Chemistry: analytical and immunological testing – Carbon containing – In an aqueous solution
Reexamination Certificate
2000-11-21
2004-05-11
Warden, Jill (Department: 1743)
Chemistry: analytical and immunological testing
Carbon containing
In an aqueous solution
C422S082010, C422S082020
Reexamination Certificate
active
06734021
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for measuring the organic carbon content of, for example, ultrapure water, and in particular to a method and apparatus for measuring the organic carbon content of a test liquid by irradiating the test liquid, such as ultrapure water, with ultraviolet light, and measuring the conductivity of the test liquid, which changes due to generated organic acids and carbon dioxide.
This application is based on Japanese Patent Application, No. Hei 11-375977, the contents of which are incorporated here by reference.
2. Description of Related Art
In modern high precision industrial manufacturing processes, for example, highly purified “ultrapure water” is frequently used in large amounts. For example, washing semiconductors, production of medicines, injections, and the like, and chemical analysis, pure water that contains substantially no impurities such as particles, various species of ions, microorganisms such as bacteria, or soluble substances such as organic compounds, is indispensable. Systems for producing such pure water normally use a combination of reverse osmosis, distillation, ion exchange, absorption processes, vacuum deaeration, ultraviolet oxidizing, and filtration methods including ultrafiltration. In particular, in the field of semiconductor manufacturing, for example, the gaps between circuits are becoming narrower with the increasing density of LSI integration, and thus in order to prevent circuit shorting, the cleaning water for the semiconductors must be of the highest purity, and not only ions, but to the extent possible, particles, bacteria, and organic materials must be eliminated.
One method of indicating the degree of purity of pure water is the TOC (total organic carbon), which represents the degree of contamination using the amount of carbon in the organic substances in the water. As a method of measuring the TOC value of pure water, the TOC measurement using the ultraviolet (UV) oxidizing method is widely used. In this TOC measurement, a test liquid is introduced into an ultraviolet irradiation part, there the test liquid is irradiated with UV light, and the organic carbon in the test liquid is changed into organic acids and carbon dioxide. Then the TOC value of the test liquid is found based on the change in conductivity of the test liquid obtained thereby.
Several types of TOC measurements for such a UV oxidizing are used. For example, the apparatus disclosed in Japanese Examined Patent Application, Second Publication, No. Sho 63-46375, is known. This apparatus irradiates the ultrapure water test liquid resting in a test cell with UV light, and at the same time measures the change in conductivity during this time interval using a conductivity detecting electrode disposed in the test cell. In addition, upon confirming that the oxidizing reaction due to the UV light has substantially completed by using the change in the rate of conductivity, the organic carbon content is found from the amount of change in conductivity up to this point in time.
In addition, an apparatus is known that provides a measuring flow path that disposes first and second conductivity sensors before and after the UV light irradiating part, causes ultrapure water to flow continuously therethrough at a fixed rate of flow, and measures the organic carbon content based on the difference in the conductivity obtained by the first and second conductivity sensors. This apparatus assumes that if the rate of flow of the ultrapure water flowing through the UV light irradiation part is constant, then the amount of UV light that the ultrapure water receives per unit of volume is constant, which implies a constant degree of progress of the oxidizing reaction. In this case, because measurement is carried out while the oxidizing reaction due to the UV light is not complete and the ultrapure water is continuously flowing, the organic carbon content can be continually measured.
Among the above-described former conventional apparatuses using a method wherein the organic carbon content is found from the amount of change in conductivity up to the substantial completion of the oxidizing reaction due to UV light, the following problems are encountered. First, while the time until the completion of the oxidative reaction depends on the components of the test liquid and the strength of the UV light, about 10 to 20 minutes is necessary. Thus, carrying out monitoring of test liquids in real time is difficult.
In addition, because the test liquid is resting in the test cell until the oxidative reaction is complete, eluate from the materials that form the test cell and the conductivity detecting electrode mix into the test liquid, and the conductivity rises. In contrast, the generated carbon dioxide may leak, causing the conductivity to fall. Therefore, the measured values must be compensated by taking into consideration the changes in conductivity that do not depend on the organic carbon content.
Furthermore, because the state of progress of the oxidative reaction is judged by the change of conductivity, a conductivity detecting electrode must always be disposed in the test cell. Thus, the structure of the test cell tends to become complicated and difficult to manufacture.
In contrast, among the above-described latter conventional apparatuses in which the ultrapure water continuously flows at a constant rate of flow, and the organic carbon content is continuously measured based on the difference in conductivity before and after irradiation by UV light, the following types of problems are encountered. First, as described above, being able to measure without the oxidizing reaction having completed assumes that if the rate of flow of ultrapure water flowing through the UV light irradiation part is constant, then the amount of ultraviolet light received per unit of volume of ultrapure water is constant. If the rate of flow of ultrapure water flowing through the UV irradiation means increases, then the amount of UV irradiation per unit of volume of ultrapure water will decrease, and thus the difference in conductivity will become small. In contrast, if the rate of flow decreases, the amount of UV irradiation per unit of volume of the ultrapure water will increase, and thus the difference in conductivity will become large. This means that in the case that the rate of flow of the ultrapure water flowing through the UV irradiation part changes, a measurement error will occur immediately. In order to avoid this type of error, the flow rate control of the ultrapure water must be carried out with extreme precision. As a result, the liquid conveyance system becomes complicated, and the cost of the system as a whole may become high.
Furthermore, in order to observe the difference in conductivity before and after the UV irradiation, two sensors, i.e., the first and second sensor, and the processing circuits for the signals from these sensors, etc., are necessary. Therefore, in these terms as well, the apparatus becomes complicated and the cost of the system may become high.
In consideration of the above, the present invention has as an object providing a method and apparatus for measurement of the organic carbon content that allows monitoring of the organic carbon amount substantially in real time, and at the same time, does not necessitate precision flow control.
SUMMARY OF THE INVENTION
In order to resolve the above-described problems, controlling the amount of UV light impinging on a flowing test liquid by adjusting the time that the UV light source is lit was investigated. The results showed that if the liquid sample passes through the oxidizing processing vessel below a predetermined rate of flow, a portion of test liquid is present that has received the complete irradiation by UV light from the commencement to the extinguishing of the lighting of the ultraviolet light source, and in this case, the amount of irradiated UV light impinging on the test liquid depends on the time that the UV light source is lit.
Specifical
Kamada Setsuko
Mizuno Masao
Saito Makoto
Cole Monique T.
DKK-TOA Corporation
Scully Scott Murphy & Presser
Warden Jill
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