Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Means for analyzing liquid or solid sample
Reexamination Certificate
2000-06-07
2003-02-18
Snay, Jeffrey (Department: 1743)
Chemical apparatus and process disinfecting, deodorizing, preser
Analyzer, structured indicator, or manipulative laboratory...
Means for analyzing liquid or solid sample
C436S108000
Reexamination Certificate
active
06521184
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and a device for measuring the concentration of urea or a similar substance in a composite solution. The concentration of urea is difficult to measure directly, and therefore, urea is catalytically decomposed by urease and the differential conductivity is measured.
The solution is preferably a medical solution but can also be a biological solution such as plasma. The present invention relates particularly to the measurement of the concentration of urea in connection with dialysis.
BACKGROUND OF THE INVENTION
The present invention is based on the technique which is disclosed in European Patent No. 0,437,789. This patent discloses, for example, a system for measuring the urea concentration in a complex solution by decomposing urea into ammonium ions catalyzed by urease. It is difficult to measure the urea directly, and it must, therefore, first be converted into ammonium ions. The change in the conductivity due to the contribution of the ammonium ions is measured by means of a conductivity meter.
In German Patent No. 39 00 119 a urea sensor of a similar type is described. A capillary is positioned in a tube, through which blood passes. By means of the capillary, plasma is drawn out of the blood and is allowed to pass through a urease column. The difference in conductivity before and after the urease column is measured and the difference is correlated to the urea content. In order to keep the temperature constant in the measuring apparatus the dialysis fluid is circulated in a closed loop around the urease column and the two conductivity measurement cells.
Japanese Patent No. 60-165551 discloses a similar arrangement, where an ion exchange column is used to remove electrolytes by means of anion-cation-exchange. In this way, the accuracy of the measured values are considerably improved, since the relative change in the conductivity becomes larger due to the fact that the initial conductivity is lower or almost zero. Furthermore, a buffer is added.
U.S. Pat. No. 3,930,957 describes a urea sensor, where an organic buffer solution is added. As an example a solution of 0.05M Tris(hydroxymethyl)aminomethane can be used, which is adjusted to a pH-value of about 6-7 by the addition of glycine.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method and apparatus for measuring the concentration of urea or similar substance in composite solutions is provided. According to the method of the present invention, a method for measuring the concentration of a decomposable compound in a solution has been discovered, comprising adding a buffer in gaseous form to the solution, measuring the conductivity of the solution, decomposing the decomposable compound so as to produce a reacted solution, measuring the conductivity of the reacted solution, and calculating the differential conductivities between the solution and the reacted solution so as to provide a measure of the concentration of the decomposable compound in the solution.
In a preferred embodiment, the buffer in gaseous form comprises carbon dioxide. Preferably, the decomposable compound comprises urea. More preferably, the solution comprises biocarbonate ions. In a preferred embodiment, the decomposing of the decomposable compound comprises catalytically reacting the solution and preferably with urease.
In accordance with one embodiment of the method of the present invention, the adding of the carbon dioxide to the solution comprises diffusing the carbon dioxide through a silicon tube into the solution.
In accordance with another embodiment of the method of the present invention, calculating of the differential conductivities comprises increasing the pressure of the solution in order to increase the solubility of the carbon dioxide in the solution. Preferably, the pressure is increased to about 0.1 MPa.
In accordance with another embodiment of the method of the present invention, calculating of the differential conductivities comprises decreasing the temperature of the solution in order to increase the solubility of the carbon dioxide in the solution. Preferably, the temperature is decreased to about 25° C.
In accordance with another embodiment of the method of the present invention, measuring of the conductivity of the solution and measuring of the conductivity of the reacted solution is carried out by means of a single measurement cell. In a preferred embodiment, the method includes measuring the conductivity of the solution by connecting the single measurement cell at a location upstream of the decomposing step and measuring the conductivity of the reacted solution by connecting the single measurement cell at a location downstream of the decomposing step.
In accordance with another embodiment of the method of the present invention, the method includes measuring the conductivity of the solution by diverting a portion of the solution from the decomposing step.
In accordance with another embodiment of the method of the present invention, the method includes diverting a portion of the solution into a flow path separate from the decomposing step, measuring the conductivity of the solution by means of a first measurement cell in the separate flow path, and measuring the conductivity of the reacted solution by means of a second measurement cell downstream of the decomposing step. In a preferred embodiment, the method includes delaying the flow of the method through the separate flow path whereby the flow of the solution through the separate flow path to the first measurement cell and the flow of the reacted solution to the second measurement cell can take approximately the same amount of time.
In accordance with another embodiment of the method of the present invention, a method is provided for measuring the concentration of a decomposable compound in a solution comprising dividing the solution into a first portion and a second portion, decomposing the decomposable compound in the first portion of the solution so as to provide a first reacted solution, equalizing the temperatures of the first reacted solution and the second portion of the solution in a heat exchanger having a mean temperature, measuring the conductivities of the temperature equalized first reacted solution and second portion of the solution, and calculating the differential conductivity between the first reacted solution and the second portion of the solution, temperature compensating the differential conductivity by means of the mean temperature of a heat exchanger, and calculating the concentration of the decomposable compound from the compensated differential conductivity. Preferably, the decomposable compound comprises urea. In a preferred embodiment, decomposing of the decomposable compound comprising catalytically reacting the decomposable compound in the solution, and preferably catalytically reacting the solution comprises reaction with urease.
In accordance with another embodiment of the method of the present invention, the measuring of the conductivities comprises measuring the conductivity of the temperature equalized first reacted solution and the second portion of the solution with separate conductivity measurement cells.
In accordance with another embodiment of the method of the present invention, the heat exchanger comprises a heat exchange fluid in heat exchange communication with the first reacted solution and the second portion of the solution, and the method includes. providing the mean temperature of the heat exchanger by measuring the temperature of the heat exchange fluid. In a preferred embodiment, the method includes measuring the conductivity of the solution by diverting a portion of the solution from the decomposing step.
In accordance with the apparatus of the present invention, apparatus is provided for measuring the concentration of a decomposable compound in a solution comprising charging means for charging a buffer in gaseous form to the solution, a reactor for decomposing the decomposable compound whereby a reacted solution is formed, and measuring means for mea
Edgson Raymond
Goodman-Jones Arfon
Olde Bo
Olsson Lars-Fride
Gambro AB
Lerner David Littenberg Krumholz & Mentlik LLP
Snay Jeffrey
LandOfFree
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