Spotting tip

Abstract: A spotting tip (12) includes a tip body (14) which is fitted on the end of a nozzle (18) for sucking liquid contained in a container (20) and inserted into the liquid (L) in the container (20) through a mouth (20a) of the container (20), and a lid member (16) which is brought into contact with the mouth (20a) of the container and closes the space between the tip (12) and the edge of the mouth (20a) when the tip (12) is inserted into the container (20) to a predetermined depth. At least one fine communicating passage (16a) is formed in at least one of the lid member (16) and the tip body (14) to communicate the inside and outside spaces of the container (20) on opposite sides of the lid member (16).

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a spotting tip comprising a tip body which is adapted to be fitted on the end of a nozzle of a liquid sucking means for sucking liquid contained in a container, said spotting tip being adapted to be inserted into liquid in the container through a mouth of the container, and a lid member being adapted to be brought into contact with the mouth of the container and to close the space between the tip and the edge of the mouth when the tip is inserted into the container to a predetermined depth, the liquid sucking means being adapted to suck a predetermined amount of the liquid into the tip body with the tip body held in the liquid, wherein at least one communicating venting passage is formed to communicate the inside and outside spaces of the container on opposite sides of the lid member. More particularly, the invention provides a spotting tip which sucks liquid to be subjected to a biochemical analysis or the like and spots the liquid on an element, device or the like for biochemical analysis. Description of the Related Art Quantitative analysis of a particular chemical component in a sample liquid is commonly carried out in various industrial fields. For example, there have been known various methods of potentiometrically analyzing an activity (or concentration) of a particular ionic substances contained in a spotted sample liquid such as liquors, beverages, city water or a body fluid such as blood, urine or saliva. Ionic activity measuring devices for measuring an activity of an ionic substance in a spotted sample liquid are disclosed, for instance, in Japanese Unexamined Patent Publication Nos. 59(1984)-30055 and 6(1994)-66759, and US-A-4 437 973. Generally such an ionic activity measuring device includes at least a set of ion selective electrode pair each having an outermost layer composed of an ion selective layer which selectively responds to a particular ion such as Na, K, Cl or the like. The ion selective electrode pair are supported between an upper frame and a lower support frame, and a pair of liquid spotting holes are provided in the upper frame respectively opposed to the electrodes. A porous bridge which establishes an electrical connection between a sample liquid spotted to one of the spotting holes and a reference liquid spotted to the other spotting hole is provided in the upper frame. Preferably the porous bridge is formed of twisted yarn of fibers. In such an ionic activity measuring device, when a reference liquid containing therein an ionic substance whose ionic activity is known is spotted to one of the spotting holes and a sample liquid containing therein the ionic substance whose ionic activity is unknown is spotted to the other spotting hole, the liquids soak into porous liquid distributing members and reach the corresponding ion selective electrodes while the interfaces of the liquids are brought into an electrical contact with each other near the middle of the porous bridge. As a result, there is produced a potential difference between the electrodes according to the difference between the activity of the ionic substance in the sample liquid and that in the reference liquid. By measuring the potential difference, the activity of the ionic substance in the sample liquid can be determined on the basis of a calibration curve or a standard curve which has been determined in advance on the basis of Nernst equation. The ionic activity measuring device is very useful for analysis of aqueous sample liquid, especially for clinical analysis of a sample liquid from a human body such as blood since the ionic activity can be easily determined by only spotting droplets of the sample liquid and the reference liquid. When spotting the sample liquid and the reference liquid, the liquids are sucked in different spotting tips and dropped onto the respective spotting holes from the ends of the tips. Each tip is fitted on a liquid sucking nozzle and dipped into the sample liquid or the reference liquid and then the sample liquid or the reference liquid is sucked into the tip in a predetermined amount in response to a sucking operation of the liquid sucking nozzle and then held there. Then the tips on the sucking nozzles are moved to predetermined positions above the ionic activity measuring device and then discharge the sample liquid and the reference liquid onto the spotting holes in response to a discharging operation of the nozzles. The sample liquid and the reference liquid may be spotted either simultaneously or in sequence generally within 60 seconds. In the container containing the sample liquid or the reference liquid, when the mouth of the container through which the spotting tip is inserted into the container is kept open for a long time, there is a possibility of the liquid evaporating to change the concentrations of the components and spoiling. Accordingly conventionally the mouth of the container is normally covered with a lid and is opened only when the liquid therein is to be sucked. The lid is put on again immediately thereafter. However shutting and opening the mouth is very troublesome and puts an obstacle in automating the liquid sucking operation. Furthermore, a tip of the type mentioned in the beginning is known from which tip Patent Abstract of Japan vol. 018 no. 525, 5 Oct. 1994 & JP-A-0 618 2234 is provided as a disposable tip for dispensing blood into another container with good accurary in the state of hermetically closing a vacuum blood collecting tube in blood inspection. This disposable tip has vent paths provided integrally with its side wall. These vent paths have upper vent ports provided at the top end of the disposable tip fitting to a nozzle base and lower vent ports provided in any part from the top end of the disposable tip to a sample and suction port. The outdoor air is infiltrated into the vacuum blood collecting tube through the vent paths until the same pressure as the atmospheric pressure is attained by provision of these vent paths simultaneously when the disposable tip is inserted into the vacuum blood collecting tube. As a result, the sample is dispensed with good accuracy by using a pump. Finally, DE-A-4 011 584 discloses a tip in the form of a disposable pipette, comprising a tubular body and an integral flange at its top end so that the tip can sit by its flange on a similar flange of a receiving container as a lid. SUMMARY OF THE INVENTION In view of the foregoing observations and description, the primary object of the present invention is to provide an alternative spotting tip for aspirating and precision dispensing liquid which can minimize evaporation of the liquid in the container and at the same time can prevent back flow of the liquid into the tip or the nozzle. Based on the recognition that the back flow of the liquid in the container can be prevented if the pressure difference between the space inside of the container and the space outside of the same on opposite sides of the lid member can be nullified, the present invention accomplishes the above object by a spotting tip of the type mentioned in the beginning, which is characterized in that said lid member is formed integrally with the tip body and said spotting tip has any one of the following features (a), (b) or (c) : (a) said communicating passage is in the form of a groove formed in the inner peripheral surface of the lid member to extend from the lower surface of the lid member to the upper surface of the same; (b) said communicating passage is in the form of a through hole formed in the lid member to extend from the lower surface of the lid member to the upper surface of the same; or (c) said communicating passage is in the form of a groove formed in the lower surface of the lid member to extend in a radial direction of the lid member. The tip body and the lid member may be formed of any material so long as it does not modify nor deteriorate the liquid in the container. For example, the tip body may be formed of an organic polymer material such as polyethylene, polypropylene, fluoropolymer, silicone resin or the like. The lid member may be formed of an organic polymer material such as polyethylene, polypropylene, fluoropolymer, silicone resin or the like or a rubber material such as silicone rubber. The fine communicating passage may be of any shape and any size so long as it can nullify the pressure difference between the space inside of the container and the space outside of the same on opposite sides of the lid member without largely deteriorating the function of the lid member to suppress evaporation of the liquid in the container. Further a plurality of the fine communicating passages may be provided unless the function of the lid member to suppress evaporation of the liquid in the container is largely deteriorated. However, in order to enhance the function of the lid member, it is preferred that the communicating passage be long to a certain extent. Further when there is only one communicating passage, communication between the inside and outside spaces can be broken if the passage is blocked with foreign matter such as dust, fine cuttings of the lid member or the like or by accident. Accordingly preferably a plurality of the fine communicating passages are provided. With the arrangement described above, the container can be held air-tight to a degree such that the liquid in the container is suppressed from evaporating and diffusing outside the container by normally holding the tip body in the container with the lid member in contact with the mouth of the container, whereby the liquid is prevented from being concentrated . Further since the ingress of foreign matters is prevented, the liquid in the container can be prevented from being contaminated and spoiling. Accordingly, even in a biochemical analysis where a fine change in the concentration of the components gives rise to a problem, the accuracy of measurement can be held high. Further since the fine communicating passage equalizes the pressures inside and outside the container, the liquid in the container cannot flow into the tip body or the nozzle even if the tip body is held inside the liquid with the lid member in contact with the mouth of the container for a long time. Accordingly the liquid can be constantly spotted in an accurate amount and the change in the concentration of the liquid due to back flow can be prevented. Further since the mouth of the container is opened and closed by the spotting tip itself, necessity of putting on and off the lid as in the conventional system can be eliminated and the spotting operation is facilitated. It is preferred that the outer surface of the tip near the liquid intake/discharge port thereof be subjected to a water-repellent treatment or hydrophobicity treatment to prevent the liquid from adhering to the outer surface of the tip body to be carried out, whereby concentration of the liquid in the container is further prevented. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained in more detail by the following embodiments thereof which are merely illustrative but do not fall under the claimed invention insofar as therein the lid member is not formed integrally with the tip body, as claimed. Figure 1 is a cross-sectional view of a spotting tip in accordance with an embodiment with the tip inserted into a container, Figure 2 is a perspective view of the spotting tip away from the container, Figures 3A, 3B, 4A and 4B are perspective views respectively showing modifications of the lid members employed in the spotting tip of the embodiment, Figure 5 is a view similar to Figure 1 showing a modification of the lid member employed in the spotting tip of the embodiment, Figure 6 is a cross-sectional view showing an experimental device which was employed in an experiment for proving the result of the invention, Figures 7A and 7B are plan views for illustrating the structures of the lid members employed in the experiment, and Figures 8A and 8B are graphs showing the result of the experiment. DESCRIPTION OF THE PREFERRED EMBODIMENT In Figures 1 and 2, a spotting tip 12 in accordance with an embodiment comprises a tip body 14 which is shaped like a cone tapered downward and an annular lid member 16 fitted on the tip body 14 at an intermediate portion thereof. The spotting tip 12 is mounted on a nozzle 18 of a liquid sucking means (not shown) by press-fitting the upper end portion 14a of the tip body 14 on the lower end portion 18a of the nozzle 18. An O-ring 30 is fitted on the lower end portion 18a of the nozzle 18 and is brought into close contact with the inner peripheral surface of the tip body 14, when the upper end portion 14a of the tip body 14 is fitted on the lower end portion 18a of the nozzle 18, to seal the space between the outer peripheral surface of the nozzle 18 and the inner peripheral surface of the tip body 14 in an air-tight fashion. A reference liquid L is contained in a container 20 having a mouth 20a. With the spotting tip 12 on the nozzle 18, the tip body 14 is inserted into the container 20 through the mouth 20a so that the lower end portion 14b (having a diameter smaller than the upper end portion 14a) of the tip body 14 is dipped into the reference liquid L. When the reference liquid L is to be spotted, a predetermined amount of the reference liquid L is sucked into the tip body 14 of the spotting tip 12 through the opening at the end of the lower end portion 14b. The lid member 16 comprises a larger diameter upper portion and a smaller diameter lower portion which is tapered downward. When the tip body 14 is inserted into the container 20 to a predetermined depth, the lower surface of the upper portion of the lid member 16 is brought into contact with the inner peripheral edge of the mouth 20a of the container 20 to shut the space between the mouth 20a and the tip body 14. The lid member 16 is formed of elastic silicone rubber so that the space between the mouth 20a and the tip body 14 is surely shut. Four grooves 22 are formed in the inner peripheral surface 16a of the lid member 16 at intervals of 90° to extend through the lid member 16 in the longitudinal direction thereof. The grooves 22 form four fine communicating passages which communicate the space Si inside the container 20 and the space So outside the container 20 when the spotting tip 12 is inserted into the container 20 so that the lid member 16 closes the mouth 20a. Each groove 22 is semi-circular in cross-section and has a radius of 0.1 to 1.0 mm (e.g., 0.5 mm). An annular shoulder 14c is formed on the outer peripheral surface of the tip body 14 at an intermediate portion thereof. The shoulder 14c is for limiting the position of the lid member 16 relative to the tip body 14 when the lid member 16 is fitted on the tip body 14 and has a width of about 0.3 mm. Even when the tip body 14 is inserted into the lid member 16 until the shoulder 14c is brought into abutment against the lid member 16, the lid member 16 is held away from the shoulder 14c at a distance of about 0.5 to 1.0 mm by virtue of the elasticity (spring back) of the lid member 16. Accordingly the fine communicating passages cannot be closed by the shoulder 14c. As can be understood from the description above, the container 20 can be held air-tight to a degree such that the reference liquid L in the container 20 is suppressed from evaporating and diffusing outside the container 20 by normally holding the tip body 14 in the container 20 with the lid member 16 in contact with the mouth 20a of the container 20 except when the liquid L is to be spotted, whereby the liquid L is prevented from being concentrated . Further since the ingress of foreign matters into the container 20 is prevented, the liquid L in the container 20 can be prevented from being contaminated and spoiling. Accordingly, even in a biochemical analysis where a fine change in the concentration of the components gives rise to a problem, the accuracy of measurement can be held high. Further since the fine communicating passages formed by the grooves 22 on the inner peripheral surface 16a of the lid member 16 communicate the inside space Si and the outside space So and equalize the pressures inside and outside the container, the liquid L in the container 20 cannot flow into the tip body 14 or the nozzle 18 even if the tip body 14 is held inside the liquid L with the lid member 16 in contact with the mouth 20a of the container 20 for a long time. Accordingly the liquid L can be constantly spotted in an accurate amount and the change in the concentration of the liquid L due to back flow can be prevented. In this particular embodiment, since the fine communicating passages are formed by elongated grooves 22, even if the liquid L evaporates and enters the passages, almost all the vapor is condensed, whereby evaporation of the liquid L outside the container 20 can be effectively prevented. Thus in accordance with the embodiment described above, evaporation of the reference liquid L outside the container 20 can be minimized and at the same time back flow of the reference liquid L into the tip body 14 or the nozzle 18 can be prevented. Further since the mouth 20a of the container 20 is opened and closed by the spotting tip 12 itself, necessity of putting on and off the lid as in the conventional system can be eliminated and the spotting operation is facilitated. Though, in the embodiment described above, the inside space Si and the outside space So of the container 20 are communicated through the fine communicating passages formed by four grooves 22 which are formed in the inner peripheral surface 16a of the lid member 16 to extend through the lid member 16 in the longitudinal direction thereof and are semi-circular in cross-section, the spaces Si and So may be communicated through only a pair of like grooves 22 as shown in Figure 3A or through a plurality of (e.g., two or four) through holes 24 formed away from the inner peripheral surface 16a of the lid member 16 as shown in Figure 3B. In the latter case, the diameter of each through hole may be, for instance, 0.2 to 1.0 mm. Though the lid member 16 is formed of silicone rubber in the embodiment described above, the lid member 16 may be formed of inexpensive plastic. In this case, the plastic lid member 16 may comprise an annular collar portion and a tubular portion extending downward from the collar portion and semi-circular grooves 22 (e.g., 2 or 4) may be formed along the inner peripheral surface 16a of the tubular portion as shown in Figure 4A. Further the plastic lid member 16 may comprise an annular collar portion and columns (e.g., 2 or 4) extending downward from the collar portion away from the inner peripheral surface 16a of the lid member 16, and a through hole 24 may be formed in each of the columns to extend therethrough as shown in Figure 4B. In another modification of the lid member 16 shown in Figure 5, the communicating passage is formed between the lower surface of the lid member 16 and the upper surface of the mouth 20a of the container 20 by one or more radial grooves 26 formed in the lower surface of the lid member 16. It is preferred that the outer surface (including the bottom surface) of the lower end portion 14b of the tip body 14 near the liquid intake/discharge port thereof be subjected to a water-repellent treatment or hydrophobicity treatment with silicone resin, fluorinated resin, fluorine-containing surface-active agent or the like. Since the tip body 14 is held at a constant height from the bottom of the container 20, the tip body 14 is dipped relatively deep into the reference liquid L when the container 20 contains a large amount of reference liquid L. The water-repellent treatment or hydrophobicity treatment prevents the reference liquid L from adhering to the outer surface of the tip body 14 and being carried out. The shape of the lid member 16 need not be limited to those described above but may be properly selected according the shape of the tip body 14 and/or the shape of the container 20. Though in the embodiment described above, the container 20 contains reference liquid L by way of example, the present invention may be applied to containers containing therein various liquids such as sample liquids, reagent solutions and the like. EXAMPLE 1 An experiment was made using an experimental device shown in Figure 6. In the experiment, the evaporation loss of the reference liquid L in the container 20 was measured. The experiment was made in the following manner. The spotting tip 12 comprised a tip body 14 formed of polypropylene and a lid member 16 formed of silicone rubber. A container 20 containing therein reference liquid L was prepared and the lid and the inner plug on the container 20 were removed. The spotting tip 12 was inserted into the container 20 through the mouth 20a thereof and the upper open end of the tip body 14 was closed with a weight 32 of 200g so that the inside space Si and the outside space So of the container 20 were communicated only through the fine communicating passages (grooves 22). The experimental device was then caused to stand in a room which was kept at a temperature of 32±0.1°C and a relative humidity of 30±2% for 24 hours. Then reduction in the weight was measured and the evaporation loss was calculated. FUJI DRI-CHEM ELECTROLYTE REFERENCE FLUID ® (trade name) was employed as the reference liquid L. FUJI DRI-CHEM CLEAN TIPS ® (trade name) was used as the tip body 14. The tip was a pipette tip coated with silicone resin on the outer surface of the lower end portion (water-repellent treatment). Containers 20 each containing reference liquid L of 6g and containers 20 each containing reference liquid L of 8g were prepared. As the lid members 16, those having four semi-circular grooves 22 as shown in Figure 7A, those having two semi-circular grooves 22, those having four circular through holes 24 as shown in Figure 7B and those having two circular through holes 24 were prepared. The radii or diameters of the grooves or holes were as shown in the following table. test # #1 & 7 #2 & 8 #3 & 9 #4 & 10 #5 & 11 #6 & 12 R or  R0.1mm R0.25mm R0.8mm 0.2mm 0.5mm 1.0mm area 1.32mm 2 1.88mm 2 2.4mm 2 0.52mm 2 0.52mm 2 1.11mm 2 number 4 4 2 4 2 2 % evp. 6g 0.3817 0.3887 0.5765 0.2209 0.1819 0.3474 8g 0.2760 0.2820 0.3650 0.1660 0.1390 0.2410 In the table, "area" means measured areas of the grooves or holes and "number" means the number of the grooves or holes. Test numbers #1 to #6 were for containers containing reference liquid L of 6g and test numbers #7 to #12 were for containers containing reference liquid L of 8g. Result of the Experiment The result of the experiment were as shown in the above table and Figures 8A and 8B. Figure 8A is for the containers containing reference liquid L of 6g and Figure 8B is for the containers containing reference liquid L of 8g. As can be understood from the table and Figures 8A and 8B, the evaporation loss increased substantially in proportional to the area of the communicating passages and the rate of increase was larger in the containers containing less liquid. When the evaporation loss is not more than about 1% after elapse of 24 hours, it may be considered that concentration of the liquid is well prevented. In this regard, the evaporation loss was not more than 0.6% in any of the test samples, which proved the effect of the invention. EXAMPLE 2 Employing the spotting tips employed in tests No.1 to No.12 in an electrolyte measuring system, measurement of electrolyte was repeated, and the evaporation loss was measured and occurrence of back flow was observed. Result of the Experiment The reference liquid L did not flow back into the spotting tip 12 or the nozzle 18 and the evaporation loss was not more than 0.7% with any of the spotting tips.

Claims: A spotting tip (12) comprising a tip body (14) which is adapted to be fitted on the end of a nozzle (18) of a liquid sucking means for sucking liquid (L) contained in a container (20), said spotting tip (12) being adapted to be inserted into liquid (L) in the container (20) through a mouth (20a) of the container (20), and a lid member (16) being adapted to be brought into contact with the mouth (20a) of the container (20) and to close the space between the tip (12) and the edge of the mouth (20a) when the tip (12) is inserted into the container (20) to a predetermined depth, the liquid sucking means being adapted to suck a predetermined amount of the liquid (L) into the tip body (14) with the tip body (14) held. in the liquid (L), wherein at least one communicating venting passage (22, 24, 26, 28) is formed to communicate the inside and outside spaces (Si, So) of the container (20) on opposite sides of the lid member (16), characterized in that said lid member (16) is formed integrally with the tip body (14) and said spotting tip has any one of the following features (a), (b) or (c): (a) said communicating passage (22) is in the form of a groove formed in the inner peripheral surface (16a) of the lid member (16) to extend from the lower surface of the lid member (16) to the upper surface of the same; (b) said communicating passage (24) is in the form of a through hole formed in the lid member (16) to extend from the lower surface of the lid member (16) to the upper surface of the same; or (c) said communicating passage (26) is in the form of a groove formed in the lower surface of the lid member (16) to extend in a radial direction of the lid member (16).

Inventors: SESHIMOTO OSAMU, SETO SHUNICHI, YAZAWA KENICHIRO, SESHIMOTO, OSAMU, SETO, SHUNICHI, YAZAWA, KENICHIRO
Applicants: FUJI PHOTO FILM CO LTD, FUJI PHOTO FILM CO., LTD.
Application year: 1995
Main classification: B01L3
IPC codes: B01L3, G01N35, B65D51