Abstract:
Frits for use in analytical instrument systems, including liquid chromatography systems, particularly HPLC and UHPLC systems, and methods of making and using the frits, are provided. The frits can have multiple layers, which may have different surface finishes on different surfaces.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims benefit of priority of U.S. Provisional No. 62/000,731 filed May 20, 2014, the entire disclosure of which is incorporated herein by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
       [0003]    Not Applicable 
       INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
       [0004]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0005]    1. Field of the Invention 
         [0006]    This disclosure relates generally to frits for use in ion chromatography, liquid chromatography and other analytical systems, including in particular high pressure and ultra-high pressure liquid chromatography systems, as well as methods for making and using such fits. 
         [0007]    2. Description of the Related Art 
         [0008]    Liquid chromatography (LC) and ion chromatography (IC) are well-known techniques for separating the constituent elements in a given sample. In a conventional LC system, a liquid solvent (referred to as the “mobile phase”) is introduced from a reservoir and is pumped through the LC system. The mobile phase exits the pump under pressure. The mobile phase then travels via tubing to a sample injection valve. As the name suggests, the sample  injection valve allows an operator to inject a sample into the LC system, where the sample will be carried along with the mobile phase. 
         [0009]    In a conventional LC system, the sample and mobile phase pass through one or more filters and often a guard column before coming to the column. A typical column usually consists of a piece of tubing which has been packed with a “packing” material. The “packing” consists of the particulate material “packed” inside the column. It usually consists of silica- or polymer-based particles, which are often chemically bonded with a chemical functionality. When the sample is carried through the column (along with the mobile phase), the various components in the sample migrate through the packing within the column at different rates (i.e., there is differential migration of the solutes). In other words, the various components in a sample will move through the column at different rates. Because of the different rates of movement, the components gradually separate as they move through the column. Differential migration is affected by factors such as the composition of the mobile phase, the composition of the stationary phase (i.e., the material with which the column is “packed”), and the temperature at which the separation takes place. Thus, such factors will influence the separation of the sample&#39;s various components. 
         [0010]    The particle sizes of chromatographic packing materials used in HPLC columns have been decreasing over time. The trend is clearly toward packing materials with smaller particle sizes. Adequate retention of the chromatographic packing material is imperative to the mechanical stability of the column and the integrity of the HPLC system. It is particularly important when separation conditions demand very high column efficiencies. In order to achieve high efficiency in a minimal amount of time, the smallest possible particle size packings are desirable. The HPLC system&#39;s extra column tubing volume must be minimized in order not to detract from the efficiency performance of the column. This requires the use of very small diameter connection tubing, which can be easily plugged by particles if they are not well retained within the HPLC column. 
         [0011]    Once the sample (with its components now separated) leaves the column, it flows with the mobile phase past a detector. The detector detects the presence of specific molecules or compounds. Two general types of detectors are used in LC applications. One type measures a change in some overall physical property of the mobile phase and the sample (such as their refractive index). The other type measures only some property of the sample (such as the absorption of ultraviolet radiation). In essence, a typical detector in a LC system can measure and provide an output in terms of mass per unit of volume (such as grams per milliliter) or mass per unit of time (such as grams per second) of the sample&#39;s components. From such an output signal, a “chromatogram” can be provided; the chromatogram can then be used by an operator to determine the chemical components present in the sample. Additionally, LC systems may utilize mass spectrometric detection for identification and quantification of the sample, either in addition to, or as an alternative to, the conventional detectors described previously. Ion chromatography relies on the detection of ions in solution, so most metallic materials in the flow path can create interference in the detection scheme, as they create background ions. 
         [0012]    In addition to the above components, a LC system will often include filters or frits, check valves, a guard column, or the like in order to prevent contamination of the sample or damage to the LC system. For example, an inlet solvent filter may be used to filter out particles from the solvent (or mobile phase) before it reaches the pump. A guard column is often placed before the analytical or preparative column; i.e., the primary column. The purpose of such a guard column is to “guard” the primary column by absorbing unwanted sample components that might otherwise bind irreversibly to the analytical or preparative column. Thus, filters or flits can be used in various components of an LC system, including, but not limited to, a column, such as a primary and/or guard column, a cross, a tee, and a union, to name but a few. For example, in U.S. Pat. No. 5,651,931, a biocompatible filter or frit, as well as a method of making such a filter or frit, is described for use in an LC system. 
         [0013]    In practice, various components in an LC system may be connected by an operator to perform a given task. For example, an operator will select an appropriate mobile phase and column, and then connect a supply of the selected mobile phase and a selected column to the LC system before operation. In order to be suitable for high performance liquid chromatography (HPLC) applications, each connection must be able to withstand the typical operating pressures of the HPLC system. If the connection is too weak, it may leak. Because the types of solvents that are sometimes used as the mobile phase are often toxic and because it is often expensive to obtain and/or prepare many samples for use, any such connection failure is a serious concern. 
         [0014]    It is fairly common for an operator to disconnect a column (or other component) from a LC system and then connect a different column (or other component) in its place after one test has finished and before the next begins. Given the importance of leak-proof connections, especially in HPLC applications, the operator must take time to be sure the connection is sufficient. Replacing a column (or other component) may occur several times in a day. Moreover, the time involved in disconnecting and then connecting a column (or other component) is unproductive because the LC system is not in use and the operator is engaged in plumbing the system instead of preparing samples or other more productive activities. Hence, the replacement of a column in a conventional LC system involves a great deal of wasted time and inefficiencies. 
         [0015]    Given concerns about the need for leak-free connections, conventional connections have been made with stainless steel tubing and stainless steel end fittings. More recently, however, it has been realized that the use of stainless steel components in a LC system have potential drawbacks in situations involving biological samples, and cannot be routinely used for ion chromatography. For example, the components in a sample may attach themselves to the wall of stainless steel tubing. This presents problems because the detector&#39;s measurements (and thus the chromatogram) of a given sample may not accurately reflect the sample if some of the sample&#39;s components or ions remain in the tubing and do not pass the detector. Perhaps of even greater concern, however, is the fact that ions from the stainless steel tubing may detach from the tubing and flow past the detector, thus leading to potentially erroneous results. Hence, there is a need for “biocompatible” or “metal-free” connections through the use of a material that is chemically inert with respect to such “biological” samples and the mobile phase used with such samples, so that ions will not be released by the tubing and thus contaminate the sample. 
         [0016]    In many applications using selector/injector valves to direct fluid flows, and in particular in liquid chromatography, the volume of fluids is small. This is particularly true when liquid chromatography is being used as an analytical method as opposed to a preparative method. Such methods often use capillary columns and are generally referred to as capillary chromatography. In capillary chromatography, it is often desired to minimize the internal volume of the selector or injector valve. One reason for this is that a valve having a large volume will contain a relatively large volume of liquid, and when a sample is injected into the valve the sample will be diluted, decreasing the resolution and sensitivity of the analytical method. 
         [0017]    Micro-fluidic analytical processes also involve small sample sizes. As used herein, sample volumes considered to involve micro-fluidic techniques can range from as low as volumes of only several picoliters or so, up to volumes of several milliliters or so, whereas more traditional LC techniques, for example, historically often involved samples of about one microliter to about 100 milliliters in volume. Thus, the micro-fluidic techniques described herein involve volumes one or more orders of magnitude smaller in size than traditional LC techniques. Micro-fluidic techniques can also be expressed as those involving fluid flow rates of about 0.5 ml/minute or less. 
         [0018]    Most conventional HPLC systems include pumps which can generate relatively high pressures of up to around 5,000 psi to 6,000 psi or so. In many situations, an operator can obtain successful results by operating a LC system at “low” pressures of anywhere from just a few psi or so up to 1,000 psi or so. More often than not, however, an operator will find it desirable to operate a LC system at relatively “higher” pressures of over 1,000 psi. 
         [0019]    Another, relatively newer liquid chromatography form is Ultra High Performance Liquid Chromatography (UHPLC) in which system pressure extends upward to 1400 bar or 20,000 psi. Both HPLC and UHPLC are examples of analytical instrumentation that utilize fluid transfer at elevated pressures. For example, in U.S. Pat. No. 8,173,070, an injection system is described for use with UHPLC applications, which are said to involve pressures in the range from 20,000 psi to 120,000 psi. In U.S. Pat. No. 7,311,502, the use of a hydraulic amplifier is described for use in UHPLC systems involving pressures in excess of 25,000 psi. In U.S. Pat. No. 7,144,502, a system for performing UHPLC is disclosed, with UHPLC described as involving pressures above 5,000 psi (and up to 60,000 psi). Applicants hereby incorporate by reference as if fully set forth herein U.S. Pat. Nos. 7,311,502, 8,173,070 and 7,144,502. 
         [0020]    As noted, liquid chromatography (as well as other analytical) systems, including HPLC or UHPLC systems, typically include several components. For example, such a system may include a pump; an injection valve or autosampler for injecting the analyte; a precolumn filter to remove particulate matter in the analyte solution that might clog the column; a packed bed to retain irreversibly adsorbed chemical material; the HPLC column itself; and a detector that analyzes the carrier fluid as it leaves the column. Ion chromatography may also utilize a suppressor column to facilitate detection dynamic range. These various components may typically be connected by a miniature fluid conduit, or tubing, such as metallic or polymeric tubing (for ion chromatography), usually having an internal diameter of 0.003 to 0.040 inch. 
         [0021]    It will be understood by those skilled in the art that, as used herein, the term “LC system” is intended in its broad sense to include all apparatus and components in a system used in connection with liquid chromatography, whether made of only a few simple components or made of numerous, sophisticated components which are computer controlled or the like. Those skilled in the art will also appreciate that an LC system is one type of an analytical instrument (AI) system. For example, gas chromatography is similar in many respects to liquid chromatography, but obviously involves a gas sample to be analyzed. Although the following discussion focuses on liquid chromatography, those skilled in the art will appreciate that much of what is said also has application to other types of AI systems and methods. 
         [0022]    Therefore, it is an object of the present disclosure to provide a liquid chromatography frit, and particularly a biocompatible liquid chromatography frit, for use in a liquid chromatography or an ion chromatography system. 
         [0023]    It is another object of the present disclosure to provide a high pressure liquid chromatography frit, and particularly a biocompatible high pressure liquid chromatography frit, for use in a HPLC or an UHPLC system. 
         [0024]    It is a further object of the present disclosure to provide a high pressure liquid chromatography frit that can be used at pressures up to about 18,000 pounds per square inch (“psi”) or more. 
         [0025]    It is an additional object of the present disclosure to provide liquid chromatography fits, and particularly high pressure liquid chromatography frits, that can provide a variety of filtration levels, including 0.5, 2, 5, 10 and 20 micron ratings, and that reduce bead blow-by. 
         [0026]    It is yet another object of the present disclosure to provide liquid chromatography frits, and particularly high pressure liquid chromatography frits, that envelop comparable to existing fits, and require less inspection than currently existing frits. 
         [0027]    It is still another object of the present disclosure to provide liquid chromatography frits, and particularly high pressure liquid chromatography frits, that realize a pressure drop that is less than existing frits. 
         [0028]    It is another object of the present disclosure to provide liquid chromatography flits, and particularly high pressure liquid chromatography frits, that have a lifetime that is greater than existing frits. 
         [0029]    It is a further object of the present disclosure to provide liquid chromatography frits, and particularly high pressure liquid chromatography fits, that cost less than existing flits. 
         [0030]    The above and other advantages of the present disclosure will become readily apparent to those skilled in the art from the following detailed description of the present disclosure, and from the attached drawings, which are briefly described below. 
       SUMMARY OF THE INVENTION 
       [0031]    The present disclosure overcomes one or more of the deficiencies of the prior art by providing flits that are well-suited for use in liquid chromatography systems, and are particularly well-suited for use in high pressure and ultra high pressure liquid chromatography systems, such as HPLC and UHPLC. 
         [0032]    The present disclosure provides a frit for use in a liquid chromatography system, comprising at least a first layer of a first film and at least a second layer of a second film, wherein the first film and the second film each have a first side having a first finish and a second side having a second finish, and wherein the at least a first layer of the first film and the at least a second layer of the second film are oriented such that the first side of the at least a second layer of the second film is positioned against the second side of the at least a first layer of the first film, and wherein the at least a second layer of the second film defines a channel from the first side of the at least a second layer of the second film to the second side of the at least a second layer of the second film. In certain embodiments the first film and the second film are the same, while in other embodiments the first film and the second film are different. In particular embodiments at least a portion of the first finish comprises a matte finish. In such embodiments the matte finish can have an Ra value of between about 25 μ-in and about 70 μ-in, between about 30 μ-in and about 65 μ-in, between about 35 μ-in and about 60 μ-in, between about 40 μ-in and about 55 μ-in, or between about 45 μ-in and about 50 μ-in. Thus, in some embodiments the matte finish has an Ra value of about 25 μ-in, about 30 μ-in, about 35 μ-in, about 40 μ-in, about 45 μ-in, about 50 μ-in, about 55 μ-in, about 60 μ-in, about 65 μ-in, or about 70 μ-in. In other embodiments the matte finish can have an Rz value of between about 150 μ-in and about 360 μ-in, between about 175 p-in and about 350 μ-in, between about 200 μ-in and about 325 μ-in, between about 225 μ-in and about 300 μ-in, or between about 250 μ-in and about 275 μ-in. Therefore, in particular embodiments the matte finish has an Rz value of about 150 μ-in, about 160 μ-in, about 170 μ-in, about 175 μ-in, about 180 μ-in, about 190 μ-in, about 200 μ-in, about 210 μ-in, about 220 μ-in, about 225 μ-in, about 230 μ-in, about 240 μ-in, about 250 μ-in, about 260 μ-in, about 270 μ-in, about 275 μ-in, about 280 μ-in, about 290 μ-in, about 300 μ-in, about 310 μ-in, about 320 μ-in, about 325 μ-in, about 330 μ-in, about 340 μ-in, about 350 μ-in, or about 360 μ-in. In further embodiments the matte finish is substantially random or non-uniform. In still other embodiments the matte finish has a lay to it. In further embodiments at least a portion of the second finish comprises a matte finish. 
         [0033]    In alternative embodiments at least a portion of the second finish is a gloss finish. In such embodiments the gloss finish can have an Ra value of between about 0.5 μ-in and about 3.0 μ-in, between about 0.75 μ-in and about 2.75 μ-in, between about 1.0 μ-in and about 2.5 μ-in, between about 1.25 μ-in and about 2.25 μ-in, or between about 1.5 μ-in and about 2.0 μ-in. Thus in particular embodiments the gloss finish has an Ra value of about 0.5 μ-in, about 0.6 μ-in, about 0.7 μ-in, about 0.75 μ-in, about 0.8 μ-in, about 0.9 μ-in, about 1.0 On, about 1.1 μ-in, about 1.2 μ-in, about 1.25 μ-in, about 1.3 μ-in, about 1.4 μ-in, about 1.5 μ-in, about 1.6 μ-in, about 1.7 μ-in, about 1.75 μ-in, about 1.8 μ-in, about 1.9 μ-in, about 2.0 μ-in, about 2.1 μ-in, about 2.2 μ-in, about 2.25 μ-in, about 2.3 μ-in, about 2.4 μ-in, about 2.5 μ-in, about 2.6 μ-in, about 2.7 μ-in, about 2.75 μ-in, about 2.8 μ-in, about 2.9 μ-in, or about 3.0 μ-in. In other embodiments the gloss finish can have an Rz value of between about 5 μ-in and about 30 μ-in, between about 7.5 μ-in and about 27.5 μ-in, between about 10 μ-in and about 25 μ-in, between about 12.5 μ-in and about 22.5 μ-in, or between about 15 μ-in and about 20 μ-in. Therefore in some embodiments the gloss finish has an Rz value of about 5 μ-in, about 6 μ-in, about 7 μ-in, about 7.5 μ-in, about 8 μ-in, about 9 μ-in, about 10 μ-in, about 11 μ-in, about 12 μ-in, about 12.5 μ-in, about 13 μ-in, about 14 μ-in, about 15 μ-in, about 16 μ-in, about 17 μ-in, about 17.5 μ-in, about 18 μ-in, about 19 μ-in, about 20 μ-in, about 21 μ-in, about 22 μ-in, about 22.5 μ-in, about 23 μ-in, about 24 μ-in, about 25 μ-in, about 26 μ-in, about 27 μ-in, about 27.5 μ-in, about 28 μ-in, about 29 μ-in, or about 30 μ-in. 
         [0034]    In further embodiments the first film or the second film comprises a biocompatible material. In yet further embodiments the first film and the second film comprises a biocompatible material. In other embodiments the first film or the second film comprises polyetheretherketone. In certain embodiments the first film and the second film have a thickness of between about 25 μm and about 250 μm, between about 50 μm and about 225 μm, between about 75 μm and about 200 μm, between about 100 μm and about 175 μm, or between about 125 gm and about 150 μm. In particular embodiments the first film and the second film have a thickness of about 25 μm, about 50 μm, about 75 μm, about 100 μm, about 125 μm, about 150 um, about 175 μm, about 200 μm, about 225 μm, or about 250 μm. 
         [0035]    In various embodiments, the presently disclosed frits can have any number of layers. Thus, in certain embodiments the frit further comprises at least a third layer of a third film having a first side having a first finish and a second side having a second finish, oriented such that the first side of the at least a third layer of the third film is positioned against the second side of the at least a second layer of the second film, and wherein the at least a third layer of the third film defines a channel from the first side of the at least a third layer of the third film to the second side of the at least a third layer of the third film. In some embodiments the first film, the second film and the third film are the same. In further embodiments the frit further comprises at least a fourth layer of a fourth film having a first side having a first finish and a second side having a second finish, oriented such that the first side of the at least a fourth layer of the fourth film is positioned against the second side of the at least a third layer of the third film, and wherein the at least a fourth layer of the fourth film defines a channel from the first side of the at least a fourth layer of the fourth film to the second side of the at least a fourth layer of the fourth film. In certain embodiments the first film, the second film, the third film and the fourth film are the same. In yet further embodiments the frit further comprises at least a fifth layer of a fifth film having a first side having a first finish and a second side having a second finish, oriented such that the first side of the at least a fifth layer of the fifth film is positioned against the second side of the at least a fourth layer of the fourth film, and wherein the at least a fifth layer of the fifth film defines a channel from the first side of the at least a fifth layer of the fifth film to the second side of the at least a fifth layer of the fifth film. In particular embodiments the first film, the second film, the third film, the fourth film and the fifth film are the same. In other embodiments the frit further comprises at least a sixth layer of a sixth film having a first side having a first finish and a second side having a second finish, oriented such that the first side of the at least a sixth layer of the sixth film is positioned against the second side of the at least a fifth layer of the fifth film, and wherein the at least a sixth layer of the sixth film defines a channel from the first side of the at least a sixth layer of the sixth film to the second side of the at least a sixth layer of the sixth film. In some embodiments the first film, the second film, the third film, the fourth film, the fifth film and the sixth film are the same. In yet other embodiments the frit further comprises at least a seventh layer of a seventh film having a first side having a first finish and a second side having a second finish, oriented such that the first side of the at least a seventh layer of the seventh film is positioned against the second side of the at least a sixth layer of the sixth film, and wherein the at least a seventh layer of the seventh film defines a channel from the first side of the at least a seventh layer of the seventh film to the second side of the at least a seventh layer of the seventh film. In certain embodiments the first film, the second film, the third film, the fourth film, the fifth film, the sixth film and the seventh film are the same. 
         [0036]    In various embodiments the frit has a thickness of between about 0.02 inches and about 0.08 inches, between about 0.03 inches and about 0.07 inches, or between about 0.04 inches and about 0.06 inches. Thus in particular embodiments the frit has a thickness of about 0.02 inches, about 0.03 inches, about 0.04 inches, about 0.05 inches, about 0.06 inches, about 0.07 inches, or about 0.08 inches. In some embodiments the first side of the at least a first layer of the first film defines at least a first fluid path. In other embodiments the at least a first layer of the first film defines a channel from the first side of the at least a first layer of the first film to the second side of the at least a first layer of the first film. Although the disclosed frits can be of any desired shape for any particular application, in certain embodiments the frit comprises a circular shape. In some embodiments the frit has an adjustable micron rating, and in other embodiments the fit can be cleaned by decompression during a back flush operation. 
         [0037]    The present disclosure also provides an analytical instrument system comprising at least one frit comprising at least a first layer of a first film and at least a second layer of a second film, wherein the first film and the second film each have a first side having a first finish and a second side having a second finish, and wherein the at least a first layer of the first film and the at least a second layer of the second film are oriented such that the first side of the at least a second layer of the second film is positioned against the second side of the at least a first layer of the first film, and wherein the at least a second layer of the second film defines a channel from the first side of the at least a second layer of the second film to the second side of the at least a second layer of the second film. In certain embodiments the first film and the second film are the same. In particular embodiments the analytical instrument system comprises an ultra high pressure or ultra high performance liquid chromatography or ion chromatography system. 
         [0038]    The present disclosure additionally provides a method of making a frit for use in a liquid chromatography system, comprising attaching at least a first layer of a first film to at least a second layer of a second film, wherein the first film and the second film each have a first side having a first finish and a second side having a second finish, and wherein the at least a first layer of the first film and the at least a second layer of the second film are oriented such that the first side of the at least a second layer of the second film is positioned against the second side of the at least a first layer of the first film, and providing a channel from the first side of the at least a second layer of the second film to the second side of the at least a second layer of the second film. In certain embodiments the first film and the second film are the same. In some embodiments the step of attaching the at least a first layer of the first film to the at least a second layer of the film uses laser welding, compression or encapsulation. In other embodiments the step of providing a channel uses drilling, punching, laser cutting, water jet cutting or machining. In particular embodiments at least a portion of the first finish comprises a matte finish. In further embodiments the matte finish is substantially random or non-uniform, and such a substantially random or non-uniform matte finish can be produced by a shot peen, bead blast or powder blast process. In alternative embodiments the matte finish has a lay to it, and such a matte finish with a lay to it can be produced by a grinding process. In additional embodiments at least a portion of the second finish comprises a matte finish. In other embodiments at least a portion of the second finish comprises a gloss finish. In certain embodiments the first side of the at least a first layer of the first film defines at least a first fluid path, an in such embodiments the at least a first fluid path can be produced by embossing, stamping, forming, molding, machining, or cutting. 
         [0039]    The present disclosure further provides a frit for use in a liquid chromatography system, comprising a central porous region surrounded by an outer solid region. In certain embodiments the central porous region is shorter than the outer solid region in a direction of fluid flow through the frit. In some embodiments the central porous region is between about 0.005 inches to about 0.03 inches shorter than the outer solid region, between about 0.005 inches to about 0.03 inches shorter than the outer solid region, between about 0.006 inches to about 0.02 inches shorter than the outer solid region, between about 0.007 inches to about 0.01 inches shorter than the outer solid region, or between about 0.008 inches to about 0.009 inches shorter than the outer solid region, in the direction of fluid flow through the frit. Thus in particular embodiments the central porous region is about 0.005 inches shorter than the outer solid region, about 0.006 inches shorter than the outer solid region, about 0.007 inches shorter than the outer solid region, about 0.008 inches shorter than the outer solid region, about 0.009 inches shorter than the outer solid region, about 0.01 inches shorter than the outer solid region, about 0.011 inches shorter than the outer solid region, about 0.012 inches shorter than the outer solid region, about 0.013 inches shorter than the outer solid region, about 0.014 inches shorter than the outer solid region, about 0.015 inches shorter than the outer solid region, about 0.016 inches shorter than the outer solid region, about 0.017 inches shorter than the outer solid region, about 0.018 inches shorter than the outer solid region, about 0.019 inches shorter than the outer solid region, about 0.02 inches shorter than the outer solid region, about 0.021 inches shorter than the outer solid region, about 0.022 inches shorter than the outer solid region, about 0.023 inches shorter than the outer solid region, about 0.024 inches shorter than the outer solid region, about 0.025 inches shorter than the outer solid region, about 0.026 inches shorter than the outer solid region, about 0.027 inches shorter than the outer solid region, about 0.028 inches shorter than the outer solid region, about 0.029 inches shorter than the outer solid region, or about 0.03 inches shorter than the outer solid region, in the direction of fluid flow through the frit. 
         [0040]    In additional embodiments the frit comprises a biocompatible material. In some embodiments the frit comprises polyetheretherketone. In various embodiments the frit has a thickness of between about 0.03 inches and about 0.1 inches, between about 0.04 inches and about 0.09 inches, between about 0.05 inches and about 0.08 inches, or between about 0.06 inches and about 0.07 inches. Thus, in particular embodiments the frit has a thickness of about 0.03 inches, about 0.04 inches, about 0.05 inches, about 0.06 inches, about 0.07 inches, about 0.08 inches, about 0.09 inches, or about 0.1 inches. 
         [0041]    The present disclosure also provides an analytical instrument system comprising at least one fit comprising a central porous region surrounded by an outer solid region. In certain embodiments the central porous region is shorter than the outer solid region in a direction of fluid flow through the frit. In other embodiments the analytical instrument system comprises an ultra high pressure or ultra high performance liquid chromatography or ion chromatography system. 
         [0042]    The present disclosure further provides a method of making a frit for use in a liquid chromatography system, comprising placing a porous material into a press, wherein a first portion of the press comes into contact with a central portion of the porous material and a second portion of the press comes into contact with an outer portion of the porous material, and wherein the first portion of the press extends further than the second portion of the press, operating the press for at least a first time to compress the porous material, resulting in a central portion of the porous material that is shorter than the outer portion of the porous material, further pressing the outer portion of the porous material to increase the density of the outer portion of the porous material, and heating the outer portion of the porous material to solidify the porous material in the outer portion, thereby creating a frit comprising a porous central portion and a solid outer portion, wherein the porous central region is shorter than the solid outer portion in a direction of fluid flow through the frit. 
         [0043]    These and other embodiments and advantages of the disclosed frits are described below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0044]      FIG. 1  is a block diagram of a conventional liquid chromatography system. 
           [0045]      FIG. 2  is a top exploded view of an embodiment of a frit in accordance with one aspect of the present disclosure. 
           [0046]      FIG. 3  is a top exploded view of an embodiment of a frit in accordance with another aspect of the present disclosure. 
           [0047]      FIG. 4  is a cross-sectional view of the frit of  FIG. 2  or  FIG. 3  at the end of a section of tubing and engaged in a port, showing fluid flow through the frit. 
           [0048]      FIG. 5  is a top exploded view of an embodiment of a frit in accordance with a further aspect of the present disclosure. 
           [0049]      FIG. 6  is a cross-sectional view of the frit of  FIG. 5  at the end of a section of tubing and engaged in a port. 
           [0050]      FIG. 7  is a cross-sectional view of the frit of  FIG. 5  at the end of a section of tubing and engaged in a port, showing a partial diagram of fluid flow through the frit. 
           [0051]      FIG. 8  is a cross-sectional view of a fitting assembly, tube and the frit of  FIG. 5  engaged in a port. 
           [0052]      FIG. 9  is a cross-sectional view of a tee connection assembly and a frit in accordance with an additional aspect of the present disclosure. 
           [0053]      FIG. 10  is a cross-sectional view of the frit from the tee connection assembly and frit of  FIG. 9 . 
           [0054]      FIG. 11  is a cross-sectional view of an embodiment of a frit in accordance with yet another aspect of the present disclosure. 
           [0055]      FIG. 12  is a front top perspective view of the frit of  FIG. 11 . 
           [0056]      FIG. 13  is an exploded top perspective view of a device that can be used to form the frit of  FIG. 11 . 
           [0057]      FIG. 14  is a cross-sectional view of the device of  FIG. 13  upon assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0058]    In  FIG. 1 , a block diagram of the essential elements of a conventional liquid chromatography (LC) system is provided. A reservoir  1101  contains a solvent or mobile phase  1102 . Tubing  1103  connects the mobile phase  1102  in the reservoir  1101  to a pump  1105 . The pump  1105  is connected to a sample injection valve  1110  which, in turn, is connected via tubing to a first end of a guard column (not shown). The second end of the guard column (not shown) is in turn connected to the first end of a primary column  1115 . The second end of the primary column  1115  is then connected via tubing to a detector  1117 . After passing through the detector  1117 , the mobile phase  1102  and the sample injected via injection valve  1110  are expended into a second reservoir  1118 , which contains the chemical waste  1119 . As noted above, the sample injection valve  1110  is used to inject a sample of a material to be studied into the LC system. The mobile phase  1102  flows through the tubing  1103  which is used to connect the various elements of the LC system together. 
         [0059]    When the sample is injected via sample injection valve  1110  in the LC system, the sample is carried by the mobile phase through the tubing into the column  1115 . As is well known in the art, the column  1115  contains a packing material which acts to separate the constituent elements of the sample. After exiting the column  1115 , the sample (as separated via the column  1115 ) then is carried to and enters a detector  1117 , which detects the presence or absence of various chemicals. The information obtained by the detector  1117  can then be stored and used by an operator of the LC system to determine the constituent elements of the sample injected into the LC system. Those skilled in the art will appreciate that  FIG. 1  and the foregoing discussion provide only a brief overview of a simplistic LC system that is conventional and well-known in the art, as is shown and described in U.S. Pat. No. 5,472,598, issued Dec. 5, 1995 to Schick, which is hereby incorporated by reference as if fully set forth herein. Those skilled in the art will also appreciate that while the discussion herein focuses on a LC system, other analytical systems can be used in connection with various embodiments of the present disclosure, such as a mass spectrometry, microflow chromatography, nanoflow chromatography, nano-scale liquid chromatography, capillary electrophoresis, or reverse-phase gradient chromatography system. 
         [0060]    Preferably, for an LC system to be biocompatible, the various components (except where otherwise noted) that may come into contact with the effluent or sample to be analyzed are made of the synthetic polymer polyetheretherketone, which is commercially available under the trademark PEEK™ from VICTREX®. The polymer PEEK has the advantage of providing a high degree of chemical inertness and therefore biocompatibility; it is chemically inert to most of the common solvents used in LC applications, such as acetone, acetonitrile, and methanol (to name a few). PEEK also can be machined by standard machining techniques to provide smooth surfaces. Those skilled in the art will appreciate that other polymers may be desirable in certain applications. 
         [0061]    Referring now to  FIG. 2 , an exploded view of a first embodiment of frit  100  is shown. Frit  100  as shown in  FIG. 2  is preferably generally circular and symmetric about a center axis, although in other embodiments (not shown) frit  100  can be any desired shape, including, but not limited to, oval, square, or triangular, just to name a few. Frit  100  comprises a plurality of layers, which in the embodiment shown in  FIG. 2  comprises seven layers. First layer  110  of the frit  100  is a solid layer having a matte finish on the top surface  111  of the first layer  110  and a gloss finish on the bottom surface  112  of the first layer  110 . Second layer  120  of the frit  100  has a matte finish on the top surface  121  of the second layer  120  and a gloss finish on the bottom surface  122  of the second layer  120 , and also defines a passageway  123  through the second layer  120  from the top surface  121  to the bottom surface  122  of the second layer  120 . Third layer  130  of the frit  100  has a matte finish on the top surface  131  of the third layer  130  and a gloss finish on the bottom surface  132  of the third layer  130 , and also defines a passageway  133  through the third layer  130  from the top surface  131  to the bottom surface  132  of the third layer  130 . Fourth layer  140  of the frit  100  has a matte finish on the top surface  141  of the fourth layer  140  and a gloss finish on the bottom surface  142  of the fourth layer  140 , and also defines a passageway  143  through the fourth layer  140  from the top surface  141  to the bottom surface  142  of the fourth layer  140 . Fifth layer  150  of the frit  100  has a matte finish on the top surface  151  of the fifth layer  150  and a gloss finish on the bottom surface  152  of the fifth layer  150 , and also defines a passageway  153  through the fifth layer  150  from the top surface  151  to the bottom surface  152  of the fifth layer  150 . Sixth layer  160  of the frit  100  has a matte finish on the top surface  161  of the sixth layer  160  and a gloss finish on the bottom surface  162  of the sixth layer  160 , and also defines a passageway  163  through the sixth layer  160  from the top surface  161  to the bottom surface  162  of the sixth layer  160 . Seventh layer  170  of the frit  100  has a matte finish on the top surface  171  of the seventh layer  170  and a gloss finish on the bottom surface  172  of the seventh layer  170 , and also defines a passageway  173  through the seventh layer  170  from the top surface  171  to the bottom surface  172  of the seventh layer  170 . The matte finish on the top surfaces ( 111 ,  121 ,  131 ,  141 ,  151 ,  161  and  171 ) can either be a random or non-uniform (non-directional) finish created from a process such as, but not limited to, shot peen, bead blast or powder blast), have a surface finish with a lay to it (a directional finish as a consequence of creating the surface finish with a process such as, but not limited to, grinding), or a mixture thereof (some layers having a random or non-uniform matte finish, others having a matte finish with a lay to it). 
         [0062]    By orienting the top (matte) surfaces ( 121 ,  131 ,  141 ,  151 ,  161  and  171 ) of the second layer  120 , third layer  130 , fourth layer  140 , fifth layer  150 , sixth layer  160  and seventh layer  170 , respectively, of frit  100  against the bottom (gloss) surfaces ( 112 ,  122 ,  132 ,  142 ,  152 , and  162 ) of the first layer  110 , second layer  120 , third layer  130 , fourth layer  140 , fifth layer  150  and sixth layer  160 , respectively, of frit  100 , gaps (not shown) are created that serve as tortious fluid channels. Fluid is forced between the layers, which filters out particulate that is greater in size than the tortious fluid channels that are created. 
         [0063]    Referring now to  FIG. 3 , an exploded view of an embodiment of another frit  200  is shown. Frit  200  is similar to frit  100  shown in  FIG. 2 , except that both the top surface and the bottom surface of each of the layers of frit  200  have a matte finish. Once again, frit  200  as shown in  FIG. 3  is preferably generally circular and symmetric about a center axis. Frit  200  comprises a plurality of layers, which in the embodiment shown in  FIG. 3  comprises seven layers. First layer  210  of the fit  200  is a solid layer having a matte finish on the top surface  211  of the first layer  210  and a matte finish on the bottom surface  212  of the first layer  210 . Second layer  220  of the frit  200  has a matte finish on the top surface  221  of the second layer  220  and a matte finish on the bottom surface  222  of the second layer  220 , and also defines a passageway  223  through the second layer  220  from the top surface  221  to the bottom surface  222  of the second layer  220 . Third layer  230  of the frit  200  has a matte finish on the top surface  231  of the third layer  230  and a matte finish on the bottom surface  232  of the third layer  230 , and also defines a passageway  233  through the third layer  230  from the top surface  231  to the bottom surface  232  of the third layer  230 . Fourth layer  240  of the frit  200  has a matte finish on the top surface  241  of the fourth layer  240  and a matte finish on the bottom surface  242  of the fourth layer  240 , and also defines a passageway  243  through the fourth layer  240  from the top surface  241  to the bottom surface  242  of the fourth layer  240 . Fifth layer  250  of the frit  200  has a matte finish on the top surface  251  of the fifth layer  250  and a matte finish on the bottom surface  252  of the fifth layer  250 , and also defines a passageway  253  through the fifth layer  250  from the top surface  251  to the bottom surface  252  of the fifth layer  250 . Sixth layer  260  of the frit  200  has a matte finish on the top surface  261  of the sixth layer  260  and a matte finish on the bottom surface  262  of the sixth layer  260 , and also defines a passageway  263  through the sixth layer  260  from the top surface  261  to the bottom surface  262  of the sixth layer  260 . Seventh layer  270  of the frit  200  has a matte finish on the top surface  271  of the seventh layer  270  and a matte finish on the bottom surface  272  of the seventh layer  270 , and also defines a passageway  273  through the seventh layer  270  from the top surface  271  to the bottom surface  272  of the seventh layer  270 . The matte top surfaces ( 211 ,  221 ,  231 ,  241 ,  251 ,  261  and  271 ) and bottom surfaces ( 212 ,  222 ,  232 ,  242 ,  252 ,  262  and  272 ) can either be a random or non-uniform (non-directional) finish created from a process such as, but not limited to, shot peen, bead blast or powder blast), have a surface finish with a lay to it (a directional finish as a consequence of creating the surface finish with a process such as, but not limited to, grinding), or a mixture thereof (some layers having a random or non-uniform matte finish, others having a matte finish with a lay to it). In certain embodiments, the frits can have a combination of one or more layers that have one surface (top or bottom) with a random or non-uniform matte finish and the other surface (top or bottom) with a matte finish with a lay to it. 
         [0064]    In frit  200 , gaps (not shown) are once again created between the layers, which serve as tortious fluid channels. Fluid is forced between the layers, which filters out particulates that are greater in size than the tortious fluid channels that are created. Although not shown, frits of the present disclosure also include those with a combination of one or more layers having a top surface with a matte finish and a bottom surface having a gloss finish, and one or more layers having a top and bottom surface with a matte finish. 
         [0065]    While a variety of different polymeric materials or metals can be used to produce the presently disclosed frits, an exemplary material that is commercially available and can be used to produce the presently disclosed frits is a film made from polyetheretherketone (PEEK), which is created with a matte finish on one side and a gloss finish on the other side (known as APTIV® PEEK film sold by Victrex® plc, Lancashire, Great Britain). Thus one embodiment of the presently disclosed frits can be produced by orienting layers of APTIV® PEEK film with the top (matte) surfaces against the bottom (gloss) surfaces, and welding, compressing or encapsulating the layers together to produce the tortious fluid channels. In addition to PEEK, other polymer materials that may be used in the frits of the present disclosure include, but are not limited to, TEFLON®, TEFZEL®, DELRIN®, polyphenylene sulfide (PPS), polypropylene, and others, as well as combinations thereof. In addition, PEEK (or other polymers) may be used that is reinforced with carbon, carbon fibers, glass fibers, or steel fibers, or the like. 
         [0066]      FIG. 4  shows a frit  400  engaged at one end of a tube  480  in a port  490 , with fluid flow designated by arrows. Frit  400  can be a frit such as those shown in  FIG. 2  or  FIG. 3 , but is shown without top and/or bottom surface features for ease of viewing. Frit  400  once again comprises seven layers, first layer  410 , having a top surface  411  and a bottom surface  412 , second layer  420 , having a top surface and a bottom surface (not discernable in  FIG. 4 ) and defining a passageway  423 , third layer  430 , having a top surface and a bottom surface (not discernable in  FIG. 4 ) and defining a passageway  433 , fourth layer  440 , having a top surface and a bottom surface (not discernable in  FIG. 4 ) and defining a passageway  443 , fifth layer  450 , having a top surface and a bottom surface (not discernable in  FIG. 4 ) and defining a passageway  453 , sixth layer  460 , having a top surface and a bottom surface (not discernable in  FIG. 4 ) and defining a passageway  463 , and seventh layer  470 , having a top surface (not discernable in  FIG. 4 ) and a bottom surface  472 , and defining a passageway  473 . First layer  410  of frit  400  is adjacent tube  480 , which defines a passageway  481 . Fluid flows through passageway  481  of tube  480  and contacts top surface  411  of the first layer  410  of frit  400 . Frit  400  is shown engaged in port  490  having port pocket  491 , passageway  492  and port base  493 . Bottom surface  472  of seventh layer  470  of frit  400  is shown to be engaged with port base  493  of port  490 . Fluid flows along top surface  411  of the first layer  410  of the frit  400  to the port pocket  491 , and then though the gaps (not shown) between the bottom surface  412  of the first layer  410  and the top surface (not discernable in  FIG. 4 ) of the second layer  420 , between the bottom surface (not discernable in  FIG. 4 ) of the second layer  420  and the top surface (not discernable in  FIG. 4 ) of the third layer  430 , between the bottom surface (not discernable in  FIG. 4 ) of the third layer  430  and the top surface (not discernable in  FIG. 4 ) of the fourth layer  440 , between the bottom surface (not discernable in  FIG. 4 ) of the fourth layer  440  and the top surface (not discernable in  FIG. 4 ) of the fifth layer  450 , between the bottom surface (not discernable in  FIG. 4 ) of the fifth layer  450  and the top surface (not discernable in  FIG. 4 ) of the sixth layer  460 , between the bottom surface (not discernable in  FIG. 4 ) of the sixth layer  460  and the top surface (not discernable in  FIG. 4 ) of the seventh layer  470 , and between the bottom surface  472  and the port base  493 , to the passageways of the layers ( 423 ,  433 ,  443 ,  453 ,  463  and  473 ), and then to the passageway  492  of the port  490 . 
         [0067]    Referring now to  FIG. 5 , an exploded view of an embodiment of another frit  500  is shown. Frit  500  as shown in  FIG. 5  is preferably generally circular and symmetric about a center axis. Frit  500  comprises a plurality of layers, which in the embodiment shown in  FIG. 5  comprises seven layers. First layer  510  of the frit  500  is a solid layer having a top surface  511  defining a plurality of fluid channels, which in the embodiment shown in  FIG. 5  comprises a first fluid channel  514 , a second fluid channel  515 , a third fluid channel  516  and a fourth fluid channel  517 , and a gloss finish on the bottom surface  512 . Second layer  520  of the frit  500  has a matte finish on the top surface  521  and a gloss finish on the bottom surface  522 , and also defines a passageway  523  through the second layer  520  from the top surface  521  to the bottom surface  522 . Third layer  530  of the frit  500  has a matte finish on the top surface  531  and a gloss finish on the bottom surface  532 , and also defines a passageway  533  through the third layer  530  from the top surface  531  to the bottom surface  532 . Fourth layer  540  of the frit  500  has a matte finish on the top surface  541  and a gloss finish on the bottom surface  542 , and also defines a passageway  543  through the fourth layer  540  from the top surface  541  to the bottom surface  542 . Fifth layer  550  of the frit  500  has a matte finish on the top surface  551  and a gloss finish on the bottom surface  552 , and also defines a passageway  553  through the fifth layer  550  from the top surface  551  to the bottom surface  552 . Sixth layer  560  of the frit  500  has a matte finish on the top surface  561  and a gloss finish on the bottom surface  562 , and also defines a passageway  563  through the sixth layer  560  from the top surface  561  to the bottom surface  562 . Seventh layer  570  of the frit  500  has a matte finish on the top surface  571  and a gloss finish on the bottom surface  572 , and also defines a passageway  573  through the seventh layer  570  from the top surface  571  to the bottom surface  572 . Once again the matte top surfaces ( 521 ,  531 ,  541 ,  551 ,  561  and  571 ) can either be a random or non-uniform (non-directional) finish created from a process such as, but not limited to, shot peen, bead blast or powder blast), have a surface finish with a lay to it (a directional finish as a consequence of creating the surface finish with a process such as, but not limited to, grinding), or a mixture thereof (some layers having a random or non-uniform matte finish, others having a matte finish with a lay to it). In certain embodiments one or more layers ( 510 ,  520 ,  530 ,  540 ,  550 ,  560  and/or  570 ) of frit  500  can have a matte finish on the bottom surface (not shown). 
         [0068]      FIG. 6  shows the frit  500  shown in  FIG. 5  engaged at one end of a tube  580  in a port  590 . Frit  500  once again comprises seven layers, first layer  510 , having a top surface  511  defining four fluid channels (only fluid channel  514  is visible in  FIG. 6 ) and a bottom surface  512 , second layer  520 , having a top surface and a bottom surface (not discernable in  FIG. 6 ) and defining a passageway  523 , third layer  530 , having a top surface and a bottom surface (not discernable in  FIG. 6 ) and defining a passageway  533 , fourth layer  540 , having a top surface and a bottom surface (not discernable in  FIG. 6 ) and defining a passageway  543 , fifth layer  550 , having a top surface and a bottom surface (not discernable in  FIG. 6 ) and defining a passageway  553 , sixth layer  560 , having a top surface and a bottom surface (not discernable in  FIG. 6 ) and defining a passageway  563 , and seventh layer  570 , having a top surface (not discernable in  FIG. 6 ) and a bottom surface  572 , and defining a passageway  573 . First layer  510  of frit  500  is adjacent tube  580 , which defines a passageway  581 . Frit  500  is shown engaged in port  590  having port pocket  591 , passageway  592  and port base  593 . Bottom surface  572  of seventh layer  570  of frit  500  is shown to be engaged with port base  593  of port  590 . 
         [0069]      FIG. 7  shows the frit  500  from  FIG. 5  engaged at one end of a tube  580  in a port  590 , as shown in  FIG. 6 , with initial fluid flow designated by arrows. Frit  500  once again comprises seven layers, first layer  510 , having a top surface  511  defining four fluid channels (only fluid channel  514  is visible in  FIG. 7 ) and a bottom surface  512 , second layer  520 , having a top surface and a bottom surface (not discernable in  FIG. 7 ) and defining a passageway  523 , third layer  530 , having a top surface and a bottom surface (not discernable in  FIG. 7 ) and defining a passageway  533 , fourth layer  540 , having a top surface and a bottom surface (not discernable in  FIG. 7 ) and defining a passageway  543 , fifth layer  550 , having a top surface and a bottom surface (not discernable in  FIG. 7 ) and defining a passageway  553 , sixth layer  560 , having a top surface and a bottom surface (not discernable in  FIG. 7 ) and defining a passageway  563 , and seventh layer  570 , having a top surface (not discernable in  FIG. 7 ) and a bottom surface  572 , and defining a passageway  573 . First layer  510  of frit  500  is adjacent tube  580 , which defines a passageway  581 . Fluid flows through passageway  581  of tube  580  and contacts first fluid channel  514  in top surface  511  of the first layer  510  of frit  500 . Frit  500  is shown engaged in port  590  having port pocket  591 , passageway  592  and port base  593 . Bottom surface  572  of seventh layer  570  of frit  500  is shown to be engaged with port base  593  of port  590 . Fluid flows along fluid channels (including first fluid channel  514 ) in top surface  511  of the first layer  510  of the frit  500  to the port pocket  591 , and then though the gaps (not shown) between the bottom surface  512  of the first layer  510  and the top surface (not discernable in  FIG. 7 ) of the second layer  520 , between the bottom surface (not discernable in  FIG. 7 ) of the second layer  520  and the top surface (not discernable in  FIG. 7 ) of the third layer  530 , between the bottom surface (not discernable in  FIG. 7 ) of the third layer  530  and the top surface (not discernable in  FIG. 7 ) of the fourth layer  540 , between the bottom surface (not discernable in  FIG. 7 ) of the fourth layer  540  and the top surface (not discernable in  FIG. 7 ) of the fifth layer  550 , between the bottom surface (not discernable in  FIG. 7 ) of the fifth layer  550  and the top surface (not discernable in  FIG. 7 ) of the sixth layer  560 , between the bottom surface (not discernable in  FIG. 7 ) of the sixth layer  560  and the top surface (not discernable in  FIG. 7 ) of the seventh layer  570 , and between the bottom surface  572  and the port base  593 , to the passageways of the layers ( 523 ,  533 ,  543 ,  553 ,  563  and  573 ), and then to the passageway  592  of the port  590 . 
         [0070]      FIG. 8  shows the frit  500  from  FIG. 5  engaged at one end of a tube  580  disposed in a fitting  585  that is engaged in a port  590 . Tube  580 , which defines a passageway  581 , is disposed in passageway  586  of fitting  585 , which also comprises head portion  587  and externally threaded portion  588 . Externally threaded portion  588  of fitting  585  is threadedly engaged with internally threaded portion  594  of port  590 , which once again has port pocket (not discernable in  FIG. 8 ), passageway  592  and port base  593 . Bottom surface  572  of seventh layer (not discernable in  FIG. 8 ) of frit  500  is shown to be engaged with port base  593  of port  590 . 
         [0071]      FIG. 9  shows an alternative embodiment of a frit  600  engaged in a tee connection assembly  690 , defining a first passageway  691  and a second passageway  692 . Shown engaged in tee connection assembly  690  are fittings  680 ,  681  and  682 . Since frit  600  does not have a solid top layer, fluid flow in frit  600  is from the inner region of frit  600  to the outer region of frit  600 . 
         [0072]    Some additional details of the frit  600  from  FIG. 9  are shown in  FIG. 10 . Frit  600  has a plurality of layers, which in the embodiment shown in  FIG. 10  comprises fourteen layers ( 601 ,  602 ,  603 ,  604 ,  605 ,  606 ,  607 ,  608 ,  609 ,  610 ,  611 ,  612 ,  613  and  614 ), each of which has a top surface ( 601   a,    602   a,    603   a,    604   a,    605   a,    606   a,    607   a,    608   a,    609   a,    610   a,    611   a,    612   a,    613   a  and  614   a,  respectively), a bottom surface ( 601  b,  602   b,    603   b,    604   b,    605   b,    606   b,    607   b,    608   b,    609   b,    610   b,    611   b,    612   b,    613   b  and  614   b,  respectively), and defines a passageway ( 601 ′,  602 ′,  603 ′,  604 ′,  605 ′,  606 ′,  607 ′,  608 ′,  609 ′,  610 ′,  611 ′,  612 ′,  613 ′ and  614 ′, respectively). Frit  600  is shown without top and/or bottom surface features for ease of viewing. The top surfaces ( 601   a,    602   a,    603   a,    604   a,    605   a,    606   a,    607   a,    608   a,    609   a,    610   a,    611   a,    612   a,    613   a  and  614   a ) generally have a matte finish, while the bottom surfaces ( 601   b,    602   b,    603   b,    604   b,    605   b,    606   b,    607   b,    608   b,    609   b,    610   b,    611   b,    612   b,    613   b  and  614   b ) can have either a gloss finish or a matte finish, and the matte surfaces can either be a random or non-uniform (non-directional) finish created from a process such as, but not limited to, shot peen, bead blast or powder blast), have a surface finish with a lay to it (a directional finish as a consequence of creating the surface finish with a process such as, but not limited to, grinding), or a mixture thereof (some layers having a random or non-uniform matte finish, others having a matte finish with a lay to it). In certain embodiments, the fits can have a combination of one or more layers that have a bottom surface with a gloss finish and one or more layers that have a matte finish, while in other embodiments the flits can have a combination of one or more layers that have one surface (top or bottom) with a random or non-uniform matte finish and the other surface (top or bottom) with a matte finish with a lay to it. 
         [0073]      FIG. 11  shows an alternative embodiment of a frit  700 . Frit  700  comprises a central porous region  710  and a solid outer region  720 . As shown in  FIG. 11 , the central porous region  710  is shorter than the solid outer region  720  of the frit  700 . In addition, central porous region  710  comprises interior area  711  and exterior area  712 . The exterior area  712  of the central porous region  710  is an intermixed area of solid and porous, since there is generally not a definite border between the solid outer region  720  and the central porous region  710  (thus there is a non-tortuous path for the beads to migrate through). The solid outer region  720  is integral to the frit  700  without an interface. The solid outer region  720  serves as a barrier to encapsulate the central porous region  710 , as well as a surface to seal against. 
         [0074]      FIG. 12  shows a front top perspective view of the alternative embodiment of frit  700  shown in  FIG. 11 . Once again, frit  700  comprises a central porous region  710  having an interior area  711  and an exterior area  712 , and a solid outer region  720 . 
         [0075]      FIG. 13  shows a top perspective cross-sectional exploded view of one embodiment of a device  800  that can be used to prepare the alternative embodiment of frit  700  shown in  FIG. 11  and  FIG. 12 . Device  800  comprises a press head  810  with no environmental heat that defines a passageway  811 , a base  820  that can be heated, for example by using an induction coil, inserts  830  and  840 , that can also be heated, for example by using an induction coil, and spacer  850  that defines passageway  851 . 
         [0076]      FIG. 14  shows a cross-sectional view of the device  800  shown in  FIG. 13  upon assembly. Device  800  once again comprises a press head  810  with no environmental heat that defines a passageway  811 , a base  820  that can be heated, for example by using an induction coil, inserts  830  and  840 , that can also be heated, for example by using an induction coil, and spacer  850  that defines passageway  851 . Frit  700  can prepared by pressing the starting polymeric material in device  800  (or alternatively can be prepared by pressing with a set of tools, not shown), and then heating base  820  and inserts  830  and  840  to melt and thus solidify the polymeric material in solid outer region  820 . Since the press head  810  has no environmental heat, the polymeric material in central porous region of frit  700  does not melt and solidify and therefore remains porous. In certain embodiments compressed air or gas, or a liquid such as water, an aqueous solution or alcohol, can flow through passageways  811  and  851  to extract heat and keep the central porous region  810  cool. 
         [0077]    The following examples are included to demonstrate preferred embodiments of the present disclosure. It should be appreciated by those of skill in the art that the techniques disclosed in the examples that follow represent techniques discovered by the inventors to function well in the practice of the present disclosure, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the present disclosure. The present disclosure is not to be limited in scope by the specific embodiments described herein, which are intended as single illustrations of individual aspects of the present disclosure, and functionally equivalent methods and components are within the scope of the present disclosure. Indeed, various modifications of the present disclosure, in addition to those shown and described herein, will become apparent to those skilled in the art from the foregoing description. Such modifications are intended to fall within the scope of the appended claims. 
       EXAMPLE 1 
       [0078]    Performance of a frit as described herein was tested. This test comprised of stacking  48  rectangular shaped strips of 250 μm (0.010 inch) thick by 0.010 inches wide by 0.500 inches long PEEK film, matte finish on one side, gloss on the other. For surface finish measurement of the film, see Table 1. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Matte Finish 
                   
                 Gloss Finish 
                   
               
             
          
           
               
                   
                 Ra (μ-in) 
                 Rz (μ-in) 
                 Ra (μ-in) 
                 Rz (μ-in) 
               
               
                   
                   
               
             
          
           
               
                   
                   
                 48 
                 273 
                 1 
                 10 
               
               
                   
                   
                 53 
                 339 
                 1 
                 9 
               
               
                   
                   
                 54 
                 332 
                 2 
                 20 
               
               
                   
                   
                 47 
                 285 
                 2 
                 13 
               
               
                   
                   
                 46 
                 241 
                 1 
                 11 
               
               
                   
                   
                 52 
                 356 
                 1 
                 11 
               
               
                   
                   
                 55 
                 329 
                 1 
                 10 
               
               
                   
                   
                 32 
                 213 
                 1 
                 11 
               
               
                   
                   
                 34 
                 188 
                 1 
                 11 
               
               
                   
                   
                 51 
                 288 
                 2 
                 12 
               
               
                   
                   
                 34 
                 195 
                 2.5 
                 12 
               
               
                   
                   
                 68 
                 344 
                 1 
                 26 
               
               
                   
                   
                 46 
                 224 
                 1 
                 10 
               
               
                   
                   
                 27 
                 154 
                 1 
                 9 
               
               
                   
                   
                 48 
                 266 
                 1 
                 11 
               
               
                   
                 Ave 
                 46.3 
                 268.5 
                 1.3 
                 12.4 
               
               
                   
                 Stdev 
                 10.7 
                 64.1 
                 0.5 
                 4.6 
               
               
                   
                   
               
             
          
         
       
     
         [0079]    The film strips were compressed. Alcohol was then forced through the stack so that it flowed through the 0.010 inch dimension, between the 0.010 thick layers. The layers were stacked so that a matte finish side was compressed against a gloss finish side. The stacks were tested on a Bubble Point Tester, Model ABT-101A (Porous Materials, Inc., Ithaca, N.Y.). Dry bubble point result was 0.27 μm and 0.25 μm from two consecutive tests. Wet bubble point result was 0.21 μm and 0.21 μm from two consecutive tests. 
         [0080]    The results indicate that the micron rating for the stack was 0.21 μm, which is within the desired range. 
       EXAMPLE 2 
       [0081]    Performance of another fit as described herein was tested. This test comprised of stacking round disks that were made from 250 μm (0.010 inch) thick film by 0.28 inches in diameter. A stack of seven disks were compressed with unknown force then laser welded on their outer edges so that they formed an integrated frit (bead running parallel to disk centerline, four equally spaced welds). Each disk was oriented so that the matte finish on one side was against a gloss finish side. Then a 0.050 center hole was drilled through six of the disks, leaving the end disc solid. Surface finish measurement of the film was the same as shown in Table 1 from Example 1, above. A nylon nut was then used to further compress the frit during bubblepoint testing. Alcohol was then forced through the center hole of the stack so that it flowed from the inside to the outside of the frit, between the disks. The frit was tested on Bubble Point Tester, Model ABT-101A (Porous Materials, Inc., Ithaca, N.Y.). This resulted in a bubblepoint rating of 0.16 μm when the nylon nut was manually tightened to a high torque value by hand, and a bubblepoint rating of 0.35 μm with a light torque value by hand. The results indicate that the micron rating for the frit was 0.35 μm, which is within the desired range. The housing was calibrated with a 5 μm OC-815-02 frit (IDEX Health &amp; Science, Oak Harbor, Wash.). The bubblepoint test indicated a rating of 3.6 μm. 
       EXAMPLE 3 
       [0082]    Performance of another frit as described herein was tested. A stack of 14 laser cut disks were installed into a modified metering valve. The disks were cut from 0.003 inch (75 μm) thick film with a matte finish on one side and a gloss finish on the other side. The disks were cut to a 0.062 inch outside diameter and a 0.003 inch center hole was made. A nut on the metering valve provided the compression on the stack. With the nut set at a moderate finger tight torque value, the bubblepoint results were 1.63 μm, 1.76 μm, and 2.05 μm (visual observation value of 2.12 μm). When the nut was loosened by ¼ turn, the results were 6.62 μm and 6.75 μm. 
         [0083]    This demonstrates that the compression on the stack effects the micron rating, which allows for the production of fits that have an adjustable micron rating. Another benefit is that the stack can be decompressed during back flush operations to allow the frit to be cleaned. The frit would then be compressed again to the appropriate micron rating. 
         [0084]    While the present disclosure has been shown and described in various embodiments, those skilled in the art will appreciate from the drawings and the foregoing discussion that various changes, modifications, and variations may be made without departing from the spirit and scope of the invention as set forth in the claims. Hence the embodiments shown and described in the drawings, specific forms, materials, and the like, and the above discussion are merely illustrative and do not limit the scope of the invention as defined in the claims herein.