performing dynamic compressibility compensation adjustments to said pump.    
     
     
         21 . The apparatus of  claim 20 , wherein: 
 said pump is operated at variable flow rates when pumping against said elevated pressure in said first fluid flow stream.    
     
     
         22 . The apparatus of  claim 20 , wherein: 
 said pump that is pumping said first fluid flow stream against a fixed elevated pressure provides a reproducible flow source to a supercritical fluid system.    
     
     
         23 . The apparatus of  claim 20 , wherein: 
 said back-pressure device is a back-pressure regulator valve.    
     
     
         24 . The apparatus of  claim 20 , wherein: 
 said pump is a dual-piston, diaphragm, or screw pump.