Titrator

Abstract

A titrating device adapted to be removably air-tight fitted onto a bottle of titrating liquid, comprising a graduated plunger-type syringe, for mounting externally on the bottle by a seal providing air-tight communication with a burette of comparable capacity as the syringe, for mounting in the bottle, so that titrating liquid in the bottle is metered into the burette and does not contact the syringe when the plunger is withdrawn while the tip of the burette is below the surface of the titrating liquid.

Description

BACKGROUND OF THE INVENTION

This invention relates to novel titrating devices.

It is conventional to employ pipetting droppers for rapid titration determinations in which the determination is based on the number of droplets of the titrating liquid consumed in the titration. As the accuracy of the dropprs increases, the less difference there is in the individual droplets with respect to their weight. Analytical error increases, the larger the size or the greater the number of droplets which are involved in the respective determination.

It has been found that a wide margin of error must be tolerated in such determinations using conventional pipetting droppers, because the droplets delivered by the same pipetting dropper are not always of equal weight, due to different wetting of the surface from which the droplets are released or the effects of the environment on the surface tension of the liquid to be released in droplet form. Another reason for inaccuracy is that it is practically impossible to manufacture a plurality of pipetting droppers which all deliver droplets of identical weight.

Therefore, it has been suggested to execute such titrations with a graduated plunger-type syringe, rather than with a pipetting dropper. In such a case, the volume of the liquid consumed in the titration is the determining factor, rather than the number (weight) of the released droplets. However, a disadvantage in the use of such a syringe is that when the titrating liquid is sucked into the syringe, an air bubble forms underneath the plunger of the syringe, which is difficult to remove, particularly in case of plastic syringes. In order to eliminate the air bubble, which is required in order to calibrate the syringe to the zero point, the syringe must be inverted and a portion of the titrating liquid squirted out of the syringe, which can then run over the fingers of the person using the syringe. This is dangerous, in particular, in case of corrosive or toxic titrating solutions. Moreover, the outside wall of the syringe must then be cleansed in some cases to prevent the inadvertent release of traces of the titrating liquid from the outer wall of the syringe during the titration, which would affect the accuracy of the determination. Consequently, such syringes have not become popular as auxiliary titrating means for rapid determination methods.

It has now been found that the above-described disadvantages can be eliminated by the specific arrangement of the titrating device of this invention.

SUMMARY OF THE INVENTION

The titrating device of this invention comprises a graduated plunger-type syringe, adapted for mounting outside a container for a titrating liquid by a hollow sealing means providing an air-tight communication between the syringe and a burette adapted for mounting inside the container by the sealing means to withdraw liquid from the container. Preferably, the syringe is disposed vertically above the burette.

DESCRIPTION OF THE DRAWING

The drawing is a vertical cross-section of a preferred embodiment of the titrating device of this invention mounted onto a container for the titrating liquid.

The embodiment shown in the drawing comprises a plunger-type syringe 1 having a plunger 1a and a barrel 1b with indexing indicia 1c on its wall and ending in a tip 1d; an annular gasket or washer sealing means 2 with a sleeve-like tubular extension 2a and an annular shoulder 2b; a sealing cap 3 with an axial aperature 3a in its top for a container 4 for the titrating liquid; a burette 5 with a lip 5a on its upper end and a dispensing tip 7 at its lower end; a transparent plastic tube or sleeve 6 fitted onto the barrel 1b of syringe; and a scraper 8 mounted in the mouth 4a of container 4.

Syringe 1 is mounted axially vertically above burette 5 and in indirect air-tight communication therewith by gasket 2 fitted into the mouth 4a of container 4 and, by means of annular shoulder 2b on the upper portion of gasket 2 immediately below extension 2a, over the top of the mouth 4a of container 4. Lip 5a of burette 5 is fitted into the lower end of aperature of gasket 2 so as to be proximate to the lower tip 1d; of barrel 1b of syringe 1. Container 4 and cap 3 are threaded so that the syringe assembly can be rigidly mounted on the container, the tightening of the cap forcing the shoulder 2b against the neck 4b of the container 4.

To withdraw a specific amount of titrating liquid from container 4, plunger 1a of syringe 1 is first depressed downwardly into barrel 1b and thereafter the titrator is fitted onto the storage vessel 4. During this step, the air trapped in the burette 5 prevents the entrance of titrating liquid into the glass tube 7. When plunger 1a of syringe 1 is moved upwardly, preferably after screwing cap 3 tightly onto container 4, i.e., partially withdrawn from barrel 1b, an amount of liquid corresponding to the change in volume of syringe 1 enters burette 5. In this manner, an exact titration can thereafter be effected, with this exactly metered quantity of liquid, by moving plunger 1a of syringe 1 downwardly, so that the titrating liquid exits from tip 7 of burette 5. The thus-consumed volume of liquid can be read off from the graduation scale 1c on the wall of barrel 1b of syringe 1.

The volume of the glass tube forming burette 5 projecting into the titrating liquid in container 4 is preferably equal to or larger than that of the syringe 1 so that no titrating liquid can enter syringe 1, even with a full utilization of the volume capacity of syringe 1. The avoidance of any contact between the titrating liquid and syringe 1 is especially of interest when the titration is to be conducted with corrosive liquids, e.g., concentrated acids or bases. In this manner, the lifetime of the syringe 1 is prolonged, particularly if the plunger is provided with a gasket.

In many cases it has proved furthermore advantageous to surround the syringe 1 with an optional transparent plastic tube or sleeve 6. This protects the graduation which is normally printed on the outside of the barrel of the syringe and, because of a certain magnifying effect, facilitates the reading of the graduation and thus enhances the accuracy of the determination.

Any desired, commercially available plunger-type syringe can be employed as syringe 1. Of special practicability in handling are syringes of a synthetic resin, e.g., polyethylene or -propylene, having a volume of between about 1 ml. and 20 ml. The container 4 can be formed of any desired inert material. Preferably, a conventional glass or plastic bottle is used.

Sealing means 2 can be formed of any material which is resistant to the titrating liquid employed. Suitable materials are, for example, rubber or elastomeric synthetic resins. As stated above seal 2 connects the upper rim of burette 5, which desirably is bent a little outwardly to form a lip 5a which ensures an air-tight fit, and the lower part of syringe 1 so that an air-tight seal is obtained. Sealing means 2 is disposed within the sealing cap 3. In order to impart extra ruggedness to the apparatus and to ensure an air-tight fit, seal 2 advantageously has a sleeve portion 2a which extends beyond the cap 3 to such an extent that it encloses the lower portion of the syringe 1 and sleeve 6.

Sealing cap 3 can be of any desired shape, for example, a screw cap. The cap need merely form a liquid tight closure for the associated container and must be resistant to the titrating liquid employed. The sleeve-like extension 2a of seal 2 projects through aperature 3a of cap 3.

Scraper 8 is advantageously mounted within the mouth of the container 4 so that it contacts the outer wall of burette 5. Scraper 8 can be made of cotton wool, glass wool, synthetic resin lips or a similar inert material, depending on the titrating liquid utilized. The only essential point is that the scraper removes any residual titrating liquid which may adhere to the outer wall of burette 5 when the titrator is removed from container 4.

Burette 5 suitably terminates at its bottom end in a tip 7 so that the metering accuracy is increased. Burette 5, like the other components of the titrator, can be made of glass or inert synthetic resin. The capacity of the burette, i.e., its internal volume, advantageously is the same as or greater than that of syringe 1 to ensure that no titrating liquid is drawn into the latter.

Syringe 1 preferably is arranged vertically above burette 5. Syringe 1 can, however, project at an angle with respect to burette 5, e.g., by forming a bend in sleeve 2a, if this should be advantageous for certain applications. One need only ensure that a tight seal is effected by sealing means 2 providing communication between burette 5 and syringe 1.

This novel and easily maintained titrator is very suitable for conducting rapid analyses, which methods have gained increasing importance nowadays. A wide field of application is in the analysis of foodstuffs and of water for general use and waste water. Among the many possible uses for the novel titrator are the determination of the total and carbonate hardness in various types of water, the determination of disinfecting chlorine in swimming waters, the determination of the hydrazine content of boiler feed water, the determination of the free and bound sulfurous acid, the total acidity of wine, and the determination of free fatty acids in baking shortening.

It has been established that with the aid of the novel device, results are achieved whose accuracy is comparable with that of conventional laboratory methods.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.

Claims

What is claimed is:

1. A titrating device comprising a container for a liquid to be titrated, said container having an opening through a neck bearing external threads, separable means for withdrawing said liquid from said container including a burette for depending into said container, a graduated plunger-type syringe for standing above said container, and hollow sealing means interconnecting said burette and said syringe in air-tight communication, the volume of said syringe being not substantially greater than the volume of said burette, and said sealing means including an upwardly extending tubular portion having an integral annular ring on the external surface thereof, and a screw cap for mounting on said threaded neck and having an aperture therein for receiving said tubular portion therethrough, said screw cap interacting with the upper surface of said annular ring for forcing the lower surface of said ring against said neck for sealing said separable means with said container.

2. The titrating device of claim 1 wherein said burette has a barrel in the form of a right circular cylinder and wherein said container includes an annular collar mounted in the neck thereof for scraping liquid from the surface of said burette as said burette is separated from said container.

3. A titrating device according to claim 1 wherein said syringe includes a cylindrical barrel portion and wherein said device includes a transparent plastic sleeve surrounding the barrel of the syringe and wherein said barrel and said surrounding sleeve are inserted into said upwardly extending tubular portion of said sealing means in an air-tight friction fit.