Chemistry: analytical and immunological testing – Automated chemical analysis – Condition or time responsive
Reexamination Certificate
1999-10-26
2002-04-16
Ludlow, Jan (Department: 1743)
Chemistry: analytical and immunological testing
Automated chemical analysis
Condition or time responsive
C422S075000, C422S077000, C436S042000, C436S163000, C700S050000, C700S267000, C702S025000, C702S031000
Reexamination Certificate
active
06372505
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process and apparatus for titrating substances by a stepwise addition of a discrete incremental quantity of titrant, at first in time intervals t
4
, then in time intervals t
5
, and finally in time intervals t
6
, while the progress of the reaction towards its end point (EP) is being monitored and the addition of titrant is being controlled. The discrete incremental quantity and the lengths of the time intervals t
4
, t
5
, t
6
are the parameters that determine the speed of titration in this process.
2. Brief Description of the Prior Art
Processes of this kind are an established practice for making quantitative determinations in laboratories, and it is known that they require a certain amount of time. Not least among the reasons is the fact that the reaction gets progressively slower as it approaches the end point, which in itself may be a source of inaccuracy, as is the case if the reaction slows down so much towards the end that it appears to have reached its end point while, in fact, there is still a certain amount of “after-consumption” that is missed in the measurement. The opposite case can also occur and is known as “over-titrating”. This happens if one attempts to speed up the process by adding another increment of titrant before a clear response to the previous increment has been observed, so that subsequently a surplus of titrant is registered, which degrades the accuracy of the measurement.
SUMMARY OF THE INVENTION
It is therefore the object of the present invention to improve the speed and/or the accuracy of the titration process. According to the invention, this is accomplished by controlling the addition of titrant through a control function that is formed by using at least one differential component (time derivative) of the reaction curve that is obtained by the incremental addition of titrant.
In particular, by employing the inventive concept, the stated objective is met even under difficult conditions as, e.g., in a Karl Fischer titration, where in many cases minute quantities of water have to be determined.
While it may be clear from the above discussion of the background of the invention that the discrete, individually added (incremental) quantity and the lengths of the time intervals in which such individual increments are added are determinant parameters for the speed of the titration process, those who are experienced in the practice of titration are also aware of the fact that there are additional parameters influencing the speed of the reaction and of the measurement. To be mentioned in particular among these additional parameters are the substances themselves that are to be titrated—the titrant, the solvent, and the pin length of the electrode—, but there are also further parameters that are of common knowledge to professionals in the art of titration. The mutual influence that such parameters have on each other is hard to determine, although their resultant reaction curves will generally be exponential curves in one form or another. Such curves, however, are easy to determine empirically and store in memory in order to introduce the change over the course of the reaction, i.e., its differential component (time derivative), into the mathematical function that controls the addition of titrant.
However, given the varying degree of influence that all of the parameters have on each other as well as on the course of the reaction, it has been found particularly advantageous to use a fuzzy-logic method to process the differential component. In addition to the distance from the end point at a given time, at least the differential component (in the sense of the above definition, i.e., determined from a curve or measured directly as differential component) can be entered as an input into the fuzzy logic. It is to be understood that the use of a fuzzy logic in this case represents a significant inventive concept, even without the input of a differential component, given that the process is influenced by an unknown multitude of different parameters that (after it has been recognized that they should be considered in the control function) could hardly be captured correctly through any other method of logic interconnection between them.
The preferred way of carrying out the inventive process is by using an apparatus that comprises an arrangement for performing a differentiating function capable of determining a differential component from the course of the reaction and for entering the differential component into a fuzzy-logic control module. In principle, however, the inventive process could also be carried out manually.
Further details of the invention are presented in the following description of an embodiment that is illustrated schematically in the drawing.
REFERENCES:
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patent: 4180440 (1979-12-01), Gibboney et al.
patent: 5291418 (1994-03-01), Sanders et al.
patent: 5618495 (1997-04-01), Mount et al.
patent: 05309376 (1993-11-01), None
Macleod S K; “Moisture determination using Karl Fischer Titrations” Analytical Chemistry, Bd. 63, Nr. 10, May 1991.
Firstenberg S et al; “A microcomputer-based digital titrator”; International Laboratory, Bd. 8, Mar. 1978.
Metrohm Program 1996; Produkatalog, Metrohm Ionenanlytik, Metrohm AG, CH-9101 Herisau XP002130986.
Harrington, P. De B et al.; “FLIN: fuzzy linear interpolating network”; Analytica Chimica ACTA; Bd. 277, Nr. 2, May 1993.
Metrohm-Program 1996; Production Catalog Metrohm Ionenanalytik, Metrohm AG, 1996.
Aichert Albert
Amrein Gregor
Laubscher, Sr. Lawrence E.
Ludlow Jan
Mehler-Toledo GmbH
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