Chemistry: analytical and immunological testing – Carbon containing – In an aqueous solution
Reexamination Certificate
1999-04-19
2002-09-03
Warden, Jill (Department: 1743)
Chemistry: analytical and immunological testing
Carbon containing
In an aqueous solution
C422S051000, C422S068100, C422S078000, C422S080000
Reexamination Certificate
active
06444474
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to microfluidic instruments for the measurement of total organic carbon (TOC) in water. More specifically the invention relates to rapid, real-time measurement of TOC.
BACKGROUND OF THE INVENTION
Highly purified water, often in large quantities, is a requirement for a variety of industries. The semiconductor industry, for example, has a particular need for highly purified water for cleaning or as a solvent in the production of integrated circuits. Pharmaceutical and chemical manufacture has a similar requirement for highly purified water. The presence of organic carbon compounds, even in trace amounts, in water used for manufacturing can be deleterious to the quality or purity of products made and the efficiency of manufacturing processes.
Coupled to the requirement for highly purified water is a requirement for accurate, reproducible assessment of water purity. Detection and quantitation of trace contaminants in water can be used to test process water quality, to validate water purification systems and to avoid introduction of contaminated water into process streams or reactions.
The measurement of total organic carbon (TOC) concentration is also used to assess contamination of potable water, municipal water supplies and in industrial and municipal effluents and waste waters.
The organic carbon content of water can be determined by methods which initially oxidize the organic carbon in a sample to CO
2
and then determine the amount of CO
2
generated in the sample. Organics in water samples can be oxidized in a number of ways by combustion, by use of chemical oxidation agents and/or by UV radiation. In total organic carbon (TOC) analysis, CO
2
can be quantitated using infrared (IR) absorption techniques, conversion to methane followed by flame ionization or by measurement of sample conductivity. See, e.g., S. J. Poirier and J. H. Wood (1978) “A New Approach to the Measurement of Organic Carbon,” American Laboratory, December:79-89, for an overview of such techniques.
Conventional TOC measurements have several significant limitations. Current devices are relatively slow, taking 120 seconds or more for each measurement. These devices usually require relatively large sample volumes and may require complex sample handling procedures. Current TOC instrumentation is often bulky and unsuitable for portable, on-line applications.
U.S. Pat. No. 3,958,941 of Regan describes a TOC measurement device which employs UV radiation to oxidize organic carbon species in a sample to CO
2
. The CO
2
generated is then transported into pure deionized water and the change in conductivity of the deionized water due to added CO
2
is measured. In the Regan method, the sample is mixed with air prior to irradiation to facilitate oxidation of organics. The CO
2
generated by oxidation in the sample is transported into the deionized water by an air-stripping system. The method is not sufficiently rapid to allow continuous real-time measurement and requires relatively large sample sizes for accurate measurement. Other methods reported for measurement of TOC in water using conductivity measurements include U.S. Pat. No. 3,224,837 of Moyat, U.S. Pat. No. 4,293,522 of Winkler and more recently U.S. Pat. Nos. 4,626,413, 4,666,860, 4,868,127 of Blades and Godec, and PCT applications WO 94/35498 (Sievers Instruments) and WO 96/01999 (Millepore).
U.S. Pat. No. 4,277,438 of Ejzak reports a TOC measurement device in which air and an oxidizing agent are added to the sample prior to UV irradiation and in which the CO
2
generated from oxidation of organics is passed into a gas stream for IR analysis. U.S. Pat. No. 4,619,902 of Bernard also relates to a TOC measurement device using IR detection for CO
2
.
The Blades and Godec patents supra all relate to a device and method for conductivity measurement of TOC in water using a single sample cell having two electrodes which can be exposed to UV radiation. Background conductivity is measured in the sample before exposure to UV light. When the UV light is switched on, conductivity is measured as a function of time and the second time derivative of the conductivity signal is measured to determine when oxidation is complete. Computer methods are applied to separate out signal due to background conductivity and obtain a measurement of TOC. Complete oxidation of organics in the sample is said to require variously 1-5 min. or 1-20 min. U.S. Pat. No. 4,666,860 further reports a method for prediction of TOC in a given sample based on measurement of conductivity at times before complete oxidation of organics has been achieved. This method requires initial calibration of the device using conductivity measurements over time for complete oxidation of a similar sample. It appears that this method is not useful for measurements where TOC may vary significantly from sample to sample. U.S. Pat. No. 4,868,127 further reports the use of a thin layer of TiO
2
formed on the titanium electrodes as an oxidation catalyst and the use of electrophoresis to accelerate reaction.
WO 96/01999 reports methods for rapid determination of TOC in water samples using conductivity measurements. TOC determinations in these methods are, however, predictions based on extrapolation from conductivity measurements at partial oxidation of the organics in a given sample.
Microfluidic devices have been employed for liquid phase analytical applications. U.S. Pat. No. 5,637,469 of Wilding et al. discloses microfabricated devices having a mesoscale flow system for the detection of analytes. Analyte detection is based on the binding of analyte to binding moieties within microfabricated channels in the flow system. Microfluidic devices do not appear to have been employed for the measurement of TOC in water samples.
The present invention represents a significant improvement over the prior art for measurement of TOC of water samples. The microfluidic TOC analysis device of this invention provides rapid measurement, not prediction, of TOC by measurement of conductance in water samples in which the organic carbon is substantially oxidized to CO
2
in times less than about 30 sec. The devices of the present invention provide accurate and reliable TOC measurements requiring relatively small sample volumes (30 &mgr;L or less). The use of small sample size increases sampling speed and decreases the time between measurements. The relatively small sample cells of this invention can be configured in a compact device suitable for portable instruments. The relatively small size of the sample cells and attendant detectors facilitate use of the TOC measurement devices of this invention in on-line applications.
SUMMARY OF THE INVENTION
This invention provides devices and methods for rapid real-time measurement of total organic carbon (TOC) in water. The invention is at least in part based on very rapid, substantially complete mineralization of organics in a water sample by UV irradiation. The irradiated sample is contained in a relatively thin light path sample volume to facilitate rapid mineralization. TOC of the water sample is determined by the detection of the CO
2
generated. The microfluidic sample cell of the TOC device of this invention is preferably configured to provide for irradiation of a relatively thin layer of sample to provide very rapid mineralization and to minimize the time required for making a TOC measurement. The method allows direct measurement of TOC of a given sample in a time shorter than about 30 seconds and more preferably provides for sufficiently rapid substantial mineralization (about 2 seconds or less) to allow real-time TOC measurements. The devices of this invention also facilitate minimal lag time between TOC measurement to allow fast, continuous measurements of TOC.
More specifically, this invention provides a device for measurement of TOC in water samples that employs a microfluidic sample cell. As used herein the term microfluidic refers to a sample cell with a sample channel, sample cavity or sample volume having at least one-dimension that is less
Carter Michael T.
Cravens Eric D.
Thomas Ross C.
Eltron Research, Inc.
Gakh Yelena
Greenlee Winner and Sullivan P.C.
Warden Jill
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