Solvent delivery system for liquid chromatography that maintains fluid integrity and pre-forms gradients

Abstract

A solvent delivery subsystem for a chromatography device performs relatively low pressure, high flow mixing of solvents to form a gradient and subsequent high pressure, low flow delivery of the gradient to the separation column. The mixing of the gradient is independent and does not interfere with the gradient delivery. To form the gradient, the outputs of an aqueous pump and an organic pump are mixed to fill a storage capillary while a downstream point from the storage capillary is vented to atmosphere. After gradient formation, the vent to atmosphere is closed, the solvent delivery system rises to high pressure, and only the aqueous pump runs for gradient delivery. To maintain integrity of the fluid stream, the solvent delivery system uses feed forward compensation and controls at least one parameter selected from the group consisting of pressure and flow in the conduit means to follow a gradual ramp.

1 . A method of forming a gradient in a liquid chromatography system having a pump that fills a storage capillary, the method comprising the steps of:
 venting the storage capillary to atmosphere; and   running the pump at relatively low pressure and higher flow rate to fill the storage capillary until the gradient is formed therein.   
     
     
         2 . A method as recited in  claim 1 , wherein the relatively low pressure is approximately 100 psi and the relatively higher flow rate is approximately fifteen times a normal chromatographic flow rate. 
     
     
         3 . A method as recited in  claim 1 , wherein a geometry of the storage capillary is sized by a length and an inner diameter to achieve a volume capacity for the gradient and to minimize formation of backpressure and gradient dispersion. 
     
     
         4 . A method as recited in  claim 3 , wherein the volume capacity of the storage capillary is sized to accommodate the gradient and an overhead of transport volume necessary to move the gradient to a separations column. 
     
     
         5 . A method as recited in  claim 1 , wherein the pump comprises an aqueous pump and an organic pump, each of said aqueous and organic pumps having an output connected to a mixing node between the pumps and the storage capillary. 
     
     
         6 . A method as recited in  claim 5 , further comprising the steps of:
 taking the organic pump offline;   closing the storage capillary from the atmosphere; and   running the aqueous pump to deliver the gradient to a separation column.   
     
     
         7 . A method as recited in  claim 6 , wherein the closing is accomplished by a valve connected upstream from the storage capillary. 
     
     
         8 . A method as recited in  claim 5 , further comprising the step of running the pumps to waste prior to gradient formation to prevent cross-contamination across the mixing node. 
     
     
         9 . A method as recited in  claim 5 , further comprising the step of running the organic pump set to zero flow to prevent cross-contamination across the mixing node. 
     
     
         10 . A method as recited in  claim 1 , further comprising the steps of: opening the valve and running at least one of the pumps in order to purge the storage capillary in readiness for forming another gradient. 
     
     
         11 - 24 . (canceled) 
     
     
         25 . A system for delivering a gradient to a liquid chromatography device having an injector that introduces the sample into a separations columns, the system comprising:
 a first leg having an aqueous pump producing an aqueous output directed through a first inline pressure transducer and a first flow transducer;   a second leg having an organic pump producing an organic output directed through a second inline pressure transducer and a second flow transducer; and   a processing device for controlling the fluid stream of each leg including:
 a closed-loop feedback mode to generate a corrective signal based on an error derived from a measured signal from at least one of the transducers to overcome parasitic losses upstream from the at least one of the transducers; and 
 an open-loop feed forward mode to generate an anticipatory control signal based on a parameter of stored energy of the system, wherein the anticipatory control signal calculates a compression flow based on a ratio of compressibility between the aqueous output and the organic output, and 
 wherein the processing device can selectively operate each leg in different modes. 
   
     
     
         26 . (canceled) 
     
     
         27 . (canceled) 
     
     
         28 . A system for changing an operational flow rate of delivery of a gradient in a liquid chromatography device, the system comprising:
 a) a pump producing an output directed through a pressure transducer and a flow transducer;   b) a storage capillary for forming the gradient from a portion of the output; and
 c) a processing device for controlling the pump and receiving signals from the transducers, wherein the processing device provides a corrective feed forward signal to the pump based upon an amount of volume in a head in the pump and a compressibility of the output. 
   
     
     
         29 - 38 . (canceled) 
     
     
         39 . A method for peak parking in a liquid chromatography system comprising the steps of:
 pre-forming a gradient from a mixture;   controlling a flow rate by using a flow transducer for closed-loop feedback;   monitoring a delivery pressure by using a pressure transducer;   calculating a target pressure based on the delivery pressure and a signal to reduce the flow rate based on an elution peak of interest; and   switching to controlling the flow rate by using the pressure transducer as closed-loop feedback with the target pressure as a set point.   
     
     
         40 . (canceled) 
     
     
         41 . (canceled) 
     
     
         42 . A nano-flow capillary liquid chromatography system comprising:
 a) an analytical subsystem having a separations column for generating a chromatogram; and   b) a solvent delivery system for forming and delivering a gradient to the analytical subsystem, wherein the solvent delivery system comprises:   an aqueous pump producing a first output;   an organic pump producing a second output mixed with the first output to produce a solution;   a processing device for controlling the pumps;   a storage capillary for forming a gradient from a portion of the solution;   a fitting connected to the storage capillary, wherein the fitting forms a first outlet connected to the nano-flow capillary liquid chromatography device and a second outlet; and   a valve connected to the second outlet and controlled by the processing device such that, during forming the gradient in the storage capillary, the valve is open to direct resident fluid to waste while the aqueous and organic pumps run.   
     
     
         43 - 60 . (canceled) 
     
     
         61 . A LC instrument comprising:
 an injection valve for creating a gradient;   an analytical column in fluid communication with the injection valve;   a pump connected to the injection valve for urging the gradient towards the analytical column; and   a device intermediate the injection valve and analytical column for storing the gradient.   
     
     
         62 - 68 . (canceled)