Measuring and testing – Sampler – sample handling – etc. – Capture device
Reexamination Certificate
2000-06-30
2001-10-16
Raevis, Robert (Department: 2856)
Measuring and testing
Sampler, sample handling, etc.
Capture device
Reexamination Certificate
active
06301980
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to the quantitative chemical analysis of liquids by means of volumetric titration, more specifically it provides a device that is more compact, rugged, and easier to use than the presently available apparatus, while maintaining accuracy of measurement.
DESCRIPTION OF THE PRIOR ART
The analysis of fluids for a specific chemical constituent is often accomplished by a procedure known as titration, in which a standard solution is mixed in increments with a sample to which has been added a color-forming indicator so that a marked color change occurs at the point where the amount of standard solution just neutralizes all of the constituent present in the sample. At this endpoint, the amount of the unknown constituent in the sample may be ascertained from the amount of standard solution used.
The prior art basic apparatus used for titration has hardly changed since the beginning, and remains cumbersome and difficult to use. The unknown is delivered to a titration flask with a pipette, then standard is added by means of a burette until the endpoint is reached. Specifically, it suffers from the following disadvantages:
a) The apparatus is of multiple pieces. At a minimum, six pieces are required: a pipette, a burette, a burette stand, a burette clamp, a titration flask, and a funnel.
b) The apparatus is expensive. The minimum cost is about 150 dollars for the above assembly.
c) The apparatus is bulky and difficult to store. The pipette, burette, and stand are all of substantial length.
d) The burette, pipette, and titration flask are made of glass and are easily broken.
e) The insides of the pipette and burette must be kept scrupulously clean to avoid drainage errors. This may require the use of dangerous or toxic cleaning agents.
f) The burette must be rinses before use with the standard. This takes time and wastes standard. Also, standard remaining in the burette at the end of a series of titrations must be discarded.
g) Because liquids wet the insides of the pipette and burette, time must be allowed for drainage of these surfaces.
h) Burette measurements are made from the position of the meniscus. The meniscus is curved and is difficult to view. If viewed from an angle, a parallax error may be made
i) A small amount of unknown or standard may be splashed on the side of the titration flask. The titration must be paused to wash down this deposit, or a titration error will occur.
j) Any partial droplet on the tip of the burette is shown by burette reading as having been delivered, but has not been delivered to the titration flask. For best accuracy, it must be washed off into the titration flask.
k) The contents of the flask must be mixed by swirling. Therefore, two hands are required, one to control delivery from the burette, the other to swirl the flask. This may be tiring to the operator.
l) The operator must add precisely the right amount of standard to achieve the endpoint. One must proceed cautiously or too much standard will be added, overshooting the end point. A good deal of time may be consumed doing a titration because of fear of overshooting the end point. This is especially true for an inexperienced operator. If the end point is overshot, the operator must then repeat the titration, or live with a less than optimum result.
m) Because the apparatus is open to the atmosphere, it is not suitable for titration of moisture sensitive, air sensitive, or volatile substances.
n) The apparatus is most accurate when a substantial portion of the contents of the burette is used for a titration. Therefore, to attain the required accuracy, it may be necessary to repeat the titration using a different amount of unknown, either by using a different pipette or by quantitatively diluting the unknown; or it may be necessary to use a standard of greater or lesser strength.
o) It is sometimes advantageous or necessary to perform reverse titrations, where the standard is titrated with the unknown. It is very inconvenient to do a series of reverse titrations, as the burette must be drained and filled with each new unknown.
p) The apparatus is not suitable for filed use. A level work surface is required.
q) A computation of the amount of unknown must be made.
Improvements have been made by the invention upon the basic apparatus. The glassware may be replaced by plastic. The burette can be arranged so that it is automatically filled. The burette may be replaced by a dispenser with digital readout. Stirring may be done with a magnetic stirrer and stir bar. However, the basic manipulations remain the same, with the result that performing a titration remains a complex and time consuming matter. Simpler methods using drip counting have been described and are used, however, they are of limited accuracy.
Automated analyzers have been developed, however they are expensive and are best used for the analysis of many similar samples. Such analyzers are not suited for field or educational use, or the analysis of a small number of samples. U.S. Pat. No. 5,817,954 issued to Kahng et. al. on Oct. 6, 1998, shows how the apparatus for automatic titration can be simplified, using some of the same ideas as the present patent.
OBJECTS OF THE INVENTION
It is the object of this invention to provide an apparatus. Specifically, some advantages are:
a) The apparatus is formed as a unitary structure.
b) The apparatus is of low cost. The cost of manufacture is substantially less than the existing apparatus.
c) The apparatus is compact and easy to store.
d) The apparatus is of rugged construction and not easily damaged.
e) The apparatus is easily cleaned with a minimal amount of water or other liquid.
f) No standard is wasted in rinsing the apparatus before use. The apparatus may be made of such a size that lesser amounts of standard and unknown are required, compared to the standard apparatus.
g) No time for the drainage of surfaces is required.
h) The amounts of unknown and standard are read from a ruled scale, with or without vernier, or from a digital display. Reading of the position of a meniscus is eliminated.
I) There is no concern about any amount of unknown or standard remaining unmixed.
j) The correction for standard measured but not mixed is small and of constant value.
k) Mixing is accomplished by a stirrer, and no manual mixing is needed.
l) There is very good indication of the nearness to the endpoint, and the adjustment to the endpoint is rapid and easily done. Therefore, the time required to do titration is much reduced.
m) The apparatus is closed to the atmosphere and is suitable for the titration of moisture or air sensitive substances.
n) A large range of concentrations of unknown can be analyzed using a given strength of standard without undue loss of accuracy.
o) Reverse titrations are easily done.
p) The apparatus is suitable for field use. A minimal work surface is required.
q) The apparatus is easily customized or programmed so that the results of titrations of a given sort can be directly read form the scale or digital display, with no computation required. Other objects and advantages will become apparent from the specifications, drawings, and description.
REFERENCES:
patent: 3410664 (1968-11-01), Fielding
patent: 4117728 (1978-10-01), Johnson
patent: 4339317 (1982-07-01), Meiattini et al.
patent: 4360662 (1982-11-01), Williams
patent: 4815632 (1989-03-01), Ball et al.
patent: 5045284 (1991-09-01), Smith et al.
patent: 5340541 (1994-08-01), Jackson et al.
patent: 5364596 (1994-11-01), Magnussen, Jr. et al.
patent: 5707848 (1998-01-01), Bryan et al.
patent: 5817954 (1998-10-01), Kahng et al.
patent: 6068615 (2000-05-01), Brown et al.
Larson Jacqueline S.
Raevis Robert
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