Patent Publication Number: US-2022212123-A1

Title: Managing solvent associated with a field flow fractionator

Description:
PRIORITY 
     This application claims priority to U.S. Provisional Patent Application No. 63/091,879, filed Oct. 14, 2020. 
    
    
     BACKGROUND 
     The present disclosure relates to field flow fractionators, and more specifically, to managing solvent associated with a field flow fractionator. 
     SUMMARY 
     The present disclosure describes an apparatus of managing solvent associated with a field flow fractionator. In an exemplary embodiment, the apparatus includes (1) a union assembly coupled to a detector flow output from at least one detector coupled to a field flow fractionator, and (2) a recycle and waste assembly coupled to an output of the union assembly and a channel cross flow output of the field flow fractionator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts an apparatus in accordance with an exemplary embodiment. 
         FIG. 2  depicts an apparatus in accordance with an exemplary embodiment. 
         FIG. 3A  depicts an apparatus in accordance with an exemplary embodiment. 
         FIG. 3B  depicts an apparatus in accordance with an exemplary embodiment. 
         FIG. 4  depicts an apparatus in accordance with an exemplary embodiment. 
         FIG. 5  depicts an apparatus in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure describes an apparatus of managing solvent associated with a field flow fractionator. In an exemplary embodiment, the apparatus includes (1) a union assembly coupled to a detector flow output from at least one detector coupled to a field flow fractionator, and (2) a recycle and waste assembly coupled to an output of the union assembly and a channel cross flow output of the field flow fractionator. 
     In an embodiment,  FIG. 1 ,  FIG. 2 ,  FIG. 4 , and  FIG. 5  show the plumbing associated with an AF4 system. Most of the control elements are associated with controlling the FFF process, but the valves and unions highlighted by the red boxes are the ISM system. Valves V1 and V2 control the routing of the cross flow and detector flow waste/recycle. Also shown in blue are a series of two-way valves that are connected to the bleed ports of each of the control valves. They are routed together with the detector flow with a four-port union in the upper right red box and are sent to waste or recycle 
     More advanced FFF apparatus may include additional fluid flows, as depicted in  FIG. 2 . For example, the introduction of the Dilution Control Module (DCM) adds an additional waste stream. During normal operation, this stream is always expected to be uncontaminated. However, it is possible that sample could, become flushed down this path. To simplify system plumbing, we choose to combine the DCM waste stream with the detector stream rather than provide a separate control; both are switched together. The DCM stream could also have been separately filtered, but this would add extra maintenance burdens. 
     The present disclosure describes an intelligent solvent management system that can automatically route solvent flows from the detector port, cross flow port, and control valve bleed ports to either recycle or waste on a per-method basis. The solvent usage and number of injections are tracked to prevent the system from running out of solvent and to alert the user that membrane should be replaced. 
     Definitions 
     Particle 
     A particle may be a constituent of a liquid sample aliquot. Such particles may be molecules of varying types and sizes, nanoparticles, virus like particles, liposomes, emulsions, bacteria, and colloids. These particles may range in size on the order of nanometer to microns. 
     Analysis of Macromolecular or Particle Species in Solution 
     The analysis of macromolecular or particle species in solution may be achieved by preparing a sample in an appropriate solvent and then injecting an aliquot thereof into a separation system such as a liquid chromatography (LC) column or field flow fractionation (FFF) channel where the different species of particles contained within the sample are separated into their various constituencies. Once separated, generally based on size, mass, or column affinity, the samples may be subjected to analysis by means of light scattering, refractive index, ultraviolet absorption, electrophoretic mobility, and viscometric response. 
     Field Flow Fractionation 
     The separation of particles in a solution by means of field flow fractionation, FFF, was studied and developed extensively by J. C. Giddings beginning in the early 1960s. The basis of these techniques lies in the interaction of a channel-constrained sample and an impressed field applied perpendicular to the direction of flow. Among those techniques of current interest is cross flow FFF, often called symmetric flow (SFlFFF), where an impressed field is achieved by introducing a secondary flow perpendicular to the sample borne fluid within the channel. There are several variations of this technique including asymmetric flow FFF (i.e., A4F), and hollow fiber (H4F) flow separation. 
     Other FFF techniques include (i) sedimentation FFF (SdFFF), where a gravitational/centrifugal cross force is applied perpendicular to the direction of the channel flow, (ii) electrical FFF (EFFF), where an electric field is applied perpendicular to the channel flow, and (ii) thermal FFF (ThFFF), where a temperature gradient is transversely applied. 
     Common to all these methods of field flow fractionation is a fluid, or mobile phase, into which is injected an aliquot of a sample whose separation into its constituent fractions is achieved by the application of a cross field. Many of the field flow fractionators allow for the control and variation of the strength of the cross field during the time the sample aliquot flows down the channel, be it electrical field, cross flow, thermal gradient, or other variable field. 
     Symmetric Flow Cross Flow Fractionator (SFlFFF) 
     As an illustration of the separation of particles by field flow fractionation, a simplification of perhaps the most straightforward system, a SFlFFF, is described. A sample is injected into an inlet port along with the spending mobile phase. The sample is allowed to undergo a so-called “relaxation phase,” where there is no applied channel flow, but larger particles are forced further down the height of the channel than smaller particles by the constantly applied cross flow. Once the channel flow is resumed, the sample aliquot begins to undergo non-steric separation while it moves down the length channel with the smaller particles leading the larger ones, as they inhabit a region of the cross section of the channel flow nearer the center of the height of the channel where the channel flow is most swift. By increasing the cross flow rate, the separation of all species continues while the larger fractions begin to trail further behind their smaller sized companions. After exiting the channel through the outlet port the fractionated sample may be analyzed using various detectors. 
     Asymmetric Flow FFF (A4F) 
     An asymmetric flow FFF (A4F) is generally considered a variation of the earlier developed SFlFFF. An A4F channel assembly may include (1) a bottom assembly structure holding a liquid-permeable frit surrounded by a sealing O-ring, (2) a permeable membrane that lies on the frit, (3) a spacer of thickness from about 75 μm to 800 μm into which has been cut a cavity, and (4) a top assembly structure generally holding a transparent plate of polycarbonate material or glass. 
     The resulting sandwich is held together with bolts or other means, such as applied pressure adequate to keep the channel sealed against leaks, where such pressure may be applied by vise or clamping mechanism so long as it is able to provide relatively even pressure across the channel assembly such that no leaks occur. The generally coffin-shaped or tapered cavity in the spacer serves as the channel in which separation will occur. The top assembly structure usually contains three holes, called ports, that pass through the top plate and are centered above the channel permitting the attachment of fittings thereto. These ports are (a) a mobile phase inlet port located near the beginning of the channel and through which is pumped the carrier liquid, the so-called mobile phase, (b) a sample port, downstream of the inlet port, into which an aliquot of the sample to be separated is introduced to the channel and focused thereunder, and (c) an exit port through which the fractionated aliquot leaves the channel near the end of the cavity. 
     Asymmetric Flow Field Flow Fractionation (AF4) systems are used to fractionate molecules and particles by the well-known Flow FFF principle. There are a number of variations of the AF4 systems that vary in the way the sample is introduced and extracted from the channel, but in general they always have at least three ports. There is an inlet port that brings fluid into the channel, a detector output port that contains the fractionated fluid stream and a cross flow output port that contains the fluid that has passed through the semipermeable membrane that forms the accumulation wall. There can be extra ports such as and injection inlet to introduce the sample near the inlet or an extra split output port to strip off the sample free carrier solvent near the detector port, but at its simplest there must always be at least three. Additionally, many of the internal components such as control valves or pressure transducers may also have bleed ports that need to be periodically flushed to eliminate bubbles or stagnant solvent. 
     Current Technologies 
     The simplest way to operate a FFF channel is to cross flow solvent to waste and to send the flow out the detector port to the analysis instruments and then also to waste. When flushing the channel or after the sample has fully eluted both the cross flow and detector flows are essentially clean solvent, so there is the opportunity of recycling these flows back into the solvent reservoir and thereby reduce the volume of solvent required for an analysis. 
     Thus, there is a need to manage solvent associated with a field flow fractionator via an intelligent solvent management system that can route the exit fluid flows to either waste or recycle depending on the experiment that is performed. 
     Referring to  FIG. 1  and  FIG. 2  in an exemplary embodiment, the apparatus includes a union assembly  110 ,  210  coupled to a detector flow output  122 ,  222  from at least one detector  120 ,  220  coupled to a field flow fractionator  150 ,  250 , and (2) a recycle and waste assembly  130 ,  230  coupled to an output  116 ,  218  of union assembly  110 ,  210  and a channel cross flow output  152 ,  252  of field flow fractionator  150 ,  250 . 
     Union Assembly 
     In an embodiment, as depicted in  FIG. 1 , union assembly  110  is coupled to at least one purge flow output  140 ,  142 ,  144  coupled to field flow fractionator  150 . In an embodiment, union assembly  110  includes a five port union  110  coupled to three purge flow outputs  140 ,  142 ,  144  coupled to field flow fractionator  150  and detector flow output  122 . In an embodiment, as depicted in  FIG. 1A  and  FIG. 1B , union assembly  110  includes a plurality of unions  112 ,  114  coupled to three purge flow outputs  140 ,  142 ,  144  coupled to field flow fractionator and the detector flow output  150 . 
     In an embodiment, as depicted in  FIG. 1 , union assembly  110  includes (a) a four port union  112  coupled to two purge flow outputs  140 ,  142  coupled to field flow fractionator  150  and detector flow output  122 , and (b) a three port union  114  coupled to a third purge flow output  144  coupled to field flow fractionator  150  and an output port of four port union  112 . 
     Dilution Control Module 
     In an embodiment, as depicted in  FIG. 2 , union assembly  210  includes a seven port union  210  coupled to four purge flow outputs  240 ,  242 ,  244 ,  246  coupled to field flow fractionator  250 , a dilution control module (DCM) waste flow output  260  coupled to field flow fractionator  250 , and detector flow output  222 . In an embodiment, as depicted in  FIG. 2A  and  FIG. 2B , union assembly  210  includes a plurality of unions  212 ,  214 ,  216  coupled to four purge flow outputs  240 ,  242 ,  244 ,  246  coupled to field flow fractionator  250 , dilution control module waste flow output  260  coupled to field flow fractionator  250 , and detector flow output  222 . In an embodiment, union assembly  210  is coupled to detector flow output  222 . 
     In an embodiment, union assembly  210  includes (a) a first four port union  212  coupled to two purge flow outputs  240 ,  244  coupled to field flow fractionator  250  and detector flow output  222 , (b) a second four port union  214  coupled to an output  213  of first four port union  212  and two purge flow outputs  242 ,  246  coupled to field flow fractionator  250 , and (c) a three port union  216  coupled to an output port  215  of second four port union  214  and DCM waste flow output  260  coupled to field flow fractionator  250 . In an embodiment, two purge flow outputs  240 ,  244  coupled to first four port union  212  include a cross flow controller purge flow output  244  and an inject flow controller purge flow output  240 . In an embodiment, two purge flow outputs  240 ,  244  coupled to first four port union  212  are cross flow controller purge flow output  244  and inject flow controller purge flow output  240 . 
     In an embodiment, two purge flow outputs  242 ,  246  coupled to second four port union  214  include a dilution control module pressure controller purge flow output  246  and an inlet flow controller purge flow output  242 . In an embodiment, two purge flow outputs  242 ,  246  coupled to second four port union  214  are dilution control module pressure controller purge flow output  246  and inlet flow controller purge flow output  242 . 
     Manifold 
     In a further embodiment, as depicted in  FIG. 3A  and  FIG. 3B , union assembly  110 ,  210  further includes a manifold  310  to house at least a subset of plurality of unions  112 ,  114 ,  212 ,  214 ,  216 . Manifold  310  could increase the reliability of the apparatus, leading to fewer leak points in the apparatus and requiring less labor for installing/maintaining the apparatus. 
     The solvent management scheme depicted in  FIG. 1  and  FIG. 2  includes a combination of discrete components connected by tubing. However, many or all of these components can be combined into a manifold, as depicted in  FIG. 3A  and  FIG. 3B . The manifold could help to reduce the space requirements of the system, and improves manufacturability by reducing the number of fluidic connections. 
     Recycle and Waste Assembly 
     In an embodiment, as depicted in  FIG. 1  and  FIG. 2 , recycle and waste assembly  130 ,  230  includes (a) a first valve  132 ,  232  (V1) coupled to channel cross flow output  152 ,  252  of field flow fractionator  150 ,  250 , (b) a second valve  134 ,  234  (V2) coupled to an output  116 ,  218  of union assembly  110 ,  210 , (c) a first three port union  136 ,  236  (U1) coupled to first valve  132 ,  232  (V1) and to second valve  134 ,  234  (V2), where an output of first three port union  136 ,  236  is coupled to a recycle receptacle  170 ,  270 , and (d) a second three port union  138 ,  238  (U2) coupled to first valve  132 ,  232  (V1) and to second valve  134 ,  234  (V2), where an output of second three port union  138 ,  238  is coupled to a waste receptacle  172 ,  272 . 
     Purge Valves 
     In a further embodiment, as depicted in  FIG. 1  and  FIG. 2 , the apparatus further includes a purge valve (PV) coupled to a proportional control valve coupled to field flow fractionator  150 ,  250 , where purge valve is configured to remove air and to remove solvent from a line coupling purge valve to proportional control valve. In an embodiment, a proportional control valve  190 ,  290  (PV1) is coupled to an inject flow controller  101 ,  201  and an inject flow port  154 ,  254  of field flow fractionator  150 ,  250 . In an embodiment, a proportional control valve  192 ,  292  (PV2) is coupled to an inlet flow controller  103 ,  203  and a channel inlet port  156 ,  256  of field flow fractionator  150 ,  250 . In an embodiment, a proportional control valve  194 ,  294  (PV3) is coupled to a cross flow controller  105 ,  205  and a channel cross flow port  158 ,  258  of field flow fractionator  150 ,  250 . In an embodiment, a proportional control valve  296  (PV4) is coupled to a pressure controller  207  and a dilution control module (DCM) port  259  of field flow fractionator  250 . 
     Mass Flow Controller 
     In a further embodiment, the apparatus further includes a mass flow controller configured to be coupled to a sample injection port of flow fractionator  150 ,  250 , where the mass flow controller is configured to control a rate of infusing a sample into a channel of flow fractionator  150 ,  250 . 
     EXAMPLE 
     A simple example should suffice to explain the utility of intelligent solvent management. Consider a typical AF4 experiment to fractionate protein samples. The inlet flow is 4 ml/min, the detector flow is 1 ml/min and the cross flow is 3 ml/min. Further assume that each run takes 30 minutes. If all of the flows are sent to waste, then each run consumes 120 ml of solvent. However, most of these waste streams consist of clean, uncontaminated solvent. If a 5 kD molecular weight cutoff membrane is used in the FFF channel then the cross flow, which has been filtered by this membrane will be free of the sample protein and is safe to recycle. In this case, the 3 ml/min cross flow is sent back into the original solvent reservoir. Now a 30-minute run will only consume 30 ml, which is only 25% of the solvent required before. Since clean solvent can be expensive to prepare or dispose of, there is a clear benefit in being parsimonious. 
     Given that there are two outlets that can be routed separately to either waste or recycle, there are four possible recycle states, summarized in Table 1. During the hypothetical experiment described above, the Recycle states would be changed during the course of the experiment:
         1. When setting up the hardware, the Recycle state is set to None to flush contaminants out of the system   2. Prior to and after the experiment, the Recycle state is set to Detector+Cross Flow to recover   3. During the experiment, the Recycle state is set to Cross Flow to recover most of the solvent, while routing the contaminated Detector output to waste       

     Now consider another experiment that consists of fractionating proteins mixed with peptides that are small enough to pass through the channel membrane. In this case the cross flow will be contaminated with the peptides and should not be recycled into the source reservoir so one should revert to sending all exit flows to waste. The last example is a night rinse, where no sample is being used but the system is left with a slow flow through the channel to avoid stagnant fluid. In this case it is safe to recycle both flows and no solvent is consumed. The last state, while possible, is not commonly used. That is the case were the cross flow is sent to waste but the detector flow is recycled. If the cross flow that is filtered by the channel membrane is not considered clean enough to recycle, it is unlikely that the unfiltered detector flow can be recycled either. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Recycle state Benefits and Downsides 
               
            
           
           
               
               
               
            
               
                 Recycle 
                 Benefit 
                 Downside 
               
               
                   
               
               
                 None 
                 No risk of solvent 
                 Highest solvent consumption 
               
               
                   
                 contamination 
                   
               
               
                 Cross Flow 
                 Low solvent 
                 Risk of contamination by low Mw  
               
               
                   
                 consumption 
                 species that passes through the  
               
               
                   
                   
                 membrane 
               
               
                 Detector 
                 None 
                 If cross flow is not safe to recycle  
               
               
                   
                   
                 neither is detector flow 
               
               
                 Detector + 
                 Zero solvent 
                 Used for flushing only 
               
               
                 Cross Flow 
                 consumption 
               
               
                   
               
            
           
         
       
     
     It is important to prevent the solvent reservoir from running dry. This can damage the pumps and filters in the system. With the ISM system, the instrument control software knows the magnitude of each flow and which port it is routed to. It computes the total amount of fluid that is lost to the waste port and how much is recycled. If the user enters into the software the initial volume of the source reservoir, it can keep a running tab of the remaining solvent. The user is given a couple of options. The first is a threshold solvent to decide whether to allow an experiment is allowed. The second option is to choose what should happen if the system runs low on solvent. It can either stop the flow, or switch the system to full recycle. Both of which prevent the solvent level from dropping further and insure that the solvent reservoir never runs dry. 
     Lastly, since each experiment has different recycle needs, the experiment method setup panel allows the user to choose between the various recycle modes described above. The options are: Recycle none, Recycle All, and Recycle XF (cross flow only). These correspond to the recycle states described above. 
     The software that tracks the solvent consumption can also track the total volume of fluid that has passed through the channel and the fraction that has passed through the fractionation membrane. This can be used to track aging of the system and signal the user when the membrane needs to be replaced. This software also counts the number of samples that have been injected into the channel and presents an injection counter to the user. This is shown  FIG. 4 . These features are useful for quality control applications where it is desirable to track the number of injections and the membrane usage to insure consistent performance. If they exceed preset maximums a warning is presented to the user. 
     The descriptions of the various embodiments of the present disclosure have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.