JPH0716614B2 - Micro pipette - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention sucks and discharges a sample liquid in a cylinder hole of a tip while an air layer is interposed between the tip of a piston shaft and a sample liquid to be sucked in, so-called PCR (Polymerase Chai).
n Reaction) method, it is an object of the present invention to provide a micropipette which is not affected by suspended bacteria in a sample solution and has high dispensing accuracy.

[0002]

2. Description of the Related Art As a first conventional example of a micropipette,
For example, the applicant of the present invention has previously filed a patent application by Japanese Patent Application No. 62-234512 (Japanese Patent Laid-Open No. 64-75042) “Variable Pipette”. The structure is such that the cylinder housing is attached to the body of the pipette, the tip is detachably attached to the tip of the cylinder housing, and the piston (plunger) of the shaft that slides in the axial direction is fitted in the cylinder chamber of the cylinder housing. . Then, the piston moves up and down in the cylinder hole in the pipette body (that is, not in the cylinder hole in the tip), so that the sample is sucked into the tip and then discharged. In principle, the tip is ejected by the eject mechanism and not reused each time, thereby preventing the possibility of sample mixing.

However, according to this, a large amount of air is always present in the space between the piston and the sample (that is, the space inside the cylinder chamber and the tip). Therefore, this pipette is applied to a microdispensing operation of 0.1 to 25 microliters such as the so-called PCR method to clone (amplify) DNA, for example. Then, when a sample solution containing DNA is aspirated and discharged to perform dispensing, the floating bacteria in the sample solution aspirated by the pipette evaporate each time during the dispensing operation several times, and Within a few times, a relatively large amount of floating bacteria may accumulate and propagate in the cylinder chamber. When a large amount of the above-mentioned miscellaneous bacteria are discharged and dispensed at one time by the dispensing work several times, not only the DNA but also a large amount of miscellaneous bacteria are cloned, and the desired accurate DN is obtained.
There is a drawback that the A cloning work cannot be identified.

A second conventional example is US Pat. No. 467.
There is a so-called positive displacement type, such as the pipettes of 2857 and 4023716. The structure is such that a tip having a relatively small diameter cylinder hole is detachably attached to the body of the pipette or an extension thereof, and a relatively small diameter piston shaft (plunger) of a shaft that slides in the axial direction. Is fitted in the cylinder hole. Then, the piston shaft moves up and down in the cylinder hole of the tip (that is, not in the pipette body), so that the sample is sucked into the tip and then discharged. In principle, the chips are similarly ejected by the eject mechanism each time.

According to this, since the piston and the cylinder have a relatively small diameter, it is suitable for the work of dispensing a small amount of the sample such as the above PCR method, and when the sample is sucked, the piston shaft has a cylinder hole. Since it reaches the lower end, there is almost no space in which air intervenes between the piston shaft and the sample when the sample is sucked. Therefore, unlike the first conventional example, there is no possibility that floating bacteria will accumulate in the cylinder chamber, and accurate DNA cloning can be performed.

[0006]

However, in the second conventional example, since no air layer is originally present between the tip of the piston shaft and the sample, when the sample is discharged by the piston shaft, the air layer is not formed. The pushing pressure eliminates the action of blowing the sample solution off the chip. Therefore, in the type in which the piston shaft does not protrude from the cylinder hole (see US Pat. No. 4,672,857), the type in which the piston shaft protrudes from the cylinder hole and in the type in which the piston shaft protrudes from the cylinder hole (see US Pat. No. 4,023,716) are used. However, there is a drawback in that a part of the sample liquid remains between the protruding piston shaft and the outer surface of the tip end, and the volumetric accuracy of the dispensing is apt to be reduced by that much.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks of the prior art, and has a structure in which a pipette body (1, 35) and an axial direction in the pipette body (1, 35) are arranged. Shaft unit (41) slidably housed and biased upward by spring means (43, 32)
A pipette having a shaft unit (41) for detachably holding a piston (54, 54 ') at its tip and detaching the piston at a lower slide limit position, and a pipette. A tip (58, 58'58 ") removably attached to the tip of the body (1, 35) and into which the piston (54, 54 ') is inserted in the cylinder hole (58c), and the pipette body ( One, three
5) is axially slidably mounted and urged upward by spring means (53), and is pushed and slid by the shaft unit (41) to push the tip downward, whereby the tip (58). , 58 ',
58 ″) and an ejector means (51) for separating the piston (54, 54 ′) from the shaft unit together with the pipette body, and the arrangement relationship between the tip and the piston is that the shaft unit (41) is When the sample is slid downward by a predetermined stroke (L ₁ ) to suck the sample into the chip, the chip (58, 58 ′,
58 ") in the cylinder hole (58c), a shaft unit (41) is set so that air of a predetermined size (l ₁ ) is interposed between the tip of the piston and the tip of the tip, and the sucked sample is discharged. After sliding by the stroke (L ₁ ) downwards and further sliding downward by the excess stroke (L ₂ ), a predetermined size (l ₂ ) is still provided between the piston tip and the tip tip in the cylinder hole. The amount of air is set to be interposed.

[0008]

According to the above construction, the sample is sucked into the chip together with a small amount of fresh air each time. Therefore, as compared with the first conventional example, in which the sample is a liquid containing DNA, in comparison with the structure in which a large amount of stagnant air (suspended bacteria are easily proliferated therein) is sucked up to the cylinder chamber of the pipette body. Accurate DN, DNA solution is not affected by floating bacteria
Amplification (cloning) of A can be performed.

Further, the sample is dispensed while a slight amount of air is interposed between the piston shaft and the sample, and further, the excess stroke (L ₂ ) is further pushed out by the exhaust air and blown off. Therefore, the sample is less likely to remain at the tip of the chip,
The dispensing volume accuracy can be improved.

[0010]

1 is a side view and FIG. 2 is a plan view of a micropipette according to the present invention, and FIGS. 3 to 5 are longitudinal sectional views of the micropipette, respectively, and lines 4-4 and 5-5 in FIG. 6 to 9 are longitudinal sectional views showing a sequential operation of the above micropipette, respectively.

1 to 3, reference numeral 1 denotes a substantially cylindrical resin body having an upper hole 1a having a substantially elliptic cross section and a lower hole 1b having a circular cross section, and further having a step portion 1c at a substantially axial center thereof. Rib 1d
(See FIG. 4), a pair of guide ridges 1e having a predetermined axial length (see FIG. 4), a dispensing amount digital display window 1f, and a screw hole 1g at the lower end.

Reference numeral 2 is a known dispense amount digital display mechanism, which has a fixed plate 3 and a pressing block 4 each having an elliptical cross section.
One drive gear 5 (having a D-shaped cross-section hole thereof is integrally rotatably fitted to a D-shaped cross-section shaft portion of an upper shaft 26 described later) between (having a central screw hole 4a), respectively corresponding to the outer circumference. Three driven gear drums 6 (each individually fitted to the upper shaft 26 so as to be separately rotatable) in which numbers 0 to 9 for digit display are arranged, and separately supported at the pinion shaft 7 are 2 The pinion gears 8 are provided in between.

The display mechanism 2 is inserted into the elliptical hole 1a of the body 1 until the fixing plate 3 comes into contact with the step 1c. In addition, 9 is a washer, 10 is a spacer ring fitted to the inner periphery of the two driven drums 6 on the right side in the figure to adjust the distance between the drums, respectively, and 11 is a screw hole of the pressing block 4. It is a nut that is inserted by screwing with the pinion shaft 7 to fix it.

A resin cap 12 is inserted into the opening of the elliptical hole 1a of the body 1 while pressing the display mechanism 2 and fixed to the body 1 with screws 13 and 14.

Reference numeral 21 denotes a lock mechanism for locking the rotation of the upper shaft 26, which will be described later, and includes a lock screw sleeve 22, a lock handle 23 that is integrally rotatably fitted to the upper end of the lock screw sleeve 22, and a D-shaped section shaft of the upper shaft 26. It comprises a lock plate 24 which is integrally rotatable with the upper shaft 26 by having a D-shaped cross-section hole which is penetrated by the portion. The lock screw sleeve 22 is screwed into the screw hole 4a of the holding block 4 and presses the lock plate 24 against the holding block 4 via the washer 25, so that the lock plate 24 is pulled and the upper shaft 26 integral therewith is pulled. It has the function of blocking or locking the rotation.

Reference numeral 26 denotes an upper shaft having a substantially D-shaped cross-section shaft portion extending over substantially the entire length thereof, and the lock mechanism 2 is provided in the body 1.
1, the display mechanism 2 is penetrated and stored. Upper shaft 2
The D-shaped cross-section shaft portion of 6 penetrates the D-shaped cross-section hole of the screw body 27 below the fixing plate 3 and can rotate integrally with the screw body 27, and a stopper collar is provided just above the lower end screw portion 26a. Two
8 is fitted and a push button 29 is attached to the upper end.

A movable nut 30 is a rib 1d of the body 1.
Inside (see FIG. 4), the guide ridges 30a on both sides thereof are guided by the guide ridges 1e, respectively, which cannot be rotated with respect to the body 1, but are mounted slidably in the axial direction and in the central screw hole 30b. The screw body 27 is screwed. The movable nut 30 is urged upward by a two-stage spring 32 arranged between the movable nut 30 and the two-stage spring receiver 31 and having a relatively strong spring force.

Reference numeral 35 denotes a resin nozzle housing, which is attached to the body 1 by screwing the upper screw portion 35a into the lower screw portion 1g of the body 1 and holds the ejector pipe 51 described later in the next screw portion 35b. A pair of axial holes 35d into which the cap 52 is screwed, and which is inserted by the pair of guide recesses 35c (see FIG. 5) on both sides thereof and the pair of axial stopper portions 51a of the ejector pipe 51.
(In practice, it is arranged at the position shown in FIG. 5, but in FIG. 3 it is shown at a position where the angle is changed by 90 degrees for the sake of clarity.)
Have. Further, the nozzle housing 35 has a step portion 35e for receiving the one-step spring receiver 37, a locking convex portion 35f for locking a tip 58 described later, and a sleeve 4 described later.
5 has a step portion 35g that is abutted by the flange portion.

Reference numeral 38 is an intermediate shaft, 39 is a lower shaft, 40 is a chuck for chucking a piston 54, which will be described later, and they are successively connected and fixed in the axial direction by screwing with each other. The shaft 26 is screwed and fixed to the threaded portion 26 a. Therefore, all the shafts 26, 38, 39, the chuck 40 and the piston 54 form an axially integral shaft unit 41. The shaft unit 41 is biased upward by a first-stage spring 43, which has a relatively weak spring force and is arranged between the E-ring 42 attached to the intermediate shaft 38 and the first-stage spring receiver 37.

The chuck 40 is similar to the so-called mechanical pencil lead holding mechanism, in which each portion is elastically outward in the radial direction by an axial cut 40a having a cross-shaped cross section in the tapered expanded portion at the lower end of the chuck. The chuck portion 40b is composed of four parts which spread in a radial direction, and the chuck portion 40b is restricted to move inward in the radial direction by the sleeve 45 biased downward by the spring 44 and chucks the piston 54. ing.

Reference numeral 51 denotes an ejector pipe, which is fitted from below onto the outer periphery of the nozzle housing 35 and has a pair of stoppers 51a extending in the axial direction with an arcuate cross section (actually, it is arranged at the position shown in FIG. In FIG. 3, for clarity, 9
(Shown at a position where the angle is changed by 0 degree) penetrates through the pair of axial holes 35d of the nozzle housing 35 and projects upward. The ejector pipe 51 has a pair of guide ridges 51.
b (see FIG. 5) is each guide groove 3 of the nozzle housing 35.
Since it is guided by 5c, it is not rotatable with respect to the nozzle housing 35, but is slidable in the axial direction. A holding cap 52 is screwed into the next-stage screw portion 35b of the nozzle housing 35. Therefore, the ejector pipe 51 is biased upward by the spring 53 housed in the holding cap 52.

Reference numeral 54 denotes a piston. As shown in FIGS. 3 and 10, a resin-made piston head portion 56 (consisting of a chucked portion 56a and a stopper portion 56b) is insert-molded on the upper end of a thin metal piston shaft 55. I will do it.

Reference numeral 58 is a resin-made substantially conical tip, and as shown in FIGS.
It has an intermediate-diameter stopper portion (storage portion) 58b and a small-diameter cylinder hole 58c, an O-ring 59 is stored in the stopper portion 58b, and an O-ring retainer 60 is press-fitted. The tip 58 is locked to the nozzle housing 35 by engaging the locking concave portion 58a with the locking convex portion 35f. At this time, the chucked portion 56a of the piston 54 is chucked by the chuck portion 40b of the chuck 40, the upper end of the stopper portion 56b is in contact with the lower end of the chuck portion 40b, and the piston shaft 55 is the cylinder hole of the tip 58. It is inserted in 58c. According to the above configuration, the space below the O-ring 59 of the cylinder hole 58c is sealed by the O-ring with respect to the space above it. Therefore, according to this seal structure, the inner diameter of the cylinder hole 58c does not have to be a size that exactly fits the outer diameter of the piston shaft 55 for the reason described later, and has a radial gap with respect to the outer diameter of the piston shaft. Such a relatively large inner diameter can be achieved, the injection molding of the chip becomes easy, and the dispensing accuracy of the sample becomes stable.

Therefore, in the above structure, the shaft unit 41 (the upper shaft 26, the intermediate shaft 38, the lower shaft 39, the chuck 40 and the piston 54) is
The stopper collar 28 is positioned by abutting the screw body 27 (which is screwed into a predetermined position with respect to the movable nut 30) by being urged upward by the weak first-stage spring 43.
At this time, the tip of the piston shaft 55 of the piston 54 is located near the upper end in the tip cylinder hole 58c. Further, at this time, since the lock plate 24 is non-rotatably fixed by the lock mechanism 21, the upper shaft 26 penetrating this, that is, the shaft unit 41 itself is non-rotatable and can only slide in the axial direction.

The movable nut 30 is urged upward by a strong two-stage spring 32 to come into contact with the fixed plate 3 to be positioned. Further, the ejector pipe 51 has a spring 53.
Is urged upward by the stepped portion 51c so that the stepped portion 51c comes into contact with the lower surface of the next stage screw portion 35b of the nozzle housing 35 and is positioned.

Next, the operation of the micropipette will be described with reference to FIGS. 6 to 9.

First, in FIG. 6, when the body 1 of the micropipette is held with one hand and the push button 29 is pushed down with the thumb, the shaft unit 41 and its piston 54 resist the first-stage spring 43 and, as shown in FIG. , And the stopper collar 28 comes into contact with the upper surface of the bottom portion of the movable nut 30 by moving downward by the first stroke L ₁ (for example, 20 mm). At this time, as shown in the figure, a space in which a small amount of air of a size l ₁ intervenes remains between the lower end of the piston shaft 55 and the lower end of the tip 58 of the cylinder hole 58c. Chip 58 in this state
Dip the lower end of the sample into the sample.

Next, when the pressing force is released while the lower end of the tip 58 is immersed in the sample, the shaft unit 41 and the piston 54 return upward to the position shown in FIG. As a result, a predetermined amount of the sample corresponding to the stroke L ₁ of the cylinder hole 58c is inserted in the tip 58 between the lower end of the piston shaft 55 and the above-mentioned dimension l.
It is inhaled with _one minute of air interposed.

Next, the tip of the tip 58 is inserted into the dispensing container and the button 29 is pushed down again. Then, similarly to the case described above, the shaft unit 41 moves down by the dimension L ₁ , and the sample is discharged from the tip 58 during this period and dispensed into another dispensing container.

When the button 29 is further pushed down at this time, the shaft unit 41 resists the first and second stage springs 43 and 32, and moves the movable nut 30 as shown in FIG.
At the same time, it moves downward by the second stroke L _{2, and the} lower surface of the movable nut 30 main body comes into contact with the upper ends of the pair of stopper portions 51 a of the ejector pipe 51. At this time, air remains by the amount of l ₂ between the lower end of the piston shaft 55 and the lower end of the tip 58. That is, even if the sample remains in the tip 58 at the time of completion of the discharge by the first stroke L ₁ , the difference (l ₁ between the dimensions l ₁ and l ₂ due to the next stroke L ₂ is caused.
The residual sample is completely discharged by being pushed and blown off by the discharge of air of -l ₂ ). Therefore, there is no sample error between inhalation and discharge, and a predetermined amount of sample can be dispensed accurately and reliably. Further, the lower end of the chuck 40 reaches a position substantially matching the lower end of the nozzle housing 35. At this time, since the sleeve 45 does not move the next stroke L _{3 by} contacting the step portion 35g of the nozzle housing 35 at the position shown in FIG. 8, the restriction of the chuck portion 40b is released during the next stroke L _3. To do.

Next, the eject operation of the tip 58 will be described. When the button 29 is further pushed down continuously from the state of FIG. 8, the shaft unit 41 moves to the 1st and 2nd stages.
As shown in FIG. 9, not only the step springs 43 and 32 but also the ejector spring 53 and the spring 44 are moved downward by the third stroke L ₃ together with the ejector pipe 51, and the lower end convex portion of the movable nut 30 is moved. Contacts the first-stage spring receiver 31.
Therefore, by the stroke L ₃ of the ejector pipe 51 moving downward, the tip 58 is pressed and moved downward so that the locking concave portion 58a is disengaged from the locking convex portion 35g.
As shown in FIG.

At the same time, the chuck portion 40b of the chuck 40
Also protrudes downward from the nozzle housing 35 by the stroke L _{3 and} the stopper portion 56b of the piston head portion 56 of the piston 54 is fitted and abutted into the stopper hole 58b of the tip 58 immediately before being detached. At the same time, as described above, since the chuck portion 40b is released from the restriction by the sleeve 45, the four portions of the chuck portion 40b elastically open outward to release the chucking of the piston 54.

Therefore, as shown in FIG. 9, the tip 58 and the piston 54 are apparently integrated and separated from the nozzle housing 35. This tip and piston 58, 5
4 is in principle abandoned without reuse or reused after washing in order to prevent the possibility of accidental mixing of the samples. Therefore, a new piston and tip are attached to the pipette next, and the same operation as above is repeated.

According to the above operation, the sample is simply the chip 5
Since it is only sucked into the pipe 8 with a small amount of fresh air each time, it is sucked with a large amount of accumulated air into the pipette body as in the first conventional example (in which airborne bacteria are easily propagated). In comparison, in particular, when the sample is a liquid containing DNA, the DNA liquid is not affected by floating bacteria, so that accurate cloning (amplification) of only DNA can be performed. Also, since the sample is dispensed with a small amount of air intervening until the end of the discharge stroke, it is difficult for the sample to remain at the tip of the tip when the sample is discharged by the piston and pushed off the tip, so the accuracy of the dispensing volume There is an advantage that it can be improved. The following "Table 1" shows the dispensing volume accuracy of the micropipette of the present invention, and "Table 2" shows the dispensing volume accuracy of the above conventional example. The measurement liquid was distilled water and the room temperature was 22 degrees Celsius.
The water temperature was 22 degrees Celsius and the humidity was 52%.

[0035]

[Table 1]

[0036]

[Table 2]

In Tables 1 and 2 above, "X" is the average value of the actual measured 10 dispensing volumes. “CV” is reproducibility, which is, so to speak, a deviation rate from the average value. "A
“C” is accuracy or precision, which is, so to speak, a deviation rate with respect to the target dispensing volume (3, 5 or 10 microliters). Of the above values, "AC" can be corrected,
"CV" is an uncorrectable value specific to the pipette, and is therefore the most important value. Comparing Tables 1 and 2 above, for "CV", the dispensing volume was 3,
It can be seen that the present invention (Table 1) is superior in that the value is much smaller and the accuracy is higher in any case of 5, 10 microliters.

Further, according to the structure of the piston 54 and the tip 58, the space below the O-ring 59 of the cylinder hole 58c is sealed by the O-ring with respect to the space above the O-ring 59 as described above. As described above, when the piston shaft 55 moves downward by the stroke L _{1 and the} lower end of the tip 58 is immersed in the sample, the lower space becomes a completely airtight state in which the upper and lower sides are sealed. Therefore, when the piston shaft 55 returns upward to the position shown in FIG. 6 by the same stroke L ₁ in this completely airtight state, the amount of air existing in the lower space is the same as the initial amount. After all, the volume of the sample sucked into the cylinder hole 58c can be accurately obtained as the volume generated by the upward displacement of the piston shaft 55, that is, "stroke L ₁ × outer diameter of the piston shaft 55". That is, in this case, based on the special condition that the lower space is in an airtight state by the O-ring 59, the suction volume may be obtained as "stroke L ₁ × inner diameter of the cylinder hole 58c" as in a general conventional example. Absent. That is, in this case, since the inner diameter of the cylinder hole 58c does not affect the suction capacity at all, it is not necessary to fit the piston shaft 55, and a large inner diameter can be obtained.

Therefore, according to the construction in which the O-ring 59 is fitted to the piston shaft 55 as described above, the inner diameter of the cylinder hole 58c of the tip 58 is up to about 0.6 mm regardless of the outer diameter of the piston shaft 55. Since the chip can be formed large, so-called injection molding of the chip becomes easy. Conversely speaking, the suction volume is determined by the cylinder hole 58c.
Since it is set in relation to the volume of the piston shaft 55 itself, regardless of the inner diameter of, the suction volume of a small value can be easily set, and the application range is expanded. Further, as compared with the conventional example in which the inner diameter of the cylinder hole is forcibly made small and the dimensional accuracy is lowered by injection molding, the dispensing accuracy is stable and the reliability can be improved.

Next, when it is desired to change the suction and dispensing volumes of the pipette, the lock handle 23 of the lock mechanism 21 is used.
When the lock screw sleeve 22 and the lock screw sleeve 22 are integrally rotated by a predetermined angle, for example, in the clockwise direction in FIG. 2 and the screw sleeve 22 is moved upward by a slight amount, the lock plate 25 becomes rotatable. That is, the shaft unit 41 is unlocked in the rotation direction.

Therefore, when the shaft unit 41 is rotated by a predetermined amount in the predetermined direction, the screw body 27 is moved up or down by a predetermined amount in the axial direction to change the stroke L _1, thereby changing the dispensing volume. . At the same time, the drive gear 5 of the display mechanism 2 rotates in the same direction by the same amount to rotate the driven gear drum 6 and digitally display the changed capacity. After the capacity is changed, the lock handle 23 is rotated in the opposite direction and the rotation of the shaft unit 41 is locked again via the lock plate 25.

FIG. 11 shows another modification of the tip and the piston. In the figure, the tip 58 'has a larger diameter of the cylinder hole 58c' than the tip of FIG. 10, and is not provided with an O-ring and an O-ring retainer. Further, the piston 54 'has a metal piston shaft 55' having a larger diameter than the piston 54 of FIG. 10, and is fitted into the lower end of the piston shaft 55 'into the cylinder hole 58c' without a radial gap. The resin piston body 61 is insert-molded. This piston 54 'and tip 58' are suitable for dispensing a larger volume than the piston and tip of FIG. 10, but like the one of FIG. 10, the DNA solution as a sample is not affected by floating bacteria. It is possible to perform accurate DNA cloning (amplification), and also to dispense the sample while interposing air in the same manner, so that the precision of the dispensing volume can be improved without the sample remaining on the tip of the chip during dispensing. There are advantages. Further, since this type of cylinder hole 58C 'itself requires precision of the inner diameter and cannot be molded into a too small inner diameter, the dispensing volume is set larger than that of the piston and pipette of FIG. The O-ring retainer is unnecessary, so the cost is low.

FIG. 12 shows a chip 58 "which is still another modification of the chip 58 of FIG.
In comparison with the tip of FIG. 10, the cylinder hole has a larger inner diameter, and the tube 62 is detachably fitted to the inner diameter. Therefore, if you want to dispense a relatively large volume of sample, use with the tube 62 removed,
When it is desired to dispense a sample having a relatively small volume, the tube 62 is attached and used. As a result, one tip 58 ″ can be conveniently applied to a wide range of dispensing volumes.

[0044]

As described above, according to the present invention, the positional relationship between the tip and the piston is such that the shaft unit (41) moves downward by a predetermined stroke (L ₁ ) so as to suck the sample into the tip. When sliding, tip (5
8, 58 ', 58 ") in the cylinder hole (58c) with a predetermined dimension (l ₁ ) between the piston tip and the tip tip.
The shaft unit (41) is set to intervene a certain amount of air, and the shaft unit (41) slides downward by the stroke (L ₁ ) and then slides downward by the excess stroke (L ₂ ). At this time, since the air of a predetermined size (l ₂ ) is still interposed between the tip of the piston and the tip of the tip in the cylinder hole, there are the following advantages.

Since the sample is simply sucked into the tip 58 together with a small amount of fresh air each time, a large amount of staying air (suspended bacteria are easily propagated therein) into the pipette body as in the first conventional example. In particular, when the sample is a liquid containing DNA, the DNA liquid is not affected by floating bacteria, so that accurate cloning (amplification) of only DNA can be performed as compared with the configuration in which the sample is a liquid containing DNA. In addition, since the sample is dispensed with a small amount of air interposed until the end of the discharge stroke, it is difficult for the sample to remain at the tip of the chip when the sample is discharged by the piston and pushed away from the chip.
The dispensing volume accuracy can be improved.

[Brief description of drawings]

FIG. 1 is a side view of a micropipette according to the present invention.

FIG. 2 is a plan view of the micropipette.

FIG. 3 is a vertical sectional view of the micropipette.

FIG. 4 is a sectional view taken along the line 4-4 in FIG.

5 is a sectional view taken along line 5-5 in FIG.

FIG. 6 is a vertical cross-sectional view of the micropipette before being pressed.

FIG. 7 is a vertical cross-sectional view of the micropipette in a one-step pressed state.

FIG. 8 is a vertical cross-sectional view of the micropipette in a two-step pressed state.

FIG. 9 is a vertical cross-sectional view of an ejecting state of the tip and the piston of the micropipette.

FIG. 10 is an enlarged vertical sectional view of a tip and a piston of the micropipette.

FIG. 11 is an enlarged vertical sectional view of a modified example of the tip and the piston.

FIG. 12 is an enlarged vertical sectional view of another modification of the tip and the piston.

[Explanation of symbols]

 1 Body 2 Dispensing Volume Display Mechanism 3 Fixed Plate 12 Cap 21 Lock Mechanism 24 Lock Plate 26 Upper Shaft 27 Screw Body 28 Stopper Collar 30 Movable Nut 32 Two-Step Spring 35 Nozzle Housing 38 Intermediate Shaft 39 Lower Shaft 40 Chuck 41 Shaft Unit 43 1st-stage spring 51 Ejector pipe 54, 54 'Piston 55, 55' Piston shaft 56 Piston head 58, 58 ', 58 "Tip 59 O-ring 60 O-ring retainer 61 Piston body 62 Tube

Claims (6)

[Claims] 1. A pipette body (1, 35) and a shaft unit housed in the pipette body (1, 35) slidably in the axial direction and biased upward by spring means (43, 32). (41), which has a shaft hole (58c) and a shaft unit (41) that detachably holds a piston (54, 54 ') at its tip and disengages the piston at a lower slide limit position. , And detachably attached to the tip of the pipette body (1, 35),
In the cylinder hole (58c), the pistons (54, 5
4 ') insert tip (58, 58'58 "),
It is attached to the pipette body (1, 35) so as to be slidable in the axial direction and urged upward by spring means (53), and is pushed and slid by the shaft unit (41) to push the tip downward. And an ejector means (51) for disengaging the tip (58, 58 ', 58 ") from the pipette body together with the piston (54, 54') detached from the shaft unit, and the arrangement of the tip and the piston. The relationship is that when the shaft unit (41) slides downward by a predetermined stroke (L ₁ ) to suck the sample into the tip, the cylinder hole (5) of the tip (58, 58 ′, 58 ″)
8c) is set so that air of a predetermined size (l ₁ ) is interposed between the tip of the piston and the tip of the tip, and the shaft unit (4
After ₁ ) slides the stroke (L ₁ ) downward,
It should be set so that when it is slid further downward by an excessive stroke (L ₂ ), a predetermined size (l ₂ ) of air is still present between the piston tip and the tip tip in the cylinder hole. Micropipette characterized by. 2. The micropipette according to claim 1, wherein
The shaft unit (41) has a chuck member (40) at its lower end, and the pistons (54, 54 ') are
It has at least a metal piston shaft (55, 55 ') and a resin chucked portion (56a) that is insert-molded at the upper end of the piston shaft and is detachably chucked by the chuck member (40). Micropipette characterized by. 3. The micropipette according to claim 2, wherein
A micropipette characterized in that the tip houses an O-ring (59), and the piston shaft (55) is hermetically inserted through the O-ring. 4. The micropipette according to claim 2, wherein
A micropipette characterized in that the piston shaft (55) is insert-molded with a piston body (61) fitted in a cylinder hole (58c) of a tip at a substantially lower end thereof. 5. The micropipette according to claim 3 or 4, wherein the tip has a stopper hole (58b) concentric with a cylinder hole (58c), and the piston (54, 5).
The piston shaft (55, 55 ') of 4') is further insert-molded with a stopper part (56b) made of resin, and when the tip and the piston are ejected, the stopper part (56b) of the piston shaft is of the tip. Cylinder hole (58
A micropipette characterized by being inserted into c). 6. The micropipette according to claim 2, wherein
The chuck member (40) is composed of four elastic portions defined by providing axially cut-outs (40a) having a cross-shaped cross section at the taper-shaped expanded portion at the lower end thereof.
b) is formed, and the chucked portion (40b) chucks the chucked portion (56a) of the piston.