Patent Application
20070068872
The invention generally relates to chromatography instruments that have plumbing, including tubing and connectors, designed to accommodate high pressure and/or low flow rates.
Various instruments utilize conduits for transportation of process fluids and sample compounds and/or for separation of sample compounds. For example, chemical-analysis instruments that utilize liquid chromatography (LC), capillary electrophoresis (CE) or capillary electro-chromatography (CEC) perform separation of sample compounds as the sample passes through a column. Such instruments include plumbing, such as conduits and connectors, that transport a variety of materials, such as solvents and sample compounds.
In addition to tubing, used, for example, for separation column(s) and/or plumbing, liquid-chromatography instruments typically include reservoirs, pumps, filters, check valves, sample-injection valves, and sample compound detectors. Typically, solvents are stored in reservoirs and delivered as required via reciprocating-cylinder based pumps. Sample materials are often injected via syringe-type pumps.
In some cases, separation columns include one or more electrodes to permit application of a voltage to a sample-containing fluid passing through and/or exiting from the conduit. CEC, for example, utilizes an electro-osmotic flow (EOF) to propel a mobile phase through a chromatographic column. In contrast, liquid chromatography, such as high-performance liquid chromatography (HPLC), relies on pressure to propel a fluid through a column.
Suitable analytical-instrument tubing withstands pressures encountering during fabrication and use, is reliable through repeated use, and has physical and chemical compatibility with process and sample compounds. Generally, a tubing material should not corrode or leach, and sample compounds should not adhere to the tube (unless required for a separation process.)
For HPLC and higher-pressure applications, tubing is typically made from stainless steel or fused silica to provide suitable strength and cleanliness. Such tubing is typically joined to other components via stainless steel connectors.
Stainless steel, however, has disadvantages in some applications due to its biocompatibility limits in comparison to some other materials; some organic molecules tend to adhere to the inner walls of steel tubing, and components of a steel alloy at times leach into fluid passing through the tubing. Organic molecules generally are less likely to stick to fused silica or suitable polymeric materials than to steel. Fused silica tubing, however, is vulnerable to fracturing while polymeric materials generally have relatively poor strength.
Typically, tubing must also be compatible with connectors that provide fluidic connections to other components of an instrument. Problems associated with the design and use of connector fittings are particularly difficult for high-pressure fabrication and operation. For example, pressures in the range of 1,000-5,000 pounds per square inch (psi) or higher are often utilized in liquid chromatography, and must be accommodated without undesirable amounts of leakage.
The invention arises, in part, from the realization that a nano-flow LC apparatus advantageously includes fluid transport tubing configured with a fused silica inner tube having a narrow inner diameter, a steel outer tube, and a polymer intermediate tube, as well as high-pressure connectors configured to mate with the steel outer tube. Conventional connectors are optionally used in such an apparatus.
The layered tubing provides the narrow dimensions and other benefits of fused silica capillary plumbing in a nano-flow LC system, while also providing the mechanical stability and good connector interface of steel tubing in high pressure applications. The steel tubing protects the capillary from damage from connectors, and the intermediate tube fixes the position of the capillary relative to the steel tubing so that the capillary does not move in response to pressure transmitted by a pressurized fluid.
Apparatus of the inventions solve problems of low efficiency, distorted peak shape, and/or leaking fittings of some prior nano-flow LC apparatus. Various nano-flow apparatus of the invention include, for example, layered tubing connected to a separation column, a sample injector, and/or a detector.
Accordingly, one embodiment of the invention features a chemical processing apparatus. The apparatus includes a separation column, a pump unit, at least one fluid transport tube for transporting the fluid between the pump unit and the separation column, and a connector disposed adjacent to an inlet or outlet end of the at least one transport tube.
The connector includes, for example, a ferrule, a compression screw, and a fitting that receives the compression screw. The connector provides a substantially fluid-tight connection between the end of the at least one transport tube and an output port of the pump unit or an input port of the column.
The pump unit is configured to deliver, to the separation column, a fluid at a pressure of at least about 10,000 psi at a flow rate of 100 μL/min or lower.
The fluid transport tube includes an outer tube including a metallic material, a liner tube including fused silica disposed in the outer tube, and an intermediate tube including a polymeric material disposed between and bonded to both the outer tube and the liner tube.
Another embodiment of the invention features LC tubing suitable for operation at pressures up to about 10,000 psi to 15,000 psi or greater and providing relatively good biocompatibility. The tubing optionally is fabricated by inserting a polymeric tube into a high-strength outer steel tube, inserting a silica capillary into the polymeric tube, and melt bonding the polymeric tube to the outer tube and the capillary.
In some alternative embodiments, a portion of a polymeric tube is melted to form a bond with adjacent tubes. The bond inhibits sliding movement of, for example, an inner capillary relative to an outer tube and/or provides a leakage barrier for the interfaces with the inner and/or outer tubes.
Some embodiments of such tubing have a variety of advantages over some conventional tubing. For example, some embodiments are relatively easy and inexpensive to manufacture. Some embodiments are compatible with commonly available metallic-based high-pressure connectors. Some of these embodiments are fabricated from standard stainless steel or titanium tubing that is suitable for operation at relatively high pressures.
Thus, as one example, a relatively high-pressure and low flow-rate compatible conduit is constructed at a relatively low cost from readily available components and integrated with other components of a nano-flow instrument by utilizing standard high-pressure connectors.
In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention.
a is a cross-sectional diagram of tubing at an intermediate stage of fabrication, in accordance with one embodiment of the invention;
b is a cross-sectional diagram of the tubing of
The phrases “chromatographic system,” “chromatographic module,” “chromatographic instrument,” and the like herein refer to equipment used to perform chemical separations. Such equipment is a portion of an instrument that includes other components or is a standalone unit. Chromatographic equipment typically moves fluids under pressure and/or electrical forces.
Depending on context, the description provided herein of some illustrative embodiments of the invention interchangeably uses the words “tube,” “conduit,” and/or “pipe.” Depending on context, the word “capillary” refers to fused-silica tubes and/or refers to tubes having a relatively narrow inner diameter. Tubes define an interior passageway, herein also referred to interchangeably as a lumen, bore, or channel. The word “column” herein refers to a tube that is used for separation of compounds in a sample, or is used to propel fluids in an electrokinetic pump.
The word “biocompatiblity” herein relates to the tendency of some organic materials to adhere to a particular tube material, as would be understood by one of ordinary skill. For example, fused silica is generally considered to be more biocompatible than is steel because organic molecules are typically less likely to adhere to fused silica than to a steel alloy.
The terms “nano-flow” and “nanoflow” are used herein to refer to fluid flow rates of less than about 100 μL/min. Nano-flow rates are useful, for example, in some applications of chromatography performed at pressures of 1,000 psi or greater, and at even higher pressures, such as 10,000 psi or greater.
Some embodiments of the invention involve apparatus that include both chromatographic and mass-spectrometric components. In some of these embodiments, a chromatographic component is placed in fluid communication with a mass-spectrometric component through use of an appropriate interface, such as an electrospray-ionization interface, as known to one of ordinary skill. Some appropriate interfaces at times create or maintain separated materials in an ionic form and typically place a stream of fluid containing the ions into an atmosphere where the stream is vaporized and the ions are received in an orifice for mass-spectrometric analyses.
Some alternative embodiments, described in more detail below with reference to
Now also referring to
The tube 200 includes an outer tube 210 and an inner tube 220. As described in more detail below, the outer tube 210 is formed of a material that provides suitable strength and reliability while the inner tube 220 is formed of a material that provides melt-bonding capability and/or suitable biocompatibility. Upon completion of fabrication, the tube 200 is suitable for use as, for example, a transport conduit or column in a chromatographic system.
As illustrated in
Subsequent to bonding of the inner tube 220 to the outer tube 220, if desired, the inner tube is trimmed (Step 150). In the illustrated example, the inner tube 220 is trimmed flush with the outer tube 210. In alternative embodiments of the invention, inner and/or outer tubes are trimmed and/or otherwise shaped as desired for compatibility with other components of an analytical system. Trimming (Step 150) in support of compatibility with conduit connectors is described below, in part with reference to
The inner tube 220 defines a lumen through which material—such as solvent and/or sample material—flows. As described in more detail below, the outer tube 210 provides, in part, mechanical support while the inner tube 220 provides, in part, compatibility with a material flowing through the tube.
In various embodiments, the polymeric material is selected for its ability to form a melt bond to the outer tube and/or for its biocompatibility. For example, biocompatibility with proteins and peptides is important in some applications. In some embodiments, the inner tube is at least partially formed of any suitable meltable polymer, including known thermoplastic polymers.
The polyaryl-ether-ketones, for example, provide one class of thermoplastic polymers that also has good biocompatibility. One of the suitable polymeric materials of this class is polyether-ether-ketone, such as PEEK polymer (available from Victrex PLC, Lancashire, United Kingdom.)
Some embodiments utilize other polymers, for example, fluoropolymers such as polytetrafluorothylene (available as TEFLON polymer from Dupont Engineering Polymers, Newark, Delware), chlorotetrafluoroethylene, polychlorotrifluoroethylene (available as NEOFLON PCTFE fluoropolymer from Fluorotherm Polymers, Inc., Fairfield, N.J.), and modified copolymer fluoropolymers (for example, a modified copolymer of tetrafluoroethylene and ethylene available as DUPONT TEFZEL fluoropolymer, which is resistant to concentrated nitric acid or sulfuric acid), and other polymers, such as polyimide (available as DUPONT VESPEL polyimide.)
In some embodiments, the inner tube is formed of a composite material. For example, in some of these embodiments, the inner tub is formed of a mixture of a polymer, such as polyether-ether-ketone, and about 5% by weight of glass, fiberglass, carbon, and/or or other particles and/or fibers.
The material of the outer tube is selected from any suitable materials, including known materials, to provide, for example, a sufficient level of mechanical strength to support fabrication and/or operating conditions. In one embodiment, a desired level of mechanical strength is obtained by the combination of an outer tube(s) and an inner tube(s). For example, the materials and wall thicknesses of the inner and outer tubes are selected to perform HPLC (at, for example, about 2 kpsi to about 5 kpsi,) or to operate at higher pressures up to about 10 kpsi to 15 kpsi or higher.
Steel and titanium, for example, have relatively high yield strength, and are thus suitable for high-pressure operation of a transport tubing, column tubing, etc. For outer tubing, some embodiments utilize standard tubing known to those having ordinary skill in the high-pressure chromatographic arts. One suitable standard tubing is 1/16 inch outer diameter (OD) 316 alloy stainless steel tubing. The inner diameter (ID) of the steel tubing is selected as desired from, for example, standard available IDs. Standard IDs are available as small as about 4 mil (about 100 μm.)
In some embodiments, an OD of an inner tube is selected to provide a slidable fit within the selected outer tubing. An ID of an inner tube is selected as desired. For example, an ID can be selected to be as small as about 2 mil (about 50 μm) or less.
After inserting (Step 130) the inner tube, bonding is initiated by heating (Step 140) sufficiently to melt at least a portion of the inner tube adjacent to the inner surface of the outer tube. Upon cooling, the melted portion solidifies and forms a fixed contact between the inner and outer tubes.
The inner tube is heated in any suitable manner. In one embodiment, the inner tube is heated indirectly by heating an adjacent portion of the outer tube. For example, the inner tube is heated by heating the outer tube sufficiently to raise the temperature of portions of the inner tube to at least a melting point temperature.
For example, in some embodiments, the entire outer tube is heated, uniformly or non-uniformly. In other embodiments, heat is directed only to one or more portions of the outer tube. As illustrated in
Heat is directed at the outer tube in any suitable manner, including known heating methods. For example, the inner and outer tubes, or portions of the tubes, are placed in one or more ovens or in cavities of heatable blocks of aluminum or steel. Such blocks are heated by, for example, resistive heaters or a heated platten. Other options for heating, such as induction heating, are available and any suitable method may be used. Various embodiments utilize any method of heat transfer that provides the desired bonding temperature and environment.
The portion of the inner tube that is melted (Step 140) has its temperature profile controlled as desired. For example, the temperature is raised gradually to a desired temperature over a period of seconds or minutes or hours. Alternatively, the portion of the inner tube is melted nearly instantaneously. In some embodiments, a suitable temperature profile that supports a good bond is empirically or theoretically determined.
In some embodiments, heating over a period of several minutes is helpful to obtain a good bond. It is desirable in some cases to controllably heat and melt the portion of the inner tube to obtain repeatable results and to avoid incorporation of bubbles or voids within a bonded region.
In some embodiments, it is undesirable to overheat the polymeric material of the inner tube when thermal breakdown or decomposition is possible. One embodiment utilizes a non-oxidizing atmosphere during heating.
After heating, the inner and outer tubes are either passively or actively cooled to ambient temperature. Cooling is accelerated by, for example, any suitable method that maintains the chemical and structural integrity of the bond and components.
Some alternative implementations of extracting (Step 145) heat during melting (Step 140) are now described. To extract heat, a fluid, such as a gas or liquid, is directed through a lumen defined by the innermost tube. In some embodiments, the fluid is a substantially inert gas, such as nitrogen or argon.
The fluid is used, for example, to ensure that melting remains localized and does not extend to the inner surface of the polymeric-material tube. The fluid is thus used, in some cases, to maintain a passageway through the inner tube during melting (Step 140).
In one embodiment, the flow of a gas through the tube is controlled by monitoring the pressure drop of the gas across the tube (i.e., the difference in pressure between an inlet end and an outlet end of the tube.) Desirable pressure drops are, for example, in a range of about 10 psi to about 100 psi. An increase in the selected pressure drop is often desirable for greater lengths of tubing and/or for smaller diameters of a passageway.
A suitable pressure drop is determined, for example, empirically. For particular selected materials and tube dimensions, a suitable pressure is determined at which the passageway through the tube remains open during bonding.
In one embodiment, gas is directed into the tube at one end of the tube while a portion of the tube adjacent to the opposite end of the tube is heated to form a bond adjacent to that end. Gas is then directed into the bonded end of the tube, and the now opposite end is heated to form a bond adjacent to that end. In this manner, a passageway is maintained through a lumen having an ID of as small as about 50 μm or less.
The remaining description, below, is directed primarily to some embodiments that utilize a steel outer tube and a polyether-ether-ketone inner tube. One having ordinary skill will understand, however, that principles of the invention are applicable to a broader range of materials and processing conditions.
Melting (Step 140), in one illustrative case, is obtained by heating portions of the inner tube to a temperature somewhat above the melting point temperature. In one embodiment, for example, the polyether-ether-ketone portion is heated to a temperature of between about 385° C. to about 405° C. The polymer is heated at the desired temperature for a period of time of about 1 to about 3 minutes, although the invention is not limited to such. It is often desirable to heat neighboring portions of the inner and outer tubes to a similar or same temperature during melting (Step 140) to obtain a good bond between the inner and outer tubes.
In one illustrative embodiment, an analytical-instrument tube includes an inner tube and an outer tube of the following dimensions and composition. The outer tube is formed of drawn 316 stainless steel and the inner tube is formed of extruded polyether-ether-ketone. The inner tube has an inner diameter (ID) of 2 mil (50 μm) or 2.5 mil (60 μm). The outer tube has an outer diameter of 1/16 inch, and has an ID selected to be compatible with the OD of the inner tube. The word “compatible” is herein used to mean that the inner tube can be inserted into the outer tube. Preferably, during insertion, the inner tube is not damaged and there is some contact around the circumference of the inner tube, i.e., there is a minimal gap between the inner and outer tubes. One having ordinary skill will understand this example is merely illustrative and non-limiting.
Optionally, more than one inner tube and/or more than one outer tube are utilized to fabricate tubing. For example, some embodiments entail fabrication of a conduit including two or more outer tubes disposed in a row (along the conduit) and/or disposed within one another. For example, in one embodiment, multiple inner tubes are inserted serially, one after another, into an outer tube. In another embodiment, multiple inner tubes are disposed side-by-side, so that the inner tubes provide multiple passageways through the completed tubing. Portions of one or more of the inserted inner tubes are then melted to bond the tubes to each other and/or to the outer tube or tubes.
In another embodiment, inner tubes are inserted within one another. In still another embodiment, outer tubes are inserted within one another. Thus, some embodiments include more than two concentrically disposed tubes. One such embodiment is described in more detail with reference to
The outer, intermediate, and liner tubes 310, 320330 are each fabricated in any desired dimensions in any suitable manner from any suitable materials, including known fabrication methods and materials. For example, the outer tube 310 and the intermediate tube 320 optionally have some or all of the compositional and dimensional features, respectively, of the outer tube 210 and the inner tube 220 described above.
The liner tube 330 optionally is a fused-silica capillary. The intermediate tube 320 optionally is melt bonded to the outer tube 310 and/or the liner tube 330. Thus, as one example, the tube 300 has a steel outer tube 310, a thermoplastic-polymer intermediate tube 320 and a fused-silica liner tube 330. The example tube 300 provides the high-pressure reliability and durability of steel tubing in conjunction with the biocompatible properties of a fused-silica capillary for contact with fluids passing through the tube 300.
The tube 300 also provides plumbing having a relatively narrow ID that is well suited to nano-flow applications. Moreover, the outer tube 310 supports use of narrow ID tubes 300 in conjunction with suitable connectors, such as known connectors, that mate with relatively large diameter metallic tubing to obtain substantially fluid-tight and durable plumbing connections at pressures of up to 1,000 psi, or up to 5,000 psi, or up to 10,000 psi, or greater. Some suitable connectors are described below with reference to
In view of the description provided herein of illustrative embodiments fabricated from inner, intermediate and/or outer tubes, numerous alternative tubing configurations will be apparent to one having ordinary skill in the chemical separation arts. For example, some embodiments include two or more concentric outer tubes and/or two or more concentric inner tubes. Inner and outer concentric tubes are alternated, in some embodiments, such that, for example, an inner tube is disposed between two outer tubes and/or an outer tube is disposed between two inner tubes.
Returning to
The method 100 is used to fabricate both straight and curved tubing, or other desired configurations. For example, in one embodiment a length of metallic tubing is bent at one or more sections to provide a desired configuration for use in a particular analytical instrument. An inner tube is inserted (Step 130) before or after bending of the outer tube. Alternatively, an outer tube is manufactured with a non-straight configuration so that bending is not required.
Tubes according to many embodiments of the invention are well suited for use with tubing connectors, such as standard connectors known to those having ordinary skill in the separation arts. It should also be understood that the above- and below-described and illustrated configurations are not intended to limit application of the invention to any particular type of connector presently available or envisioned or yet to be developed. Moreover, end portions of tubes, according to some embodiments of the invention, are configured to mate with desired types of connectors. For example, in some embodiments, an inner or outer surface of an end portion of the tube is threaded to mate with a threaded connector.
Merely as one illustrative example, convenient use of a tube with a standard connector is described with reference to
Only the proximal end of the fitting body 410 is shown in
In view of the above description, one having ordinary skill in the separation arts will understand that the tubes 300a, 200, 300 may be used in conjunction with any suitable connectors, including known connectors. One suitable commercially available connector, which includes a fitting, ferrule, and compression screw, is the SLIPFREE® connector (available from Waters Corporation, Milford, Mass.)
In view of the description contained herein, it will be apparent to one of ordinary skill that many other connectors are usable with various tubing embodiments of the invention. For example, some suitable connectors utilize a two-ferrule system. Such connectors have applications, for example, in high-pressure environments, for example, at pressures up to about 15,000 psi and greater.
One example of a connector that is suitable for use at very high pressure is the Swagelok gaugeable SAF 2507 super duplex tube fitting (available from the Swagelok Company, Solon, Ohio.) This connector includes front and back ferrules formed from different steel alloys. The back ferrule drives the front ferrule into a fitting body and onto the surface of a tube to create a seal.
Each section of the tubing 500b, 500c, 500d is similar, for example, to any of the tubing 200, 300, 300a described above with reference to
In some alternative implementations, the apparatus 500 is based on a known high-pressure chromatographic instrument, though modified to include plumbing in accordance with the above described features. One suitable commercially available instrument is the nanoACQUITY UPLC™ System (available from Waters Corporation, Milford, Mass.)
The control module 570—including, for example, a personal computer or workstation—receives data and/or provides control signals via wired and/or wireless communications to, for example, the pump 540, the injector 560, and/or the detector 580. The control module 570 supports, for example, automation of sample analyses. The control module 570, in various alternative embodiments, includes software, firmware, and/or hardware (e.g., such as an application-specific integrated circuit), and includes, if desired, a user interface.
The column 540 contains any suitable stationary medium. For example, the medium optionally contains any suitable medium for nano-flow chromatography, such as a particulate medium known to one of ordinary skill. Some suitable media include silica or hybrid sorbents having particle diameters in a range of approximately 1 μm to approximately 5 μm.
In some embodiments, a particulate medium includes hybrid particles, as found, for example, in the BEH Technology™ Acquity UPLC™ 1.7 μm columns (available from Waters Corporation, Milford, Mass.) Other embodiments include larger particles, such as 3 μm or 5 μm particles. Some of these embodiments involve trap columns.
Suitable columns are up to 25 cm in length, or greater, and have inner diameters in a range of, for example 20 μm to 300 μm, for example, 75 μm, 100 μm or 150 μm.
The pump unit 540 is configured to provide nano-flow of solvent at pressures of at least approximately 5,000 psi or 10,000 psi or greater. The pump unit includes any suitable pump components, including known pump components, such as those found in Acquity UPLC™ liquid chromatography instruments (available from Waters Corporation, Milford, Mass.)
The nano-flow apparatus 500 is suitable for, for example, 200 nL/min to 100 μL/min flow-rate separations that provide relatively good sensitivity, resolution and reproducibility. Such separations are desirable, for example, for biomarker discovery and for proteomics applications for protein identification and characterization. Thus, for example, scientists are aided in their investigations of large protein populations or proteomes to identify and quantify proteins that are either up-regulated or down-regulated. Observed changes in protein expression, for example, may provide an indication of disease states. Identifying subtle changes can provide valuable information for drug development. The nano-flow separation also suitably supports subsequent mass spectrometric analysis.
As mentioned, in some embodiments of the invention, the separation column itself has the above-described layered structure. Such separation columns have an inner diameter within a range of, for example, approximately 20 μm to approximately 300 μm, and are preferably packed with a suitable medium, such as any of the above-described media.
Variations, modifications, and other implementations of what is described herein will occur to those of ordinary skill in the art without departing from the spirit and the scope of the invention as claimed. For example, though the embodiments of tubes illustrated herein have circular cross sections, the invention encompasses tubes that have non-circular cross sections. Accordingly, the invention is to be defined not by the preceding illustrative description but instead by the spirit and scope of the following claims.
This application claims priority to and benefit of U.S. Provisional Patent Application No. 60/719,070, filed on Sep. 21, 2005, the entire contents of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60719070 | Sep 2005 | US |
