JPH0449912B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Application of the Invention) The present invention relates to a dispensing method and apparatus for taking out a small amount of liquid from a liquid reservoir and injecting it into a predetermined container or the like with high accuracy. (Background of the invention) Generally, for biochemical analysis such as immune reaction (IA),
As a part of a liquid chromatography device, for example, a dispensing device for dispensing a sample liquid in minute amounts of several microns to several hundred microns is used. The configuration of such a conventional dispensing device is that a cylinder device connected to the inner space of the nozzle is provided to a nozzle device for aspirating and discharging the target liquid, and the target liquid is sucked into the inner space of the nozzle by the forward movement of the piston of the cylinder device. It is common that the piston is moved back and forth, and the sucked liquid is then discharged. However, when such a dispensing device is used for dispensing a very small amount of liquid as described above, it has been found that a significant dispensing error occurs. This dispensing error is, for example, approximately 0.3 to 0.5 mm for the lower end diameter of the inverted conical nozzle and 0.3 to 0.5 mm for the nozzle tube thickness.
When a liquid of about 200μ is sucked in and discharged by the reciprocating movement of the piston of a cylinder device, it may appear as a diameter of about several micrometers, and in systems that require strict dispensing accuracy. , the error cannot necessarily be said to be small, and the influence of the error becomes even more significant when dispensing an extremely small amount of several microns to several tens of microns. (Object of the Invention) The present invention was made in view of the above-mentioned problems, and its purpose is to provide a dispensing method that dramatically improves the precision of dispensing a small amount of liquid, and to provide a method for implementing this method. An object of the present invention is to provide a dispensing device that can be suitably used. Another object of the present invention is to provide a method and apparatus for dispensing liquid such as a sample, which is particularly suitable for use in a biochemical analysis system. (Summary of the Invention) A feature of the dispensing method according to the present invention, which has been made to achieve the above object, is that the liquid sucked into the nozzle device is applied with discharge pressure from a cylinder device and a pressure gas supply source. This is a dispensing method in which the liquid is discharged from the nozzle device by applying the discharge pressure, and the dispensing stroke of the cylinder device is continuously performed over almost the entire range of the dispensing operation in which the liquid is discharged by applying the discharge pressure. At least at the beginning and end of the discharge stroke, the discharge pressure applied from the pressure gas supply source is superimposed on the discharge pressure of the cylinder device for a short period of time. The dispensing device suitably used in such a method is characterized by a nozzle device for sucking in and discharging the liquid, and a device connected to the nozzle interior of the nozzle device to apply negative pressure for sucking the liquid and A cylinder device that applies discharge pressure for discharging, and a pressure gas supply source that is branched and connected in the middle of a connection path from the interior of the nozzle to the cylinder device and applies discharge pressure to the interior of the nozzle for liquid discharge. A connection path is provided between the pressure gas supply source and the branch connection point, and is temporarily opened at least at the beginning (at the start of driving) and at the end (at the end of driving) of the stroke of the cylinder device. The valve device is configured to include a valve device. The reason for adopting such a method and apparatus in the present invention is as follows. That is, according to the present inventor's investigation of the cause of the dispensing error as described above, this is due to the following:
This is due to the fact that the liquid to be sucked/discharged wraps around the lower end of the nozzle and adheres to the outer wall of the nozzle, or it adheres to and remains on the inner surface of the nozzle. The discharge speed at the end of liquid discharge and the discharge speed at the beginning of liquid discharge are determined by the positive pressure (discharge pressure) from the cylinder device.
This is thought to be due to the fact that in the case of a dispensing method in which liquid is discharged only by application, the discharge speed is lower than that in the middle stage of liquid discharge. This problem is particularly noticeable when the liquid has good wettability with the nozzle forming material, such as biological samples, and when the piston of the cylinder device is driven by a screw using a pulse motor for microdispensing. It becomes noticeable when This can be seen, for example, in Figure 6 a, b.
This will be explained with reference to FIGS. 7a and 7b. Figure 6a shows the case where the cylinder device is driven in a rectangular manner by a pulse motor.
Figure 7a shows the case of trapezoidal drive using a pulse motor. Due to the slow rise and fall and the influence of the compressibility of the gas, the speed of liquid discharge shows a gentle curve at the end and beginning of liquid discharge. Therefore, in the present invention, in order to discharge liquid from the nozzle, the operation of applying air pressure from a pressure gas supply source is performed for a short period of time to increase the discharge pressure by the nozzle device near the beginning and end of the discharge stroke by the nozzle device. By adopting the overlapping method, it is possible to minimize the amount of liquid remaining due to adhesion on the outer surface of the lower end of the nozzle as described above. This allows the liquid discharged from the nozzle to wrap around and adhere to the outer surface of the nozzle by superimposing the discharge pressure from the pressure gas supply source, especially in the initial acceleration region when the discharge stroke of the cylinder device starts. In addition, by similarly superimposing the discharge pressure from the pressure gas supply source in the deceleration region of the discharge stroke of the cylinder device at the end of liquid discharge, so-called tearing can be improved. Figures 4a to 4c are comparative examples in which air pressure is applied from a pressurized gas source only at the end of liquid dispensing during the dispensing operation, and Figures 5a to 5c are examples of the present invention. FIG. 4 is a diagram illustrating the liquid discharge speed when the air pressure application operation is performed at the initial and final stages of liquid dispensing in the dispensing operation, and these diagrams show that in the case of the present invention, It can be seen that a high liquid ejection rate can be obtained in both the final stages of dispensing. Although it is preferable to use a cylinder device to suck liquid into the nozzle, this cylinder device for sucking liquid can also be used as it is as a cylinder device for discharging liquid. Between the initial stage and the final stage of liquid discharge, both the cylinder operation and the air pressure applying operation may be performed in parallel. In particular, the present invention continuously operates the cylinder over almost the entire range of liquid discharge, and applies air pressure from the pressure gas supply source to the cylinder device at both the initial and final stages of liquid discharge due to the cylinder operation. It has become clear that extremely high dispensing accuracy can be obtained by superimposing the air pressure on the stroke. In a preferred embodiment of the present invention, at the beginning of liquid discharge, the valve device is temporarily opened for a short time at the same time as the cylinder operation is started, and the speed at which the liquid inside the nozzle is discharged is rapidly increased. Subsequently, the liquid inside the nozzle is discharged by operating the cylinder, and at the end of the discharge, the valve device is opened again to ensure air pressure for liquid discharge, and the droplets at the lower end of the nozzle are properly cut off. The air pressure application operation at the end of the first stage liquid discharge is as follows:
It is usually 0.2 to 1 sec, preferably 0.2 to 0.5 sec, and the initial air pressure application operation is preferably about 0.1 to 0.2 sec. The nozzle device to which the present invention is applied may be any suitable device, such as a fixed nozzle type, a movable type that moves the nozzle up or down, etc., and is not limited to the structure of the nozzle device, but generally the nozzle In many cases, a replacement nozzle tip is attached to the bottom end. The cylinder device connected to the nozzle interior of the nozzle device and used mainly for sucking liquid is a mechanical type in which the piston is moved by a screw drive means using a pulse motor, or a pneumatic type in which the piston is moved using gas pressure. Any type of formula is fine,
By moving the piston forward from the initial position, negative pressure is applied to the interior of the nozzle communicating with the cylinder to suck in a predetermined amount of liquid, and the piston is returned to the initial position when or after the liquid is discharged. In addition, the pressure gas supply source connected to provide air pressure for discharging liquid from the nozzle device, and the valve device in the middle of the connection path may be an accumulator, pump, pressure cylinder, etc. that stores pressure air. Although it is generally constructed by combining a normally closed electromagnetic valve, it is also preferable to additionally provide a flow rate regulating valve or the like as part of the valve device in the middle of the connection path. Opening and closing of valve devices such as solenoid valves should be performed using a manual switch or, in the case of automated devices, a sequence control circuit that synchronizes with other operating devices for dispensing. Can be done. The operation of applying air pressure for liquid discharge is to apply air pressure at an appropriate level to eliminate liquid adhesion on the inner and outer surfaces of the lower end of the nozzle, and generally the gauge pressure is 0.1 to 5 atm. The pressure is preferably about 0.1 to 0.5 atm. If the air pressure is too low, liquid adhesion will not be resolved sufficiently.
If it is too large, the liquid discharged from the lower end of the nozzle may scatter. The temporary opening of the valve device for applying air pressure only needs to be slightly longer than the time sufficient to discharge the liquid inside the nozzle, so that the air pressure for liquid discharge is increased at the final stage when the liquid inside the nozzle is discharged. This ensures that the droplets at the bottom end of the nozzle are well cut. Further, if the pressure gas supply source generates pressure only when necessary, the valve device may be a check valve (one-way valve). (Embodiments of the Invention) Hereinafter, the implementation state of the present invention will be described based on the drawings. In FIG. 1, reference numeral 1 denotes a nozzle chip that is replaced and attached to a nozzle holder 2 by an unillustrated exchange device, and the nozzle holder 2 is provided with a flow path that communicates the inside of the nozzle chip 1 with an air pipe 3. . The air pipe 3 is branched at the end opposite to the end connected to the nozzle holder 2, and one of the branches is communicated with a cylinder air chamber 5 of a screw-driven cylinder device 4 driven by a pulse motor 6. The other branch is connected to an air pressure accumulator (not shown) via a valve device 9 consisting of a normally closed electromagnetic valve 7 and a flow rate regulating valve 8. The solenoid valve 7 is connected to a control circuit (not shown), and is temporarily opened for a certain period of time in synchronization with other devices when liquid discharge is required. Next, we will discuss its operation. First, the nozzle tip 1 is attached to the nozzle holder 2, and its lower end is immersed to a certain depth into a sample in a predetermined sample container. In this state, the piston of the cylinder device 4 is moved forward (downward in the figure) to suck the sample into the interior of the nozzle tip 1. The amount of sample sucked can be determined with sufficient accuracy by controlling the amount of piston reciprocation of the cylinder device 4. In this embodiment, it is also possible to handle diluted sample dispensing by first sucking dilution water into the nozzle tip 1 and second sucking the sample. Next, while the piston of the cylinder device is kept fixed, the nozzle tip is pulled out of the sample container in an upward motion, and is brought close to and facing above a predetermined sample dispensing container. In this state, for example, when the piston of the cylinder device is moved back, the solenoid valve 7 is temporarily switched to the open state, and the pressure air determined by the flow rate adjustment valve 8 is temporarily applied from the pressure accumulator into the nozzle tip 1. By this, the internal liquid is discharged into the sample dispensing container. At the end of the discharge, the electromagnetic valve 7 is temporarily switched to the open state again to make the dripping at the lower end of the nozzle good. By such operations, 1
The first dispensing operation is completed. You can repeat this operation from now on. Using the apparatus shown in FIG. 1, the liquid was discharged from the nozzle tip 1 according to the following procedure under the conditions described below, and the results of the dispensing accuracy (CV value) are shown in Table 1. Comparative example 1...Liquid discharge by cylinder operation only Comparative example 2...Liquid discharge by continuous cylinder operation → final air pressure application operation (operated according to Fig. 4) Example...Cylinder operation start and simultaneous temporary operation Liquid discharge by sequentially applying air pressure → cylinder operation → final air pressure application operation (operate according to Fig. 5) Lower end diameter of nozzle tip 0.3 mm Wall thickness 0.3 to 0.5 mm Sample 8% BSA in Saline Dispensing amount (sample intake/discharge amount) (See Table 1) (Sample + diluent) 200μ Discharge operation cylinder operation 200μ/2sec Air pressure (gauge pressure) 0.1 atm Air pressure application time comparison example 2 (final stage only)... …0.5sec Initial stage of example …0.1sec Final stage…0.5sec Flow rate adjustment 10ml/10sec

[Table] From the above results, the dispensing accuracy of the example performed according to the present invention is lower than that of comparative examples 1 and 2.
It can be seen that the CV values are all less than 1, and the degree of variation is significantly smaller than that of the comparative example, indicating a significant improvement. Therefore, it is extremely effective when used in analysis systems where dispensing accuracy affects measurement results. Furthermore, in this embodiment, the pressure applied at the beginning of discharge causes the inside of the nozzle to be discharged at a speed higher than a certain level from the beginning, so that the liquid does not go around the outer surface of the nozzle. In particular, in the case of a highly viscous solution, the flow of the solution on the inner surface of the nozzle is slow and the pressure applied by the cylinder alone will cause the solution to be forced out slowly, so the above-mentioned influence is significant, but this can be easily overcome by the method of the present invention. Furthermore, there is an effect that the solution adhering to the lower end of the nozzle is rapidly expelled by applying pressure at the final stage of ejection, so that no solution remains. Note that the present invention is not limited to the embodiment shown in FIG. 1, but can be implemented in various modified embodiments. For example, in the example shown in FIG. 2, a bellows type air pump 10 is used as the pressure gas supply source, and a check valve 11 is used instead of the valve device, and the other configuration is the same as the example shown in FIG. 1. The same is true. In the case of this example, pressurized air is generated mechanically using a cylinder device or the like or by compressing the air pump 8, and this is transmitted to the inside of the nozzle tip via the check valve 11. The advantage is that the supply source and valve equipment are inexpensive. In relation to the cylinder device, the check valve preferably has a set pressure that does not open during liquid suction. The example shown in FIG. 3 uses a compressor (not shown) and a regulator 12 as the pressure gas supply source, except that the solenoid valve 7' is normally open to the atmosphere. This is similar to the example shown in FIG. In this example, the pressure air from the pressure gas supply source is normally released to the atmosphere through the solenoid valve 7', so there is an effect that the pressure air does not leak to the cylinder device side. In the case of this example, the air pressure generated by the compressor can also be used as a power source for other equipment in the analysis and measurement device including this dispensing device.
This provides major advantages such as an increase in the degree of freedom in overall design and the use of common equipment. (Effects of the Invention) As described above, according to the present invention, dispensing errors due to liquid adhesion at the lower end of the nozzle occur when dispensing a small amount of liquid, as experimentally confirmed in the above Examples and Comparative Examples. The effects of this are greatly reduced, and high dispensing accuracy (small CV value) can be obtained for various analysis and measurement devices that require strict dispensing accuracy, and the effect is significant. In addition, in the case where the cylinder device for sucking liquid is also used for discharging liquid, the stroke during the backward movement of the piston must be larger than the stroke during the forward movement of the piston in consideration of the compressibility of the gas. The present invention solves the problem of an invalid stroke (during suction), which leads to further elongation of air cylinder devices that are made smaller in diameter and longer in order to achieve higher precision, and difficulties in managing suction amount and adjusting discharge speed. The device does not have such difficulties and is extremely effective in achieving compact and highly accurate dispensing.

[Brief explanation of the drawing]

1 to 3 are diagrams each showing an example of a general configuration of an embodiment of the present invention. Figure 4 is a diagram for explaining the liquid discharge speed from the nozzle of Comparative Example 2, Figure 5 is a diagram for explaining the liquid discharge rate by the method of the present invention, and Figures 6 and 7 are for the cylinder. FIG. 6 is a diagram illustrating the speed of liquid discharge based only on operation. 1: Nozzle chip, 2: Nozzle holder, 3: Air pipe, 4: Cylinder device, 6: Pulse motor,
7: Solenoid valve, 8: Flow rate adjustment valve, 9: Valve device, 1
0: Air pump, 11: Check valve, 12: Regulator.

Claims (1)

[Scope of Claims] 1. A dispensing method in which liquid sucked into a nozzle device is discharged from the nozzle device by applying discharge pressure from a cylinder device and a pressure gas supply source, comprising:
The discharge stroke of the cylinder device is continuously performed over approximately the entire range of the dispensing operation in which liquid is discharged by applying discharge pressure, and the pressurized gas is supplied at least at the beginning and end of the discharge stroke of the cylinder device. A method for dispensing a small amount of liquid, characterized in that the discharge pressure from the source is superimposed on the discharge pressure of the cylinder device. 2. A nozzle device for sucking/discharging liquid;
A cylinder device that is connected to the nozzle interior of this nozzle device and applies negative pressure for sucking liquid and applies discharge pressure for discharging the liquid, and a connecting path from the nozzle interior to the cylinder device. a pressure gas supply source that is branch-connected to apply discharge pressure to the interior of the nozzle for liquid discharge; 1. A micro-liquid dispensing device comprising: a valve device that is opened for a short period of time at the beginning and end of a stroke of the device. 3. The micro-liquid dispensing device according to claim 2, wherein the nozzle device is assembled with a replaceable disposable tip.