Microliter syringe for dispensing small, accurately measured quantities of fluid specimens

Abstract

A microliter syringe has a hollow guide mounted to one end of a syringe body into which a plunger is inserted. The plunger can be smoothly inserted into, and removed from, the syringe body through the guide without causing any eventual bending or buckling.

Description

This invention relates to a microliter syringe for dispensing small, accurately measured quantities of fluid specimens, and particularly to a microsyringe in which a plunger can be smoothly inserted into and removed from the syringe body.

A microliter syringe as used in a gas chromatography analysis etc. is adapted to dispense small quantities of medicament and a stainless wire of, for example, 0.5 mm in diameter is used as a plunger for the syringe. When this plunger is inserted into a syringe, it is liable to buckle. To prevent such buckling, a variety of proposals has been made to this date. However, microliter syringes of the prior art are rather elaborate in design to avoid such buckling.

Furthermore, the syringe is required to have such a construction as is easily cleaned for repeated use, and any complicated construction is therefore undesirable, since a delicate operation is carried out.

It is accordingly the object of this invention to provide an easily cleanable microliter syringe of simple construction, in which a plunger is smoothly inserted into and removed from a syringe body through a hollow guide without causing any buckling.

According to this invention there is provided a microsyringe comprising a syringe body having an inner bore for permitting liquid to be inserted along its axial direction; a cannula mounted to one end of the syringe body and communicating with the inner bore of the syringe body; a flexible hollow guide mounted to the other end of the syringe body and communicating with the inner bore of the syringe body; and a plunger adapted to be slidably reciprocated within the bore of the hollow guide and the bore of the syringe body.

This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawing, in which:

FIG. 1 is a side view showing a microliter syringe according to this invention;

FIG. 2 is a cross-sectional view, partly broken away, showing an upper section of the microliter syringe of FIG. 1;

FIGS. 3A to 3C are cross-sectional views each showing a modification of a hollow guide for the microliter syringe according to this invention;

FIG. 4 is a cross-sectional view, partly broken away, showing the manner in which a plunger is inserted slantwise into a syringe body through a guide; and

FIG. 5 is a cross-sectional view, partly broken away, showing the manner in which a plunger is inserted slantwise into a syringe body, wherein a flexible hollow guide is not employed.

This invention will be further explained by reference to the accompanying drawing.

In FIG. 1 there is shown a syringe body 1 made of a cylindrical, thick-walled transparent glass. In the central portion of the syringe body is provided an axially penetrating inner bore 2 into which liquid can be introduced. A cannula 3 is mounted to one end of the syringe body 1 so as to communicate with the inner bore 2. A scale 4 for indicating an amount of liquid is marked on the outer surface of the syringe body 1. To the other end of the syringe body a flange 5 is mounted to permit a plunger 8 to be easily reciprocated. In the flange 5 a mounting hole 6 is provided coaxially with the inner bore and a hollow guide 7 can be detachably fitted into the mounting hole. The hollow guide 7 is made of either plastic resin such as fluorine resin etc. or a flexible material such as glass fiber etc. and is substantialy cylindrical in shape. The guide is larger in outer diameter at its base end portion than at its free end portion. As a result, the guide is more flexible at its free end portion than at its base end portion. As shown in FIG. 2, a rib 6' is provided short of the base end of the guide. The rib is snap-fitted into a groove provided in the inner surface of the mounting hole 6. The rib may be provided on the inner surface of the mounting hole and, in this case, the associated groove is provided in the outer surface of the guide. The guide 7 can be easily snap-fitted into the flange 5 by merely pushing the former into the hole of the latter and it can be easily removed from the flange by merely pulling the guide relative to the flange. The guide 7 may be detachably screw-threaded into the flange. Any detachable arrangement may be adopted in this case.

The plunger 8 is made of a stainless steel having an outer diameter of, for example, 0.5 mm and is intimately insertible into the bore of the guide 7 and the inner bore of the syringe body. A knob 10 is mounted at the top of the plunger 8. It is preferred that a length l.sub.1 between the knob 10 and the top end of the guide 7, which is defined when the plunger 8 is pushed down to its limit i.e. the forward end of the plunger 8 is abutted against the penetrating end of the cannula 3 to indicate a zero position on the scale, be not more than several millimeters or preferably of the order of 1 mm. A length l.sub.2 between the upper end surface of the flange 5 and the lower end surface of the knob is preferably at least sufficient for a human finger to be inserted therebetween. The hollow guide 7 may take a variety of forms as shown in FIGS. 3A, 3B and 3C. The guide shown in FIG. 3A takes a cylindrical form. The guide shown in FIG. 3B takes a frusto-conical form and, therefore, pliability is increased toward the top of the frusto-conical guide. The guide shown in FIG. 3C is similar in shape to that shown in FIGS. 1-2 and the mouth of the guide is funnel-shaped, permitting an easy insertion of the plunger as well as preventing buckling of the plunger.

According to a microliter syringe so constructed, even if during the insertion of the plunger 8 into the guide the plunger is displaced slantwise as shown in FIG. 4, the guide is pliably bent at a flexible section 9 and the plunger 8 can be smoothly pushed into the bore of the syringe body without any appreciable resistance. Furthermore, even if the plunger is pliably bent, the guide is correspondingly bent so that the plunger does not buckle. And any tendency for the plunger to be eventually bent can also be avoided due to the pliable or flexible nature of the hollow guide.

When the plunger is manually pushed down to the zero position on the scale and abutted against the penetrating end of the cannula, a manual depressing force is concentrated on the exposed portion of the plunger. Since, however, the length l.sub.1 so defined between the upper end surface of the plunger and the lower end surface of the knob is not more than several millimeters or preferably of the order of about 1 mm, the plunger does not buckle even if any slant force is applied to the plunger. If any guide is not mounted to the syringe body through the flange, a space necessary for a manual operation is required between the flange 5 and the knob 10 and, consequently, the exposed surface of the plunger as defined between the flange and the knob is made longer. In this case, if further manual depressing force is applied to the knob, the plunger tends to be eventually bent or buckle at the upper end surface of the flange 5. According to this invention, a length between the knob 10 and the guide 7 can be reduced to about 1 mm and a resistance to buckling is further increased. Furthermore, any eventual bending or plastic deformation as well as buckling of the plunger can be avoided due to the pliable section 9 of the guide.

The plunger 8 and guide 7 can be, after removal from the syringe body, cleaned separately. The guide is easy to handle during cleaning, since it is detachably mounted to the syringe body through the flange.

As explained above, according to this invention the flexible or pliable guide is mounted to the syringe body. This arrangement can prevent any eventual bending or buckling of the plunger as occurring when the plunger is inserted into the syringe body and even when the insertion is nearly completed. Furthermore, the arrangement provides a longer space between the flange and the knob due to the presence of the guide so that the plunger can be easily manipulated. As the hollow guide is simple in construction and is removably mounted, for example, through the flange, to the syringe body, a cleaning operation can be easily carried out. Consequently, practical advantages are obtained according to this invention.

It is to be noted that the guide can be fixedly secured to the syringe body if circumstances permit.

Claims

What is claimed is:

1. A microliter syringe for dispensing small, arcuately measured quantities of fluid specimens, comprising:

a syringe body having a small bore therethrough;

a cannula mounted on one end of said body and communicating with the said bore;

an elongated plunger of bendable material extending slidably in said bore, the diameters of said plunger and bore being of the order of 0.5 mm whereby said plunger is readily bendable; and

a guide means mounted on the other end of said body with said plunger extending slidably therethrough, said guide means being readily bendable in response to lateral forces on said plunger outwardly of said guide whereby said guide means prevents kinking of said plunger upon operation of said syringe with the portion of said plunger in said bore being angularly related to the portion thereof extending outwardly of said body.

2. A microliter syringe according to claim 1 in which said guide means is more readily bendable at its free end portion than at its base portion.

3. A microliter syringe according to claim 2 in which said guide means is thinner at its free end portion than at its base portion.

4. A microliter syringe according to claim 1 in which said guide means is made of a flexible plastic resin.

5. A microliter syringe according to claim 1 in which said guide means is substantially cylindrical in shape.

6. A microliter syringe according to claim 1 in which a knob is mounted on the free end of the plunger; a flange is mounted on the said other end of the syringe body; and wherein the distance between the flange and the knob is sufficient for a human finger to be inserted therebetween; and the distance between the knob and the upper end of the guide means when the plunger is pushed down to its limit is about 1 mm.

7. A microliter syringe according to claim 1 in which said guide means is provided with a funnel-shaped mouth at its outer end for guiding said plunger therethrough.