Patent Publication Number: US-2020298251-A1

Title: Magnetic separation method and automated analyzer

Description:
TECHNICAL FIELD 
     The present disclosure relates to a magnetic separation method and an automated analyzer for separating a substance to be measured from coexisting substances using magnetic beads. 
     BACKGROUND ART 
     In analyzing a liquid sample derived from a biological body such as blood or urine with high sensitivity, a technique for selectively identifying a substance to be measured from a sample containing a large amount of coexisting substances is essential. As such a technique, a labeled antibody method for separating the substance to be measured from the sample using magnetic beads is known. 
     In the above labeled antibody method, the magnetic beads to which a non-labeled antibody that performs an antigen-antibody reaction with the substance to be measured is bound and a labeled antibody labeled with a labeling substance are included in the sample, and a target substance to be measured is bound to the magnetic beads and the labeling substance. Then, the magnetic beads are magnetically separated from the sample to remove the coexisting substances, the substance to be measured is eluted from the magnetic beads, and a content of the target substance can be measured by photometry of the labeling substance. 
     In an automated analyzer that can carry out the above series of processes, a concentration of the substance to be measured may be increased in order to improve a sensitivity of a measurement. For example, the substance to be measured is bound to the magnetic beads, a washing process is carried out to remove the coexisting substances by capturing the magnetic beads by magnetic separation and aspirating a reaction solution, the substance to be measured is eluted with a relatively small amount of liquid in an elution process, and a high sensitivity measurement is performed by increasing the concentration of the substance to be measured. Further, in the washing process, the magnetic separation and stirring are performed while gradually reducing an amount of a washing liquid to be injected, so that the magnetic beads are prevented from remaining on a reaction vessel wall surface. 
     PTL 1 discloses a method in which a plurality of magnets are provided in a longitudinal direction to reduce an amount of the magnetic beads flowing out due to a washing operation in a Bound/Free separation (BF separation, a separation of an antigen-antibody conjugate and a non-conjugate) process involving a pre-magnetization and a main magnetism. 
     PTL 2 describes a technology in which a magnetic force of a magnet provided on an aspirate and discharge system side of a pipette tip or the like of a dispenser is used to adsorb a magnetic body in a short time and with almost perfect accuracy. 
     PTL 3 discloses an automated analyzer including a unit configured to increase a liquid amount in a reaction vessel before a reaction solution discharging process in a magnetic separation process, and describes that a series of processes of injecting a buffer solution, capturing magnetic beads, and discharging a reaction solution may be performed a plurality of times as necessary. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: JP-A-2016-085093 
         PTL 2: JP-A-H8-062224 
         PTL 3: JP-A-2014-122826 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in the method described in PTL 1, a relationship between a magnet height and the liquid amount of the washing liquid in a two-stage BF separation process is not considered. Therefore, in a case where a surface height of a liquid when injecting the washing liquid in the washing process matches a position where a strong magnetic field where the magnetic beads easily aggregate is generated, it is possible that the magnetic beads aggregate near the surface of the liquid, resulting in poor washing efficiency. In other words, when a plurality of washing processes are performed with the same magnetic separation device while the liquid amount of the washing liquid is reduced, the magnetic beads may aggregate on the vessel wall surface near the surface of the liquid. In a state where the magnetic beads are excessively aggregated, it is difficult to separate impurities which are non-magnetic components, which causes a reduction in washing efficiency. For the above reasons, the washing process in which the liquid amount changes requires using different magnetic separation devices according to the liquid amount, and an operation process is complicated. 
     Further, in the method described in PTL 2, when the amount of the washing liquid to be used is reduced, the same pipette tip is used, so that there is a possibility that washing cannot be performed sufficiently. On the other hand, when the pipette tip having a plurality of diameters is used in order to cope with a problem of insufficient washing, labor and cost are greatly increased. 
     Furthermore, in the method described in PTL 3, when the buffer solution is increased, a large amount of the buffer solution is used, and the cost is increased. 
     The present disclosure has been made in view of the above circumstances, and provides a technology that can use a single device to highly efficiently carry out a plurality of washing processes for gradually reducing a liquid amount of a magnetic bead solution in a reaction vessel. 
     Solution to Problem 
     In order to solve the above problems, the present disclosure provides a magnetic separation method including a plurality of washing processes for separating a magnetic substance and a nonmagnetic substance using a magnetic separation device and a stirring mechanism, in which the plurality of washing processes includes at least a first washing process and a second washing process, the first washing process includes: a step of inserting a reaction vessel containing a solution including the magnetic substance and the nonmagnetic substance into a recess provided in the magnetic separation device and capturing the magnetic substance using a plurality of magnets that are each disposed along a peripheral direction of the recess such that the same pole faces the reaction vessel; a step of aspirating the solution with the magnetic substance being captured; a step of discharging liquid to the reaction vessel such that a surface of the liquid goes to a position higher than upper edges of the magnets; and a step of removing the reaction vessel from the magnetic separation device and stirring the liquid held by the reaction vessel using the stirring mechanism, and the second washing process includes: a step of inserting the reaction vessel into the magnetic separation device and aspirating the liquid with the magnetic substance being captured; a step of discharging the liquid to the reaction vessel such that a surface of the liquid goes to a position lower than the upper edges of the magnets where magnetic field intensity is lower than that at a position of the upper edges of the magnets; and a step of removing the reaction vessel from the magnetic separation device and stirring the liquid held by the reaction vessel using the stirring mechanism. 
     In addition, the present disclosure provides a magnetic separation method including a plurality of washing processes for separating a magnetic substance and a nonmagnetic substance using a magnetic separation device and a stirring mechanism, in which the plurality of washing processes includes at least a first washing process and a second washing process, the first washing process includes: a step of inserting a reaction vessel containing a solution including the magnetic substance and the nonmagnetic substance into a recess provided in the magnetic separation device and capturing the magnetic substance using a plurality of magnets, the magnets being disposed such that a first stage and a second stage positioned below the first stage along a vertical direction of the recess are each provided with an equal number of magnets, the magnets in the first stage and the magnets in the second stage are vertically adjacent to each other with different poles, two adjacent magnets in the first stage have poles different from each other facing the reaction vessel, and two magnets facing each other have the same pole facing the reaction vessel; a step of aspirating the solution with the magnetic substance being captured; a step of discharging liquid to the reaction vessel such that a surface of the liquid goes to a position higher than upper edges of the magnets; and a step of removing the reaction vessel from the magnetic separation device and stirring the liquid held by the reaction vessel using the stirring mechanism, and the second washing process includes: a step of inserting the reaction vessel into the magnetic separation device and aspirating the liquid with the magnetic substance being captured; a step of discharging liquid to the reaction vessel such that a surface of the liquid goes to a position lower than a position higher than the upper edges of the magnets in the first stage where magnetic field intensity is lower as compared with at a center of the magnets in the first stage or the magnets in the second stage; and a step of removing the reaction vessel from the magnetic separation device and stirring the liquid held by the reaction vessel using the stirring mechanism. 
     Advantageous Effect 
     According to the present disclosure, the plurality of washing processes for gradually reducing the liquid amount of the magnetic bead solution in the reaction vessel can be highly efficiently carried out using the single device. Problems, configurations, and effects other than those described above will be further clarified with the following description of embodiments. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram of an automated analyzer  1  according to the present disclosure. 
         FIG. 2  is a schematic diagram showing a flow of a process for extracting a substance to be measured contained in a sample. 
         FIG. 3  is a diagram showing a first washing process. 
         FIG. 4  is a schematic diagram showing a flow of an elution process. 
         FIG. 5  shows an example of a magnetic separation device according to the present embodiment. 
         FIG. 6  shows states of capturing magnetic beads in the magnetic separation device. 
         FIG. 7  shows a magnetic separation device according to a second embodiment of the present disclosure. 
         FIG. 8  shows states of capturing magnetic beads in the magnetic separation device according to the second embodiment. 
         FIG. 9  shows magnet arrangements according to a third embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The embodiments of the present disclosure are not limited to the embodiments to be described below, and various modifications can be made within the scope of the technical idea thereof. Corresponding parts of the drawings used in the description of each embodiment to be described below are denoted by the same reference numerals, and a repetitive description will be omitted. 
     Although the embodiments of the present disclosure are mainly directed to an immunoassay analyzer, the present disclosure is applicable to all automated analyzers. The present disclosure can also be applied to, for example, an automated clinical analyzer, a gene analyzer, a mass spectrometer, and a bacteria test device. 
     First Embodiment 
     [Configuration of Automated Analyzer] 
       FIG. 1  is a schematic diagram of an automated analyzer  1  according to the present disclosure. The automated analyzer  1  includes an analysis unit  101  for performing an analysis operation, a control unit  102  for controlling an operation of an entire device, an input unit  103  for a user to input information to the device, and a display unit  104  for displaying information to the user. The input unit  103  and the display unit  104  may be the same, and a touch-panel type monitor is one example thereof. Further, the control unit  102  is a Central Processing Unit (CPU), for example, that reads and executes a program for controlling an amount of a washing liquid to be discharged. 
     The analysis unit  101  includes a first transport mechanism  112  for transporting a sample container  111  containing a sample to a sample collection position, a sample dispensing mechanism  113  for discharging the sample, a dispensing tip attaching and detaching section  114  for attaching and detaching a disposable dispensing tip for the sample dispensing mechanism  113  to the sample dispensing mechanism  113 , a dispensing tip mounting rack  115  on which the dispensing tip is mounted, a reaction vessel mounting rack  117  on which a reaction vessel  116  is mounted, a second transport mechanism  118  for transporting the dispensing tip and the reaction vessel  116 , a reaction vessel disk  120  capable of holding a liquid in the reaction vessel  116  at a constant temperature and having a plurality of openings  119 , a reagent disk  122  for holding a reagent container  121  containing a measurement reagent, a reagent dispensing mechanism  123  for discharging the measurement reagent into the reaction vessel  116 , a magnetic separation device  124  provided with magnets for capturing magnetic beads in the reaction vessel  116  to an inner wall of the reaction vessel  116 , a stirring mechanism  126  that stirs the liquid contained in the reaction vessel  116  in a non-contact manner, a transporting and aspirating-discharging mechanism  125  that transports the reaction vessel  116  between the disk  120 , the magnetic separation device  124 , and the stirring mechanism  126 , and that can aspirate and discharge a solution in the reaction vessel  116 , a detector  131  that detects components in blood, and a dispensing mechanism for detector  132  for aspirating the components in the blood extracted from the reaction vessel  116  and discharging the components to the detector  131 . 
     An outline of an analysis process of the automated analyzer  1  will be described below with reference to  FIG. 1 . Before the analysis, the automated analyzer  1  transports the reaction vessel  116  from the reaction vessel mounting rack  117  and disposes the reaction vessel  116  in the openings  119  on the reaction vessel disk  120 . 
     The sample dispensing mechanism  113  accesses the dispensing tip attaching and detaching section  114  such that the dispensing tip can be attached to a tip before dispensing the sample. The sample dispensing mechanism  113  aspirates the sample from the sample container  111  via the dispensing tip and discharges the sample to the reaction vessel  116  on the reaction vessel disk  120 . When a sample dispensing from one sample container  111  is completed, the sample dispensing mechanism  113  discards the dispensing tip to the dispensing tip attaching and detaching section  114 . 
     The reagent dispensing mechanism  123  aspirates the measurement reagent from the reagent container  121  containing the magnetic beads on the reagent disk  122  and discharges the measurement reagent to the reaction vessel  116  on the reaction vessel disk  120 . The reaction vessel disk  120  functions as, for example, an incubator, and incubates the reaction vessel  116  disposed in the openings  119  for a predetermined time. 
     A reaction proceeds due to the incubation of a certain period of time, and a substance to be measured and the magnetic beads are bound in the reaction vessel  116 . Thereafter, the automated analyzer  1  performs a washing process and an elution process in order to improve the analysis accuracy. The expression “the substance to be measured and the magnetic beads are bound” means that, for example, a non-labeled antibody bound to the magnetic beads and the substance to be measured are bound by an antigen-antibody reaction. 
     [Extraction of Substance to be Measured] 
       FIG. 2  is a schematic diagram showing a flow of a process for extracting the substance to be measured contained in the sample. In order to extract the substance to be measured from the sample, the automated analyzer  1  performs the washing process and the elution process. As shown in  FIG. 2 , in the present embodiment, the washing process is performed three times to wash and remove coexisting substances floating in the solution without binding to magnetic beads  21 . The automated analyzer  1  sequentially reduces an amount of a washing liquid  23  to be injected in each of the three washing processes. For example, an amount of a washing liquid  23  for a first time is 250 μL, an amount of the washing liquid  23  for a second time is 160 μL, and an amount of the washing liquid  23  for a third time is 80 μL. In the elution process, the substance to be measured is eluted from the magnetic beads  21  by injecting 40 μL of eluate and controlling a temperature. 
       FIG. 3  is a diagram showing a first washing process. Hereinafter, the washing process will be described with reference to  FIGS. 1 and 3 . 
     The reaction vessel  116  containing the solution in which the magnetic beads  21  are suspended is transported to the magnetic separation device  124  by a gripping mechanism  127  of the transporting and aspirating-discharging mechanism  125 . Magnets  22  are disposed around a recess of the magnetic separation device  124  into which the reaction vessel  116  is inserted, and the magnetic beads  21  are captured on the inner wall of the reaction vessel  116  by a magnetic field generated by the magnets  22 . In an example shown in  FIG. 3 , the magnets  22  are stacked in two stages, and have a configuration in which the S pole of an upper magnet  22  faces the reaction vessel  116  and the N pole of a lower magnet  22  faces the reaction vessel  116 . In this case, magnetic field intensity is high at both upper and lower edges of the magnets  22 , so that the magnetic beads  21  are easily aggregated at both the upper and lower edges of the magnets  22 . As described later, it is preferable that a height of the magnets  22  is a height in consideration of a height of a liquid surface of the solution to be injected into the reaction vessel  116 . Further, the magnets  22  used for the magnetic separation device  124  are preferably neodymium-based magnets which are magnets having a high coercive force per unit volume from a viewpoint of a dimension. The magnets  22  may be electromagnets. 
     After supplementing the magnetic beads  21 , the automated analyzer  1  uses an aspirating nozzle  128  of the transporting and aspirating-discharging mechanism  125  to remove the solution that does not include the magnetic beads  21  in the reaction vessel  116  by aspirating the solution with the aspirating nozzle  128 . Subsequently, the automated analyzer  1  discharges the washing liquid  23  from a discharging nozzle  129  of the transporting and aspirating-discharging mechanism  125  to the reaction vessel  116 . For example, the amount of the washing liquid to be discharged in the first washing process is adjusted such that the height of the liquid surface is at a position higher than the upper magnet  22  (a position where the magnetic field intensity is low). By adjusting the height of the liquid surface to the position where the magnetic field intensity is low, in a subsequent washing process, it is possible to prevent the case where the magnetic beads  21  aggregate near the liquid surface, the magnetic beads  21  are aspirated when aspirating the solution, and the solution is insufficiently aspirated due to a surface tension. 
     Thereafter, the reaction vessel  116  containing the magnetic beads  21  and the washing liquid  23  is transported to the stirring mechanism  126  by the gripping mechanism  127  of the transporting and aspirating-discharging mechanism  125 . Since the magnetic beads  21  in the reaction vessel  116  transferred to the stirring mechanism  126  are not affected by the magnetic field, the magnetic beads  21  are isolated and re-suspended in the solution by being stirred by the stirring mechanism  126 . Examples of a non-contact stirring mechanism  126  include a mechanism for applying a rotation operation combining rotation and revolution to the reaction vessel  116 , that is, a mechanism that performs an eccentric stirring. When the non-contact stirring mechanism  126  is used, the sample or reagent is not taken out due to the solution adhering to a stirrer, so that the analysis accuracy is improved. After the magnetic beads  21  are re-suspended by the stirring mechanism  126 , the reaction vessel  116  is transported to the magnetic separation device  124  again, and a second washing process is performed. 
     In the first embodiment, the automated analyzer  1  performs the above washing process three times. Here, in the second and subsequent washing processes, the amount of the washing liquid  23  to be discharged into the reaction vessel  116  is controlled to be smaller than an amount of the solution contained in the reaction vessel  116  before an aspirating operation, and therefore, the amount of the washing liquid  23  discharged at a second time is smaller than the amount of the washing liquid  23  discharged at a first time. Similarly, the amount of the washing liquid  23  discharged at a third time is smaller than the amount of the washing liquid  23  discharged at the second time. In addition, the amount of the washing liquid  23  discharged in each washing process is controlled such that a position of the liquid surface is the position where the magnetic field intensity is low, so that the position of the liquid surface of the washing liquid  23  discharged at the second time is adjusted such that the height of the liquid surface is positioned at a center of the upper magnet (the position where the magnetic field intensity is low), and the position of the liquid surface of the washing liquid  23  discharged at the third time is adjusted such that the height of liquid surface is positioned at a center of the lower magnet (the position where the magnetic field intensity is low). As described above, the washing process is performed by repeating magnetic separation and stirring a plurality of times, so that the coexisting substances removed. 
     The automated analyzer  1  according to the first embodiment can save the amount of the washing liquid  23  to be used by performing a plurality of washing processes in which the amount of the washing liquid  23  to be discharged is sequentially reduced as described above. In addition, the automated analyzer  1  of the first embodiment controls a discharge amount of the washing liquid  23  in each washing process such that the position of the liquid surface of the washing liquid  23  is the position where the magnetic field intensity is low, so that it is possible to prevent the case where the magnetic beads are aspirated when aspirating the solution, and the solution is insufficiently aspirated due to the surface tension. 
       FIG. 4  is a schematic diagram showing a flow of the elution process. Hereinafter, the elution process will be described with reference to  FIGS. 1, 2 and 4 .  FIG. 4  shows a flow after the third washing process is performed. After the third washing process is completed, the automated analyzer  1  magnetically separates the magnetic beads  21  again with the magnetic separation device  124 , and aspirates the solution. Subsequently, the automated analyzer  1  discharges a smaller amount of the eluate than a reaction solution into the reaction vessel  116  and stirs the reaction vessel  116  with the stirring mechanism  126 . Thereafter, the automated analyzer  1  transfers the reaction vessel  116  to the reaction vessel disk  120 , controls the temperature of the reaction vessel  116  in an incubator  24  to promote a reaction, and elutes the substance to be measured from the magnetic beads  21 . Then, by performing the magnetic separation again, a concentrated liquid containing the substance to be measured with the magnetic beads  21  being removed is created. 
     Subsequently, the automated analyzer  1  aspirates the concentrated liquid in the reaction vessel  116  on the magnetic separation device  124  by the dispensing mechanism for detector  132  and transports the concentrated liquid to the detector  131 . The detector  131  includes a unit configured to detect an amount of light such as a photomultiplier tube, so as to measure the amount of the light emitted from the reaction solution (the concentrated liquid finally aspirated). Thereafter, the control unit  102  calculates a concentration value from light emission data using a calibration curve, and displays a calculated analysis result on the display unit  104 . 
       FIG. 5  shows a part of the magnetic separation device  124  according to the present embodiment.  FIG. 5( a )  shows a positional relationship between the reaction vessel  116  and the magnets  22 . In an example shown in  FIG. 5( a ) , the magnets  22  are disposed in two upper and lower stages.  FIGS. 5( b ) and 5( c )  show plan views of the magnetic separation device  124 , and magnet arrangements of a first stage (an upper stage) and a second stage (a lower stage) from a top are shown, respectively. In the present embodiment, an example in which the number of stages of the magnets  22  is two is shown, but the number of the stages of the magnets  22  may be three or more. Further, in the present embodiment, four magnets  22  are disposed in one stage, but an effect the same as in the present embodiment can be obtained as long as the amount of disposed magnets is an even number. For example, six or eight magnets  22  may be disposed in one stage. The height of the magnets  22  in each stage is the same, for example. Hereinafter, a reference numeral of the upper magnets is  51 , and a reference numeral of the lower magnets is  52 . 
     Four upper magnets  51  shown in  FIG. 5( b )  are disposed at equal intervals in a peripheral direction of the reaction vessel  116 , with the S pole facing the center of the reaction vessel  116 . On the other hand, four lower magnets  52  shown in  FIG. 5( c )  are disposed at the equal intervals in the peripheral direction of the reaction vessel  116 , as the upper magnets  51 , but the orientation of the magnetic pole is different from that of the upper magnets  51 , that is, the N pole faces the center of the reaction vessel  116 . In addition, in  FIG. 5( a ) , all magnetic poles of the upper magnets  51  on a reaction vessel side are disposed as the S pole, and all the magnetic poles of the lower magnets  52  on the reaction vessel side are the N pole, but the magnetic poles of the upper magnets  52  may be the N pole, and the magnetic poles of the lower magnets  51  may be the S pole. That is, the magnets are arranged such that the magnetic pole of all magnets  22  in each stage facing the center of the reaction vessel  116  is the same, and the magnetic poles of magnets  22  disposed adjacently in the upper-lower direction are different from each other. In this way, a magnetic field distribution facilitating the supplementing of the magnetic beads  21  can be obtained. 
       FIG. 6  shows states of capturing the magnetic beads  21  in the magnetic separation device  124 . In a case of the magnet arrangements according to the present embodiment, strong magnetic fields are generated at both the upper and lower edges of the magnets  51  and  52 , and therefore, the magnetic beads  21  have a feature of being captured at both edges of upper edges and lower edges of the magnets  51  and  52  as shown in  FIG. 6( a ) .  FIG. 6( a )  shows a pattern in which the magnetic beads  21  are captured on the inner wall of the reaction vessel  116 . As shown in  FIG. 6( a ) , a liquid surface  61  of the washing liquid  23  in the first washing process is set higher than the upper magnets  51 . In addition, as shown in  FIG. 6( b ) , a liquid surface  62  of the washing liquid  23  in the second washing process is set near the center of the upper magnets  51 . Further, as shown in  FIG. 6( c ) , a liquid surface  63  of the washing liquid  23  in the third washing process is set near the center of the lower magnets  52 . In the second and subsequent washing processes of the present embodiment, the liquid surface of the washing liquid  23  is set near the center of the magnets  51  and  52 , and appropriate liquid surface ranges  64  and  65  are shown in a mesh pattern in  FIGS. 6( b ) and 6( c ) . A position of the mesh is a portion where the magnetic field intensity generated by the magnet arrangements of the present embodiment is low and does not overlap with a portion where the magnetic beads  21  aggregate. The position of the liquid surface may be a position where the mesh is provided. As described above, since the liquid surface and a position where the magnetic field intensity is high (a position where the magnetic beads  21  are easily collected) do not overlap, the magnetic beads  21  do not aggregate near the liquid surface. 
     According to the present embodiment, the magnetic beads  21  are always captured below the liquid surface, and the magnetic beads  21  do not aggregate on the liquid surface during the washing process in which a liquid amount is reduced. As a result, according to the automated analyzer  1 , deterioration in the efficiency of the washing processes for removing impurities can be prevented, and a highly accurate measurement can be performed. 
     Second Embodiment 
     Next, the second embodiment will be described with reference to  FIGS. 7 and 8 . An automated analyzer according to the second embodiment is different from the automated analyzer  1  according to the first embodiment in the arrangement of the magnets  22  and a discharge control of the solution in the magnetic separation device. In  FIGS. 7 and 8 , components having the same reference numerals as those in  FIGS. 1 to 6  indicate the same parts, and a repetitive description will be omitted. In the first embodiment, the upper magnets  51  are disposed at the equal intervals in the peripheral direction of the reaction vessel  116 , with the S pols facing the center of the reaction vessel  116 . On the other hand, according to the second embodiment, the magnets  22  of each stage are arranged such that, two magnets  22  facing each other have the same pole facing the center of the reaction vessel  116 , and two adjacent magnets have poles different from each other facing the center of the reaction vessel  116 . That is, the S pole and the N pole are alternately disposed along a periphery of the reaction vessel  116 . 
       FIG. 7  shows positions of a magnetic separation device according to a second embodiment of the present disclosure.  FIG. 7( a )  shows the positional relationship between the reaction vessel  116  and two-stage magnets  22  disposed in the magnetic separation device.  FIGS. 7( b ) and 7( c )  show the plan views of the magnetic separation device, and the magnet arrangements of the upper stage and the lower stage are shown, respectively. In the present embodiment, the number of the stages of the magnets  22  is shown as two as an example, but three or more stages may be provided. Further, in the present embodiment, as for the magnets  22 , four magnets  22  are disposed in one stage, but the effect the same as in the present embodiment can be obtained as long as the amount of disposed magnets is an even number. 
     First-stage (upper stage) magnets  71  from a top view as shown in  FIG. 7( b )  are disposed at the equal intervals in the peripheral direction of the reaction vessel  116 , in which two magnets  22  facing each other have the same pole facing the center of the reaction vessel  116 , and two adjacent magnets  22  have different poles facing the center of the reaction vessel  116 . On the other hand, second-stage (lower stage) magnets  72  from the top view as shown in  FIG. 7( c )  are disposed at the equal intervals in the peripheral direction of the reaction vessel  116 , in which two magnets  22  facing each other have the same pole facing the center of the reaction vessel  116 , and two adjacent magnets  22  have poles different from each other facing the center of the reaction vessel  116 . Further, the magnets are arranged such that the magnetic poles of the magnets  22  disposed adjacently in the upper-lower direction are different from each other. 
       FIG. 8  shows states of capturing the magnetic beads  21  in the magnetic separation device according to the second embodiment. In a case of the magnet arrangements according to the second embodiment, since the strong magnetic fields are generated near the center of the magnets  71  and  72 , the magnetic beads  21  are captured near the center of the magnets  71  and  72 .  FIG. 8( a )  shows a distribution pattern of the magnetic beads  21  when the magnetic beads  21  are captured on the inner wall of the reaction vessel  116  in the first washing process. As shown in  FIG. 8( a ) , in the first washing process, the liquid surface  61  of the washing liquid is set to a position higher than the upper magnets  71 .  FIG. 8( b )  shows the distribution pattern of the magnetic beads  21  when the magnetic beads  21  are captured on the inner wall of the reaction vessel  116  in the second washing process. As shown in  FIG. 8( b ) , in the second washing process, the liquid surface  62  of the washing liquid is set to a position near the upper edges of the upper magnets  71 . Further, as shown in  FIG. 8( c ) , the liquid surface  63  of the washing liquid is set near a portion between the upper magnets  71  and the lower magnets  72  in the third washing process. That is, according to the magnet arrangements of the second embodiment, the distribution pattern of the magnetic beads  21  generated when the magnetic beads  21  are captured on the inner wall of the reaction vessel  116  may be set so as not to overlap with the liquid surface. In other words, in each washing process, the automated analyzer controls the discharge amount of the washing liquid such that the height of the liquid surface is at the position where the magnetic field intensity is low. 
     According to the present embodiment, the magnetic beads  21  are always captured below the liquid surface, and the magnetic beads  21  do not aggregate on the liquid surface during the washing process in which the liquid amount is reduced. As a result, deterioration in the efficiency of the washing processes for removing impurities can be prevented, and a highly efficient automated analyzer can be obtained. 
     Third Embodiment 
     In the first embodiment and the second embodiment, heights of the magnets  22  in each of the upper and lower stages are the same. However, the heights of the magnets  22  may be different at each stage.  FIG. 9  shows magnet arrangements according to the third embodiment. In the magnetic separation device  124  shown in the third embodiment, the height of the upper magnets  91  is higher than the height of the lower magnets  92 . Even in such a case, the fact that the magnetic field intensity is high at both upper and lower edges of the magnets is the same as above, so that the magnetic beads  21  are captured at both upper and lower edges of the magnets in each stage. Therefore, as shown in  FIG. 9 , a distance between positions where the magnetic beads  21  are densely captured differs depending on the height of the magnets. In the case of the magnet arrangements as shown in  FIG. 9 , the liquid surface range  64  of the washing liquid  23  (a mesh pattern portion in the figure) in the second washing process can be made larger as compared with that in the first embodiment. In this way, by making the heights of the magnets it each stage different from each other, instead of being the same, it is possible to widen an applicable range of the discharge amount of the washing liquid  23  in the washing process. The liquid surface range  65  of the washing liquid  23  in the third washing process is the same as that in the first embodiment. 
     In the first to third embodiments described above, the positions of the liquid surfaces  61 ,  62 , and  63  of the washing liquid are defined based on, for example, a position where an inner wall surface of the reaction vessel  116  is in contact with the washing liquid in consideration of an influence of a meniscus force. For example, when a contact angle is small, that is, when the liquid surface is a concave, the position where the inner wall surface of the reaction vessel  116  is in contact with the washing liquid is higher than the center of the liquid surface. In addition, when the contact angle is big, that is, when the liquid surface is a convex, the position where the inner wall surface of the reaction vessel  116  is in contact with the washing liquid is lower than the center of the liquid surface. 
     &lt;Modification&gt; 
     In the first to third embodiments, the magnets  22  are disposed in two upper and lower stages. However, the magnets  22  may be disposed in only one stage. In this case, as for the magnets  22 , for example, all magnets  22  have the same pole facing the reaction vessel  116 , and are disposed at the equal intervals around the reaction vessel  116 . That is, the magnets  22  are disposed such that the magnetic field intensity is high at both upper and lower edges of the magnets  22 . Alternatively, the magnets  22  may be disposed so as to have a magnetization pattern the same as that in the first to third embodiments. In this case, the automated analyzer adjusts the amount of the washing liquid  23  in the first washing process such that the position of liquid surface is higher than the upper edges of the magnets  22 , and adjusts the amount of the washing liquid  23  in the second washing process such that the liquid surface is positioned in the center of the magnets  22 . 
     The invention is not limited to the embodiments described above and includes various modifications. For example, the embodiments described above have been described in detail for easy understanding of the invention, and the invention is not necessarily limited to those including all the configurations described above. In addition, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. In addition, a part of the configuration of each embodiment may be added, deleted, or replaced with another configuration. 
     REFERENCE SIGN LIST 
     
         
         
           
               1 : automated analyzer 
               101 : analysis unit 
               102 : control unit 
               103 : input unit 
               104 : display unit 
               111 : sample container 
               112 : first transport mechanism 
               113 : sample dispensing mechanism 
               114 : dispensing tip attaching and detaching section 
               115 : dispensing tip mounting rack 
               116 : reaction vessel 
               117 : reaction vessel mounting rack 
               118 : second transport mechanism 
               119 : opening on reaction vessel disk 
               120 : reaction vessel disk 
               121 : reagent container for measurement 
               122 : reagent disk 
               123 : reagent dispensing mechanism 
               124 : magnetic separation device 
               125 : transporting and aspirating-discharging mechanism 
               126 : stirring mechanism 
               127 : gripping mechanism 
               128 : aspirating nozzle 
               129 : discharging nozzle 
               131 : detector 
               132 : dispensing mechanism for detector 
               21 : magnetic beads 
               22 : magnet 
               23 : washing liquid 
               24 : incubator 
               51 : first-stage magnet 
               52 : second-stage magnet 
               61  to  63 : liquid surface 
               64  and  65 : applicable liquid surface range