Patent Description:
The invention relates generally to liquid chromatography systems. More particularly, the invention relates to a mixer for mixing solvent composition streams in a liquid chromatography system.

Chromatography systems and methods can be applied to separate a mixture. In liquid chromatography, a sample containing a number of components to be separated is injected into a system flow and directed to a chromatographic column. The column separates the mixture by differential retention into its individual components. Typically, the components elute from the column as distinct bands separated in time.

A typical liquid chromatography system includes one or more pumps for delivering a fluid (the "mobile phase") at a controlled flow rate and composition, an injector to introduce a sample solution into the flowing mobile phase, a chromatographic column that contains a packing material or sorbent (the "stationary phase"), and a detector to detect the presence and amount of the sample components in the mobile phase leaving the column. Some liquid chromatography systems may require that a sample be diluted before the sample is injected into the mobile phase flowing to the chromatography column. When the mobile phase passes through the stationary phase, each component of the sample typically emerges from the column at a different time because different components in the sample generally have different affinities for the packing material. The presence of a particular component in the mobile phase exiting the column may be detected by measuring changes in a physical or chemical property of the eluent. By plotting the detector signal as a function of time, response "peaks" corresponding to the presence and quantities of the components of the sample may be observed.

In gradient elution chromatography, the mobile phase is typically generated by pumping and then mixing two or more independently controlled solvent packet volumes when mixing is performed at low pressure. The volumes of the solvent packets are typically fractions of a pump stroke volume of a reciprocating pump. These solvent packets are concatenated to form a serial train of solvent plugs of different composition at low pressure (e.g., atmospheric pressure) before arriving at the pump system. Alternatively, the solvent packets are merged at high pressure in a tee junction downstream from the pump system. A mixer is typically used to ensure that the time-programmed composition of the mobile phase at the inlet of the chromatographic column is accurate and has a low compositional noise level through the duration of the chromatographic separation to maximize detection sensitivity.

Two types of mixers are often used to perform the desired mixing of the solvent packets. The first type is a column packed with large (e.g., <NUM> nominal diameter) nonporous beads. The void mixer volume may vary from a few tens of microliters to more than several hundred microliters, according to the type of liquid chromatography system being used. The second type is a microfluidic device in which the received solvent composition flow is split into multiple flow paths of differing lengths which are subsequently merged to provide a single outlet flow. Regardless of the type of mixer, the goal is to eliminate the periodic composition noise generated by the reciprocating pumps in the pump system.

The first type of mixer is subject to poor mixer to mixer reproducibility due to the random nature of the packing of the columns with the nonporous beads. Furthermore, this type of mixer has limited mixing capability and compositional noise reduction because packed column beds are generally intended for separation of fractions as opposed to mixing. These problems exist even with larger sized beads. The second type of mixer is more difficult to manufacture due to its structural complexity and is not designed to eliminate periodic noise. The second type generates a wide retention time distribution (RTD) of a pulse input. Furthermore, the second type of mixer has an asymmetric retention time distribution which limits its ability to rapidly achieve the time-programmed composition of the mobile phase.

A prior art arrangement is known from <CIT>, which relates to a liquid chromatography apparatus. A second prior art arrangement is known from <CIT>, which relates to a flow distribution system for distributing and dividing the flows of at least two separate fluids. A third prior art arrangement is known from <CIT>, which relates to a device for mixing a plastic melt flow.

The present invention provides a mixer for a liquid chromatography system as defined in the claims.

In an aspect of the present disclosure, a mixer for liquid chromatography includes a flow distributor, a mixing disk and a flow collector. The fundamental rationale for the design of a disk-shaped mixer is that, for a fixed mixer volume Vmixer, filled with a dispersive material of plate height H, the volume-based dispersion or variance, <MAT>, of the RTD is inversely proportional to its length L: <MAT>.

The flow distributor has a distributor inlet port and a distributor outlet port. The distributor inlet port is configured to receive a flow of a compositional solvent stream and the distributor outlet port has an outlet cross-section and is configured to provide the compositional solvent stream distributed across the outlet cross-section. The mixing disk has an inlet face, an outlet face and a plurality of channels each having an inlet end at the inlet face and an outlet end at the outlet face. The inlet face is in communication with the distributor outlet port. The channels have a flow direction anisotropy between the inlet and outlet faces. The flow collector has a collector inlet port and a collector outlet port. The collector inlet port has an inlet cross-section and is in communication with the outlet face of the mixing disk to receive the flow of the compositional solvent stream after passing through the mixing disk.

The mixing disk may include a dispersive medium having a random porous structure. The channels may have a tortuosity of at least five and no greater than ten. The mixing disk may be formed of a material comprising a glass, a polymer or a metal. The mixer disk may have a void volume that is greater than a volume of the flow distributor and greater than a volume of the flow collector. The mixing disk may include at least one mesh layer.

The mixer may have a retention time distribution that is dependent on a structure of the channels between the inlet face and the outlet face of the mixing disk. Individual flows of the compositional solvent stream distributed across the outlet cross-section of the flow distributor may have a diameter between approximately <NUM> to approximately <NUM>.

An area of the outlet cross-section of the flow distributor may be equal to a cross-sectional area of the inlet face of the mixing disk. An area of the inlet cross-section of the flow collector may be equal to a cross-sectional area of the outlet face of the mixing disk.

The flow distributor may include an angular dispersion plate and/or a radial dispersion plate. The flow distributor may be a fractal flow distributor. The flow collector may include an angular dispersion plate and/or a radial dispersion plate. The flow collector may be a fractal flow collector.

The flow distributor may include a plurality of openings at the distributor outlet port and a plurality of internal flow paths defined between the distributor inlet port and the distributor outlet port to conduct the compositional solvent stream to the distributor outlet ports. The openings may be disposed along a plurality of concentric circles defined on the distribution outlet port. The flow collector may include a plurality of openings at the collector inlet port and a plurality of internal flow paths defined between the collector inlet port and the collector outlet port to conduct the compositional stream from the mixing disk to the collector outlet port. The openings at the distributor outlet port may be arranged identically to the openings at the collector inlet port. The number of openings at the distributor outlet port may be different from the number of openings at the collector inlet port.

The flow collector may include a plurality of openings at the collector inlet port and a plurality of internal flow paths defined between the collector inlet port and the collector outlet port to conduct the compositional stream from the mixing disk to the collector outlet port. The openings may be disposed along a plurality of concentric circles defined on the collector input port.

The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the technology.

Reference in the specification to an "example," "embodiment" or "implementation" means that a particular feature, structure or characteristic described in connection with the example, embodiment or implementation is included in at least one embodiment of the teaching. References to a particular example, embodiment or implementation within the specification do not necessarily all refer to the same embodiment.

As used herein, a mobile phase is a solvent or mixture of solvents used to carry a sample and to pass through the stationary phase of a liquid chromatography system. The mobile phase may be a gradient mobile phase in which the composition of the mobile phase changes with time. The mobile phase may also be referred to herein as the system flow which typically flows from the source of the mobile phase to at least the detector of the liquid chromatography system.

In brief overview, a passive mixer having a disk-shaped mixing element is described. The mixer improves the accuracy and precision of a time-programmed composition of a mobile phase delivered by reciprocating pumps in a liquid chromatography system. The mixer includes a flow distributor, a mixing disk and a flow collector. The mixing disk has an inlet face, an outlet face and a plurality of channels each having an inlet end at the inlet face and an outlet end at the outlet face. The channels have a flow direction anisotropy between the inlet and outlet faces. A compositional solvent stream is distributed across an inlet face of the mixing disk by the flow distributor and is collected after exiting at the outlet face after passing through the mixing disk such that the output of the mixer is a mixed compositional solvent stream.

<FIG> is a block diagram of a liquid chromatography system <NUM> that can include an embodiment of the mixers described below. The system <NUM> includes a system processor <NUM> (e.g., microprocessor and controller) in communication with a user interface device <NUM> for receiving input parameters and displaying system information to an operator. The system processor <NUM> communicates with a solvent manager <NUM> which provides one or more solvents for a mobile phase. For example, the solvent manager <NUM> may include a mixer to mix two or more solvents and may provide a gradient mobile phase. A sample provided by a sample manager <NUM> is injected into the mobile phase upstream from a chromatographic column <NUM> at an injection valve <NUM>. The sample manager <NUM> can include one or more sources of a sample such as a sample reservoir, vial or other container that holds a volume of the sample. In some embodiments, the sample manager <NUM> is a flow through needle sample manager that includes a sample needle and sample syringe used to aspirate a sample from a sample source. In some instances, the sample manager <NUM> provides a diluted sample that includes the sample and a diluent. The chromatographic column <NUM> is coupled to a detector <NUM> which provides a signal to the system processor <NUM>. The signal is responsive to various components detected in the eluent from the column <NUM>. After passing through the detector <NUM>, the system flow exits to a waste port; however, when used for fraction collection, a diverter valve may be included to temporarily redirect the system flow to one or more collection vessels.

<FIG> is a graphical depiction of the presence of a solvent B in a mobile phase as a function of time for different liquid chromatography systems each having a conventional mixer. The horizontal axis depicts time and the vertical axis depicts absorption units based on the system detector. The plots illustrate how different systems respond to a programmed stepwise decrease (vertical dashed line <NUM> at time t) of solvent B (acetone) from <NUM>% to <NUM>% in an aqueous mobile phase composition. In the absence of the mixer, a sharp transition may be achieved; however, a large compositional noise may be present.

<FIG> is a graphical depiction of the presence of a solvent in the mobile phase of a liquid chromatography system over time. The vertical axis represents absorption units and corresponds to the presence of a particular solvent component (e.g., acetonitrile in an aqueous solvent composition). The upper plot <NUM> is for a reciprocating pump having a <NUM>µL pump stroke volume and the lower plot <NUM> is for a reciprocating pump having a <NUM>µL pump stroke volume. The high frequency noise evident in the plots <NUM> and <NUM> is due to the operation of the plunger in the reciprocating pumps.

<FIG> is a highly schematic diagram of a mixer <NUM> that can be used for mixing a compositional solvent stream in a liquid chromatography system. The mixer <NUM> includes a flow distributor <NUM>, a mixing disk <NUM> and a flow collector <NUM>.

The flow distributor has a distributor inlet port <NUM> and a distributor outlet port <NUM> having an outlet cross-section. The flow distributor <NUM> distributes the composition solvent stream received at the distributor inlet port <NUM> substantially evenly across the outlet cross-section at the distributor outlet port <NUM>.

The mixing disk <NUM> has an inlet face <NUM>, an outlet face <NUM> and channels that have inlet ends at the inlet face <NUM> and outlet ends at the outlet face <NUM>. In some embodiments, the mixing disk <NUM> is a circular disk; however, alternative embodiments may include disks having other shapes such as a rectangular edge or other non-circular outer edge. The inlet face <NUM> is in communication with the distributor outlet port <NUM>. The channels have a flow direction anisotropy between the inlet face <NUM> and outlet face <NUM>. For example, the flow path length defined between the inlet and outlet ends of each channel may generally be different and vary across a range of flow path lengths as described in more detail below. Each channel generally does not have a direct path between the inlet face <NUM> and outlet face <NUM> but instead is defined by changes in direction such that channel direction varies along its length. For example, each path may have one or more upward, downward and/or sideways excursions (i.e., radial excursions) such that the path is substantially nonlinear. In some embodiments, channels may allow the liquid to flow backwards along portions of a flow path although in such embodiments the pressure resistance may be significant. The channel direction at a portion along its length includes a longitudinal component (defined along a "thickness axis" that is perpendicular to the disk faces) and a radial component (defined in a plane orthogonal to the thickness axis). Thus, the width of an individual solvent component of a solvent packet is broadened in its passage through the mixing disk <NUM> as the packet is distributed into different channels having different flow path lengths through the disk material and the stacked packets of solvents generated by the gradient proportional valve can be mixed effectively in the mixing disk volume. The solvent component is thereby mixed with adjacent solvent components that are also broadened by passage through the mixing disk <NUM>. The mixing disk <NUM> can be fabricated using a three-dimensional (3D) manufacturing process (e.g., by stereolithography) to achieve mixer-to-mixer reproducibility of the mixer properties.

The flow collector <NUM> has a collector inlet port <NUM> and a collector outlet port <NUM>. The collector inlet port <NUM> has an inlet cross-section and is in communication with the outlet face <NUM> of the mixing disk <NUM> to thereby receive the flow of the compositional solvent stream after passing through the mixing disk <NUM>. The flow collector <NUM> substantially evenly collects and combines the flows from the ends of the channels at the outlet face <NUM> of the mixing disk <NUM> into a single flow at the collector output port <NUM>.

In some embodiments, the area of the outlet cross section of the flow distributor <NUM> is substantially equal to a cross-sectional area of the inlet face <NUM> of the mixing disk <NUM>. Similarly, an area of the inlet cross-section of the flow collector <NUM> may be substantially equal to a cross-sectional area of the of the outlet face <NUM> of the mixing disk <NUM>. The flow distributor <NUM> may be a radial flow distributor, an angular flow distributor, a combination of radial and angular flow distributors, or a fractal flow distributor. Similarly, the flow collector <NUM> may be a radial flow collector, an angular flow collector, a combination of a radial and angular flow collector, or a fractal flow collector. These types of flow distributors <NUM> and flow collectors <NUM> enable most of the volume of the mixing disk <NUM> to be used for mixing. Similarly, use of a disk for mixing yields maximum mixing for a given mixer volume.

In the absence of a flow restriction, the limited divergence of the received solvent stream would not spread across the full input face <NUM> of the mixing disk <NUM>. Moreover, the performance of the mixer <NUM> is proportional to the square of the mixer volume. Thus, the flow distributor <NUM> is used to evenly distribute the compositional solvent stream receive at the inlet port <NUM> into a large number (e.g., at least ten) of individual flows incident at the inlet face <NUM> of the mixing disk <NUM>. For example, the solvent flow at the inlet port <NUM> may be approximately <NUM> to <NUM> in diameter and each individual flow may similarly be approximately <NUM> to approximately <NUM> in diameter. The flow collector <NUM> similarly evenly collects the individual flows exiting from the outlet face <NUM> of the mixing disk <NUM> into a single flow of approximately <NUM> to <NUM> in diameter. This range of diameters can induce significant molecular dispersion in the mixing disk <NUM> and provide a flow restriction that is greater than the flow restrictions of the flow distributor <NUM> and flow collector <NUM>.

As used herein, tortuosity means a ratio of a flow path length of a channel between its ends normalized to the straight-line distance between its ends. Thus, tortuosity is a characterization of the convoluted channels for fluid dispersion through the mixing medium. The tortuosity of the mixing disk <NUM> is given by the average flow path length of the channels relative to the thickness of the mixing disk <NUM>. In some embodiments, the tortuosity of the channels is at least five and, in other embodiments, the tortuosity of the channels does not exceed ten. The mixer <NUM> may be characterized by a RTD which is determined by the different flow path lengths through the mixing disk <NUM>. The objective of the random channel structure through the mixing disk <NUM> is to enlarge the RTD. The flow anisotropy and multichannel tortuosity of the mixing disk <NUM> enables a skewness for the RTD to be reduced to a value close to zero and allows the solvent composition of the solvent mixture at the collector outlet port <NUM> to more quickly achieve the programmed solvent composition.

In some embodiments, the flow path lengths are randomly defined according to the internal porous structure of the mixing disk <NUM>. The mixing disk <NUM> may be formed from a dispersive material having a random porous structure. In this instance, the flow path lengths of the channels are substantially uncorrelated to each other.

The void volume of the mixing disk <NUM> is preferable selected based on the pump stroke volume for the pump system. In some embodiments, the value of the void volume is between about two time the pump stroke volume to about three times the pump stroke volume. For instance, based on three times the pump stroke volume, a <NUM> mixer may be used with a pump system having a <NUM>µL pump stroke volume.

In some embodiments, the mixing disk <NUM> is manufactured via a machining process or 3D printing. The mixing disk <NUM> may include a predefined arrangement of channels having a range of path flow path lengths or include a labyrinth of channels. The disk material preferably is a chemically inert material such as a glass, polymer or metal. In one preferred implementation, the mixing disk <NUM> is a cleaned passivated stainless steel disordered structure that is inert with respect to the solvents.

The volumes of the flow distributor <NUM> and flow collector <NUM> are preferably small compared to the void volume of the mixing disk <NUM> to thereby limit the total pressure drop across the mixer <NUM>. In one example, the pressure drop across the mixer <NUM> does not exceed <NUM> MPa (<NUM>,<NUM> psi) at a flow rate of <NUM>/min. for water at room temperature.

<FIG> and <FIG> show a perspective view and cutaway schematic view, respectively, of an example of a mixer <NUM> for a liquid chromatography system. The mixer <NUM> is formed from stacked layers of metal mesh in which combinations of certain mesh layers substantially correspond to the flow collector <NUM>, mixing disk <NUM> and flow collector <NUM> of the mixer <NUM> of <FIG> to enable evaluation of mixing performance.

The mixer <NUM> includes a housing <NUM>, an inlet <NUM> to receive a solvent composition flow along flow axis <NUM>, and and an outlet <NUM> to provide a mixed solvent composition flow. The inlet <NUM> is configured to receive a fitting to couple to a conduit (e.g., stainless steel tubing) that conducts the solvent composition stream. Similarly, the outlet <NUM> is configured to receive a fitting to couple to a conduit to conduct the mixed solvent composition stream from the mixer <NUM>. Due to the symmetrical construction of the mesh mixer <NUM>, the roles of the inlet <NUM> and outlet <NUM> may be reversed.

The mixer <NUM> includes a first pair of mesh layers 80A and 80B, a second pair of mesh layers 82A and 82B, and a group of three mesh layers 84A, 84B and 84C. In one embodiment, the two pairs of mesh layers <NUM> and <NUM> are used as substitutes for the flow distributor and flow collector. Each layer <NUM> or <NUM> is a <NUM> thick stainless steel mesh with a <NUM> mesh interstitial spacing. Each pair of layers <NUM> and <NUM> acts as a flow restrictor to approximate an ideal flow distribution or ideal flow collection. Each of the three layers <NUM> in the middle of the layer stack is a <NUM> thick stainless steel mesh with a <NUM> mesh interstitial spacing. The group of layers <NUM> forms a porous dispersive structure that acts as the mixing disk. It will be noted that in an improved implementation a disordered, or random, material would be used instead of the group of layers <NUM> with a preferential diffusion in the radial direction thereby increasing the tortuosity and enabling an improvement in the reduction of skewness of the RTD.

<FIG> and 6C show the output response of a <NUM> packed bed mixer, a multi-path channel mixer and a mixer utilizing a mixing disk, respectively. Each plot within a figure represents the response of the mixer to a composition impulse in the solvent flow received at the mixer inlet at a different flow rate. The position of each plot with respect to the x-axis is not based on when the response is observed but may be shifted to permit easier observation of the individual plots; however, the shape and width of each plot does represent the shape and duration of each response. Plots displayed to the right are at slower flow rates and exhibit the most spread in time. The flow rates ranged from <NUM>/min. to <NUM>/min.

<FIG> is a graphical representation of mixing performance (normalized dispersion) as a function of solvent flow rate for nine different mixers and <FIG> is a graphical representation of the symmetry, expressed as peak skewness, as a function of solvent flow rate for the mixers in <FIG>. Mixing performance is expressed as σ<NUM>/V<NUM> where σ<NUM> is the variance and V is the mixing volume for the mixer where an ideal value for σ<NUM>/V<NUM> is one. The skewness value is defined as µ<NUM> / σ<NUM> where µ<NUM> is the volume-based third central moment of the concentration distribution. In evaluating the performance characteristics of a mixer, it should be recognized that there is a tradeoff between dispersion performance and symmetry.

Although the packed bed mixers have poor mixing performance by one to two orders of magnitude, their symmetry is best as packed bed mixers have skewness values close to zero at all flow rates. In contrast, the two multi-flow path mixers have better mixing performance; however, their peak skewness is poor at higher flow rates.

The disk mixers have good mixing performance like the multi-flow path mixers and better symmetry than the multi-flow path mixers. Although the <NUM> and <NUM> mesh mixers mix well, they exhibit "tailing" and therefore have bad symmetry as evident in <FIG>. The <NUM>, <NUM> and <NUM> mesh mixers have the best overall performance based on good mixing and better skewness, disregarding the two packed bed mixers which have poor mixing. Although the multi-flow path mixers are better for skewness at low flow rates, as flow rates increase their symmetry rapidly becomes worse. The mesh mixers are significantly more independent from flow rate, especially the <NUM>, <NUM> and <NUM> mesh mixers. There is no mixer that is optimum for both mixing and symmetry. The tradeoff is based on selecting mixers having good mixing (<FIG>) and then identifying one or more mixers from that group based on skewness at all relevant flow rates (<FIG>). In some instances, the identification is based on an acceptable skewness value that is also substantially independent of flow rate.

An evaluation of disk mixer performance based on disk mixers using <NUM> and <NUM> media grade stainless steel was performed. <FIG> shows a graphical presentation of the measurement data. Each data point is plotted as a function of mixer volume in microliters according to the x-axis and noise in micro-absorption units according to the y-axis. The noise value for each data point is determined as an average of the maximum peak to peak noise for sixty measurement windows with each window having a duration of ten seconds. The four plots corresponding to a disk mixer having a <NUM> mixer disk medium, a disk mixer having the <NUM> disk mixer medium in combination with an additional split flow mixer, a disk mixer having a <NUM> disk mixer medium, and a disk mixer having the <NUM> disk mixer medium in combination with an additional split flow mixer. The disk mixer media were obtained from Mott Corporation of Farmington, CT. The measurement results show that the periodic pump noise is no longer observable, even for the lower mixer volumes, with only random peak to peak noise in the measurement windows contributing to the measured noise values. At the higher mixer volumes, the plotted noise values are not significantly greater than the ultraviolet (UV) detector background noise.

<FIG> are a side, end view and cutaway side view, respectively, of an example of a mixer <NUM> that can be used to mix a compositional solvent stream in a liquid chromatography system. The mixer includes a first housing part <NUM>, a second housing part <NUM>, an annular ring <NUM>, a flow distributor <NUM>, a mixing disk <NUM> and a flow collector <NUM>. The flow distributor <NUM>, mixing disk <NUM> and flow collector <NUM> are held within the annular ring <NUM>. The first housing part <NUM> includes threads on an outer surface which engage threads on an inner bore surface of the second housing part <NUM>. The first housing part <NUM> is inserted into the second housing part <NUM> until both components are in contact with opposite sides of the annular ring <NUM>. A pair of gaskets 114A and 114B create a fluidic seal between the annular ring <NUM> and the first housing part <NUM> and the annular ring <NUM> and the second housing part <NUM>, respectively. Liquid entering the mixer <NUM> at mixer port 116A exits at mixer port 116B. The mixer <NUM> may alternatively be used with liquid flowing in the reverse direction, that is, by entering at mixer port 116B and exiting at mixer port 116A.

<FIG> is an exploded view of the annular ring <NUM> and the components held within the ring <NUM>. The flow distributor <NUM> includes an inlet angular dispersion plate <NUM> and an inlet radial dispersion plate <NUM>. The mixing disk <NUM> includes a disk <NUM> having a random porous structure disposed between two fine mesh disks 124A and 124B (e.g., two metal mesh screens each having a <NUM> spacing). The flow collector <NUM> includes an outlet radial dispersion plate <NUM> and an outlet angular dispersion plate <NUM>.

The inlet and outlet angular dispersion plates <NUM> and <NUM>, respectively, include a central opening <NUM> and <NUM>, respectively, with slots <NUM> extending radially from the central opening <NUM> and <NUM>. The slots <NUM> are wedge-shaped, that is, increasing in width with increasing distance from the center. The inlet and outlet radial dispersion plates <NUM> and <NUM>, respectively, include an arrangement of concentric arc-shaped slots <NUM> arranged at one of three different radii from the center of the plate. The widths of the slots are greater for increased distance from the center. The combination of an angular dispersion plate and a radial dispersion plate act to efficiently distribute or collect independent flows into or out from the mixing disk <NUM>. It will be recognized that the materials and dimensions of the plates <NUM> and <NUM>, as well as the arrangement (including the number and dimensions) of the slots <NUM> and <NUM> in a plate may be different in other embodiments.

<FIG> is an example of a fractal flow distributor <NUM> that can be fabricated, for example, using a 3D-printing stereolithography process. The distributor <NUM> includes a central through hole that is split into two ramification channels each of which is again split into two ramification channels each of which is further split into another two ramification channels and so on. The splitting of channels occurs through the thickness of the distributor plate or disk to generate a fractal distribution of the flow over a surface. <FIG> is another example of a fractal flow distributor <NUM> that can be fabricated using a similar fabrication process. In this example, the distributor <NUM> includes a structure that splits into three ramification channels each of which is split and leads to three ramification channels each of which leads to another three ramification channels.

<FIG> is an example of a portion of a mixing disk <NUM> that can be made using a 3D fabrication process, such as stereolithography, with a polymer material. For example, use of the photomasks shown in <FIG> may be alternately used in a sequential UV cure of a polymer material to build square-like features of <NUM> on a side. First, straight channels are formed using the photomask shown in <FIG> then a square cross-section channel is formed using the photomask shown in <FIG>. The thickness of the resulting slice depends on the intensity of the UV light source, the concentration of a photo-initiator compound in the polymer material, monomer concentration and the UV exposure time. The curing process can be repeated multiple times with removal of unpolymerized material between cure cycles. In this way many layers can be stacked to fabricate various 3D structures by translating and/or rotating (e.g., see photomasks in <FIG>) each slice relative to the other slices. This process is just one example of a fabrication technique for forming a mixing disk and it will be recognized that other fabrication techniques can also be used.

In various embodiments described above, the flow distributors and flow collectors are similarly constructed. For example, the structure of the flow distributor from the distributor inlet port to the distributor outlet port can be the same as the structure of the flow collector from the collector outlet port to the collector inlet port.

In one embodiment, a flow distributor is made of a single disk-shaped plate <NUM> having a first (upstream) surface 160A and a second (downstream) surface 160B as shown in <FIG>, respectively. The first surface 160A shows a fractal distribution path structure. A series of fluidic paths start from an open circular central region <NUM> that receives the flow from the distributor inlet. First flow paths 164A extend at one end radially from the central region <NUM> to an opposite end at a midpoint of a second flow path 164B that is perpendicular to the first flow paths 164A. Each end of a second flow path 164B is near or at a midpoint of a third flow path 164C. As illustrated, there are <NUM> first flow paths 164A, <NUM> second flow paths 164B and <NUM> third flow paths 164C. At each end of each of the third flow paths 164C is an opening <NUM> at the downstream surface 160B.

The fluidic paths and other features of the flow distributor may be formed in a variety of ways. For example, known micro-machining techniques may be utilized. Alternatively, an etching process may be utilized to form the desired structure.

Each opening <NUM> is defined along one of two concentric circles of radius R<NUM> or R<NUM> with each circle being concentric with the mixer flow axis. Thus, a flow received at the distributor inlet port is internally separated into <NUM> flows, each of which is separated into four flows so that the number of flows exiting the second surface 160B is <NUM>. The diameters of the openings <NUM> are preferably equal. In a non-limiting numerical example, the total area defined by all <NUM> openings is approximately five percent of the total surface area of the second surface 160B.

In one embodiment (Embodiment A), the flow distributor and flow collector are of identical construction, i.e., the mixer exhibits axial mirror symmetry about the mixing disk. In other words, the first surface 160A of the flow distributor is identical to the second surface of the flow collector and the second surface 160B of the flow distributor is identical to the first surface of the flow collector. The mixer is therefore configured such that the features of the flow collector are arranged in an inverse axial flow direction to those of the flow distributor but are otherwise the same. <FIG> illustrates the relationship between the openings <NUM> in the second (downstream) plate 160B of a flow distributor with respect to the openings <NUM> in a first (upstream) surface 170A of a flow collector in a mixer constructed in this manner. Each opening <NUM> and <NUM> is located on one of the two concentric circles of radius R<NUM> and R<NUM>. The openings at the distributor outlet port are arranged identically to the openings at the collector inlet port. Thus, there is a one-to-one correspondence between each opening <NUM> in the second surface 160B of the flow distributor with a respective opening <NUM> in the first surface 170A of the flow collector. However, in other embodiments, the flow distributor and flow collector do not define a symmetrical arrangement about the mixing disk, as described further below.

<FIG> depict the upstream surface 180A and downstream surface 180B, respectively, used in a different implementation of a flow distributor. The first surface 180A shows a series of fluidic paths that start from an open circular central region <NUM> that receives the flow from the distributor inlet. First flow paths 184A extend at one end radially from the central region <NUM> to an opposite end at a midpoint of a short second flow path 184B arranged perpendicular to the first flow paths 184A. Each end of each second flow path 184B is coupled to one end of each of three third flow paths 184C. As illustrated, there are <NUM> first flow paths 184A, <NUM> second flow paths 184B and <NUM> third flow paths 184C. At each end of each of the third flow paths 184C is an opening <NUM> at the downstream surface 180B.

Each opening <NUM> is defined along one of four concentric circles of radius R<NUM>', R<NUM>', R<NUM>' and R<NUM>', all of which are concentric with the mixer flow axis. A flow received at the distributor inlet port is separated into <NUM> flows, each of which is separated into two flows which are each further separated into three flows such that the number of flows exiting the second surface 180B is <NUM>. Thus, the number of individual flows incident on the upstream surface of the mixing disk is greater than that for the embodiment illustrated in <FIG>.

In one embodiment (Embodiment B) of a mixer, both the flow distributor and flow collector are formed as identical components each having <NUM> openings and are symmetrically arranged about the mixing disk.

In another embodiment (Embodiment C), a mixer is constructed using a flow distributor as shown in <FIG> and a flow collector as shown in <FIG>. Thus, the flow distributor includes <NUM> openings <NUM> adjacent to the upstream side of the mixing disk while the flow collector includes <NUM> openings <NUM> at the downstream side of the mixing disk. <FIG> illustrates the relationship between the openings <NUM> in the second surface 160B of the flow distributor with respect to the openings <NUM> in the first (upstream) surface 180A of the flow collector in a mixer constructed in this manner. It can be seen that the concentric circles of radii R<NUM> and R<NUM> on which the openings <NUM> are defined are different from the concentric circles of radii R<NUM>', R<NUM>', R<NUM>' and R<NUM>' on which the openings <NUM> are defined.

In yet another embodiment (Embodiment D), a mixer is constructed using a flow distributor as shown in <FIG> and a flow collector formed according to the structure shown in <FIG>. In this arrangement, the flow distributor includes <NUM> openings <NUM> adjacent to the upstream side of the mixing disk and the flow collector includes <NUM> openings <NUM> at the downstream side of the mixing disk. As with Embodiment C, the concentric circles for the openings <NUM> and <NUM> are different.

An evaluation of performance was made using a pulse input of an analyte to determine the retention time distribution for mixers according to Embodiments A to D. Measurement results showed that Embodiment B has a higher peak and a marginally narrower width in its retention time distribution relative to that for Embodiment A. Embodiments C and D had nearly identical retention time distributions with peaks heights similar to that of Embodiment B; however, Embodiments C and D had retention time distributions with better symmetry.

Claim 1:
A mixer (<NUM>) for a liquid chromatography system comprising:
a flow distributor (<NUM>) having a distributor inlet port (<NUM>) having a distributor inlet cross-section and a distributor outlet port (<NUM>) having a distributor outlet cross-section which is greater than the distributor inlet cross-section, the distributor inlet port (<NUM>) configured to receive a flow of a compositional solvent stream and the distributor outlet port (<NUM>) configured to provide the compositional solvent stream distributed across the distributor outlet cross-section;
a mixing disk (<NUM>) having an inlet face (<NUM>), an outlet face (<NUM>) and a plurality of channels each having an inlet end at the inlet face (<NUM>) and an outlet end at the outlet face (<NUM>), the inlet face (<NUM>) being in communication with the distributor outlet port (<NUM>), the channels having a flow direction anisotropy between the inlet (<NUM>) and outlet (<NUM>) faces; and
a flow collector (<NUM>) having a collector inlet port (<NUM>) having a collector inlet cross-section and a collector outlet port (<NUM>) having a collector outlet cross-section which is less than the collector inlet cross-section, the collector inlet port (<NUM>) being in communication with the outlet face (<NUM>) of the mixing disk (<NUM>) to receive the flow of the compositional solvent stream after passing through the mixing disk (<NUM>).