Method for producing a gradient elution

Abstract

The method of proportioning two liquids comprising periodically controlling the operation of a valving .[.means.]. .Iadd.arrangement .Iaddend.to control the amount of each liquid supplied to a mixing region during each period of valve operation to produce a supply of eluent having a precisely controlled time varying concentration of each liquid.

What is claimed is: 
     
       1. A method of producing an eluent containing a time varying concentration of two liquids, comprising the steps of: a. supplying a first liquid to a first operative portion of normally closed valving means;   b. supplying a second liquid to a second operative portion of said normally closed valving means;   c. alternately activating said first operative portion of said valving means for a first set period of time to allow a first set volume of said first liquid to enter a mixing region and then activating said second operative portion of said valving means for a second set period of time to allow a second set volume of said second liquid to enter said mixing region and mix with said first set volume of first liquid to form a mixture containing a set concentration of said first and second liquids.Iadd., said first and second set periods of time being such that the volume of said first and second liquid entering said mixing region during each period when either operative portion of said valving means is activated is less than the volume of said mixing region; .Iaddend.   d. allowing a portion of said mixture to leave said mixing region thereby producing an eluent having a concentration of said first and second liquid, the instantaneous concentration of which is equal to the instantaneous concentration of said first and second liquids at the downstream end of said mixing region at the time said portion of said mixture leaves said mixing region; and   e. varying said first and second set periods of time during which said first and second operative portions of said valving means are respectively activated, whereby the concentrations of said first and second liquids in said mixture are gradually changed so that an eluent having a time varying concentration of said first and second liquids is produced.   
     
     
       2. The method of claim 1 wherein the step of supplying a first liquid to the first operative portion of the valve means is accomplished by pumping a first quantity of the first liquid directly to the first operative portion of the valve means, and the step of supplying a second liquid to the second operative portion of the valving means is accomplished by transferring a quantity of the second liquid to a long narrow holding chamber and then pumping the second liquid contained in the holding tube to the second operative portion of the valving means by pumping a second quantity of the first liquid to the upstream side of the holding tube. 
     
     
       3. The method of claim 1 wherein the first and second liquids are supplied to the first and second operative portions of the valving means at a constant pressure.