Abstract:
Disclosed is a liquid chromatograph provided with: a first flow path switching means which switches between connection of a sample storage loop to a mobile phase flow path and separation of the sample storage loop from the mobile phase flow path; a needle which suctions and discharges a sample; a weighing means which performs suction and discharge of the sample to the needle while weighing the sample; a cleaning solution feeding means which feeds a cleaning solution; a second flow path switching means which switches between at least two types of cleaning solutions; a third flow path switching means which switches between connection of the needle and the weighing means and connection of the needle and the cleaning solution feeding means; and a control means which controls operation of the first flow path switching means, the weighing means, the cleaning solution feeding means, the second flow path switching means, and the third flow path switching means, wherein the total amount of the sample is injected into the sample storage loop and the cleaning solution is injected into a flow path from the sample storage loop to a sample inlet.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a liquid chromatograph, a sample introduction device for a liquid chromatograph, and a method for cleaning a sample introduction device for a liquid chromatograph. 
       BACKGROUND ART 
       [0002]    In a liquid chromatograph, which is a type of liquid sample analyzer, a mobile phase (eluting solvent) is sucked by a pump, and the mobile phase is transferred to a column together with a sample introduced by an automatic sample introduction device. The sample introduced into the column is separated into respective components, which are detected by various detectors. In general, in a field of apparatuses referred to as high performance liquid chromatographs (HPLC), analysis is required to be performed at high pressure of 20 MPa to 40 MPa at the maximum. A pump for such a HPLC is required to be capable of supplying a mobile phase correctly and precisely even at high pressure. 
         [0003]    An automatic sample introduction device is an device for sucking a sample liquid using a needle from sample retaining containers arranged in a sample rack, subsequently storing the sample in a sample storage loop, and automatically injecting the sample into a mobile phase flow path of a liquid chromatograph. Many automatic sample introduction devices are used that have pretreatment functions of diluting a sample before injecting the sample into a mobile phase flow path and of mixing the sample with a reagent to make a label, or the like. 
         [0004]    Injection schemes in such automatic sample introduction devices are classified into two types: a direct injection scheme (e.g., see Patent Literatures 1 and 2) integrating a needle and a sample storage loop into a part of a mobile phase flow path at high pressure, and a loop injection scheme (e.g., see Patent Literatures 3 and 4) integrating only a sample storage loop into a part of a mobile phase flow path at high pressure. 
         [0005]    According to the direct injection scheme, a sample temporarily stored in the needle and the sample storage loop is flushed into a column by a mobile phase at the start of analysis, and the contents of the needle and the sample storage loop are continuously flushed by the mobile phase during analysis. Accordingly, this scheme is advantageous in that the sucked sample can be introduced into the column without waste, which negates the need of another means for cleaning the inside of the needle contaminated with the sample. 
         [0006]    However, because of the principle that integrates the needle into a part of the mobile phase flow path during analysis, a structure for retaining liquid tightness between the needle and a sample inlet of a sample retaining container at high pressure is required, which is disadvantageous in being unsuitable for sample handling, such as dilution and mixing in pretreatment. 
         [0007]    On the contrary, according to the loop injection scheme, the needle is out of the mobile phase flow path at high pressure during analysis. Accordingly, even in analysis, needle can be moved and sample can be measured, which negates the need of a structure of retaining liquid tightness between the needle and the sample inlet of the sample retaining container. Thus, pretreatment on the sample can advantageously be performed in analysis. However, another means for cleaning the inside of the needle and a process therefor are required instead, which is disadvantageous in that the time required for sample injection is longer than that in the direct injection scheme. 
         [0008]    Thus, the above two types of injection schemes have advantages and disadvantages with respect to each other. Accordingly, it is preferable that any of the schemes be selectable in conformity with purposes and applications of analysis. 
       PRIOR ART DOCUMENTS 
     Patent Literature 
       [0000]    
       
         Patent Literature 1: JP-A-1-248055 
         Patent Literature 2: JP-A-2006-292641 
         Patent Literature 3: JP-A-6-235722 
         Patent Literature 4: JP-A-61-114143 
       
     
       SUMMARY OF INVENTION 
     Problem to be Solved by the Invention 
       [0013]    In the sample introduction unit of the above mentioned loop injection type, in case of that it is desired that the whole amount of the sample is introduced in the column laconically, in a process of temporarily storing in the sample storage loop the sample to be introduced into the column, both of the washing solution and the actual sample solution are stored simultaneously in the sample storage loop. That is, the washing solution is introduced into the column finally, whereby there are the following problems in the prior art. 
         [0014]    At first, in a case of that the mobile phase and the washing solution are different in their solvents, the washing solution itseft reaches a detector without being strongly held in the column, or substantially passing straight therethrough. Here, in a case of that the mobile phase and the washing solution are different in wave-length characteristic with respect to optical absorption, a difference in the optical absorption is detected by the detector, and recorded in a chromatogram. This ghost peak by the washing solution causes a problem especially when a fine amount of the sample is analyzed in high sensitibity. 
         [0015]    At second, even in a case of that the mobile phase and the washing solution are equal in their solvents, especially when a solubility of a component of the sample into the washing solution is high, an attenuation of the sample solution is accelerated in the above mentioned sample introduction process, so that the sample solution is stored in the sample storage loop with an enlarged band-width. As a result of this, the sample solution with the enlarged band-width reaches the column, whereby a peak width of the chromatogram of the component of the sample detected by the detector is enlarged. That is, there is a problem of that a separation performance of a target component is deteriorated to increase an analysis time period, and a processing performance as the chromatograph device is decreased. Further, additionally, there is a problem of that a peak height of the chromatogram of the component of the sample is reduced, whereby a sensitivity of the liquid chromatogram is decreased. 
         [0016]    An object of the invention is to provide a liquid chromatograph, a sample introduction device for the liquid chromatograph and a cleaning method of the sample introduction device for the liquid chromatograph, wherein a ghost peak is prevented from being detected, and a separation performance of the chromatogram is improved, so that a time period of analysis with high sensitivity is prevented from being entended. 
       Means for Solving the Problem 
       [0017]    For achieving the above object, the invention comprises a first flow passage switching means including a sample storage loop to switch the sample storage loop between a connection thereof to a flow passage of a mobile phase and a disconnection thereof from the flow passage of the mobile phase, a needle for sucking and discharging a sample, a metering means performing sucking of the sample into the needle and discharging the sample while metrizing the sample, a washing solution feeding means transferring a washing solution, a second flow passage switching means switching at least two kinds of the washing solution, a third flow passage switching means performing switching between a connection between the needle and the metering means and a connection between the needle and the washing solution feeding means, and a control means controlling operations of the first flow passage switching means, the metering means, the washing solution feeding means, the second flow passage switching means and the third flow passage switching means. 
         [0018]    Further, in the invention, the whole of the sample is injected into the sample storage loop while the washing solution is injected into a flow passage extending from the sample storage loop to a sample injection port. 
       Advantageous Effects of Invention 
       [0019]    The present invention prevents a ghost peak from being detected, and improves the degree of separation of a chromatogram, thereby providing a liquid chromatograph, a sample introduction device for a liquid chromatograph, and a method for cleaning a sample introduction device for a liquid chromatograph that have a high sensitivity and can prevent analysis time from becoming long. 
         [0020]    Other objects characteristics and advantages of the present invention will be apparent from description of embodiments of the present invention pertaining to accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0021]      FIG. 1  is a schematic diagram of a configuration of a liquid chromatography apparatus including a loop injection automatic sample introduction device, which is an embodiment of the present invention. 
           [0022]      FIG. 2  is a functional diagram showing a control target of an operation controller. 
           [0023]      FIG. 3  is a schematic diagram of a configuration of a liquid chromatography apparatus as with  FIG. 1 . 
           [0024]      FIG. 4  is a schematic diagram of a configuration of a liquid chromatography apparatus as with  FIG. 1 . 
           [0025]      FIG. 5  is a schematic diagram of a configuration of a liquid chromatography apparatus as with  FIG. 1 . 
           [0026]      FIG. 6  is a schematic diagram of a configuration of a liquid chromatography apparatus as with  FIG. 1 . 
           [0027]      FIG. 7  is a schematic diagram of a configuration of a liquid chromatography apparatus as with  FIG. 1 . 
           [0028]      FIG. 8  is a schematic diagram of a configuration of a liquid chromatography apparatus as with  FIG. 1 . 
           [0029]      FIG. 9  is a schematic diagram of a configuration of a liquid chromatography apparatus as with  FIG. 1 . 
           [0030]      FIG. 10  is a schematic diagram of a configuration of a liquid chromatography apparatus as with  FIG. 1 . 
           [0031]      FIG. 11  is a schematic diagram of a configuration of a liquid chromatography apparatus as with  FIG. 1 . 
           [0032]      FIG. 12  is a schematic diagram of a configuration of a liquid chromatography apparatus as with  FIG. 1 . 
           [0033]      FIG. 13A  is a graph showing an example of a chromatogram. 
           [0034]      FIG. 13B  is a graph showing an example of a chromatogram. 
           [0035]      FIG. 14A  is a graph showing an example of a chromatogram. 
           [0036]      FIG. 14B  is a graph showing an example of a chromatogram. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0037]    Embodiments of the present invention will be described below with reference to accompanying drawings. 
       Embodiments 
       [0038]      FIG. 1  is a schematic diagram of a configuration of a liquid chromatography apparatus including a loop injection automatic sample introduction device, which is an embodiment of the present invention. A sample retaining container  1  is arranged on a sample rack  14 . A needle  2  is moved among the sample retaining container  1 , a cleaning tank  10 , a sample inlet  3  of a 6-port 2-position injection valve  8  by a needle moving mechanism, not shown. 
         [0039]    The 6-port 2-position injection valve  8  includes six ports, and a flow path allowing two adjoining ports thereamong to communicate with each other. In an injection position, the port P 1  communicates with the port P 6 , the port P 2  communicates with the port P 3 , and the port P 4  communicates with the port P 5 , as shown in the drawing. Furthermore, the port P 1  is connected with a pump  7 . The port P 2  is connected with a column  6 . The port P 3  and the port P 6  are connected with each other through a sample storage loop  5 . The port P 4  is connected with the sample inlet  3 . The port P 5  is connected with a drain  22  for discharging waste fluid. Moreover, the column  6  is connected to a detector  30  via a tube. The detector  30  detects a separated sample supplied from the column  6 , and transmits a detection signal to a data processor, not shown. 
         [0040]    The 6-port 2-position injection valve  8  can take another position by being turned by 60 degrees. As shown by broken lines in  FIG. 1 , in a load position, the port P 1  communicates with the port P 2 , the port P 3  communicates with the port P 4 , and the port P 5  communicates with the port P 6 . 
         [0041]    In the load position, the pump  7 , the port P 1 , the port P 2  and the column  6  communicate with each other in this order. The sample is not injected into a mobile phase transferred from the pump  7 , and the mobile phase flows to the column. The needle  2 , the sample inlet  3 , the port P 4 , the port P 3 , the sample storage loop  5 , the port P 6 , the port P 5  and the drain  22  communicate with each other in this order. The sample sucked from the sample retaining container  1  by the needle  2  is injected through the sample inlet  3 , and the sample storage loop  5  is filled with the sample. 
         [0042]    In the injection position, the sample retained in the sample storage loop  5  is flushed to the column  6  by the mobile phase transferred from the pump  7 . In the case where the sample is changed, the needle  2  is positioned at the cleaning tank  10  to clean the needle  2 , and a cleaning solution is caused to flow from the cleaning pump  15  to the needle  2  via a syringe valve  16 . The needle  2  is positioned at the sample inlet  3 , thereby cleaning the injection valve  8 . 
         [0043]    The cleaning pump  15 , the syringe valve  16 , a plunger cleaning flow path  17 , a three-way valve  18 , a cleaning solution container  20 , a cleaning solution container  21 , a deaerator  24  and a deaerator  25  are collectively referred to as a cleaning unit. 
         [0044]    The 5-port 4-position syringe valve  16  has five ports, and is provided with passages including four positions indicated by solid lines and broken lines in the diagram. The passage allows two of the ports to communicate with each other. The port P 1  communicates with the cleaning tank  10 . The port P 2  communicates with the needle  2 . The port P 3  communicates with a syringe  11  for measuring the sample. The port P 4  communicates with the plunger cleaning flow path  17  for cleaning the plunger of the pump  7 . The port P 5  communicates with the cleaning pump  15 . The four positions can be taken by turning by  45  degrees. In the first position, the port P 5  communicates with the port P 1 , and the port P 2  communicates with the port P 3 . In the second position, the port P 5  communicates with the port P 2  and the port P 3  communicates with the port P 4 . The third position, which is indicated by the solid line in the diagram, only allows the port P 5  to communicate with the port P 3 . The fourth position only allows the port P 5  to communicate with the port P 4 . 
         [0045]    Two types of cleaning solutions are prepared according to the usage. The cleaning solution A is retained in the cleaning solution container  20 . The cleaning solution B is retained in the cleaning solution container  21 . Any one of the cleaning solutions A and B according to the three-way valve  18  is sucked by the cleaning pump  15  via deaerators  24  and  25 , and transferred through the syringe valve  16  and a buffer tube  13  to the needle  2 . Communication between the plunger cleaning flow path  17  and the pump  7  allows salts that are included in the mobile phase and deposited on the surface of the plunger of the pump  7  to be cleaned. 
         [0046]    During the syringe valve  16  being in the position where the port P 1  communicates with the port P 5  and the port P 2  communicates with the port P 3 , the needle  2  is connected with the syringe  11  for measuring the sample, via the buffer tube  13 . The liquid in the tube between the needle  2  and the syringe  11  is sucked and discharged by operating the syringe  11  upward and downward. 
         [0047]      FIG. 2  is a functional diagram showing control targets of an operation controller  201  that controls movable mechanisms, such as valves of the liquid chromatography apparatus. 
         [0048]    The operation controller  201  includes a processor executing a control program preliminarily held in a memory, not shown, and transmits operation instructions to a needle moving mechanism  202 , a syringe operation mechanism  203 , a cleaning unit operation mechanism  204 , a syringe valve operation mechanism  205 , a three-way valve operation mechanism  206 , and an injection valve operation mechanism  207 . 
         [0049]    The movement, sucking and discharging operations of the syringe  11  are controlled by the syringe operation mechanism  203 . The cleaning unit is operated by the cleaning unit operation mechanism  204 . The syringe valve  16  is operated by the syringe valve operation mechanism  205 . The three-way valve  18  is operated by the three-way valve operation mechanism  206 . The injection valve  8  is operated by the injection valve operation mechanism  207 . 
         [0050]    Next, a sample injection process will be described. The loop injection scheme in this embodiment transfers the total amount of the sample sucked from the needle  2  to the sample storage loop  5  of the injection valve  8 , and causes the sample to reach the column  6  for separating the sample. Accordingly, this scheme is also referred to as the total amount injection scheme. Here, terms are defined as follows. 
         [0051]    vi: injection volume, which is a net volume of sample introduction to the mobile phase flow path. 
         [0052]    vf: feed volume. 
         [0053]    vd: dead volume, which ranges from the sample inlet to the injection valve. 
         [0054]    va: air volume, which is a volume of an air layer before and after the sample. 
         [0055]    Here, the setting of whether the sample is sandwiched before and after va or not can be selected by the automatic sample introduction device. 
         [0056]    The aforementioned  FIG. 1  shows the flow path where the automatic sample introduction device is initialized and in an idle state. The mobile phase into which no sample has been injected flows from the pump  7  to the column  6  via the sample storage loop  5  of the injection valve  8 . Meanwhile, the cleaning solution container  20  for retaining the cleaning solution A is connected with the syringe  11  via the port P 3 , which communicates with the three-way valve  18 , the cleaning pump  15  and the port P 5  of the syringe valve  16 , thereby cleaning the inside of the syringe  11  with the cleaning solution A. The needle  2  is positioned above the cleaning tank  10 , and liquid dropping from the needle  2  is received by the cleaning tank  10 . 
         [0057]      FIG. 3  is a schematic diagram of a configuration of a liquid chromatography apparatus, as with  FIG. 1 , and shows a state where the contents of the buffer tube  13  and the needle  2  are replaced with the cleaning solution B retained in the cleaning solution container  21 , thereby cleaning the tube and the needle. The needle  2  is moved to the sample inlet  3  to communicate with the port P 4  of the injection valve  8 . The syringe valve  16  is turned clockwise by  45  degrees from the state of  FIG. 1 . The turn switches the position to that where the port P 5  communicates with the port P 2  and the port P 3  communicates with the port P 4 . Furthermore, the three-way valve  18  is switched to the cleaning solution container  21  retaining the cleaning solution B. The cleaning pump  15  transfers the cleaning solution B to the syringe valve  16 , the buffer tube  13 , the needle  2  and the injection valve  8 , thereby cleaning the inside of the port P 5  communicating with the port P 4  of the injection valve  8 . The cleaning solution B is then discharged from the drain  22 . 
         [0058]      FIG. 4  is a schematic diagram of a configuration of a liquid chromatography apparatus, as with  FIG. 1 , and shows a state where the outside of the needle  2  is cleaned with the cleaning solution A in the cleaning tank  10 . The positions of the ports of the injection valve  8  are not changed, and the syringe valve  16  is turned clockwise by  45  degrees from the state in  FIG. 3 , thereby switching the position to that where the port P 5  communicates with the port P 1  and the port P 2  communicates with the port P 3 . The cleaning pump  15  transfers the cleaning solution A in the cleaning solution container  20  to the cleaning tank  10  via the syringe valve  16 , thereby soaking the needle  2  in the cleaning solution A in the cleaning tank  10 . The cleaning solution A is sucked by the syringe  11 , thereby filling the tube including the syringe valve  16  and the needle  2  with this solution. The amount of suction is vf+vd, i.e., the sum of the feed volume and the dead volume. The needle  2  is soaked in the cleaning tank  10 , thereby cleaning the outside of the needle  2 . 
         [0059]      FIG. 5  is a schematic diagram of a configuration of a liquid chromatography apparatus, as with  FIG. 1 , and shows a process of sucking the sample. As shown in  FIG. 5 , the positions of the ports of the syringe valve  16  and the injection valve  8  are not changed, and the needle  2  is moved from the cleaning tank  10  to the sample retaining container  1 . In the process of the movement, air is sucked by the syringe  11 . The amount of suction is half an air volume va. Next, the needle  2  is moved to the sample retaining container  1 , and the sample is sucked by the syringe  11 . The amount of suction is the injection volume vi. 
         [0060]      FIG. 6  is a schematic diagram of a configuration of a liquid chromatography apparatus, as with  FIG. 1 , and shows a state where the outside of the needle  2  is cleaned with the cleaning solution A after the sample is sucked. As shown in  FIG. 6 , the positions of the syringe valve  16  and the injection valve  8  are not changed, and the needle  2  is moved from the sample retaining container  1  to the cleaning tank  10 . In the process of the movement, air having an amount half as large as the air volume va is sucked by the syringe  11 . After the needle  2  is moved to the cleaning tank  10 , the cleaning pump  15  transfers the cleaning solution A to the cleaning tank  10  to clean the outside of the needle  2 . The cleaning solution A overflown from the cleaning tank  10  is discharged from the drain  23 . 
         [0061]      FIG. 7  is a schematic diagram of a configuration of a liquid chromatography apparatus, as with  FIG. 1 , and shows a state where the needle  2  is moved to the sample inlet  3  of the injection valve  8 . As shown in  FIG. 7 , the positions of the ports of the syringe valve  16  and the injection valve  8  are not changed, and the needle  2  is moved to the sample inlet  3  of the injection valve  8 , thus preparing injection of the sample from the port P 4  to the injection valve  8 . 
         [0062]      FIG. 8  is a schematic diagram of a configuration of a liquid chromatography apparatus, as with  FIG. 1 , and shows a state where the pressure in the sample storage loop  5  is reduced. In the states up to the state shown in  FIG. 7 , the sample storage loop  5  is connected with the pump  7  to allow the inside of this loop to serve as the mobile phase flow path. Accordingly, the pressure is higher than atmospheric pressure. As shown in  FIG. 8 , the positions of the ports of the syringe valve  16  are not changed, and the injection valve  8  is turned counterclockwise by  60  degrees. The turn separates the sample storage loop  5  of the injection valve  8  from the mobile phase flow path of the pump  7 , thus separating the sample storage loop  5  at high pressure from the mobile phase flow path. This separation allows the pressure in the sample storage loop  5  to be released to atmospheric pressure through the drain  22 . 
         [0063]      FIG. 9  is a schematic diagram of a configuration of a liquid chromatography apparatus, as with  FIG. 1 , and shows a process of transferring the sample sucked by the needle  2  to the injection valve  8 . As shown in  FIG. 9 , the positions of the ports of the syringe valve  16  and the injection valve  8  are not changed, and the cleaning solution A and air in the syringe  11  are flushed, thereby transferring the sample in the needle  2  to the sample storage loop  5  in the injection valve  8  through the port P 4  of the injection valve  8 . The amount flushed by the syringe  11  is the sum of the feed volume, the injection volume, the dead volume and the air volume, i.e., vf+vi+vd+va. After the sample with the volume vi sucked by the process in  FIG. 5  is transferred, the cleaning solution A with the volume of sucked by the process in  FIG. 4  is transferred to the injection valve  8 . Accordingly, the sample storage loop  5  can be filled with the total amount of the sample. 
         [0064]      FIG. 10  is a schematic diagram of a configuration of a liquid chromatography apparatus, as with  FIG. 1 , and shows a process of introducing the sample retained in the sample storage loop  5  to the mobile phase flow path. As shown in  FIG. 10 , the positions of the ports of the syringe valve  16  are not changed, and the injection valve  8  is turned clockwise by 60 degrees, thereby causing the port P 3  of the sample storage loop  5  to communicate with the port P 2  connected with the column  6 , causing the port P 6  of the sample storage loop  5  to communicate with the port P 1  connected with the pump  7 . With the communication, the pump  7  causes the mobile phase to flow to the sample storage loop  5 , and transfers the mobile phase to the column  6  together with the sample. Meanwhile, for preparation for the next process, the syringe  11  is moved to the top dead center. This movement discharges the liquid in which the cleaning solution A in the needle  2  and the residue of the sample are mixed, from the sample inlet  3  to the drain  22  through the ports P 4  and P 5  of the injection valve  8 . 
         [0065]      FIG. 11  is a schematic diagram of a configuration of a liquid chromatography apparatus, as with  FIG. 1 , and shows a process of cleaning the inside of the needle  2  with the cleaning solution A. As shown in  FIG. 11 , the positions of the ports of the injection valve  8  are not changed, and the syringe valve  16  is turned counterclockwise by 45 degrees, thereby switching the position to that where the port P 5  communicates with the port P 2  and the port P 3  communicates with the port P 4 . The cleaning pump  15  transfers the cleaning solution A retained in the cleaning solution container  20  to the needle  2  via the syringe valve  16 , and the inside of the needle  2  is cleaned with the cleaning solution A. The cleaning solution A is then discharged from the drain  22 . 
         [0066]    After cleaning of the needle  2  shown in  FIG. 11  is completed, the syringe valve  16  is turned counterclockwise by  45  degrees. The turn causes the port P 5  of the syringe valve  16  to communicate with the port P 3 , thereby causing the state to transition to the idle state shown in  FIG. 1 . The needle  2  is moved above the cleaning tank  10 . 
         [0067]      FIG. 12  is a schematic diagram of a configuration of a liquid chromatography apparatus, as with  FIG. 1 , and shows a process performed after cleaning of the needle  2  shown in  FIG. 10  in the case where cleaning of the plunger of the pump  7  is preset. The syringe valve  16  is turned counterclockwise by  90  degrees, thereby switching the position to that where the port P 5  communicates with the port P 4 . In the case of cleaning the plunger with the cleaning solution B instead of the cleaning solution A, the three-way valve  18  is switched to be connected to the cleaning solution container  21 , and the cleaning solution B is sucked by the cleaning pump  15  and transferred from the plunger cleaning flow path  17  to the plunger of the pump  7 , not shown. The cleaning time is preset. After completion, the syringe valve  16  is turned clockwise by 45 degrees, thereby causing the state to transition to the idle state shown in  FIG. 1 . 
         [0068]      FIGS. 13A ,  13 B,  14 A and  14 B are graphs showing examples of chromatograms.  FIG. 13A  shows a result of a conventional device configuration.  FIG. 13B  shows a result of the device configuration of the present invention. Analysis conditions are set such that the sample is  60  ppm methylparaben, the sample solution is methanol, the mobile phase is 60% methanol aqueous solution, the cleaning solution A is methanol, the cleaning solution B is 60% methanol aqueous solution, the flow rate of the mobile phase is 1 milliliter/min., the column is ODS, the dimensions are 4.6 mmID×150 mmL, the particle diameter is 5 μm, the column temperature is 40° C., the absorbance detection wavelength is 265 nm, and the injection volume is 10 microliters. 
         [0069]      FIG. 13A  shows a chromatogram in the case where the process shown in  FIG. 3  is not performed.  FIG. 13B  shows a chromatogram in the case where the process shown in  FIG. 3  is performed. In the chromatogram shown in  FIG. 13A , a ghost peak, which is caused by difference in absorbance between the mobile phase of 60% methanol aqueous solution and the cleaning solution A of methanol and is due to the cleaning solution A of methanol, is detected, before the peak of methylparaben as the target component. In contrast, in  FIG. 13B , the ghost peak is completely eliminated in the chromatogram shown in  FIG. 13B , because the content in the tube including the buffer tube  13  and the needle  2  is replaced with the cleaning solution B of 60% methanol aqueous solution in the process shown in  FIG. 3 . 
         [0070]      FIG. 14A  shows a result of the conventional device configuration.  FIG. 14B  shows a result of the device configuration of the present invention. The analysis conditions are set such that the sample is 60 ppm methylparaben, the sample solution is 60% methanol aqueous solution, the mobile phase is 60% methanol aqueous solution, the cleaning solution A is 60% methanol aqueous solution, the cleaning solution B is distilled water, the flow rate of the mobile phase is 1 milliliter/min., the column is ODS, the dimensions are 4.6 mmID×150 mmL, the particle diameter is 5 μm, the column temperature is 40° C., the absorbance detection wavelength is 265 nm, and the injection volume is 10 microliters.  FIG. 14A  is a chromatogram in the case where the process shown in  FIG. 3  is not performed.  FIG. 14B  shows a chromatogram in the case where the process shown in  FIG. 3  is performed. In the chromatogram of  FIG. 14A , the sample solution of methylparaben as the target component easily dissolves in the cleaning solution A of 60% methanol aqueous solution. Accordingly, the solution is diluted in the sample introduction process, and reaches the column while having a wide bandwidth in the analysis flow path. As a result, the peak width of methylparaben detected by the detector is increased. The peak height of methylparaben is reduced. In contrast, in the chromatogram of  FIG. 14B  where the process shown in  FIG. 3  is performed, the content in the tube including the buffer tube  13  and the needle  2  is replaced with the cleaning solution B of distilled water. As a result, the peak width of methylparaben is reduced, and the peak height is increased by approximately 17%, thus allowing the sensitivity of the liquid chromatograph to be improved. 
         [0071]    As described above, in the loop injection scheme, for introducing the total amount of the sample into the column without waste, in the process of temporarily storing the sample to be introduced into the column in the sample storage loop, not only the actual sample solution but also the cleaning solution is also stored in the sample storage loop at the same time. However, according to the embodiment of the present invention, the amount of storage of the cleaning solution can be reduced. Accordingly, the ghost peak on the chromatogram can be eliminated, the peak width can be prevented from being increased, and the degree of separation of the chromatogram is not degraded or the degree of separation is improved, thereby allowing high sensitivity to be achieved. 
         [0072]    As described above, the present invention provides a liquid chromatograph and a sample introduction device for a liquid chromatograph that have a high sensitivity and can prevent analysis time from being increased. 
         [0073]    The above description has been made on the embodiment. However, the present invention is not limited thereto. Instead, it is apparent for those skilled in the art that various changes and modifications may be made within the scope of the spirit of the present invention and attached claims. 
       REFERENCE SIGNS LIST 
       [0074]      1  sample retaining container 
         [0075]      2  needle 
         [0076]      3  sample inlet 
         [0077]      5  sample storage loop 
         [0078]      6  column 
         [0079]      7  pump 
         [0080]      8  injection valve 
         [0081]      10  cleaning tank 
         [0082]      11  syringe 
         [0083]      13  buffer tube 
         [0084]      14  sample rack 
         [0085]      15  cleaning pump 
         [0086]      16  syringe valve 
         [0087]      17  plunger cleaning flow path 
         [0088]      18  three-way valve 
         [0089]      20 ,  21  cleaning solution container 
         [0090]      22 ,  23  drain 
         [0091]      24 ,  25  deaerator 
         [0092]      201  operation controller 
         [0093]      202  needle moving mechanism 
         [0094]      203  syringe operation mechanism 
         [0095]      204  cleaning unit operation mechanism 
         [0096]      205  syringe valve operation mechanism 
         [0097]      206  three-way valve operation mechanism 
         [0098]      207  injection valve operation mechanism