Abstract:
The present invention is a pressurized fluid sample injector system consisting of a sample needle, multiport valve, sample loop, metering syringe and a pressure assist pump. The speed of sample transport into the sample loop is increased by pressurizing the fluid in the system and metering the sample into the sample loop. The elevated system pressure allows the fluids to be moved faster than the vapor pressure would normally allow in a system at ambient pressure.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of U.S. application Ser. No. 11/072,906, filed Mar. 4, 2005, which is a continuation of PCT/US03/28249, designating the U.S. and filed Sep. 10, 2003, which claims benefit of U.S. Provisional Application No. 60/409,836, filed Sep. 11, 2002. The entire contents of these applications are incorporated herein by reference. 
     
    
     STATEMENT ON FEDERALLY SPONSORED RESEARCH  
       [0002]     N/A  
       FIELD OF THE INVENTION  
       [0003]     The present invention relates to sample handling and injection systems and in particular to apparatus and methods for increasing the speed of the injection cycle.  
       BACKGROUND OF THE INVENTION  
       [0004]     In one form of liquid chromatography sample injection, a sample is drawn into a needle or capillary and then loaded into a sample loop by pulling the fluid through the needle and any associated tubes into the sample loop. After the sample is in the sample loop, the sample loop is connected to an injection mechanism, such as a pump/detector system, that pushes the sample through a liquid chromatography column where a separation takes place. The sample can be pulled through the system of tubes at a flow rate that is directly related to the vapor pressure of the fluid. If the fluid is drawn through the tubing too quickly, the fluid can vaporize and cause undesirable results in sample integrity as well as sample positioning within the sample loop. This phenomenon forces the sample loading flow rate to remain below the flow rate that will cause vaporization. In most cases this limitation means that sample loading is a significant portion of the overall sample injection cycle time. With screening processes requiring many sample injection cycles, there is impetus to reduce the sample injection cycle. One way to reduce the sample injection cycle, is to speed up the sample loading process.  
       SUMMARY OF THE INVENTION  
       [0005]     In the present invention, sample loading speed is increased significantly by pressurizing the fluid system, thus avoiding vaporization of the fluid. This process allows the sample to be transported through the system faster than in a system that draws the sample into a sample loop without utilizing an elevated pressure. Ultimately, the faster sample loading time reduces the overall cycle time between sample injections.  
         [0006]     The invention embodies a pressurized sample injector system, which utilizes elevated pressure to aid sample delivery to a sample loop. In one embodiment, the sample loop is connected across a multiport valve that allows the sample loop to be alternately connected to the sample loading mechanism and the separation mechanism. The sample loading mechanism consists of an aspirating needle, which has already aspirated a sample from a container, that is sealed to a pressure vessel for the loading operation. The aspirating needle is connected to one side of the sample loop through the multiport valve. A metering syringe is connected to the other side of the sample loop through the multiport valve. After the aspirating needle is sealed in the pressure vessel, a pressure assist pump is substantially sealed to the pressure vessel creating a substantially sealed path through the pressure assist pump, the sample loop and the metering syringe.  
         [0007]     With the multiport valve in a first position, a sample is aspirated from a container holding the sample into the sample needle. The needle tip is then connected to the pressure vessel and the pressure assist pump and the fluid path is pressurized. The sample is transported from the aspirating needle to the sample loop by creating a pressure differential across the path from the pressure vessel to the metering syringe. After the multiport valve is moved to a second position, the sample is moved from the sample loop to an analytical column by a gradient pump. The second position of the multiport valve disconnects the metering syringe and the aspirating needle from the sample loop and connects the aspirating needle directly to the metering syringe allowing wash cycle(s) to cleanse the flow path while the injection and separation are proceeding.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The above noted and other features of the invention will be better understood from the following detailed description, when considered in connection with the accompanying drawings, in which:  
         [0009]      FIG. 1  depicts part of the apparatus;  
         [0010]      FIG. 2  depicts the steps of sample aspiration;  
         [0011]      FIG. 3  depicts one embodiment of the apparatus during pressurization;  
         [0012]      FIG. 4  depicts the pressurization of a sample;  
         [0013]      FIG. 5A  depicts the apparatus during metering;  
         [0014]      FIG. 5B  depicts a partial loop sample in the sample loop after metering;  
         [0015]      FIG. 5C  depicts a full loop sample with overfill in the sample loop after metering; and  
         [0016]      FIG. 6  depicts one embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0017]     The numerous teachings of the present application will be described with particular reference to the presently preferred embodiment. However, it should be understood that these embodiments provide only a few examples of the advantageous uses of the teachings herein. In general, statements made in the specification of the present application do not necessarily delimit any of the various claimed inventions. It will be obvious to those skilled in the art that various modifications can be made without departing from the spirit and scope of this invention.  
         [0018]     In  FIG. 1 a  simplified method of moving a sample quickly is illustrated. A quantity of sample  10  is held in a container  12 . A first end of an aspirating needle  14  is in fluid communication with a first end of a sample loop  18  and the second end of the sample loop  18  is in fluid communication with a metering syringe  20 . The fluid path from the needle  14  to the syringe  20  is filled with a solute. A second end of the aspirating needle  14  is placed in the sample  10  through a seal  7  that allows the sample  10  to be held under pressure. Once the sample is pressurized, the entire fluid path from the sample  10  to the metering syringe  20  is under pressure.  
         [0019]     When the plunger of the metering syringe  20  is pulled back, a pressure differential is established between the metering syringe  20  and the sample  10  which transports the sample liquid through the needle  14  and into the sample loop more swiftly than in a fluidic system that is not under pressure.  
         [0020]     In the system as depicted in  FIG. 1 , there is frequently the need to conserve sample  10  rather than fill the entire fluid path with sample  10 . In these cases, after the sample  10  is aspired into the aspirating needle  14 , the needle is lifted from the sample  10  and placed in a pressurized bath of fluid (not shown). The fluid then brackets the sample within the fluid path as the sample is loaded into the sample loop  18 . The system must adjust the amount of sample used to account for the fact that the fluid and the sample mix at the interface between fluids, but this technique does save sample over the method that fills the entire fluid path with sample.  
         [0021]     When the needle is moved between successive sealed baths of fluid, the device of  FIG. 1  is useful for loading a sequence of fluids into a lengthy loop. However, the handling of the samples could be simplified, the concentration of the samples can be made consistent and the amount of sample used can be minimized using air gaps between samples and by connecting the sample loop across the ports of a suitably configured multiport valve.  
         [0022]     As shown in the embodiment depicted in  FIG. 2 , in order to minimize dilution of the aspirated metered sample  11 , the metered sample  11  is typically bracketed by air gaps within the aspirating needle. The aspirating needle starts filled with fluid  9  and, as shown in  FIG. 2A , before aspiration the metering syringe (not shown) is drawn back to pull in a volume of air  13  at the tip of the aspirating needle  14 . At  2 B, the aspirating needle  14  is placed into the sample  10  and the metering syringe is further pulled back a metered amount which draws a predetermined metered sample portion  11  into the aspirating needle  14 . In one embodiment shown at  2 C, the aspirating needle  14  is then lifted from the sample  10  and a post-sample air gap  15  is drawn into the aspirating needle  14  by the metering syringe.  
         [0023]      FIG. 3  depicts an embodiment of the invention showing pressurization of the metered sample  11  while in the aspirating needle  14  and the use of a multiport valve  16 . The apparatus is shown after aspiration of the metered sample  11 . The aspirating needle  14  containing the metered sample  11  is placed in a pressurized fluid  28  held in a pressure vessel  42  adapted for this purpose. The aspirating needle  14  is sealed to the pressure vessel  42  by seal  32 . A pressure assist pump  30  is in fluid communication with the pressure vessel  42  to pressurized fluid  28 . With the aspirating needle in the pressurized fluid  28 , the entire sample path from the pressurized fluid  28 , through the aspirating needle  14 , the sample loop  18  and to the metering syringe  20  is pressurized. All of the connections of the present invention substantially seal the sample path from ambient pressure. A relief flow means  36  may be used in conjunction with the pressure assist pump to further regulate the pressure on the pressurized fluid  28 . A pressure monitor  38  may be connected to the pressurized fluid line for diagnostic and/or control purposes.  
         [0024]      FIG. 4  depicts the metered sample  11 , bracketed by air gaps, being pressurized in the aspirating needle  14  before being transported under pressure to the sample loop  18 . In one embodiment, the aspirating needle  14  is sealed to the pressure vessel  42  by an O-ring  32 . A lip seal or any other means for substantially sealing the aspirating needle  14  to the pressure vessel  42  is appropriate. As the pressure on the pressurized fluid  28  increases, the air gaps  13 ,  15  are compressed and a quantity  17  of the pressurized fluid  28  is drawn into the aspirating needle  14 .  
         [0025]     The multiport valve  16  has two positions: in the first position (illustrated in  FIG. 3 ) ports one and three, two and four, and five and six are fluidically connected; in the second position, ports one and two, three and five and four and six are fluidically connected. In one embodiment, the aspirating needle  14  is connected to the first port  1 . The sample loop  18  is connected across the multiport valve  16  utilizing ports  3  and  4 . The metering syringe  20  is connected to the multiport valve  16  at port  2 . In many embodiments, a gradient pump (not shown) is connected to the multiport valve  16  at port  5  and an analytical column (not shown) is connected to the multiport valve  16  at port  6 . The multiport valve is adapted to operate up to the pressures being provided by the pressure assist pump and/or the gradient pump. When the multiport valve is in the first position as shown in  FIG. 3 , the gradient pump and column are maintained in fluid communication by the multiport valve  16  and the aspirating needle  14 , sample loop  18  and metering syringe  20  are maintained in fluid communication by the multiport valve  16 . The first position is also used to draw the metered sample  11  into the aspirating needle  14  before the transport operation depicted by  FIG. 3 . In the second position (not shown), the multiport valve  16  maintains the gradient pump, sample loop  18  and analytic column in one fluidic path, while the aspirating needle  14  and metering syringe  20  are maintained in fluid communication in a separate fluidic path. This position allows the gradient pump to push the metered sample  11  from the sample loop  18  onto the analytic column while the rest of the device undergoes a cleaning operation.  
         [0026]     The metering syringe  20  is for drawing a metered amount of fluid through the sample path. The metering syringe  20  functions by creating a vacuum in the syringe. The vacuum creates a pressure differential between the aspirating needle  14  and the metering syringe  20  that pulls fluid toward the syringe. By controlling the volume of fluid pulled into the syringe  20 , the device controls how far the leading edge of the metered sample  11  moves along the sample path. The metering syringe  20  can be any pump operating on this principle.  
         [0027]     Multiport valves having different numbers of ports may be utilized in the device. For instance, a four port valve with two positions could be used to draw the metered sample into a sample loop in one position and isolate the sample loop in the second position. Sample loops so filled could be disconnected and retained for further processing. Control means to position the aspirating needle, control the multiport valve and position the metering syringe are needed to coordinate the components.  
         [0028]     In a preferred embodiment shown in  FIG. 5A , the pressure assist pump  30  is a wash syringe  34 , which may also be used to supply wash fluid for cleansing the sample path. In  FIG. 5A , the metering syringe  20  is drawn back creating a pressure differential across the sample path. When the metering syringe  20  is drawn back a calibrated distance, the metered sample  11  is positioned in the sample loop  18 , and fluid from the pressurized fluid  28  fills the remainder of the sample path behind the metered sample  11 . Since the wash syringe  34  is sealed to the fluid path and has maintained the pressure on the pressurized fluid  28 , the metered sample  11  experiences little pressure variation and does not vaporize. Therefore, the metered sample  11  can be moved rapidly into the sample loop  18 .  
         [0029]      FIG. 5B  illustrates a partial loop placement used to position the metered sample  11  in the sample loop  18  when very small quantities of sample  10  are available. Here the sample loop  18  extends from port  3  to port  4  of the multiport valve  16  and the metered sample  11  is centered in the loop  18 . When the metered sample  11  does not fill the sample loop  18 , the remainder of the sample loop  18  is occupied by transport fluids  17 ,  9  and the air gaps  13 ,  15 . Centering the metered sample  11  in a partial loop placement is preferred, but satisfactory result will be obtained as long as the entire metered sample  11  is brought into the sample loop  18 . Partial loop placement can assure that a known quantity of sample  10  is used, but the sample will be diluted by the transport fluids in the sample loop  18  and the quantity of air in the air gaps is transferred to the analytical column. Small air gaps are required for partial loop placements to minimize the effects of the air on the analytical column.  
         [0030]     When sufficient sample  10  is available, the metered sample  11  is positioned using a “full loop with over fill” as illustrated in  FIG. 5   c.  Here, more sample  10  than can be held by the sample loop  18  is drawn into the aspirating needle  14 . In one embodiment, when the metering syringe  20  is drawn back, it positions the metered sample  11  centered in the sample loop  18 . Because the loop is overfilled, the metered sample  11  not only fills the sample loop  18  but also extends past the sample loop ports  3 ,  4 , and usually past the connection port  1  for the aspirating needle  14  and the connection port  2  for the metering syringe  20 . This positioning places the air gaps  13 ,  15  well beyond the sample loop  18 . The advantage of the full loop with over fill is that it assures that a known quantity of full strength sample is injected into the analytical column from the sample loop  18  during the loading phase of the cycle.  
         [0031]     In a second embodiment of the full loop with overflow, the metered sample  11  is not centered but rather is positioned with the trailing air gap  15  just before sample loop port  3 . This embodiment takes account of the fact that sample near the leading air gap  13  may become diluted due to dispersion. Consistent concentration of sample is optimized by minimizing the amount of possibly diluted sample near the leading air gap  13  that is positioned in the sample loop  18 , and maximizing the amount of concentrated sample near the trailing air gap  17  positioned in the sample loop  18 .  
         [0032]     Since the metered sample  11  is pressurized within the sample path, the metered sample  11  does not vaporize when it is transported into the sample loop  18 . Determination of the pressurization level for optimum performance takes the viscosity of the sample and other fluids, the desired positioning speed and the internal diameters (ID) of the sample needle, the interconnecting tubing, the multiport valve, and the metering syringe into account. As an example, in one instance using the parameters listed in Table 1, sample movement speeds of 600-2000 μL/min were attained. This system exhibited a sample load time up to 10 times greater than could be achieved without pressurization. Pressures beyond 150 psig can be used, but the unpressurized air gap size must be increased significantly creating an undesirable effect on cycle time.  
                           TABLE 1                                       Sample, fluid filler   50% Methyl Alcohol (MeOH) and 50%           and wash fluid   Water (H 2 0)           Valve ID   0.006 in           loop ID   0.016 in           aspirating needle ID   0.010 in           sample sizes   1 μL and 5 μL           pressure   150 psig           interconnecting tubing   none                      
 
         [0033]     In the preferred embodiment depicted in  FIG. 6 , the apparatus is set up to operate in a cycle having two phases: one phase transports the metered sample  11  into the sample loop  18  and the second phase cleans the fluid path while the metered sample  11  is being pushed through the analytical column. The cleaning mechanism shown in the figure is representative only, as cleaning technology is well known in the art. A wash syringe pump is used to pressurize the fluid path during the sample transport phase of the cycle. The wash syringe  34 , acting as the pressure assist pump  30 , maintains a wash block  42 , functioning as the pressure vessel, at the desired pressure. A pressure regulating vent  40  is used to maintain a substantially constant pressure while the aspirating needle  14  is in the wash block  42 . The wash block  42  is constructed so that excess fluid from the pressure regulating vent and the upper portion of a sealed chamber  29  is directed to a collection area  33  that drains into a waste container  41 .  
         [0034]     Once the metered sample  11  has been aspirated into the aspirating needle  14 , the aspirating needle  14  is inserted in the O-ring  32  of the wash block  42  and the volume of fluid between the metering syringe  20  and the pressure assist pump  30  is pressurized to assist sample movement. Valve  44 , at the head of the metering syringe  20 , is set to provide connection between the multiport valve  16  and the metering syringe  20  during this part of the cycle. Pressure is created in the system by dispensing fluid from the pressure assist pump  30 , here the wash syringe  34 , and is held constant by the pressure regulating vent  40 . With the system at the operating pressure, the metering syringe  20  meters back a pre-determined volume in order to transport the metered sample  11  from the the aspirating needle  14  into the sample loop  18 . After the sample is positioned in the sample loop  18 , the multiport valve  16  is actuated and the sample in the sample loop  18  is connected to the gradient pump and analytical column for injection into the analytical column.  
         [0035]     Once the sample loop  18  has been removed from the fluid path, the apparatus changes to the cleaning phase. The aspirating needle  14  is withdrawn from the O-ring  32  and held above the collection area  33 . Valve  46  changes state to allow the wash syringe to be recharged from a wash reservoir  48 . Valve  44  changes state to allow wash fluid to be supplied from wash reservoir  48  to the line connected to multiport valve port  2 , through the multiport valve  16  to the aspirating needle  14  where it is flushed into the waste  41 . Typically, there is sufficient time to run a number of cycles of cleaning fluid through the fluidic path before the sample loop is reconnected to the apparatus.  
         [0036]     The invention allows a sample to be transported into a sample loop in significantly less time than it takes at atmospheric pressure, where transport speed is constrained by the vapor pressure of the fluids transported. Sample positioning accuracy is also improved over other chromatography systems as well. While the above is a description of specific embodiments of the present invention, modifications, alternatives and equivalents may be used while remaining within the scope and spirit of the following claims. Additionally, although the preferred embodiment has been illustrated and described, it will be obvious to those skilled in the art that various modifications can be made without departing from the spirit and scope of this invention. Such modifications are to be considered as included in the following claims unless the claims expressly recite differently.