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Nano-flow liquid chromatographic apparatus having robust capillary tubingRelated Patent Categories: Liquid Purification Or Separation, Processes, ChromatographyNano-flow liquid chromatographic apparatus having robust capillary tubing description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070068872, Nano-flow liquid chromatographic apparatus having robust capillary tubing. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] 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. TECHNICAL FIELD [0002] The invention generally relates to chromatography instruments that have plumbing, including tubing and connectors, designed to accommodate high pressure and/or low flow rates. BACKGROUND INFORMATION [0003] 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. [0004] 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. [0005] 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. [0006] 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.) [0007] 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. [0008] 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. [0009] 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. SUMMARY OF THE INVENTION [0010] 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. [0011] 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. [0012] 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. [0013] 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. [0014] 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. [0015] 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 .mu.L/min or lower. [0016] 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. [0017] 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. [0018] 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. [0019] 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. [0020] 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. Continue reading about Nano-flow liquid chromatographic apparatus having robust capillary tubing... 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