Liquid chromatographic method and system

Abstract

A chromatographic monitor includes an array of flow cells with individual light sensors that are collectively an array of photodiodes. The output from the photodiodes are multiplexed. To prevent losing information, the photodiodes are each connected to a different one of a plurality of inputs to the multiplexer through a corresponding one of a plurality of circuits that stores energy during the time the one inlet is not connected through the multiplexer to the signal processing circuitry that forms a part of an absorbance monitor. Preferably, the energy storing circuit is a non-switching circuit with low bandwidth and a flat-topped response to an impulse. This improves the signal to noise ratio. A one pole low pass filter with a (1−1/e) Dirac pulse fall time and equal to the multiplex entire cycle repeat time can perform this function and a one pole low pass filter provides satisfactory results. Still better results can be obtained from a three pole, one or two percent overshoot filter with combined minimum frequency bandwidth and fast rise time. A rise time equal to ½ the multiplex entire cycle.

1 . A multiplex system for measuring a plurality of sources, comprising: 
 a plurality of sources of signals representing measured values;    a time division multiplex circuit having a plurality of input means at least some of which a arranged to receive signals from a corresponding one of said source of signals in said plurality of sources of signals representing measured values;    said time division multiplex circuit having a multiplex cycle time during which it multiplexes at least some of said plurality of input means whereby it conducts signals from each individual input means of said some of said plurality of input means for a stroke time; and    at least one circuit means arranged to receive energy from at least one of said sources of signals for a substantial portion of said multiplex cycle time and apply it to a corresponding one of said plurality of multiplex circuit input means during said stroke time.    
   
   
       2 . A multiplex system in accordance with  claim 1  in which said at least one circuit means is a non-switching circuit with low bandwidth, whereby sensitivity is improved.  
   
   
       3 . A liquid chromatographic system in accordance with  claim 2  in which said at least one circuit means has a fast rise time, flat topped response to an impulse and a pulse duration that lasts at least a substantial portion of the multiplex cycle time.  
   
   
       4 . A method of multiplexing signal sources, comprising the steps of: 
 multiplexing signals from at least a some of said plurality of signal sources during a multiplex cycle time during at least one of said plurality of a plurality of signals from at least one of said plurality of signal sources being conducted to an output terminal occurring during one stroke portion of said multiplex cycle time; and    transmitting energy from said at least one of said signal sources for a substantial portion of said multiplex cycle time and applying it to a corresponding one of said plurality of multiplex circuit input means during said stroke time.    
   
   
       5 . A multiple channel liquid chromatographic system, comprising: 
 at least two syringe pumps for pumping solvent in said system wherein each of said at least two syringe pumps includes a piston and a cylinder;    a moving frame attached to at least two pistons of said two syringe pumps, wherein movement of each of the pistons with respect to a corresponding cylinder of said syringe pumps is carried out by the moving frame,    at least one time-proportioning electronically controllable liquid gradient switching valve;    a first mixing means;    a second mixing means;    said second mixing means being a pump cylinder with an offset inlet that forms eddy currents in the pump cylinder;    the first mixing means residing in a fluid flow path between the at least one time-proportioning electronically controllable liquid gradient switching valve and the said at least one of said at least two syringe pumps inlet and the second mixing means resides in the cylinder of the at least one of said at least two syringe pumps downstream of the inlet of the at least one time-proportioning electronically controllable liquid gradient switching valve; wherein the fluid flow path between the said at least one time-proportioning electronically controllable liquid gradient switching valve and the at least one of said at least two syringe pumps inlet is a flow passageway sized to produce formation of elongated streams of first and second solvents with mixing in the said passageway, which in combination with mixing caused by eddy currents in the pump cylinder makes each step of the gradient sufficiently flat and reproducible for a desired set of chromatographic separation processes.    
   
   
       6 . A multiple channel liquid chromatographic system in accordance with  claim 5  wherein the flow passageway has a volume less than one-tenth that of a single charge, wherein the flow passageway has a diameter of less than one-half the diameter of the pump cylinder; said flow producing good axial mixing and poor transverse mixing on a small scale charge and an outlet of said flow passageway injecting into the pump cylinder where the flow becomes turbulent flow thus enhancing transverse mixing and axial mixing on a large scale.  
   
   
       7 . A multiple channel liquid chromatographic system in accordance with  claim 6  wherein the flow passageway has a volume of at least one-tenth that of a single charge; said flow producing good axial mixing on a small scale and an outlet of said flow passageway injecting into the pump cylinder where the flow undergoes enhanced transverse mixing.  
   
   
       8 . A multiple channel liquid chromatographic system in accordance with  claim 6  wherein the flow passageway has a volume of at least one-tenth that of a single charge wherein the distance required for further transverse mixing is small; said flow producing good axial mixing and an outlet of said flow passageway injecting into the larger diameter pump cylinder where the flow becomes turbulent and undergoes transverse mixing and axial mixing.  
   
   
       9 . A multiple channel liquid chromatographic system in accordance with  claim 7  in which said at least one time-proportioning electronically controllable liquid gradient switching valve is arranged to produce consecutive pulses of liquid from at least one of said at least two sources of liquid to a refill inlet at a fluid velocity high enough to induce turbulent mixing in a space between a head of said piston and that part of the cylinder not occluded by the piston.  
   
   
       10 . A multiple channel liquid chromatographic system in accordance with  claim 9  further including means for synchronizing the at least one time-proportioning electronically controllable liquid gradient switching valve with refill movement of said piston so that one charge of each desired fluid at a desired volume proportion is deposited in each pump and mixed to form at least one part of a step of a stepped gradient.  
   
   
       11 . A multiple channel liquid chromatographic system in accordance with  claim 10  further including: 
 first means for shutting off fluid flow between the said pump and said at least one time-proportioning electronically controllable liquid gradient switching valve during delivery;    second means for synchronizing the at least one time-proportioning electronically controllable liquid gradient switching valve with refill movement of said piston so that one charge of each desired fluid at a desired volume proportion is deposited in each pump and mixed to form at least one part of a step of a stepped gradient; and    control means for repeating the said first and second means at consecutively different or same fluid proportions to produce an entire stepped gradient.    
   
   
       12 . A multiple channel liquid chromatographic system in accordance with  claim 11  wherein at least two equal charges of each of two fluids are alternately delivered to an inlet of at least one of said at least two syringe pumps; said two fluids being mixed in the at least one time-proportioning electronically controllable liquid gradient switching valve during a rapid, energetic refill, and then delivered as a single step of a step gradient to the rest of said system in the order of sample injection device, chromatographic column, and fraction collector.  
   
   
       13 . A method of performing liquid chromatography comprising: 
 drawing at least first and second fluid solvent into a plurality of pumps from at least a corresponding first and second source of fluid;    pumping said fluid from said plurality of pumps;    said step of pumping said fluid including the step of mixing said at least first and second fluids in said pumps whereby a gradient is formed;    said step of mixing including the step of mixing said at least first and second fluids prior to pumping said at least first and second fluids from said pumps;    said step of mixing further including the step of drawing said first and second fluids through at least one flow path, wherein the flow path is shaped to produce good axial mixing and poor transverse mixing by stretching out flow streams of each of said first and second fluids; and    injecting said fluids into a pump cylinder where it undergoes enhanced transverse mixing and axial mixing from eddy currents in the pump cylinder.    
   
   
       14 . The method of  claim 13  wherein the enhanced mixing occurs because the axially-mixed liquid entering the pump facilitates further mixing because the distance required for further transverse mixing is small.  
   
   
       15 . A method according to  claim 14  wherein the enhanced mixing occurs because the tendency of some pairs of liquids not to mix at their interfaces decreases because this interface is already degraded at or before the outlet of flow means.