EP0900594A2 - Plunger type burette for burette system - Google Patents

Abstract

The cylinder (11) is molded to close tolerances in a plastic containing 10-100% of a cyclo olefin copolymer (COC) and can be interchanged on the burette arrangement. One end of the cylinder is closed by a piston (13) to retain the fluid and a cap seals the outlet during storage of the cylinder and contents. When in use the elastomer cap is removed and replaced by a connector to a metering tube and titrating tip.

Description

The invention relates to a piston burette for a burette arrangement with a burette cylinder which has an outflow opening at one end and in which a piston is slidably disposed.

A burette is a calibrated scale with a reagent fillable transparent tube with an outlet for controlled dispensing of the reagent used in the dimensional analysis for the volumetric determination of substances. A special embodiment represent the piston burettes, mainly in analytical chemistry to determine unknown amounts of substances in samples using titrimetry or used in microbiology or genetic engineering. You hire high-precision work equipment, so that the geometric training of Piston burette, especially on the inside diameter of the burette cylinder, high demands are made.

While the classic burettes use gravity to reagent from a vertical one, provided with a tap at the bottom and with the In the case of piston burettes, the reagent-filled glass tube is discharged Glass tube designed as a burette cylinder, in which to convey the Reagent a piston is slidably disposed. The dosed volume is measured and displayed by the displacement of the piston.

Piston burettes of this type are common prior art.

6 shows the principle of such a piston burette. In a as Cylinder 4 acting, calibrated glass tube is a piston 3, the manually up or down by means of a motor (not shown) can be. There are two valves for the operation of the known piston burette 1, 2 necessary, the valve 1 when sucking the reagent into the Cylinder 4 opens and valve 2 releases the reagent from the Cylinder opens. When the piston is retired - in any one Position between upper and lower end point as limits - are both Valves closed. The position of the valves is marked in Fig. 6.

When used in analytical chemistry, the suction valve 1 is over an intake hose 6 connected to a storage vessel 7 in which a Reagent of known composition and concentration is located. The Outlet valve 2 is via a metering hose 5 with a device in which Usually a titration tip connected above one (not shown) presentation vessel with the unknown solution (analysis vessel) located.

When performing the analysis, a downward movement of the Piston 3 sucked the reagent from the storage vessel 7 and after Switch the valve system when moving the piston into the other Direction over the titration tip in precise volume steps into the Test tube delivered. The analysis is considered complete when the reaction in the Analysis vessel is complete and this with the help of a sensor or an im Color change was determined. The amount of dispensed reagent solution is shown on the display on the piston burette read or determined from the number of volume steps and from that the Analysis result calculated.

In the known burette arrangements, the piston burette is fixed in the Burette arrangement integrated. You therefore need a burette cylinder Relatively complex valve system connected upstream via two openings, since the The correctness of the volume determination depends largely on the precision, with which the valve system works, in particular what possible leaks as well Dead volumes in the valve system affects. Crucial for the correctness and Accuracy of volume determination is also the high constancy of Inside diameter over the length of the burette cylinder. For this, in usually specially calibrated glass tubes are used, so-called precision diluters, in a hot forming process on a precise inner mandrel be shrunk on. The known burette cylinders made of glass are therefore In addition to the disadvantage of sensitivity to breakage, it is very expensive a multiple use with the need for a complex Cleaning procedure when changing the reagent. The disadvantage is that Valve system, the piston burette, the suction line from the test tube and the flask is cleaned, dried and assembled.

Furthermore, a separate storage vessel for the reagent is required, which over Connection lines is connected to the valve system.

A metering device with a piston / cylinder system is also known (DE 43 10 808 A1), which can be used analogously to a burette, but is not a piston burette. This known metering device, which as prefilled unit can be designed as a single-use item of glass cylinders manufactured in the usual way with fluctuating Diameter from cylinder to cylinder and takes into account the Fluctuations in diameter by doing this for each individual The inner diameter of the burette cylinder is determined and, preferably on the Dosing cylinder machine-readable stored in the form of a bar code, d. H. is marked and during the dosing process when calculating the dosing stroke is taken into account electronically.

This well-known conception has decisive fundamental disadvantages.

It has to be done in a complex process for each individual dosing cylinder the individual inner diameter is measured and saved or marked become.

The electronic "diameter preparation" will continue to Changing the dosing cylinder with prefilled dosing cylinders difficult. It the new diameter must be set, what actuations the electronic dosing unit and thus appropriately trained personnel makes necessary.

Another disadvantage of the known metering cylinder is that Diameter-matched piston plugs must be used once a corresponding storage and logistics and on the other hand one "Search process" necessary in the manufacture of prefilled dosing cylinders makes. Wouldn't you do that? H. you would only plug one predetermined diameter, it would lead to mechanical problems Dosing cylinders with a narrow diameter, which in the worst case lead to this could not that the frictional forces between the piston and the inner wall of the cylinder can be overcome more, especially since the aforementioned script too Lubricants makes no comments.

The invention is based on the object, the one mentioned To design piston burettes so that their structure and handling are essential are easier than in the known case.

• der im Wege des Spritzgießens mit hoher Präzision und engtolerierten Maßen als Kunststoff-Spritzgußteil ausgebildet ist, welcher zwischen 10 % und 100 % aus einem Cycloolefin-Copolymer (COC) besteht,
• der als mit einer Reagenz vorgefüllte und lang lagerfähige selbständige Einheit ausgebildet ist, die an der Bürettenanordnung wechselbar anbringbar ist,
• von dem ein, eine Ausflußöffnung vorgebendes Ende im Lagerungszustand mit einem abnehmbaren Verschlußelement und im Anwendungsfall mit einem Anschlußstück eines Dosierschlauches versehbar ist, und
• dessen anderes Ende mit einem Kolben verschließbar ist, der verschiebbar in dem Bürettenzylinder aufgenommen ist.

This object is achieved according to the invention with a buret cylinder,

• which is made by injection molding with high precision and tight tolerances as a plastic injection molded part, which consists of between 10% and 100% of a cycloolefin copolymer (COC),
• which is designed as a self-contained unit which is prefilled with a reagent and can be stored for a long time and which can be exchangeably attached to the burette arrangement,
• from which an end defining an outflow opening in the storage state can be provided with a removable closure element and in use with a connector of a metering hose, and
• whose other end can be closed with a piston which is slidably received in the burette cylinder.

This concept makes it possible for the first time in an economical way To produce burette cylinders that have a precise inner diameter and for all burette cylinders manufactured to the specified dimensions is equal to. These burette cylinders produced in this way therefore have cylinder too Cylinder with a constant constant diameter.

The complex described in the case of DE 43 10 808 A1, which Manufacture of the dosing cylinder more expensive measures are not necessary at Invention, as it were, by the simple manufacturing process itself - that Injection molding - virtually "from ovo" a constant from cylinder to cylinder Diameter is specified. But the cost situation is just at Disposable items, which are the subject of the invention, an essential one Point of view.

The plastic burette cylinder according to the invention is inexpensive with high Precision can be produced and is therefore suitable for a single use, so that all cleaning procedures are eliminated. For the different Reagents are filled with differently filled burette cylinders different volumes as storage containers.

The plastic burette cylinder according to the invention is also unbreakable easy to integrate into the standard burette arrangements and on easy to manufacture with tight tolerances, especially if it is in Injection molding is made. The injection mold gives that necessary tight tolerances for the burette cylinder precisely. The Selection of the transparent plastic type enables visual control the content, control of air bubbles etc. It can be colored, to be able to use reagents that require light protection.

The plastic used, which contains cycloolefin copolymers (COC), is very inert to the usual reagents, and he also has a very low water vapor permeability, resulting in a relatively long storage period of the pre-filled burette cylinder, as long as it serves as a storage container, is given without the concentration of the reagent being in an impermissible manner changed. Its hardness also prevents mechanical deformation of the burette cylinder when dosing.

By using the reagent, e.g. the titration solution, already pre-filled Burette cylinder, the need for the burette cylinder is eliminated Upstream valve system with a reservoir for the reagent, whereby also the burette cylinder no longer has an inlet opening, but only one Must have outlet opening for the pre-filled reagent. The pre-filled Burette cylinders can also be used as storage containers for the reagent to be used. Since the invention Piston burette simple and therefore quick, as well as safe on the The piston burette arrangement can be put on, the invention also ensures a quick and safe operation of the arrangement, as well as the conversion to another reagent. In the case of the invention, in contrast to that described dosing unit according to DE 43 10 808 A1 the change of pre-filled buret cylinder purely mechanically in manual mode without one to pay attention to further conditions, since the diameter of each prefilled buret cylinders are constant in their manufacture.

For oxidation-sensitive reagents, such as thiosulfate solutions, which are caused by Oxygen could be oxidized during storage, according to a further embodiment of the invention as a material for the Burette cylinder uses plastics made of polyethylene naphthylate (PEN), Polyethylene terephalate (PET) or blends consist of it.

In the case of very sensitive reagents, the plastic wall of the Burette cylinder according to a further embodiment of the invention with a Barrier layer, preferably against oxygen, or provided for the storage period an outer packaging (bag) made of aluminum foil or special Provide gas barrier films.

The burette cylinder can also be multi-layered from different plastics be constructed.

According to a development of the invention, the burette cylinder can be used for Reduced frictional forces when moving the piston with a Lubricants such as silicone oil may be provided; this is already useful at the formation of the brush cylinder in the injection molding process with in Plastic mass introduced. These lubricants support in the case of In addition to the hard plastic COC, the goal of a mechanical To avoid deformation of the plastic buret cylinder what is still in the described DE 43 10 808 A 1 as a major disadvantage of the known Plastic dosing cylinder is shown.

The only outlet opening on the dosing, especially burette cylinder sealing cap consists in particular of an elastomer, preferably made of rubber such as halogenobutyl rubber, silicone elastomer or thermoplastic elastomers.

The movable piston is preferably made of a rigid plastic, such as e.g. made of fluoropolymers, PTFE, ETFE, FEP or other plastics a low coefficient of friction and high chemical resistance. Elastomers with a fluoropolymer coating can also be used For simple applications, common rubber materials are also e.g. B. bromine or chlorobutyl rubbers can be used.

Based on the embodiments shown in the drawings Invention explained in more detail.

Fig. 1

einen Längsschnitt durch die erfindungsgemäße Kolbenbürette mit einer verriegelbaren Kegelverbindung an der Ausflußöffnung,

Fig. 2

einen Längsschnitt durch eine Ausführungsform einer Abschlußkappe für die Kegelverbindung nach Fig. 1,

Fig. 3

eine schematische Darstellung eines Dosierschlauches mit Titrierspitze und einem Anschluß an die Kegelverbindung nach Fig. 1,

Fig. 4

einen Ausschnitt aus einem Längsschnitt des erfindungsgemäßen Bürettenzylinders mit einer einfachen Kegelverbindung an seiner Ausflußöffnung.

Fig. 5

einen Ausschnitt aus einem Längsschnitt des Bürettenzylinders mit einem abgerundeten Kopf und einer Elastomerkappe als Verschluß, und

Fig. 6

in einer schematischen Darstellung eine herkömmliche Bürettenanordnung.

Show it:

Fig. 1

2 shows a longitudinal section through the piston burette according to the invention with a lockable conical connection at the outflow opening,

Fig. 2

2 shows a longitudinal section through an embodiment of an end cap for the cone connection according to FIG. 1,

Fig. 3

1 shows a schematic illustration of a metering tube with a titration tip and a connection to the cone connection according to FIG. 1,

Fig. 4

a section of a longitudinal section of the buret cylinder according to the invention with a simple cone connection at its outlet opening.

Fig. 5

a section of a longitudinal section of the burette cylinder with a rounded head and an elastomer cap as a closure, and

Fig. 6

a conventional burette arrangement in a schematic representation.

1 shows a piston burette for a burette arrangement 10, consisting of from a burette cylinder 11, one at its upper end Outflow opening 12 has a lockable cone connection 12a. Instead of the taper connection, a bayonet connection is also possible, Screw connection, press coupling, etc. In the burette cylinder 11 is a Piston 13 slidably arranged, which also functions as a Has plug during storage of the piston burette. Of the Burette cylinder 11 is formed with a flange-like extension 14 provided and symbolically indicated by this flange Fastening means 15, which can be realized in a known manner, with connected to the buret arrangement 10. Instead of the flange, a External thread for screwing in the burette cylinder or a smooth one Cylinder which is clamped in a twist-lok or similar drill chuck etc. be provided.

Within this burette arrangement is a drive 16 for moving the Piston 13 - shown symbolically - arranged.

Instead of the motor movement, the arrangement can also be made in this way be that the piston is manually movable.

The brush cylinder 11 is prefilled with a reagent 17, the Cylinder on one side through the piston 13 and on the other side with its outflow opening 12 with a closure element 18 according to FIG. 2 is tightly closed. This closure element 18 is by means of a flange-like lower edge 18a, which is also only partially peripheral can be, and acts as an external thread, in the taper connection 12a can be screwed in, the inner extension 18b directly opening 12 seals.

These thus designed burette cylinders 11 are after they have been filled initially stored, i.e. they also form that immediately Storage container for the reagent to be used and are only in Use case associated with the buret arrangement, i.e. on her put on. Then the cap 18 is removed and the 3 including its titration tip 20 with a cap-like taper connection 21, similar to that 2 is provided with an external thread 21a, screwed onto the cone connection 12a. After that is the piston burette ready for use.

The burette cylinder 11 is made of plastic. Special meaning with regard to long-term storage, the plastics have the consist predominantly of transparent cycloolefin copolymers (COC), e.g. the plastic TOPAS® type 8007 from Hoechst AG, or APEL® from Mitsui Petrochemical or Zeonex® from Nippon Zeon.

The wall thickness of the burette cylinder is preferably approximately 1 mm a tolerance of the inner diameter of less than 0.1 mm, which is a results in very high dosing accuracy.

2 preferably consists of Halogenobutyl rubber, with other suitable elastomers as well thermoplastic elastomers (TPE) can be used.

The piston 13 is preferably made of PTFE or also from a Halogenobutyl rubber or TPE.

For oxidation sensitive liquid reagents, e.g. Thiosulfate solutions that can be oxidized by oxygen during storage preferably a plastic with low oxygen permeation such as Polyvinyl chloride (PVC), polyethylene naphthylate (PEN) or other polyester application.

For very sensitive reagents, it is advisable to use the plastic existing buret cylinder 11, as shown in part in Fig. 1, a Apply barrier layer 22 against oxygen. The application of a Such a barrier layer belongs to the state of the art according to DE 44 38 359A1 Technology.

Preferably, the burette cylinder 11 including the molded one Flange 14 made by injection molding. It can be a lubricant already in the molding of the burette cylinder into the plastic mass be introduced.

4 is a variant for the formation of the head of the Burette cylinder 11 shown. Instead of the lockable taper connection 1 is a non-lockable taper connection 12b according to FIG. 4 provided that, as long as the burette cylinder acts as a storage container, can also be closed with an elastomer cap analogous to FIG. 2, with the Connection of the dosing hose 19 the same connection (see Fig. 3 element 21) can be used.

1 and 4, the head of the burette cylinder 11 is angular. It it goes without saying that it can also have other forms, for. B. rounded Contours with a tapered conical connection. Such The embodiment in connection with an elastomer cap 23 is shown in FIG. 5 shown.

The burette cylinder can also have the configuration of standardized Have pre-filled syringes according to DIN 13 098.

Typical filling volumes of the burette cylinders are between 2 ml and 100 ml, the inside diameter of the burette cylinder depends on the particular one required Dosing accuracy, it is typically in the range of approx. 4 mm to approx. 26 mm.

Instead of the trapezoidal closure element 18 according to Figure 2 can also other closure elements, e.g. a toggle lock with predetermined breaking point, be provided.

Claims (8)

Piston burette for a burette arrangement, with a burette cylinder (11), which is made by injection molding with high precision and tight tolerances as a plastic injection molded part, which consists of between 10% and 100% of a cycloolefin copolymer (COC), which is designed as an independent unit which is prefilled with a reagent (17) and can be stored for a long time and which can be exchangeably attached to the burette arrangement (10), one end of which defines an outflow opening (12) in the storage state with a removable closure element (18, 23) and in the application case with a connecting piece (21) of a metering hose, and the other end of which can be closed with a piston (13) which is slidably received in the burette cylinder (11). Piston burette according to claim 1, characterized in that the plastic is a polyethylene naphthylate (PEN), polyethylene or polypropylene or propylene / ethylene copolymers or a polyethylene / polypropylene blend. Piston burette according to claim 1 or 2, characterized in that the plastic wall of the burette cylinder (11) is provided with a barrier layer (22). Piston burette according to one of claims 1 to 3, characterized in that the inner wall of the burette cylinder (11) is provided with a lubricant. Piston burette according to claim 4, characterized in that the lubricant is silicone oil. Piston burette according to one of claims 1 to 5, characterized in that the closure element (18, 23) consists of an elastomer, preferably of rubber. Piston burette according to one of claims 1 to 6, characterized in that the piston (13) consists of fluoropolymers or synthetic rubbers or natural rubbers or rubbers, rubber or Teflon laminated with fluoropolymers. Piston burette according to one of claims 1 to 7, characterized in that the burette cylinder (11) is constructed in several layers from different plastics.

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