A DISPOSABLE PRESELECTED-VOLUME CAPILLARY PIPET DEVICE AND METHOD OF PREPARING A LIQUID SAMPLE FOR TESTING

Abstract: A disposable preselected-volume capillary pipet device comprises a capillary tube having an admitting-emitting end for liquids and a vent end for passing air from the tube as the liquid is being drawn into the tube by capillary action, a port at the admitting-emitting end for admitting and emitting liquids to the capillary tube, a port at the vent end of the tube for passing air freely from the tube, a barrier plug for passing air and stopping the passage of liquid through the tube, with the barrier plug being positioned in the tube at a preselected dis­ tance from the admitting-emitting port to define a liquid chamber of preselected volume, and a plunger for pushing the barrier plug from the vent end to push the preselected volume of liquid out of the liquid chamber. The barrier plug may be mounted in the tube or in the head of the plunger. The method includes admitting a volume of liquid to be tested into the capillary tube by capillary action, venting the air in the tube through the barrier plug and the vent end during the admitting of the liquid into the capillary tube by capillary ac­ tion, stopping the admitting of the liquid when the liquid con­ tacts and wets the barrier plug to obtain a preselected volume of liquid in the chamber, and discharging the liquid from the chamber by pushing the barrier plug through the chamber.

Description: The invention relates to a disposable preselected-volume capillary pipet device comprising a capillary tube having an admitting-emitting end for liquids and a vent end for passing air from the tube as the liquid is being drawn into the tube by capillary action, a port at the admitting-emitting end for admitting and emitting liquids to the capillary tube, a port at the vent end of the tube for passing air freely from the tube, and hydrophobic barrier means for passing air and stopping the passage of liquid through the tube, said barrier means being positioned in the tube at a preselected distance from the admitting-emitting port to define a liquid chamber of preselected volume. The invention further relates to a method of preparing a liquid sample for testing, comprising the steps of providing a capillary tube having an admitting-emitting end for passing liquid and a vent end for passing air, and a barrier means positioned between the ends to define a preselected volume of liquid in a chamber formed between the barrier means and the admitting-emitting end, admitting a volume of liquid to be tested into a capillary tube by capillary action, venting the air in the tube through the barrier means and the vent end during the admitting of the liquid into the capillary tube by capillary action, stopping the admitting of the liquid when the liquid contacts and wets the barrier means to obtain a preselected volume of liquid in the chamber, and discharging the liquid from the chamber. A capillary pipet device of the generic kind is known from the US-A-3741732 and used for transferring liquids such as a specimen of blood from a patient to a test tube or testing apparatus. A drop of blood is produced by sticking the finger of a patient with a needle, the blood is picked up by a pipet and is taken to a machine where the blood is tested and analyzed. Capillary tubes are excellent for drawing blood from this drop because the capillary tubes suck the blood up into the tubes at a speed that does not also draw up air bubbles, which are undesireable. In the known capillary pipet device the advancing liquid is stopped by the barrier means having a small hole which will not be passed by the liquid but by air. However the barrier means does not hold the liquid as it does not stop the passage of air before it is wet or after it is wet. If the tube is hold upright, without placing the finger on the top of the tube, the liquid will drain out. Another problem arises in trying to eject all blood from the capillary tube. Liquid bubbles at the end and the last drop of liquid is always hard to get out. It may be possible to get the last drop out of the tube by shaking but this is messy and the last drop may not go where desired. In any event, prior methods do not deliver a precise volume of blood to a testing machine, and without a precise volume of blood the testing machine cannot perform its tests accurately. The problem underlying the invention is to provide a disposable and inexpensive capillary pipet device and a method of preparing a sample for testing which are accurate in delivering a preselected volume of liquid for testing by discharging every drop of liquid. Starting out from the device of the generic kind this problem is solved in that piston means are provided for pushing the barrier means from the vent end to the admitting-emitting end to push the preselected volume of liquid out of the liquid chamber and the hydrophobic barrier means is made of a material that passes air freely, yet stops passage of air upon being contacted by the liquid. Preferably the device includes a stop shoulder flared inwardly from the admitting-emitting port to stop the barrier means from discharging from the capillary tube as the piston means pushes the liquid out of the chamber. Conveniently the vent end of the capillary tube has a flange that flares outwardly for easy insertion of the piston means. Advantageously said piston means is a plunger comprising a tube or a solid rod of smaller outside diameter than the inside diameter of the capillary tube. In a preferred embodiment of the invention said piston means is a plunger positioned in the capillary tube with the barrier means being positioned in the head end of the plunger, and the plunger being hollow. This embodiment preferably includes a wax seal connecting the plunger to the vent end of the capillary tube to temporarily hold the barrier means in desired position in the capillary tube and to permit breaking the wax seal by pushing the plunger toward or away from the admitting-emitting port. The problem underlying the invention is also solved by a method wherein the liquid is discharged by pushing the barrier means through the chamber to the admitting-emitting end. Advantageously the barrier means is pushed through the chamber by pushing a plunger against the barrier means. In another preferred method the barrier means is located in the head of a plunger formed by a hollow tube, the plunger is positioned in the capillary tube during the capillary action of filling the chamber with liquid, and the liquid is discharged from the capillary tube by pushing the plunger through the chamber to the admitting-emitting end. With the capillary pipet device of the invention and the method of preparing a liquid sample for testing it is possible to deliver the whole liquid sample including the last drop. As the delivered preselected volume is precise, tests of the liquid sample can be performed very accurately. Embodiments of the invention are further explained by means of drawings, wherein Fig. 1 is a view in vertical section of a first embodiment of a capillary pipet device, Fig. 2 is a view in side elevation of a plunger consisting of a solid rod, Fig. 3 is a view in vertical section of a second embodiment of the capillary pipet device, Fig. 4 is a view of the capillary pipet device of Fig. 3 in disassembled condition. The disposable preselected-volume capillary pipet device 10 is used for taking a preselected volume of liquid, such as blood from a patient, and delivering it to a test tube or testing apparatus. Capillary pipet device 10 comprises a capillary tube 12, preferrably made of glass, having an intake-emission, or admitting-emitting end 14 for admitting a liquid and discharging it, and a vent end 16 for passing air from tube 12 as liquid is being drawn into the tube by capillary action. A port 18 is formed at admitting-emitting end 14 for admitting and emitting liquids to and from the capillary tube 12, and a vent port 20 is formed at the vent end of tube 12 for passing air freely from the tube. Barrier means 22 is provided for passing air through the tube 12 to the vent end 16 and for stopping the passage of liquid, and is positioned in tube 12 at a preselected distance from admitting-emitting port 18 to define a liquid chamber 24 of preselected volume. Piston means is provided for pushing barrier means 22 to port 18 to push the preselected volume of liquid out of chamber 24 and deliver it to testing apparatus. The piston means comprises a plunger 26 which is preferrably a glass capillary tube of smaller outside diameter than the inside diameter of tube 12. Being hollow, plunger 26 does not impede the venting of air from tube 12 and may be positioned inside tube 12 during the capillary action of filling chamber 24 with liquid. Fig. 2 shows an alternative plunger 28 which is a solid glass rod that may be used to push barrier means 22 and the liquid from chamber 24 after the chamber has been filled. However, plunger 28 may not be positioned in tube 12 during the filling operation because it would prevent the venting of air from tube 12. Port 18 is provided with a stop shoulder 30 that flares inwardly to stop the barrier means 22 from discharging from tube 12 when the piston means pushes it through the tube. The barrier means 22 is made of a hydrophobic material that passes air freely to vent it from tube 12 so as to not impede or slow down the capillary action of drawing the liquid into the tube. Barrier means 22 also stops passage of air and liquid upon being contacted by the liquid after chamber 24 has been filled with a preselected volume of the liquid. Vent port 20 is provided with a flange 32 that flares outwardly for easy insertion of the barrier means 22 and the piston means. Turning to the embodiment of the invention shown in Figs. 3 and 4, there is shown a disposable preselected-volume capillary pipet device 40 wherein the piston means comprises a plunger 42, a tube preferrably of glass, positioned in capillary tube 12 with the barrier means 22 being positioned in head end 44 of plunger 42. As shown in Fig. 3, a wax seal 46 may be used to connect the plunger 42 to the vent end 16 of the capillary tube 12 to temporarily hold the barrier means 22 in desired position in capillary tube 12 during the filling operation. When chamber 24 is filled with liquid, the wax seal 46 is easily broken by the action of pushing plunger 42 toward port 18. The method of preparing a liquid sample for testing comprises the steps of providing a capillary tube 12 having an admitting-emitting end 14 for passing liquid and a vent end 16 for passing air, and a barrier means 22 positioned between ends 14 and 16 to define a preselected volume of liquid in the chamber 24 formed between barrier means 22 and admitting-emitting end 14, venting the air in tube 12 through the barrier means 22 and the vent end 16 during the admitting of the liquid into the capillary tube 12 by capillary action, stopping the admitting of liquid when the liquid contacts and wets the barrier means 22 to obtain a preselected volume of liquid in the chamber 24, and discharging the liquid from chamber 24 by pushing the barrier means 22 through chamber 24. The barrier means 22 may be located in tube 12 as shown in Fig. 1, or it may be located in head end 44 of plunger 42, as shown in Figs. 3 and 4. The capillary pipet device 10, of Fig. 1, is assembled by the manufacturer who precisely positions barrier means 22 in tube 12. The capillary pipet device 40, of Figs. 3 and 4, may be assembled by the manufacturer as shown in Fig. 3. However, it may also be shipped to the user in unassembled condition as shown in Fig. 4, and the user may place plunger 42 at any desired position in tube 12, using scribe marks 48 to choose the size of chamber 24 that he wants. And, of course, the user may alter the volume setting of pipet device 40 as shown in Fig. 3, if he wishes, by pushing or pulling plunger 42 to break wax seal 46, and setting plunger 42 at a desired scribe mark 48. Hydrophobic substances suitable for use in barrier means 22 are known to the art. Barrier means 22 may be made of a hydrophobic material such as polyethylene or other type polyolefins, styrofoam aerated, light-weight multicellular polystyrene plastic, or any other plastic material which has hydrophobic characteristics, or may be a wettable material which is coated with a hydrophobic coating such as paraffin wax, beeswax or various plastics. The hydrophobic material can include a reactive polymer, mixed with a non-reactive foamed polyethylene polymer, which gels on being wetted by an aqueous liquid such as blood to form an impervious liquid and air barrier capable of withstanding a pressure of 1 bar or more.

Claims: A disposable preselected-volume capillary pipet device (10) comprising a capillary tube (12) having an admitting-emitting end (14) for liquids and a vent end (16) for passing air from the tube (12) as the liquid is being drawn into the tube (12) by capillary action, a port (18) at the admitting-emitting end (14) for admitting and emitting liquids to the capillary tube (12), a port (20) at the vent end (16) of the tube (12) for passing air freely from the tube (12), and hydrophobic barrier means (22) for passing air and stopping the passage of liquid through the tube (12), said barrier means (22) being positioned in the tube (12) at a preselected distance from the admitting-emitting port (18) to define a liquid chamber (24) of preselected volume, characterised in that piston means (26, 28, 42) are provided for pushing the barrier means (22) from the vent end (16) to the admitting-emitting end (14) to push the preselected volume of liquid out of the liquid chamber (24) and the hydrophobic barrier means (22) is made of a material that passes air freely, yet stops passage of air upon being contacted by the liquid. Device according to claim 1, characterised by a stop shoulder (30) flared inwardly from the admitting-emitting port (18) to stop the barrier means (22) from discharging from the capillary tube (12) as the piston means (26, 28) pushes the liquid out of the chamber (24). Device according to anyone of the claim 1 or 2, characterized in that the vent end (16) of the capillary tube (12) has a flange (32) that flares outwardly for easy insertion of the piston means (26, 28, 42). Device according to anyone of the claims 1 to 3, characterized in that said piston means is a plunger comprising a tube (26, 42) or a solid rod (28) of smaller outside diameter than the inside diameter of the capillary tube (12). Device according to claim 1, 3 or 4 characterised in that said piston means is a plunger (42) positioned in the capillary tube (12) with the barrier means (22) being positioned in the head end (44) of the plunger (42), and the plunger (42) being hollow. Device according to claim 5 characterized by a wax seal (46) connecting the plunger (42) to the vent end (16) of the capillary tube (12) to temporarily hold the barrier means (22) in desired position in the capillary tube (12) and to permit breaking the wax seal (46) by pushing the plunger (42) toward or away from the admitting-emitting port (18). A method of preparing a liquid sample for testing, comprising the steps of providing a capillary tube having an admitting-emitting end for passing liquid and a vent end for passing air, and a barrier means positioned between the ends to define a preselected volume of liquid in a chamber formed between the barrier means and the admitting-emitting end, admitting a volume of liquid to be tested into a capillary tube by capillary action, venting the air in the tube through the barrier means and the vent end during the admitting of the liquid into the capillary tube by capillary action, stopping the admitting of the liquid when the liquid contacts and wets the barrier means to obtain a preselected volume of liquid in the chamber, and discharging the liquid from the chamber characterized in that the liquid is discharged by pushing the barrier means through the chamber to the admitting-emitting end. The method of claim 7, including pushing the barrier means through the chamber by pushing a plunger against the barrier means. The method of claim 8 including locating the barrier means in the head of a plunger formed by a hollow tube, positioning the plunger in the capillary tube during the capillary action of filling the chamber with liquid, and discharging the liquid from the capillary tube by pushing the plunger through the chamber to the admitting-emitting end.

Inventors: KENNEY, JAMES W.
Applicants: DRUMMOND SCIENTIFIC COMPANY
Application year: 1986
Main classification: B01L3
IPC codes: G01N1, B01L3, A61B5