Chemistry: analytical and immunological testing – Carbon containing – In an aqueous solution
Reexamination Certificate
2000-08-21
2004-05-18
Soderquist, Arlen (Department: 1743)
Chemistry: analytical and immunological testing
Carbon containing
In an aqueous solution
C422S051000, C422S068100, C422S078000, C422S080000, C422S105000, C422S105000, C422S145000
Reexamination Certificate
active
06737276
ABSTRACT:
The invention concerns a procedure for the determination of the total organic carbon (TOC) content of liquids, in particular that of ultra-pure water, whereby a sample of the liquid under investigation is directed into a reaction chamber and is treated statically batch by batch by the use of UV radiation, for oxidising carbon mainly to carbon dioxide, the sample quantity is then transferred by liquid entering the reaction chamber from the outside to a measuring cell connected to the reaction chamber, where the conductivity is measured and then the carbon content (TOC) is found from the conductivity measurements.
The TOC content of a liquid is the total content of organic carbon. The determination of this carbon content, in particular in ultra-pure water, is of special importance to modern high technologies. At this point, ultra-pure water which is necessary for semiconductor production is intended. However, the pharmaceutical industry also depends upon the reliable monitoring of traces of organic contamination. Even the slightest contamination with hydrocarbon compounds, aliphatics and/or aromatic alcohols etc. is to be avoided at all costs. In the past, methods of measurement and their attendant apparatus have been developed, which were able to determine the content of organic carbon in ultra-pure water over a wide range, from a few ppm (parts per million; 10
−6
) to a few ppb (parts per billion; 10
−9
).
U.S. Pat. No. 3,958,941 describes a procedure whereby with the aid of a dual circuit system the organic components are oxidised in a reaction chamber by irradiation with UV light. The carbon dioxide produced by this procedure is transferred to a measuring cell filled with ultra-pure water, via a separate (air-) duct. The conductivity of the contents of the measuring cell is determined, which increases due to the reaction with the introduction of carbon dioxide.
A method such as this requires the execution of various measurements in advance, in order to calibrate the measuring cell, or the conductivity measuring apparatus used. Apart from that, the accuracy when only a small amount of organic carbon compounds is present is low, as measuring errors caused by the UV radiation cannot be ruled out. Moreover, it is mandatory that the carbon dioxide developed in the reaction chamber be transferred to the measuring cell and dissolved in the ultra-pure water. This type of procedure is not just complicated, but also leads to undesirable sources of error, for example the solubility of the carbon dioxide in the measuring cell changes, depending upon temperature. Apart from this, atmospheric carbon dioxide which unintentionally finds its way into the apparatus, can interfere with the accuracy of measurement.
An attempt at overcoming the above-mentioned drawbacks is made in the European script 0 150 923. The carbon content of a static water sample is determined in such a way that this water sample is placed in a chamber with conductivity sensors and statically held there. A UV lamp, which is mounted on the outside of the chamber, irradiates the water sample until the carbon compounds are completely oxidised. The difference in the conductivities measured before and after UV irradiation should then represent the equivalent of the TOC content. The system described in EP 0 150 923 is completely closed and together with its static measurements, may well prevent the influence of contamination and the introduction of carbon dioxide from the atmosphere. However, the price paid for this is the disadvantage that the UV lamp which is mounted outside of the chamber or measuring cell, has a relatively small angle of illumination, and can deliver very little effective radiation into the measuring cell or oxidation chamber. In addition, a quartz window is fitted as the optically transparent closure of the measuring cell, which corresponds to radiation losses due to absorption and reflection. These losses are in addition to the unavoidable losses caused by the quartz glass envelope of the UV lamp.
Moreover, due to the measuring electrodes which are mounted inside the oxidation chamber or measuring cell, it is necessary that a thick stratum of water awaiting irradiation be present, which exceeds the effective penetration of the UV radiation. Consequently, the organic contents of the static water in the chamber are oxidised only very incompletely and slowly. Although TOC concentrations in the order of ppb can be determined using this apparatus, this leads to undesirably high measuring errors, especially in the lowest measuring range. In fact, oxidation times of up to approx. 10 minutes are necessary, which produce conductivity values which asymptotically approach a limit which has to be mathematically determined. In any case, the conductivity measurement can only be taken while the UV lamp is switched on, which—as in the case of U.S. Pat. No. 3,958,941—creates considerable interference in the measuring electronics, which have to be present, as UV lamps are usually driven by a high voltage in the order of several hundred volts.
A further disadvantage of EP 0 150 923 is that, due to the relatively large quantity of water contained in the measuring cell or oxidation chamber, the measurement of conductivity reacts slowly, thus displaying a large time constant. Also, due to the design of this apparatus, areas of shadow can form behind the measuring electrodes, which will not be reached by the UV radiation. In addition, the UV lamp will operate at high temperatures the longer it is in use, making not just a heat sink necessary, but also possibly leading to undesirable measuring errors, due to overheating, as the conductivity determined is not just a function of the carbon dioxide concentration in the water, but also of temperature. Consequently it is important to maintain the liquid or water in the measuring cell at as constant a temperature as possible, which is not possible in the case of the present scheme due to the peculiarities of the design, making a rapid temperature measurement, and possibly temperature compensation necessary. In addition, a further (indirect) effect comes into play, which can be explained by the fact that the intensity of illumination of a mercury vapour lamp, regularly used to produce the UV radiation, decreases with rising temperature. In any case, considerable problems are caused by the long oxidation times, which need to be avoided at all costs, in order to increase the accuracy of the measurements.
Above and beyond this, it is known from the German publication 32 23 167 that water can be continuously examined for decomposable organic and/or inorganic carbon compounds. To this purpose, the water under investigation is continuously passed through an irradiation cell, where here the pH value is set to between 7.0 and 7.3. There is a subsequent irradiation of the water under investigation with UV light, and a continuous transfer of the gas mixture which contains the volatile products of decomposition from the irradiation cell to a measuring cell. The above-mentioned volatile products of decomposition are continuously partially extracted from the water under investigation by means of a circulation gas. Then the IR (infrared) absorption of the circulation gas is measured and/or the circulation gas is transferred to a conductivity cell which supports a continuous stream, and partially dissolved there, whereby the conductivity of the water changes. The inorganic carbon compounds which are normally broken down by acids, do not need to be first removed, in order to determine the presence of organic carbon compounds. The procedure for the determination of the organic carbon content is practically the same as described in U.S. Pat. No. 3,958,941, mentioned above, and result in the same disadvantages as described before.
Finally, an apparatus for the production of ultra-pure water is known from the U.S. Pat. No. 5,272,091 which consists of an oxidation chamber set in the main stream, in which the entire quantity of water to be purified is treated with UV radiation as it passes thr
Bendlin Herbert
Messerschmitt Erich
Voss Werner
Cole Monique T.
Maihak Aktiengesellschaft
Schulman B. Aaron
Soderquist Arlen
Stites & Harbison PLLC
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