Abstract:
First and second aspirator manipulation units operate a single-pipette in a coagulation analyzer for aspirating plasma samples from both rubber-capped as well as uncapped vessels. A first holder in the first aspirator manipulation unit actually retains the pipette, while a second holder in the second aspirator manipulation unit is configured to enclose the first holder leaving a predetermined amount of play. To move the pipette toward a sample vessel in a rack that has been shifted into aspiration position, the holders in the manipulation units are inter-fitted, and are translated down. If the pipette strikes a cap, a sensing means in the first aspirator manipulation unit signals a controller to operate the first aspirator manipulation unit to back the pipette upward slightly. Thereupon, the controller, via the second aspirator manipulation unit, actuates the second holder alone to press on the first holder to stab the pipette through the cap. For this operation, the pipette tip is cut obliquely and the rim of its inner wall is specially chamfered to prevent the punctured rubber in the cap from clogging the tip. After the pipette aspirates an aliquot of the plasma sample, the controller actuates the second holder in reverse to draw the pipette out from the cap. The first aspirator manipulation unit carries out other pipette manipulation operations alone. Accordingly, the pipette is driven differentially in accordance with the capped/uncapped status of the vessel present in the aspiration position.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to precision aspirators, suited for use in automated liquid sample analyzers, for taking up liquid from containers by suction. In particular the invention relates to precision aspirators employing liquid suction tubes that can pierce caps sealing the mouths of containers holding diagnostic samples and reagents, and that can discriminate among such containers. 
     2. Description of Related Art 
     Automated liquid sample analyzers, for example, blood-sample analyzing machines, employ an aspirating pipette to take up a predetermined amount, or aliquot, of sample liquid such as blood plasma sequentially from a row of tubular sample containers. The sample containers are held in a sample rack that is transferred in container-by-container increments into an aspirating position beneath the pipette. Each container is paused in the aspirating position, in which a mechanism manipulating the pipette brings it down into the container, actuates suction through the pipette to take up an aliquot, brings the pipette back up, and shifts it to an ejecting position. In the ejecting position, the aliquot is ejected into, for example, a reaction vessel containing reagents for a blood-analyzing test. 
     Some of the containers loaded into the sample rack may be sealed, with a rubber cap for example, or otherwise stoppered. The tips of the needle-type aspirating pipettes used for taking up aliquots from sample containers are cut obliquely to pierce a sealed or stoppered container. 
     An aspirating tube having an aspiration aperture formed on its circumferential surface apart from the tip, so that when the aspirating tube penetrates a rubber cap, rubber debris does not clog the aspirating tube, as Japanese Laid-Open Pat. App. No. 9-304400 discloses, is known. 
     On the other hand, Japanese Pat. No. 2511549, corresponding to U.S. Pat. No. 5,201,232, discloses a liquid sampling device having a sampling probe for withdrawing sample liquids from open containers, as well as a sampling needle for closed containers. Therefore, the liquid sampling device is operable to suit either type of containers—capped (closed) containers, or uncapped (open) containers. Furthermore, the disclosed liquid sampling device distinguishes open containers from closed containers using a detector that reads an identification label or card provided on the container exterior. 
     Nevertheless, the device as taught in Japanese Pat. No. 2511549, in order to identify the containers from which it withdraws samples, requires special labels or cards affixed to the containers, as well as a detector to read them. Consequently, if the labels or cards are affixed improperly, the device cannot identify containers correctly. In addition, equipping the device with two kinds of aspirators makes the mechanism large and complex. 
     If for example a single aspirating tube is to be used for both open and closed containers, some situations make it desirable to provide the aspiration aperture in the tip of the aspirating tube. For instance, the desire to improve quantitating accuracy in micro-samples of a few μl, to decrease sample-liquid dead volume (the quantity that cannot be aspirated and remains in the container), or to decrease the amount of aspirating tube immersed into a sample liquid in order to prevent inter-contamination of the liquids necessitates that the aspiration aperture be in the tip of the aspirating tube. However, if the aspiration aperture is provided in the tip of the aspirating tube, the tube is likely to get clogged when it penetrates the cap of a closed container. 
     In conventional liquid sampling devices, the aspirating tube is shifted vertically to take up an aliquot, which operation requires relatively little force to bring the pipette down into an open container, yet considerably greater force to stab the pipette through a sealed container. Supplying large force for an open container leads to mechanical losses, hampers agility and, leads to operational problems such as damage to the aspirating tube by its being crushed on the bottom of the container due to the container&#39;s vertical position. For example, to shift horizontally the liquid aspirating tube and its large drive source if integrated into one unit confronts the practical problems that the unit cannot travel horizontally at high speed due to its large size and weight, and that the horizontal shifting mechanism then also must be large. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to enable correct identification of liquid sample containers by employing a container-identifying device of simple constitution. 
     Another object of the present invention is to prevent the aspiration aperture in the sharp tip of an aspirating pipette from becoming clogged. 
     A further object of the present invention is to enable manipulation of a sample-liquid aspirating pipette for both closed and open containers by accordingly supplying appropriate force, in an aspirator adapted for operation in, for example, an automated analyzer. 
     An aspirator in accordance with the present invention functions in an automated analyzer to aspirate liquid aliquots from a row of capped and uncapped containers in a sample rack. horizontally transferred by a sampler incrementally into an aspiration position. Essential components of the aspirator include a needle pipette having an obliquely cut aspiration tip, first and second aspirator manipulation units, external force sensing means associated with the first aspirator manipulation unit for detecting external force acting on the pipette, and liquid-surface detecting means operative through the pipette. 
     The first aspirator manipulation unit includes a first holder that retains the pipette vertically, and a first drive means that vertically translates the first holder into and out of a container in the aspiration position. The second aspirator manipulation unit includes a second holder configured to enclose the first holder, leaving a predetermined amount of play. A second drive means for the second aspirator manipulation unit cooperates with the first drive means to translate the second holder vertically in tandem with the first holder, and operates independently of the first drive means to drive the second holder against the first holder. 
     An aspirator controller is connected to the first and second drive means and is responsive to both the external force sensing means and the liquid-surface detecting means; accordingly the aspirator controls the first and second aspirator manipulation units. 
     The aspirator controller is programmed to actuate the first and second drive means to translate the first and second holders vertically in tandem. If no external force is detected acting on the pipette by the external force sensing means, the controller continues to direct the first and second drive means to bring the pipette down until it contacts liquid in a container in the aspiration position. If the needle pipette does not contact liquid in the container in the aspiration position after the first and second holders have been translated a predetermined distance, the controller halts the first and second drive means. If external force is detected acting on the pipette by the external force sensing means, i.e., if the pipette tip strikes the top of a capped or stoppered container, the controller halts the first drive means and continues actuating the second drive means. This operation presses the second holder onto the first holder to stab the pipette through the cap or stopper. 
     Therein, to prevent the punctured rubber in the cap from clogging the tip, the obliquely cut aspiration tip of said needle pipette is inner-rim chamfered. 
     The aspirator operates automatically and checks for the presence of a cap/stopper on each container. Accordingly, in translating the first and second holders downward to the container, if the pipette does not encounter a cap/stopper, the second holder remains separated from the first holder within the predetermined amount of play. Consequently, the first holder, retaining the pipette, is shifted solely by the force from the first drive source. 
     On the other hand, if the container currently in the aspiration position is closed, the second holder alone is driven, and presses down on the first holder. Consequently, the stabbing pipette is actuated solely by the force from the second drive source. 
     Accordingly, the first drive source supplies relatively small force to the pipette in translating it vertically, whereas the second drive source supplies relatively large force to the pipette to stab it vertically through a cap/stopper. That is, the drive mode (the magnitude of force supplied) for shifting the pipette is altered accordingly, eliminating mechanical losses occurring otherwise, and gaining agility and reliability in the operation of the aspirator. 
     The aspirator in accordance with the present invention employs the pipette to discriminate closed from open containers, wherein the fact that a present container is either open or capped/stoppered is identified. Furthermore, since the aspirator can determine absence of liquid contact and of external force acting on the pipette after translating the pipette a predetermined distance, the aspirator therefore can determine that there is no liquid present or that there is no container present. The drive sources in this case can be controlled accordingly not to lower the pipette any further, preventing it from damage. 
     In accordance with the present invention, as described above, since the presence of a cap/stopper is directly detected using the pipette, misjudgment in identifying containers is unlikely. 
     The pipette employed in an aspirator embodied in accordance with the present invention is preferably made of metal for strength, and because the aspirator&#39;s liquid-surface detection capability derives from capacitance established in the pipette. Further, to impart anticorrosion and anti-abrasion properties to the pipette, it is preferable that it is manufactured from stainless steel tubing whose outer surface is coated with a hard coating such as chromium nitride (CrN). 
     As noted above, to prevent clogging at the tip of the pipette, the obliquely cut surface is preferably inner-rim chamfered; i.e., formed not to give rise to acute-angle edges on the inner circumferential rim of the tip opening The entire inner circumferential rim of the obliquely cut pipette tip opening may be chamfered to remove any and all acute-angle edges present on the rim. However, only that half of the inner circumferential rim where acute-angle edges arise when the pipette tip is cut may alone be chamfered. 
     Types of liquid that may be aspirated by the pipette are not particularly limited; one example wherein the aspirator is employed in an automated analyzer, however, is blood samples such as plasma. In automated analyzers, containers holding the liquid samples for assaying are preferably loaded into a sample rack that is conveyed into aspirating position beneath the pipette. More specifically, in automated analyzers a device known as a sampler functions to transfer the sample rack, into which a plurality of containers are set or “loaded,” sequentially into position beneath the pipette for aspirating aliquots from the containers vessel-by-vessel. 
     Concerning use of the aspirator, it is preferable that the first aspirator manipulation unit including the external force detection means is horizontally shiftable. 
     From the foregoing explanation, it will be understood that though the surface of the liquid contained differs in position with each open container, in response to the liquid-surface detection means the controller halts the first drive source to stop the downward travel of the pipette. In particular, the amount of liquid that attaches unnecessarily to the aspirating tube may be minimized. In addition, though the position of the bottom of each open container may differ, in response to the external force detection means the controller halts the first drive source to stop the downward travel of the pipette. This prevents the pipette from crashing and breaking on the bottom of the container. 
     With closed containers, after the pipette has been stabbed through a cap/stopper, in response to the liquid-surface detection means the controller halts the second drive source to stop the downward travel of the pipette. 
     It is preferable that the external force detection means includes a sensor that detects colliding of the pipette tip against an obstacle. This type of sensor is usually known as a “crash sensor” and is provided for detecting crashing of the pipette against an object. The pipette is stopped immediately after it hits an object and is evacuated in order to avoid damaging itself. In accordance with the present invention, then, the containers employed in an automated analyzer into which the aspirator as described above is adapted may be identified using such a crash sensor provided in the aspirator. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic rendering of the general configuration of an aspirator in accordance with the present invention, seen from the left side of the device with respect to an operator; 
     FIG. 2 is a partially cut away, partly in section, fragmentary view corresponding to FIG. 1, illustrating details of the aspirator mechanism; 
     FIG. 3 is a fragmentary, enlarged view depicting the tip of a pipette employed in the aspirator; 
     FIG. 4 is a transverse sectional view corresponding to FIG. 3; 
     FIG. 5 is a fragmentary, enlarged sectional view illustrating the tip of a conventional pipette penetrating a stoppered sample vessel; 
     FIG. 6 is a front elevational view of a blood coagulation analyzer sample rack into which a row of vessels is loaded, from which aliquots are taken up by the aspirator; and 
     FIGS. 7A and 7B are a flow chart of a control program executed by an aspirator controller in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The aspirator in this embodiment is built into a blood coagulation analyzer. FIG. 2 is an end view seen from the left side of the blood coagulation analyzer with respect to an operator, wherein the right side of the figure is the front end of the device and the left side is the device interior. A sample rack  66  that holds a plurality of sample containers  68  lined in a row is transferred one container at a time by a sampler (not shown) in the direction in the figure from the reverse to the obverse face of the sheet. 
     As shown in FIG. 1, the aspirator comprises a first aspirator manipulation unit  10  and a second aspirator manipulation unit  11 . The first aspirator manipulation unit  10  is provided with a first holder  30  that holds a pipette  12 , which is a liquid aspirating pipe, and a first drive source  43  that shifts the first holder  30  up and down. The second aspirator manipulation unit  11  is provided with a second holder  74  that engages the first holder  30 , and a second drive source  86  that shifts the second holder  74  up and down. The first aspirator manipulation unit  10  is made to be horizontally shiftable. The double-dotted broken lines in FIG. 1 indicate the situation in which the first aspirator manipulation unit  10  is in its forward-most position, and the first holder  30  is adjacent and the second holder  74  where the two can engage. The solid lines indicate the situation in which the first aspirator manipulation unit  10  is in its rearward position, and the first holder  30  is apart from the second holder  74  where the two cannot engage. 
     The pipette  12  has an inner passage  14  (referring to FIG.  4 ), and is a cylindrical pipe made of stainless steel having an outer diameter of 2.0 mm, an inner diameter of 1.3 mm and overall length of 130 mm. An electric wire  34  is attached to the upper end portion of the pipette  12 . The electric wire  34  is connected to a liquid-surface detection circuit  35 , which detects liquid surfaces based on the change in capacitance when the tip of the pipette  12  contacts the surface of a liquid. A tube  36  is joined to the top end of the pipette  12 , and connected to a liquid quantity meter  37  such as a syringe pump. In this embodiment, the first aspirator manipulation unit  10  is shifted horizontally by respective third and fourth drive sources  94 ,  96 . 
     Referring to FIGS. 3 and 4, the pipette  12  near the lower end is constricted, narrowing to 1.2 mm outer diameter and 0.5 mm inner diameter, and as shown in the figures is sharply cut obliquely with respect to the pipette axis. The inner passage  14  opens in aperture  18  on oblique-cut surface  16 . Merely by being cut just obliquely, an acute-angle edge arises on the inner wall rim  21  of the oblique-cut surface  16  (the acute-angle edge arises around the upper half  20 , and an obtuse angle edge arises around the lower half  22 .) 
     FIG. 5 shows the situation wherein a conventional pipette  13  stabs a rubber cap. An acute-angle edge  23  present on the inner wall rim severs the rubber cap  24  when the pipette  13  stabs it, and a portion of the severed rubber cap (a rubber crumb) gets into the opening such that it is immediately blocked. 
     Therein, a chamfering process for removing the acute-angle edge is carried out on the upper circular half  20  of the oblique-cut surface  16  on the constricted lower end of the pipette  12 . This accordingly does away with the acute-angle edge around the entire inner wall rim. Even in continuous tests of at least 30,000 times it was confirmed that no blockage occurred in the piercing end of a pipette thus configured. 
     A region of the outer wall of the pipette  12 , about 80 mm from the bottom, is subjected to a chromium nitride (CrN) coating process in order to elevate its anti-abrasion properties. 
     Turning again to the end view in FIG. 2 of an embodiment of an aspirator, a first chassis  44  serves as a framework for the first aspirator manipulation unit  10 . A belt  42  connects pulleys  40  and  41 , and pulley  41  is directly connected to the shaft of the first drive source  43  (a stepping motor in this embodiment). A rocker piece  50  is pivotably supported on a second chassis  38  and is attached to a portion of the belt  42  via a clasp  48 . The second chassis  38  is guided by vertically restricting guide shafts  46  and  47  that are mounted on the first chassis  44 . The first holder  30 , in which the pipette  12  is retained, is also mounted on the second chassis  38 . Accordingly, by actuating the first drive source (stepping motor)  43  to turn the pulley  41 , the rocker piece  50  can be shifted up and down in attachment to the belt  42 , wherein the first holder  30 , the second chassis  38 , and the rocker piece  50  are shifted together vertically. 
     An urging means  52 , in this case a coiled compression spring, is disposed between the second chassis  38  and the rocker piece  50 . In the state wherein no external force is acting on the pipette  12 , the rocker piece  50  is urged clockwise in FIG. 2 on a fulcrum  51 , and contacts an abutment  56  provided on the second chassis  38 . 
     An external force detection means  54  for detecting upward external force when acting on the pipette  12  is provided in the first aspirator manipulation unit  10 , as indicated in FIG.  1 . The external force detection means  54  comprises a sensor  53 , in this case a micro-switch, and an external force detection circuit  55  to which the sensor  53  is electrically connected. 
     If when descending the pipette  12  comes into contact with something such that an external force acts upwardly on it, the fulcrum  51  side of the second chassis  38  halts, but the clasp  48  side of the rocker piece  50  shifts downwardly. The rocker piece  50  is therefore rotated relatively counterclockwise as indicated by the double dotted broken lines in FIG. 2, against the compressive force of the spring  52 . The micro-switch  53  senses this very slight fluctuation, which is detected by the external force detection circuit  55  through its electrical connection to the micro-switch  53 . 
     A guide grommet  58 , attached to the first chassis  44 , functions as a guiding means for the vertically travelling pipette  12 . Because the pipette  12  is  100  mm or longer, the guide grommet  58  is furnished in this embodiment so that the pipette  12  will not quiver horizontally when it is travelling. 
     A washing element  60  having a through-hole  63  (shown in FIG. 1) cleanses the wall of the pipette  12  by supplying cleansing fluid from a port  62  to the through-hole  63 , and discharging waste fluid from a port  64 . The washing element  60  is shifted up and down by a drive source  72 , in this case an air cylinder, via a link  70  guided on vertically disposed guide rail  71 . 
     Whereas the first aspirator manipulation unit  10  has just been described, the second aspirator manipulation unit  11  will in turn be explained. The second holder  74  is engageable with the first holder  30 . The blood coagulation analyzer is configured in this embodiment such that two holders  30  and  74  couple by convex-concave intermeshing. Specifically, the first holder  30  includes convex part  32 . The second holder  74  has a concave part  76  into which the convex part  32  fits with a gap. The vertical width of the convex part  32  is about 6 mm, and that of the concave portion  76 , 14 mm. Accordingly, the first holder  30  has room to travel without interference from the second holder  74 , i.e., it has non-interference margin of 8 mm. 
     The second holder  74  is shifted up and down by a mechanism as follows. A drive shaft  80  having a spiral groove is rotatably supported on bearings  84  and  85 . A carriage  82  is screwed onto the drive shaft  80  and travels vertically following the rotation of the drive shaft  80 . A pulley  89  is attached to one end of the drive shaft  80 . The second drive source  86  herein is a stepping motor, to which a pulley  88  is fixed. A belt  90  around the pulleys  88  and  89  accordingly transmits rotation of the stepping motor  86  to the drive shaft  80  and in turn the carriage  82 . The second holder  74  is joined to the carriage  82  via a link  78  and is guided in its travel by the guide rail  71 . 
     During engagement of the second holder  74  with the first holder  30 , current supply to the first stepping motor  43  is lost, wherein rotating the second stepping motor  86  causes the second holder  74  to press on and shift the first holder  30 . The external force in so doing compels the first stepping motor  43  to rotate. 
     In this embodiment, the blood coagulation analyzer is configured such that the first aspirator manipulation unit  10  is shifted back and forth (right and left in FIG. 1) by the third drive source  94 , herein also a stepping motor. Moreover, the analyzer is configured such that the first aspirator manipulation unit  10  is shifted laterally (in and out of the plane of FIG. 1) by the fourth drive source  96 , also a stepping motor. When the first aspirator manipulation unit  10  is at the front end of the analyzer (right side in FIGS.  1  and  2 ), the first holder  30  and the second holder  74  come into engagement. When the first aspirator manipulation unit  10  is rearward (left side in the figures), the engagement of the two is released, wherein the pipette  12  is shifted vertically solely by the rotation of the first stepping motor  43 . 
     In this embodiment of the present invention, the sample liquid held in the sample containers is plasma, and the (not shown) sampler sets the sample containers into the sample rack  66 , which in this instance can accommodate  10  containers, and conveys them sequentially into position beneath the aspirator. Specifically, the sample rack  66  is shifted intermittently from right to left in the FIG. 6 orientation one container at a time. 
     The sample containers used in this embodiment are gross divided into three categories. The first type, capped containers A, B, C, D, E, and F, rides on the bottom wall of the sample rack  66  (the container bottoms contact the sample rack bottom wall). The caps on each container differ. The second type, open container G, also rides on the bottom wall of the sample rack  66  (the container bottom contacts the sample rack bottom wall). The third type, open containers H, I, and J, are loaded above the sample rack bottom wall—the containers are either furnished with a flange which sits on the upper wall of the sample rack (H, J), or which sits the upper end of an open container for loading (I). The bottom of any of the third type of open container does not contact the bottom wall of the sample rack. 
     In the present embodiment, the underside of the through-hole  63  through the washing element  60  flares into a tapered cup  61 , enabling containers to be held without slipping out of position even wherein they are peculiar, like container F (vacuum blood-sampling tube “MONOVETTE” made by Sarstedt Co.) in FIG.  6 . 
     Referring now to the FIG. 7 flow chart, the following details a program for operating the aspirator embodied in a sample analyzer in conformity with the present invention. A control unit  92 , indicated in FIG. 1, receives signals from the sensor  53  via the external force detection means  54  and drives each of the stepping motors—i.e., the first through fourth drive sources  43 ,  86 ,  94  and  96 —respectively in accordance with the program. 
     Steps S1.1 through S1.3: Detecting Presence of Container Caps 
     In the situation wherein the first aspirator manipulation unit  10  is located in its forward-most position, the pipette  12  is lowered a predetermined distance from its initial position (uppermost point), going through the washing element  60  (S1.1). The pipette  12  is lowered herein by rotating the first and second stepping motors  43  and  86  to lower together the first and second holders  30  and  74  while maintaining their non-interfering engaged state, as described above. During this operation, in step S1.2 the control unit  92  monitors signals from the external force detection circuit  55 . If external force acting on the pipette  12  is detected, the control unit  92  determines that a cap is present on a shut container and, in step S2-1.1, halts the first stepping motor  43 . If the control unit  92  does not detect external force acting on the pipette  12  when it has been lowered the predetermined distance, the control unit  92  determines that an open container is present without a cap (S1.3). The capped/uncapped information determined in step S1.2 is stored for reference in step 4, noted below. 
     Steps S2-1.1 through S2-1.5: Lowering Pipette wherein Container is Capped (Piercing) 
     Following step S2-1.1, which halts the first stepping motor  43  upon detection of external force in step S1.2, in step S2-1.2 the tip of the pipette  12  is separated from the cap by rotating the halted first stepping motor  43  very slightly in the reverse direction. Then, in step S2-1.3, by running the drive source  72 , the tapered cup  61  on the underside of the washing element  60  is lowered onto the cap  69  (as indicated in FIGS. 1 and 2) of the present one of the containers  68  to press-hold it. In step S2-1.4 the current supply to the first stepping motor  43  is stopped and the second stepping motor  86  is rotated, actuating the second holder  74  to push the first holder  30  down, stabbing the pipette  12  through the cap  69  on the present container  68 . Herein, accordingly, the power of the second motor  86  alone lowers the pipette  12 . Then, in accordance with either liquid-surface detection information from the liquid-surface detection circuit  35 , or previously established position information indicating that the pipette  12  has reached a lowermost point, in step S2-1.5 the second stepping motor  86  is halted, which also stops the pipette  12 . 
     Steps S2-2.1 and S2-2.2: Lowering Pipette wherein Container is Open 
     If the pipette  12  has not encountered an external force acting upon it after it has been lowered the predetermined distance in step S1.3, in step S2-2.1 the pipette  12  is lowered further. Herein, by continuously rotating the first and second stepping motors  43  and  86 , the first holder  30  is lowered without it contacting the second holder  74 . Accordingly, the power of the first stepping motor  43  lowers the pipette  12 . Then, in accordance with information from either the liquid-surface detection circuit  35  or the external force detection circuit  55 , or in accordance with previously established position information indicating that the pipette  12  has reached a lowermost point, in step S2-2.2 the first stepping motor  43  is halted, which also stops the pipette  12 . 
     Steps S3.1 Through S3.3: Aspirating Sample Liquid 
     Step 3.1 determines based on the result of either step S2-2.2 or S2-1.5 whether upon lowering the pipette  12  into the present one of the containers  68  the surface of the liquid sample (plasma) has been detected. If so, in step S3.2, the pipette  12  is lowered a predetermined distance according to the aspiration volume, and the liquid quantity meter  37  is operated to aspirate the predetermined volume (in the present embodiment, 5 to 500 μl) of plasma through the aperture  18  at the tip of the pipette  12 . 
     If the lowering pipette  12  is halted in step S2-1.5 by reaching its lowermost point, or is halted in step 2-2.2 by the detection of external force or by reaching its lowermost point, that means there is no plasma to be aspirated. Therefore, in step 3.3 a “Will Not Execute Aspiration/No Sample Liquid” error message is output. 
     Steps S4, S4-1.2 and S41.2: Raising Pipette wherein Container is Capped 
     If step  4  determines from the information recorded in step S1.2 that the present container  68  is capped, then in step S4-1.1, with the current supply to the first stepping motor  43  stopped, the second stepping motor  86  is reverse-rotated. Accordingly, the second holder  74  pushes up the first holder  30 , and the pipette  12  is pulled out of the cap  69  on the present container  68 . Herein, the power of the second stepping motor  86  alone raises the pipette  12 . At the same time, washing liquid is supplied to the washing element  60  to clean the outer wall of the pipette  12  and waste fluid is discharged. When the pipette  12  is completely pulled out, in step S4-1.2 the washing element  60  is raised to release the hold on the present container  68 , and the pipette  12  is returned to the initial position. 
     Steps S4, S4-2.1 and S4-2.2: Raising Pipette wherein Container is Open 
     If step 4 determines from the information recorded in step S1.2 that the present container  68  is not capped, then in step S4-2.1 the first and second stepping motors  43  and  86  are reverse-rotated to raise the first holder  30  without it contacting the second holder  74 . Herein, solely the power of the first stepping motor  43  raises the pipette  12 . At the same time, washing liquid is supplied to the washing element  60  to clean the outer wall of the pipette  12  and waste fluid is discharged. In step S4-2.2 the pipette  12  is returned to the initial position. 
     Step S5: Shifting Pipette Rearward 
     Rotating the motor  94  shifts the first aspirator manipulation unit  10  rearward. This accordingly releases the engagement of the first holder  30  with the second holder  74  completely. The first aspirator manipulation unit  10  further may be shifted laterally as necessary by rotating the stepping motor  96 . 
     Step S6: Lowering Pipette 
     The pipette  12  is lowered a predetermined amount by rotating the first stepping motor  43  only, since engagement of the first holder  30  with the second holder  74  is released. 
     Step S7: Sample Liquid Ejection 
     By operating the liquid quantity meter  37 , a predetermined volume of plasma is ejected through the aperture  18  in the tip of the pipette  12  into a reaction vessel (not illustrated). 
     Step S8: Raising Pipette 
     This step reverse-rotates the first stepping motor  43  to raise the pipette  12 . Then, the inner and outer walls of the pipette  12  are cleansed by, for example, driving stepping motor  94  or  96  to transfer the pipette  12  to a not-shown washing vessel, and cleansing it there. Alternatively, the inner and outer walls of the pipette  12  may be cleansed by supplying washing liquid through the inner passage  14 , and also supplying washing liquid to the washing element  60 , and discharging the waste fluid from the washing element  60 . 
     Step S9: Shifting Pipette Forward 
     This step reverse-rotates the motor  94  to shift the first aspirator manipulation unit  10  forward, and returns the pipette  12  to its initial position. This brings the first holder  30  into the state in which it can engage with the second holder  74 . 
     Step S10: Sample Rack Transfer 
     The sampler is driven to shift the sample rack  66  by one container  68 , and stopped. Then, the above-noted steps are executed in sequence. 
     Various details of the present invention may be changed without departing from its spirit nor its scope. Furthermore, the foregoing description of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.