WO2008005845A2

WO2008005845A2 - Mitigation of sample-introduction decompression effects in high-pressure liquid chromatography

Info

Publication number: WO2008005845A2
Application number: PCT/US2007/072498
Authority: WO
Inventors: James E. Usowicz; Peyton C. Beals; Miguel Soares
Original assignee: Waters Investments Limited
Priority date: 2006-06-30
Filing date: 2007-06-29
Publication date: 2008-01-10
Also published as: JP2009543068A; WO2008005845A3; EP2035788A2

Abstract

A method for processing a fluid is applied to systems that include a valve unit that has a sample-loading state and a sample-injecting state. The sample-loading state disposes a sample loop in fluidic communication with a sample conduit. The sample-injecting state disposes the sample loop in fluidic communication with a process conduit. The method involves transferring a sample through both the sample conduit and the valve unit so that a leading end of the sample exits the valve unit. After transitioning the valve unit to the sample-loading state and allowing the sample loop to decompress, at least some of the transferred sample is loaded into the sample loop. A fluid-processing instrument includes a value unit and a control unit that manages operation of the instrument. The control unit is configured, for example, to implement the above-described method.

Description

MITIGATION OF SAMPLE-INTRODUCTION DECOMPRESSION EFFECTS IN HIGH-PRESSURE LIQUID CHROMATOGRAPHY

TECHNICAL FIELD

The invention relates to fluid processing and, in particular, to injection of samples into fluid-processing systems that process samples under high pressure. BACKGROUND OF THE INVENTION

Gas and liquid chromatography are processes used in analytical and preparative chemistry; a stationary inert porous material is held in a vessel or conduit, such as a column, while a fluid containing a sample of interest is passed through the porous material. In a typical case, the stationary material includes particles.

A typical liquid chromatography system includes, for example, a mobile-phase pump, a sample injector, a column, and a detector. The pump propels a mobile-phase fluid along a fluidic path that passes through the injector, column, and detector. The injector introduces a sample into the mobile-phase fluid prior to entry of the fluid into the column.

Distinct chemical compounds contained in the fluid often have distinct affinities for the medium held in the column. Consequently, as the fluid moves through the chromatographic column, various chemical compounds are delayed in their transit through the column by varying amounts of time in response to their interaction with the stationary porous material in the column. As a result, as the compounds are carried through the medium, the compounds separate into bands which elute from the column at different times.

Thus, the different chemical compounds in a sample solution elute separately from the column, as separate concentration peaks. The various separated chemicals can be detected by, for example, a refractometer, an absorbtometer, or some other detecting device into which the fluid flows upon leaving the chromatographic column, such as a mass spectrometer. In addition to tubing, including separation column(s), liquid- chromatography (LC) instruments typically include reservoirs, pumps, filters, check valves, sample-injection valves, and sample compound detectors. Typically, mobile-phase solvents are stored in reservoirs, and delivered as required via reciprocating-cylinder based pumps. Sample materials are often injected via syringe-type pumps. For example, some LC systems inject a sample by aspirating (pulling) a fluid-based sample into a tube via a needle or capillary and then into a sample loop. The sample is then injected from the sample loop into the mobile-phase stream on its way to a separation column. Typically, tubing must 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, for example, in high-performance (also known as high-pressure) liquid chromatography (HPLC.)

SUMMARY

The invention arises, in part, from the realization that, prior to loading of a sample into a sample loop, the sample can be disposed in a portion of system tubing that is shielded from sample-loop decompression effects.

Thus, some embodiments of the invention mitigate HPLC performance degradation that often arises from the effect of sample-loop decompression.

Decompression can cause, for example, mixing of an interface(s) of a sample awaiting transport into the sample loop.

In some embodiments, the sample is moved to a system location that is removed from locations that experience decompression effects; isolating the sample from decompression effects reduces dilution of the sample at an interface between the sample and another solution, such as a pre-sample buffer solution. For example, sample integrity is increased significantly by forcing decompression effects to occur downstream of a sample loop, by, for example, positioning a sample on an opposite side of a sample loop from a low-pressure side that is open to, for example, an ambient pressure. Some embodiments reduce decompression and/or mixing at an interface between a mobile phase or pre-sample buffer and a sample by positioning of the sample downstream relative to a sample loop disposed between the sample and a sample source at ambient pressure. For example, in an HPLC system, a sample can be drawn through a valve prior to loading the sample into a sample loop, in contrast to some prior approaches in which the sample is disposed by an entry port of the valve. Principles of the invention can be advantageously applied to a variety of elevated-pressure fluidic processing systems, such as, for example, HPLC systems.

For example, some embodiments of the invention entail HPLC systems that include known sample injection valves, such as a six-port valve. These embodiments mitigate performance degradation caused by decompression of a sample loop. Some embodiments of the invention provide advantages over some prior systems. For example, these embodiments provide accurate delivery, consistent delivery, use of less overfill volume, and/or wider linear operating range.

Accordingly, in one aspect, the invention features a method for processing a fluid. The method is applied, for example, to systems that include a valve unit that has a sample-loading state and a sample-injecting state. The sample-loading state disposes a sample loop in fluidic communication with a sample conduit. The sample-injecting state disposes the sample loop in fluidic communication with a process conduit. The method involves transferring a sample through both the sample conduit and the valve unit so that a leading end of the sample exits the valve unit. After transitioning the valve unit to the sample-loading state, at least some of the transferred sample is loaded into the sample loop.

In another aspect, the invention features a fluid-processing instrument. The instrument includes a value unit, such as the above-described valve unit, and a control unit that manages operation of the instrument. The control unit is configured, for example, to implement the above-described method for processing a fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

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. FIG. 1 is a block diagram of a fluid-processing system, in accordance with one embodiment of the invention;

FIG. 2 is a flow diagram of a method for processing a fluid, in accordance with one embodiment of the invention;

FIG. 3 is a flow diagram of a method for processing a fluid, in accordance with one embodiment of the invention;

FIG. 4 is a diagram of a 6-port valve; and

FIGS. 5a though 5e illustrate operation of the valve of FIG. 4, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

The word "chromatography" and the like herein refer to equipment and/or methods used to perform separation of chemical compounds. Chromatographic equipment typically moves fluids under pressure and/or electrical forces. The acronym "HPLC" is used herein generally to refer to liquid chromatography performed at pressures of approximately 1 ,000 to

2,000 psi or greater. Various embodiments of the invention are applicable to HPLC and to LC performed at greater pressures.

The term "sample loop" is used herein to refer broadly to any suitable container, vessel, conduit, or tube that temporarily holds a sample portion prior to injection and separation, including, for example, sample loops that are known to one having ordinary skill in HPLC.

Depending on context, the description provided herein of some illustrative embodiments of the invention interchangeably uses the words "tube," "conduit," "capillary," and/or "pipe." Depending on context, the word "capillary" refers to fused-silica tubes and/or refers to relatively narrow tubes. Tubes define an interior passageway, herein also referred to interchangeably as a lumen, bore, or channel. The word "column" herein refers to a vessel, including, for example, one or more tubes, within which separation of compounds occurs.

Some embodiments of the invention involve instruments that include both chromatographic and mass-spectrometric modules. In some of these embodiments, a chromatographic module is placed in fluidic communication with a mass-spectrometric module through use of an appropriate interface, such as an electrospray-ionization interface. 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. First referring to FIGS. 1 and 2, some embodiments of the invention relate to methods and systems for processing a fluid in which sample-loop decompression effects are mitigated.

FIG. 1 is a block diagram of a fluid-processing system 100, according to one embodiment of the invention. The system 100 includes a valve unit 110, a sample loop 120 in fluidic communication with the valve unit 110, first and second portions of a sample conduit 150A, 150B, a sample source 130 in fluidic communication with the valve unit 110 via the first portion of the sample conduit 150A, a sample pump 160, such as a syringe, in fluidic communication with the valve unit 110 via the second portion of the sample conduit 150B, first and second portions of a process conduit 140A, 140B, a separation column 170 in fluidic communication with the valve unit 110 via the first portion of the process conduit 140A, and a process-fluid source 180 in fluidic communication with the valve unit 110 via the second portion of the process conduit 140B.

The valve unit 110 provides switchable fluidic connections to connect the a sample loop 120 alternately to the sample-conduit portions 150A, 150B and the process-conduit portions 140A, 140B (one example of a valve unit is described below in more detail with reference to FIGS. 4.) The valve unit 110 supports loading of a sample into the sample loop 120 and injection of the loaded sample into the first portion of the process conduit 140A.

The valve unit 110 thus has a sample-loading state and a sample- injecting state. The sample-loading state disposes the sample loop 120 in fluidic communication between the portions of the sample conduit 150A, 150B, and the sample-injecting state disposes the sample loop 120 in fluidic communication between the portions of the process conduit 140A, 140B.

The valve unit 110 includes any component that is suitable for switchably connecting conduits in a chromatographic system. For example, in one alternative, the system 100 is implemented as a HPLC system. In this case, the valve unit 110 is, for example, any suitable commercially available valve that supports sample loading and/or injection in a HPLC system. For example, the valve unit is optionally a 6- or 10-port loop injection valve (available, for example, from Bio-Chem Valve/Omnifit, Booton, New Jersey.)

The sample loop 120 is any suitable sample-holding component, such as a sample loop known to one having ordinary skill in chromatography. For example, the sample loop 120 has any desired volume, for example, a fixed volume of 2, 5, 10, or 20 microliters. The sample pump 160 is any suitable pumping device, including known devices such as a chromatographic metering syringe. Sample material is draw into the first portion of the sample conduit 150A via any suitable interface, such as a needle or capillary.

The separation column 170 includes one or more columns of any suitable type. For example, the process column suitably is a chromatographic column constructed in any suitable manner, including those known to one having ordinary skill in the chromatographic arts.

The process-fluid source 180 delivers a process fluid, such as a mobile phase, through the second portion of the process conduit 140B to the sample loop 120 to inject the sample into the first portion of the process conduit 140A to deliver the sample to the column 170. In one implementation of the system 100, the source 180 includes a solvent pump that delivers a solvent under pressure. The pump is any suitable pump or pumps, such as those known to one having ordinary skill in HPLC. In one illustrative manner of operation of the instrument 100, the sample pump is filled with a weak wash solution. The valve unit 110 is placed in the sample loading state, and the sample pump 160 draws (or pulls) a portion of sample from the sample source 130 into the first portion of the sample conduit 150A. Prior to drawing the sample into the sample conduit 150A, an air gap and/or a buffer solution are optionally drawn into the conduit portion 150A. The sample is then drawn into and through the valve unit 110 and disposed at a location S1 in the second portion of the sample conduit 150B.

The valve unit 110 is switched to the load state, and the sample pump 160 pushes the sample from the location S1 into the sample loop 120

(location S2.) The valve unit 110 is switched to the injecting state, and the process-fluid source 180 pushes the sample from the location S2 in the sample loop 120 to the location S3 in the first portion of the process conduit 140A and then into the separation column 170. The pressure in the process conduit 140A, 140B is generally at the operating pressure of the process-fluid source 180 (approximately 1 ,000 psi or greater for HPLC implementation of the system 100) while the pressure in the first portion of the sample conduit 150A is generally at ambient pressure, for example, at an atmospheric pressure of approximately 14 psi. Thus, generally, when the sample loop 120 is switched by the valve unit 110 from connection to the process-conduit portions 140A, 140B to the sample-conduit portions 150A, 150B, the high pressure in the sample loop 120 drops to the ambient pressure; the pressure drop is generally accommodated mostly by movement (and mixing) of fluid in the first portion of the sample conduit 140A because the second portion 150B is preferably sealed from the ambient environment by the sample pump 160. Disposing at least a portion of the sample at the location S1 thus substantially removes the sample from a location in the sample conduit 150A and/or portions of the valve unit 110 that experience mixing during switching of the valve unit 110.

During processing, an operator of the instrument 100 is free to vary the presence and order of fluids, e.g., air, buffer solutions, sample, etc., that are sequentially drawn into the portions of sample conduit 150A, 150B, as desired. Prior to loading of a next sample, one or both portions of the sample conduit 150A, 150B and portions of the valve unit 110 are optionally cleansed. Cleansing is optionally formed with a weak wash solution known to one having ordinary skill in chromatography. For example, a wash solution is pushed by the sample pump 160 through the second portion of the sample conduit 150B, the valve unit 110, and the first portion of the sample conduit 150A to cleanse a fluidic pathway defined by the three components 150B, 110, 150A.

Some or all of the components, in alternative embodiments, are microfluidic components. For example, such components are optionally constructed in a ceramic-based microfluidic substrate.

FIG. 2 is a flow diagram of a method 200 for processing a fluid, such as for separating sample components of the fluid. The method 200 includes providing 210 a valve unit in fluidic communication with a sample conduit and a sample loop, transferring 220 a sample through both the sample conduit and the valve unit so that at least a leading end of the sample exits the valve unit, transitioning 230 the valve unit to a sample-loading state, and loading 240 at least some of the transferred sample into the sample loop. The method 200 is optionally implemented with the instrument 100 described above or with any other suitable processing equipment.

Preferably, the sample is transferred 220 through the value unit until the trailing end of the sample exits the valve unit. The full sample is available for loading into the sample loop and protected from sample loop decompression effects when the valve unit is transitioned 230 to the sample- loading state.

For HPLC implementations, the method 200 is implemented with any valve suited to HPLC sample injection including known or commercially available valves. One possible detailed implementation of the method 200 is described below with reference to FIGS. 5A to 5E.

FIG. 3 is a flow diagram of a method 300 for processing a fluid, according to a embodiment of the invention related to that illustrated by FIG. 2. The method 300 includes providing 310 a sample conduit having at least two portions, transferring 320 a sample into the second portion of the sample conduit, connecting 330 a pressurized sample loop between the first and second portions of the sample conduit, and loading 340 at least some of the transferred sample into the sample loop. The pressurized sample loop decompresses when connected 330 to the portions of the sample conduit. The method 300 is optionally implemented with the instrument 100 described above or with any other suitable processing equipment. For convenience in the following description of the method, reference is made to components shown in FIG. 1. The first portion of the sample conduit 150A has a first end in fluidic communication with a relatively low-pressure environment, such as an ambient atmospheric environment, and the second portion 150B is substantially sealed from the ambient environment. Connecting 330 occurs by fluidicly connecting each end of the pressurized sample loop 120 to a respective one of the sample-conduit portions 150A, 150B; the sample loop 120 thus depressurizes substantially by displacing a fluid in the first portion of the sample conduit 150A toward an end of the conduit portion 150A that is in communication with the relatively low-pressure environment. The sample is protected from substantial interfacial mixing upon decompression of the sample loop.

Preferably, the sample is transferred 220 through the value unit 110 until the entire sample exits the valve, that is, until the trailing end of the sample exits the valve unit. The full sample it then protected and available for loading.

In one illustrative sample-analysis recipe, prior to aspiration of the sample into the sample conduit 150A, a pre-sample buffer having a volume of, for example, 2.5 microliters is aspirated into the sample conduit 150A. After aspiration of the sample, a post-sample buffer having a volume of, for example, 1.0 microliters is aspirated into the sample conduit 150A. Prior to the pre-sample buffer, an air gap having a volume of, for example, 1.0 microliters is aspirated into the sample conduit. The sample has any suitable volume, and may be over-sampled to assist the complete filing of the sample loop with sample material.

Next referring to FIG. 4 and FIGS. 5A though 5E, some embodiments of the invention, as mentioned above, utilize a 6-port valve. One having ordinary skill will understand that other valves, such as commercially available valves having more than six ports, are usable in alternative embodiments.

FIG. 4 is a two-dimensional diagram of a 6-port valve 410 having six ports P1, P2, P3, P4, P5, P6. The 6-port valve 410 is optionally utilized to implement, for example, the system 100 and the methods 200, 300 described above. For example, the valve 410 is optionally utilized as the valve unit 110 illustrated in FIG. 1. As illustrated in FIG. 4, a first port P1 is in communication with a sample source via a sample-source conduit, a second port P2 is in communication with a sample pump, such as a syringe, via a sample-pump conduit, third and fourth ports P3, P4 are in communication respectively with either end of a sample loop, a fifth port P5 is in communication with a separation column via a column conduit, and a sixth port P6 is in communication with a solvent pump via a solvent-pump conduit.

Next referring to FIGS. 5A to 5E, the valve 410 is used to illustrate the operation of a 6-port or other multi-port valve for processing a fluid according to one example. The location of a sample is indicated in FIGS. 5A through 5E by a dashed line segment. FIGS. 5A to 5E illustrate the movement of a sample relative to the valve 410 during processing, as mediated by the valve 410. As illustrated in FIG. 5A, a sample is drawn in from the sample-source conduit, and admitted to the valve 410 via the first port P1. As illustrated in FIG. 5B, and in contrast to some prior approaches, prior to loading into the sample loop, the sample is drawn through the valve 410 and out of the second port P2 so that the sample is disposed in the sample-pump conduit such that the valve unit 410 is disposed between the sample and the sample-source conduit.

As illustrated in FIG. 5C, the valve 410 is then switched to a sample- loading state such that the sample-pump conduit is fluidicily connected to one end of the sample loop via two ports P2, P4. At this time the other end of the sample loop is connected to the sample-source conduit via two ports P1 , P3. When the transition occurs, pressurized process fluid in the sample loop decompresses, substantially by causing fluid movement along the sample- source conduit.

As illustrated in FIG. 5D, the sample is then pushed by the sample pump from the sample-pump conduit through the ports P2, P4 into the sample loop. After loading, as illustrated in FIG. 5E, the valve 410 is switched back to the sample-injection state. The solvent pump pumps solvent and/or other fluidic components along the solvent-pump conduit into the port P6 and through the sample loop, thus injecting the sample from the sample loop via the port P5 into the column conduit and column.

Returning to FIG. 1, the system 100 optionally includes a control unit that mediates its operation. The control unit - including, for example, a personal computer or workstation - exchanges data and/or control signals via wired and/or wireless communications with, for example, the valve unit 110, the process-fluid source 140, and/or the sample pump 160. The control unit supports, for example, automation of sample analyses. The control unit, 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 control unit is optionally configured to implement the methods 200, 300 described above. In view of the description provided herein, one having ordinary skill in the chromatographic arts will recognize that various embodiments of the invention are not limited to specific features described above. For example, other embodiments of the invention have alternative numbers and/or portions of conduits, more than one valve unit, and/or more than one column.

Some embodiments of the invention relating to HPLC systems provide several advantages over some prior approaches to sample injection. These embodiments provide greater accuracy in sample delivery, with greater preservation of accuracy as sample size is decreased. 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, in some embodiments, a sample entry end of a sample conduit is sealed after aspiration of a sample, such that the sample is sealed from the ambient environment and its associated pressure sink. Some of the these embodiments pressurize the sample conduit to a pressure greater than ambient. Accordingly, the invention is to be defined not by the preceding illustrative description but instead by the spirit and scope of the following claims.

What is claimed is:

Claims

CLAIMS 1. A method for processing a fluid, comprising: providing a valve unit having at least a sample-loading state and a sample-injecting state, the sample-loading state disposing a sample loop in fluidic communication with a sample conduit, and the sample-injecting state disposing the sample loop in fluidic communication with a process conduit; transferring, while the valve unit is in the sample-injecting state, a sample through both the sample conduit and the valve unit so that a leading end of the sample exits the valve unit; transitioning the valve unit to the sample-loading state; and loading at least some of the transferred sample into the sample loop.

2. The method of claim 1 , wherein transitioning the valve unit is associated with decompression of the sample loop from a pressure level of the process conduit to a lower pressure level of the sample conduit.

3. The method of claim 2, wherein the pressure level of the sample conduit is associated with an ambient atmospheric pressure.

4. The method of claim 1 , wherein the decompression of the sample loop is associated with displacement and mixing of fluid in the sample conduit.

5. The method of claim 1 , wherein transferring the sample comprises disposing the leading end of the sample distal to the valve unit and a trailing end of the sample proximal to the valve unit.

6. The method of claim 5, wherein the trailing end of the sample is disposed adjacent to an outlet port of the valve unit.

7. The method of claim 1 , wherein loading comprises pushing the at least some of the sample.

8. The method of claim 1 , further comprising transferring a pre-sample buffer into the sample conduit prior to transferring the sample.

9. The method of claim 1 , wherein the valve unit comprises a six-port injection valve.

10. The method of claim 1 , wherein a first end of the sample conduit is attached to a first port of the valve unit, first and second ends of the sample loop are respectively attached to second and third ports of the valve unit, and a first end of the process conduit is attached to a fourth port of the valve unit.

11. The method of claim 1 , further comprising providing a chromatographic column in fluidic communication with a second end of the process conduit.

12. The method of claim 1 , wherein transferring the sample comprises pulling, by a syringe, the sample through the valve unit.

13. The method of claim 1 , further comprising providing a solvent pump that is in fluidic communication with the sample loop when the valve unit is in the sample-injecting state.

14. The method of claim 1 , wherein the sample loop has a sample-volume capacity in a range of about 2 microliters to about 20 microliters.

15. The method of claim 1 , wherein the sample loop comprises a tube.

16. The method of claim 15, wherein the sample loop comprises a fixed sample loop.

17. A method for processing a sample in a liquid-chromatography system, comprising: providing a sample conduit comprising two portions, the first portion having a first end in fluidic communication with an ambient environment, the second portion having a first end sealed from the ambient environment; transferring the sample into the second portion of the sample conduit; fluidicly connecting a first end of a pressurized sample loop to a second end of the first portion and fluidicly connecting a second end of the pressurized sample loop to a second end of the second portion, thereby permitting the sample loop to depressurize substantially by displacing a fluid in the first portion of the sample conduit toward the first end in fluidic communication with the ambient environment; and loading at least some of the transferred sample into the sample loop.

18. A fluid-processing instrument, comprising: a valve unit having at least a sample-loading state and a sample-injecting state, the sample-loading state disposing a sample loop in fluidic communication with a sample conduit, and the sample-injecting state disposing the sample loop in fluidic communication with a process conduit; and a control unit configured to implement the steps of, transferring, while the valve unit is in the sample-injecting state, a sample through both the sample conduit and the valve unit so that a leading end of the sample exits the valve unit; transitioning the valve unit to the sample-loading state; and loading at least some of the transferred sample into the sample loop.

19. The instrument of claim 18, wherein transferring the sample comprises disposing the leading end of the sample distal to the valve unit and a trailing end of the sample proximal to the valve unit.

20. The instrument of claim 18, further comprising a chromatographic column in fluidic communication with the process conduit.

21. The instrument of claim 18, further comprising a syringe in fluidic communication with the valve unit, wherein transferring the sample comprises pulling, by the syringe, the sample through the valve unit.