Sample Injector With Metering Device Balancing Pressure Differences In An Intermediate Valve State

Abstract

A sample injector for use in a fluid separation system for separating compounds of a fluidic sample in a mobile phase, the sample injector comprising a switchable valve, a sample loop in fluid communication with the valve and configured for receiving the fluidic sample, a metering device in fluid communication with the sample loop and configured for introducing a metered amount of the fluidic sample on the sample loop, and a control unit configured for controlling switching of the valve to transfer the sample loop between a low pressure state and a high pressure state via an intermediate state and for controlling the metering device during the intermediate state to at least partially equilibrate a pressure difference in the sample loop between the low pressure state and the high pressure state.

Claims

1. A method of injecting a sample volume into a chromatography column of a chromatography system, the chromatography system comprising: a sample loop in fluid communication with an injection valve, wherein the sample loop comprises a sample conveying device for loading the sample volume in the sample loop, wherein the sample conveying device comprises a pump volume structure and a moveable element, wherein the moveable element is guidable within the pump volume structure; and a high-pressure fluidic path in fluid communication with the chromatography column and a high-pressure pump, wherein the method comprising: flowing an eluent into the high-pressure fluidic path at a pump pressure generated by the high-pressure pump; isolating the sample loop from the high-pressure fluidic path, wherein the isolating of the sample loop comprises placing the injection valve in a PRESSURE COMPENSATION position; while the sample loop is isolated from the high-pressure fluidic path, sucking the sample volume into the sample loop from a sample vial by moving the moveable element with a stepping motor relative to the pump volume structure; while the sample volume is loaded into the sample loop, and while the sample loop is isolated from the high-pressure fluidic path, moving the moveable element relative to the pump volume structure, a predetermined first distance, wherein the predetermined first distance is based at least in part upon a compressibility of the eluent in the sample loop and the pump pressure; while the compressed sample volume is compressed to the high pressure, connecting the sample loop to the high-pressure fluidic path; and while the compressed sample volume is compressed to the high pressure, conveying the compressed sample volume from the sample loop to the chromatography column.

2. The method of claim 1, wherein the sample loop includes a first connecting piece and a second connecting piece, wherein the first connecting piece is connected to a first sample loop port of the injection valve and to the sample conveying device, wherein the second connecting piece is connected to a second sample loop port of the injection valve and to the sample conveying device, wherein the second connecting piece includes an intake segment and a feed segment, wherein the intake segment and the feed segment are configured to be separated.

3. The method of claim 1, wherein in the PRESSURE COMPENSATION position, i) first and second sample loop ports of the injection valve are closed so as to facilitate a pressurization of the sample loop, and ii) first and second high-pressure ports of the injection valve are connected so as to operatively connect the high-pressure pump in fluid communication with the high-pressure fluidic path to the chromatography column, the method further comprising: determining the compressibility of the eluent with the high-pressure pump.

4. The method of claim 1 further including: after the compressed sample volume has been conveyed from the sample loop to the chromatography column, isolating the sample loop from the high-pressure fluidic path; and while the sample loop is isolated from the high-pressure fluidic path, moving the moveable element relative to the pump volume structure, a predetermined second distance, to thereby decompress the sample loop to a pressure that essentially corresponds to an atmospheric pressure.

5. The method of claim 1, wherein the moveable element is connected to the stepping motor which is operable to move the moveable element within the pump volume structure, and the method further comprises: measuring a force exerted upon the moveable element by the stepping motor.

6. The method of claim 1, wherein the compressibility of the eluent and an elasticity of the sample loop are stored for use by the chromatography system.

7. The method of claim 1, wherein the pump volume structure comprises a syringe and the moveable element comprises a plunger.

8. The method of claim 1, wherein the sample volume comprises the eluent, wherein the predetermined first distance is also based at least in part upon an elasticity of the sample loop.

9. The method of claim 1, wherein the stepping motor comprises an integrated sensor measuring a force applied by the stepping motor on the moveable element.

10. The method of claim 1 further comprising: after the compressed sample volume has been conveyed from the sample loop to the chromatography column, isolating the sample loop from the high-pressure fluidic path; and while the sample loop is isolated from the high-pressure fluidic path, moving the moveable element relative to the pump volume structure, a predetermined second distance, wherein the predetermined second distance is based at least in part upon a compressibility of an eluent in the sample loop, to thereby decompress the sample loop to a pressure that essentially corresponds to an atmospheric pressure.

11. The method of claim 10, wherein the predetermined second distance is also based at least in part upon the pump pressure.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0058] Other objects and many of the attendant advantages of embodiments of the present invention will be readily appreciated and become better understood by reference to the following more detailed description of embodiments in connection with the accompanied drawing(s). Features that are substantially or functionally equal or similar will be referred to by the same reference sign(s).

[0059] FIG. 1 shows a liquid separation system, in accordance with embodiments of the present invention, for instance used in high performance liquid chromatography (HPLC).

[0060] FIG. 2 to FIG. 4 shows an exemplary embodiment of a sample injector according to the present invention in different operation modes.

[0061] FIG. 5 to FIG. 9 shows another exemplary embodiment of a sample injector according to the present invention in different operation modes.

[0062] Referring now in greater detail to the drawings, FIG. 1 depicts a general schematic of a liquid separation system 10. A pump 20 receives a mobile phase from a solvent supply 25, typically via a degasser 27, which degases and thus reduces the amount of dissolved gases in the mobile phase. The pump 20—as a mobile phase drive—drives the mobile phase through a separating device 30 (such as a chromatographic column) comprising a stationary phase. A sampling unit 40 (compare the detailed description of FIG. 2 to FIG. 9) can be provided between the pump 20 and the separating device 30 in order to subject or add (often referred to as sample introduction) a sample fluid into the mobile phase. The stationary phase of the separating device 30 is adapted for separating compounds of the sample liquid. A detector 50 is provided for detecting separated compounds of the sample fluid. A fractionating unit 60 can be provided for outputting separated compounds of sample fluid.

[0063] While the mobile phase can be comprised of one solvent only, it may also be mixed from plural solvents. Such mixing might be a low pressure mixing and provided upstream of the pump 20, so that the pump 20 already receives and pumps the mixed solvents as the mobile phase. Alternatively, the pump 20 might be comprised of plural individual pumping units, with plural of the pumping units each receiving and pumping a different solvent or mixture, so that the mixing of the mobile phase (as received by the separating device 30) occurs at high pressure and downstream of the pump 20 (or as part thereof). The composition (mixture) of the mobile phase may be kept constant over time, the so called isocratic mode, or varied over time, the so called gradient mode.

[0064] A data processing unit 70, which can be a conventional PC or workstation, might be coupled (as indicated by the dotted arrows) to one or more of the devices in the liquid separation system 10 in order to receive information and/or control operation. For example, the data processing unit 70 might control operation of the pump 20 (for instance setting control parameters) and receive therefrom information regarding the actual working conditions (such as output pressure, flow rate, etc. at an outlet of the pump). The data processing unit 70 might also control operation of the solvent supply 25 (for instance setting the solvent/s or solvent mixture to be supplied) and/or the degasser 27 (for instance setting control parameters such as vacuum level) and might receive therefrom information regarding the actual working conditions (such as solvent composition supplied over time, flow rate, vacuum level, etc.). The data processing unit 70 might further control operation of the sampling unit 40 (for instance controlling sample injection or synchronization sample injection with operating conditions of the pump 20). The separating device 30 might also be controlled by the data processing unit 70 (for instance selecting a specific flow path or column, setting operation temperature, etc.), and send—in return—information (for instance operating conditions) to the data processing unit 70. Accordingly, the detector 50 might be controlled by the data processing unit 70 (for instance with respect to spectral or wavelength settings, setting time constants, start/stop data acquisition), and send information (for instance about the detected sample compounds) to the data processing unit 70. The data processing unit 70 might also control operation of the fractionating unit 60 (for instance in conjunction with data received from the detector 50) and provides data back.

[0065] Reference numeral 90 schematically illustrates a switchable valve which is controllable for selectively enabling or disabling specific fluidic paths within apparatus 10.

[0066] In the following, referring to FIG. 2, a sample injector 200 for use in a fluid separation system 10 as described in FIG. 1 for separating components of a fluidic sample in a mobile phase according to an exemplary embodiment of the invention will be explained.

[0067] The sample injector 200 comprises a switchable valve 202 (which corresponds to reference numeral 90 in FIG. 1), a sample loop 204 in fluid communication with the valve 202 and configured for receiving the fluidic sample from a vial 230, a metering pump 206 in fluid communication with the sample loop 204 and configured for introducing a metered amount of the fluidic sample on the sample loop 204, and a control unit 208 (such as a microprocessor or a central processing unit, CPU) configured for controlling switching of the valve 202 to transfer the sample loop 204 between a low pressure state and a high pressure state via an intermediate state, as will be described below in further detail. Control unit 208 is further adapted for controlling the metering device 206 to at least partially equilibrate, during the intermediate state, a pressure difference in the sample loop 204 between the low pressure state and the high pressure state. Thus, the metering device 206 (metering pump) is configured to generate a high pressure (in opposite to conventional syringe pumps). This metering device 206 is arranged within the split loop 204. The split loop 204 can be compressed. The precompression may be performed up to a system pressure of the pump 20.

[0068] As can be derived from FIG. 2 to FIG. 4, the switchable valve 202 comprises two valve members which are rotatable with respect to one another. By rotating these two valve members along a rotation axis which is perpendicular to the paper plane of FIG. 2, a plurality of ports 216 formed in one of the valve members and a plurality of oblong arcuate grooves 218 formed in the other one of the valve members can be selectively brought in or out of fluid communication with one another. Since the various ports 216 are connected to dedicated ones of fluidic channels of the fluidic system as shown in FIG. 2, automatically switching the valve 202 under control of the control unit 208 may allow to operate the fluidic system 10 in different fluid communication configurations. The valve 202 is configured as a six port high pressure valve in the embodiment of FIG. 2.

[0069] Fluid communication between the high pressure pump 20 and the separation column 30 can be accomplished by an according switching state of the valve 202. In such a fluidic path, a high pressure of for instance 100 MPa may be present which may be generated by the high pressure pump 20. In contrast to this, the pressure state in the sample loop 204 may be for instance smaller than 0.1 MPa when introducing a sample into the sample loop 204. When this sample loaded on sample loop 204 is to be loaded on column 30, the pressure in sample loop 204 is also high, for instance 100 MPa.

[0070] For the purpose of loading the sample on the sample loop 204, a needle 224 may be driven out of a correspondingly shaped seat 226 using a drive 228 so that the needle 224 can be immersed into vial 230 accommodating a fluidic sample to be loaded onto the sample loop 204. A loop capillary 240 is provided in the sample loop 204 for at least partially accommodating the introduced sample.

[0071] In a further operation mode, the needle 224 may be immersed in a flush port 232. Waste containers 234, 236 may be provided for receiving a waste fluid which can be pumped through the fluidic channels shown in FIG. 2. Furthermore, for flushing the fluidic system 200, fluid from a flush solvent vial 238 may be sucked by a peristaltic pump 250 and may be pumped through corresponding channels of the fluidic system shown in FIG. 2.

[0072] The metering device 206 is configured as a high pressure metering device, i.e. as a metering device which is capable of providing a pressure of up to 100 MPa in the sample loop 204 by correspondingly moving a reciprocating piston 210 of the high pressure metering device 206.

[0073] Before describing further details of the sample injector 200, some basic recognitions of the present inventors will be summarized based on which exemplary embodiments of the invention have been developed.

[0074] According to an exemplary embodiment, flow perturbances may be reduced and component lifetime of a HPLC autosampler may be increased by a precompression and/or decompression of its loop volume.

[0075] HPLC injection system used for pressures above 60 MPa (for instance 120 MPa) are conventionally faced with various problems. The volume within the split loop (in the embodiment of FIG. 2, the split loop includes particularly high pressure metering device 206, loop capillary 240, needle 224, needle seat 226, seat capillary 270) may be exposed to very high pressures in a main pass position which is illustrated in FIG. 2. Since liquids (mobile phase and sample) under such high pressures are no longer incompressible, this loop volume is being compressed.

[0076] Furthermore, switching the injector valve 202 to a bypass position as shown in FIG. 4 conventionally leads to a very fast decompression of the loop volume because it gets connected to atmospheric pressure suddenly. This fast decompression generates a strong acceleration of the liquid which passes with high flow rates through the channels of the injector valve 202. This high flow rate (also called “water jetting”) may cause delamination of a coating on the valve stator due to cavitation and erosion on the polymeric valve rotor seal.

[0077] On the other hand does the pump 20 deliver flow while the valve 202 switches to a main pass mode shown in FIG. 2. During this time, the valve channel is getting deconnected from the pump 20. The pump 20 is pumping against the closed channel which results in a pressure increase.

[0078] At the same time the column 30 gets deconnected from the pump 20 and flow is no longer delivered on top of the column 30. Concurrently the system after the column 30 is open and via detector cell connected to an atmospheric pressure. This may also cause the column pressure to decrease.

[0079] The above-mentioned problems of conventional systems which may be overcome by the embodiments shown in FIG. 2 to FIG. 9 have different consequences. Firstly, the jet stream generated during decompression causes damage on rotor seal and stator of the valve 202. This may result in a reduced valve lifetime. Switching the valve 202 furthermore causes pressure/flow disturbances (perturbances) like pressure peaks. This may lead to precision problems of flow rates, etc. The closed valve 202 causes the column pressure to drop. The reconnected valve 202 on the other hand forwards the flow generated by the pump 20 via split loop to the column 30. The pressure may be at reduced level. However, at the beginning of this operation, the column pressure may be still higher as the split loop pressure. In that case there is a possibility for a reverse flow to develop. After this, the pressure starts equilibrating and the pump 20 delivers a positive flow towards the column 30. The pressure peaks and the reverse flow may conventionally reduce the lifetime of a column 30.

[0080] Exemplary embodiments of the invention, for instance the systems described in FIG. 2 to FIG. 9 may overcome these conventional problems by taking particularly the measures explained in the following. In order to reduce the observed effects, a modified valve 202 and modified operation procedures are provided. The modified valve 202 has flow channels which are different in length (compare different lengths of the arcuate sections of the grooves 218 in FIG. 2) and the modified operations include stops to provide an intermediate valve state in an inclined position (compare FIG. 3).

[0081] By clockwise turning the valve 202 from main pass (or start/inject) position as shown in FIG. 2, the column 30 is connected to the pump 20 via the split loop or sample loop 204. At the inclined position (pre/decompression mode as shown in FIG. 3), column 30 is connected directly to the pump 20. In this inclined position, the split loop (i.e. loop capillary 240 plus metering device 206 plus needle 224 plus seat capillary 270) is now isolated from the pump 20 and the column 30 but is still under high pressure. In order to reduce that high pressure, piston 210 of the metering device 206 can be drawn back a controlled amount for instance until the loop pressure equals atmospheric pressure. For instance, this can be done by using a metering device as disclosed for instance in EP 0,327,658 B1, U.S. Pat. No. 4,939,943 which allows high pressure applications.

[0082] With the loop pressure being brought close to atmospheric pressure, the valve 202 can be again turned clockwise to its bypass position which is shown in FIG. 4. This bypass position may also be denoted as a load position. Since there is no pressure gradient between the internal loop pressure and the atmospheric pressure, no water jetting can develop. Therefore, both the delamination of the stator coating and the erosion of the polymer rotor may be eliminated or at least suppressed. The result is an increased lifetime of the valve 202 and of the entire sampling unit 200.

[0083] The valve 202 is in the bypass or load position in FIG. 4, and the autosampler is ready to take a sample from vial 230. In a first procedure, the needle 224 may be lifted and moved into the sample vial 230 or a well position (for instance of a multi-well plate). Now, the piston 210 of the metering device 206 may be drawn back to a controlled preset amount (for instance 2 .mu.l). Next, the needle 224 is seated in its seat 226, and the split loop 204 is closed thereby.

[0084] The valve 202 is then turned counterclockwise to the inclined position shown in FIG. 3 where the pump 20 is still connected to the column 30. The split loop 204 is closed on both ends. If now the piston 210 of the metering device 206 is moved forward in a controlled manner, its displacement generates a positive pressure and precompresses the trapped volume. This pressure, potentially sensed by a pressure sensor 220, is being increased until it equals the system pressure.

[0085] This is the trigger to turn the valve 202 completely to the main pass position which is illustrated in FIG. 2. Because the pressure of the system and the split loop 204 are equal at beginning of this operation, there will be only a very small pressure drop causing only minimum flow disturbances. The pump 20 delivers the mobile phase through the split loop 204 and pushes the sample onto the column 30 where the chromatographical separation of the sample may start.

[0086] Hence, FIG. 2 to FIG. 4 show schematically three positions of the injection valve 202 of the autosampler 200 within HPLC system 10 during the injection cycle.

[0087] In the main pass position shown in FIG. 2, a start or inject position is shown where the rotor seal flow channels connect pump 20 with the split loop 204 and the seat capillary of the split loop 204 with the separation column 30.

[0088] In the inclined position shown in FIG. 3, the split loop volume gets decompressed or precompressed.

[0089] In the bypass position shown in FIG. 4, the flow channels of the rotor seal connect the pump 20 directly to the separation column 30 and the split loop 204 to the waste outlet 236.

[0090] Next, referring to FIG. 5 to FIG. 9, a sample injector 500 in a liquid chromatography system 10 according to another embodiment of the invention will be explained.

[0091] FIG. 5 illustrates a load or bypass position, FIG. 6 illustrates a precompress position and FIG. 7 illustrates an inject position (or main pass position) of the sample injector 500.

[0092] A main difference between the sample injector 500 and the sample injector 200 is the arrangement of the valve 502 which in an embodiment of FIG. 5 to FIG. 9 is configured as a multi-position/seven port high pressure valve.

[0093] Furthermore, in the embodiment of FIG. 5 to FIG. 9, three different flush solvent vials 238 are provided and three different flush ports 232 are provided. Selection between three flush channels A, B and C can be performed by correspondingly switching a low pressure selection valve 504. Furthermore, a low pressure flush pump 506 is provided for performing the flushing performance.

[0094] The multi-position valve 502 is provided for additionally precompressing, pump priming and pressure testing. All drawn sample gets injected. Additional flush pump 506 may be for instance a syringe pump from the company Tecan. Such an additional flush pump 506 may allow flushing of the sample loop 204 using the three flush ports A, B, C (for instance two organic flush ports and one water flush port).

[0095] FIG. 8 illustrates the system of FIG. 5 to FIG. 7 in a prime pump position, and FIG. 9 illustrates the system 500 in a pressure test position.

[0096] It should be noted that the term “comprising” does not exclude other elements or features and the “a” or “an” does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims shall not be construed as limiting the scope of the claims.