Device for pipetting and/or diluting

#This invention relates to a dispenser and/or diluter and, more particularly, to a hand-held dispenser which can repeatably deliver a precise quantity of liquid and which can also repeatably collect a precise quantity of a first liquid and then deliver the first liquid diluted with a predetermined amount of a second liquid.

#There have been previously devised various types of apparatus for repeatably delivering a precise amount of liquid. Many types of hand-held syringes are capable of this task. However, in most cases it is necessary to refill the syringe after each use or to provide a number of different "stop" positions for the syringe plunger. This latter technique requires special operator control and generally yields only a very limited number of samples for each full stroke of the piston.

#Responsive to the need for a repeatable liquid delivery system having the capacity for delivering large numbers of samples without refilling, there have been devised various types of plunger bottle dispensers, examples being disclosed in U.S. Pat. Nos. 3,191,807, 3,430,813, 3,730,398 and 3,741,444. Typically, these units comprise a plunger and a first check valve which allows liquid to pass into a chamber when the plunger is released. A second check valve allows the liquid to be delivered when the plunger is depressed, and a relatively large capacity bottle serves as the source from which liquid is drawn in through the first check valve. This type of bottle dispenser system is found to operate satisfactorily in some applications, but there is a degree of inconvenience associated with the size and bulk of the bottle and the frequent necessity of bringing test tubes or vessels to the vicinity where the bottle is located. It is one object of the invention to provide solutions to these prior art problems as set forth.

#FIG. 1 is a cross-sectional view taken vertically through a device in accordance with an embodiment of the invention;

#FIG. 2 illustrates a modified version of the embodiment of FIG. 1, shown half in perspective and half in cross section.

#FIG. 3 illustrates operation of the loading feature of the invention.

#Referring to FIG. 1, there is shown a pipetting device 10 which is also useful as a pipetting/diluting device. A tubular body 20 has a front end 21, a middle portion 29, and a rear end 22, each of which has a different internal diameter in the present embodiment. The central bore in the body narrows at the front end thereof to form a receiving/dispensing tip 23.

#A hollow enclosure 30 is mounted over the rear end 22 of the body 20 and encloses the volume 31A. The forward wall of enclosure 30 is circular plate 29A which comprises the rearmost wall of middle body portion 29. The enclosure 30 is vented to the outside environment at 32. Openings 28 in the plate 29A connect the volume 31A and a volume 31B within the body portion 29, and these connected volumes are collectively defined as a back chamber 31.

#A plunger 40 is slideable in the bore in body 20 and extends from the rear thereof for manual activation. The plunger is shown at the bottom of its stroke in FIG. 1 and at the top of its stroke in FIGS. 2 and 3. The plunger 40 has a rear portion 42 which conforms circumferentially to the inner surface of rear end 22 of body 20, a central portion 49 and a front portion 43 which conforms circumferentially to the inner surface of front end 21 of body 20. The bore space in the body 20 forward of the front portion 43 of plunger 40 is defined as a front chamber 52. The plunger 40 has a communicating passage 45 between the back chamber 31 and the front chamber 52. The communicating passage 45 consists of the connected passageways labelled 45A, 45B and 45C in the FIGURE. In the present embodiment the passageways 45A comprise a pair of apertures on opposing sides of the plunger, as shown, and the passageways 45C comprise a pair of apertures in a removeable auxiliary plunger 80, to be described. When the auxiliary plunger is removed, the passageway 45C is merely a continuation of passageway 45B. A one-way valve 61, which may be a lip valve of the type illustrated, is mounted in passageway 45B over an annular flange at the end of plunger central portion 49. The valve 61 allows flow in the communicating passage 45 only from the back chamber 31 toward the front chamber 52.