Measuring and testing – Sampler – sample handling – etc. – Capture device
Reexamination Certificate
1998-08-27
2001-02-06
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Sampler, sample handling, etc.
Capture device
C073S863000, C073S864000, C073S864020, C073S864510, C422S180000
Reexamination Certificate
active
06182517
ABSTRACT:
The invention relates to a burette tip for titrating a fluid and the use of a burette tip. Such burette tips are used when titrating for metering a titrating agent.
When titrating, a titrating agent is added to a sample fluid until a certain effect is observed. From the consumption of the titrating agent the content of a component of the sample fluid responsible for this effect can be determined. The measuring accuracy thus depends considerably on the accuracy with which the consumption of the titrating agent is evaluated or with which the titrating agent may be metered.
Often the titration is carried out with a burette tip submersed into the sample fluid. If the titrating agent is specifically heavier than the sample fluid when the titrating agent and the sample fluid have differing concentrations, or the titrating agent and the sample fluid on their bordering surface have differing speeds, the sample fluid may enter into the burette tip and the titrating agent may exit into the sample fluid. This may lead to inaccuracies in measurement.
It is known (for example with the Metrohm titroprocessor 636) to apply a microvalve acting in the manner of a one-way valve, which is closed with a membrane which although letting titrating agent exit does not let any sample fluid enter (microvalve for diffusion-preventing burette tips from Metrohm, product number 6.2726.060). From CH 660 131 it is also known to provide burette tips with a siphon which is to prevent the diffusion. Burette tips with a siphon do not prevent the diffusion of titrating agent and sample fluid of differing concentrations. Also diffusion by way of differing speeds at the border surface is not prevented. Furthermore the manufacture of the above mentioned microvalve is complicated since the membrane must be placed onto the front part of the microvalve with a great precision. A further disadvantage of known microvalves may lie in the fact that the membrane and the valve seat are accessible from the outside, which with an incorrect handling leads to an increased susceptibility of the microvalve to mechanical damage. A disadvantage of known microvalves of hard materials may also lie in the fact that the membrane must be opened with a relatively large pressure of the titrating agent. The smallest damage on the valve seat and/or on the membrane may however already lead to the undesirable entering of sample fluid or the outflow of the titrating agent.
It is the object of the present invention to avoid the disadvantages of the known devices, thus in particular to provide a burette tip for titrating a fluid which is less succeptible to mechanical damage and which can be manufactured in a simple and economical manner.
According to the invention these objects are achieved with a burette tip with the features described below.
The burette tip comprises a membrane (mostly of a soft plastic) and a (in any case comparatively) hard seat for this membrane. For protecting the membrane and/or the seat from mechanical damage the burette tip according to the invention comprises a covering. The covering covers the membrane and the seat for the membrane at least partly.
Advantageously the covering consists of a circumferential annular wall which encloses the membrane and the seat and where appropriate of a cover part which partly covers the surface of the membrane. The membrane should not be completely covered by the cover part so that fluid may still exit.
A particularly simple embodiment example results when the membrane is pressed simultaneously with the cover part against the seat. For this the cover part may be provided with a projection arranged in a central region.
The burette tip can be particularly simply manufactured when the cover part can be latched on the annular wall. The annular wall may for example be provided with a deepening with a resting surface for receiving the cover part. Advantageously the annular wall projects slightly beyond the cover part applied into the deepening.
In a preferred embodiment part the burette tip consists exclusively of the cover part, a burette body comprising the seat and the membrane. The membrane is held between the cover part and the burette body. The burette body and the cover part are advantageously integrally formed as plastic injection moulding parts. Such a burette tip may be particularly simply manufactured. The burette body and the cover part are injection moulded. The membrane is applied into the burette body onto the seat and the cover part is latched into the deepening of the annular wall of the burette body. The cover part simultaneously presses the membrane against the seat of the membrane.
The cover part is advantageously formed as an circular ring which is provided with webs running through the centre of the circle. The projection for pressing the membrane against the seat may be mounted in the center of the circular ring.
Alternatively it is also conceivable to form the cover part as a circular disk provided with openings.
In an alternative embodiment example it is also conceivable to form the burette body without a circumferential annular wall and to form the covering as a curved cover cap which covers and encloses the membrane and the valve seat simultaneously.
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patent: 4683916 (1987-08-01), Raines
patent: 4729401 (1988-03-01), Raines
patent: 4812293 (1989-03-01), McLaurin et al.
patent: 5325889 (1994-07-01), Paul et al.
patent: 0 250 243 A2 (1987-12-01), None
International Search Report.
Larkin Daniel S.
Loo Dennis
Metrohm AG
Shoemaker and Mattare Ltd.
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