CA2228337A1

CA2228337A1 - Method and apparatus for the measurement of dissolved carbon

Info

Publication number: CA2228337A1
Application number: CA002228337A
Authority: CA
Inventors: Kevin J. O'neill; Richard Hutte; Richard D. Godec
Original assignee: Sievers Instruments Inc
Current assignee: Suez WTS Analytical Instruments Inc
Priority date: 1995-12-04
Filing date: 1998-01-29
Publication date: 1999-07-29
Also published as: WO1997021096A1

Abstract

Apparatus and methods for the measurement of total organic carbon, total inorganic carbon and total carbon of water are described. The sample is acidified and split into an inorganic carbon stream and a total carbon stream. The inorganic carbon in the inorganic stream is oxidized using an oxidizer potential that varies over an oxidizer potential period, and both the organic carbon in the total carbon stream are oxidized. The resulting carbon dioxide is measured in each stream using carbon dioxide sensors employing a gas permeable membrane dividing deionized water from the oxidized sample water and a pair temperature and conductivity cells.

Description

Field of the Invention The present invention relates to an improved method and apparatus for the determination of the concentration of organic carbon, inorganic carbon and total carbon in aqueous process streams and in bulk solutions. Particularly, the method of the present invention in a preferred embodiment includes the acidification of an aqueous sample stream, the oxidation of the sample stream to produce dissolved carbon dioxide gas, and the sensitive and selective detection of carbon dioxide utilizing a gas permeaole membrane and conductometric detection to determine the levels of or~~anic carbon, inor~Tanic carbon andior total carbon.
Back~~round of the Invention The measurement of the total organic carbon (TOC) concentration and total carbon (organic plus inor~~anic) concentration in water has become a standard method for accessin~~ the level of contamination of organic compounds in potable waters, industrial process waters, and municipal and industrial haste haters. In addition to widespread terrestrial applications, the measurement of TOC is one of the primary means of determining the purity of potable and process waters for manned space based systems including the space shuttle, the proposed space station and for future manned explorations of the moon and planets.
The United States Environmental Protection Agency recently promulgated new rules aimed at reducing the levels of disinfectant by-products in drinking water.
Formed from the reaction of chlorine and other disinfectants with naturally occurring organic matter, disinfectant by-products arc potentially hazardous compounds. Such compounds include trihalomethanes (CHCI,, CHBrCI,, etc.), haloacetic acids, and other halogenated species. The new rules also C~ ,I()SI.,I IZ('I'2(';1 S(':1K_' li'I'f>

include monitoring the levels of natural organic material in raw water, during the treatment process and in the finished water by measurement of total organic carbon concentration.
A variety of prior art approaches for measuring the total organic carbon content of water have been proposed. Eor example, See United States Patent Nos. 3,958,941 of Regan; 3,224,837 of Moyat; 4,293,522 of Winkler; 4,277,438 of Ejzak; 4,626,413 and 4,666,860 of Blades et al.;
and 4,619,902 of Bernard.
Representative of the devices described in these references are the methods disclosed in United States Patent No. 3,958,941 of Regan. In Regan an aqueous sample is introduced into a circulating water stream that flows through a reaction chamber where the sample is mixed with air and exposed to ultraviolet (U.V.) radiation to promote the oxidation of organic compounds to form carbon dioxide. The carbon dioxide formed in the reaction chamber is then removed from solution by an air stripping system and introduced into a second chamber containing water that has been purified to remove ionic compounds. The conductivity of the water in the second chamber is measured, and any increase in conductivity is related to the concentration of carbon dioxide formed in the first reactor. The conductivity measurement can be used, therefore, to determine the concentration of organic compounds in the original sample.
The Regan device is slow, cannot be used for the continuous monitoring of TOC
concentration in aqueous streams, cannot be scaled down without increasing interference from NO,, SOZ, and HzS to unacceptable levels, and is generally unsatisfactory. In addition, Regan does not disclose that an aqueous solution of acid must be added to the sample stream to reduce the pH to a value of less than about 4 to ensure a reasonable removal rate of carbon dioxide using the air stripping system described. The oxidation method disclosed by Regan is unsatisfactory for the measurement of refractory compounds, particularly urea. In Regan, an aqueous sample of 20 to 100 mL containing 0.5 mg/L organic carbon is required to generate sufficient carbon dioxide for accurate detection) thus limiting the utility of the device for the measurement of sub-part per million levels of TOC in smaller sample sizes. Finally) in practice, the Regan system requires frequent recalibration--typically once per day--due to variations in background conductivity. Also, the concentration of organic carbon in the calibration standard must be approximately equal to the concentration of organic carbon in the sample.
Because of this, G:\IOS L\I I :CP?CA\SCAN2. W PD

recalibration is required when analyzing aqueous samples containing higher or lower levels of organic carbon when compared with the calibration standard.
The use of aqueous solutions of persulfate salts for the oxidation of organic compounds is widely known. Smit and Hoogland (16 Electrochima Acta, 1-18 (1971)) demonstrate that persulfate ions and other oxidizing agents can be electrochemically generated.
In United States Patent No. 4,504,373 of Mani et al., a method for the electrochemical generation of acid and base from aqueous salt solutions is disclosed.
An improved method and apparatus for the measurement of organic content of aqueous samples is disclosed in United States Patent No. 4,277,438 of Ejzak. Ejzak describes a multistage reactor design which provides for the addition of oxygen and a chemical oxidizing agent, preferably sodium persulfate) to the aqueous sample stream prior to oxidation of the stream using ultraviolet radiation in a series of reactors. Ejzak also describes the use of an inorganic carbon stripping process--before oxidation of the organic carbon- - that includes the addition of phosphoric acid to the sample stream. After oxidation, the sample stream is passed into a gas-liquid separator where the added oxygen acts as a cagier gas to strip carbon dioxide and other gases from the aqueous solution. In the preferred embodiment, the gas stream is then passed through an acid mist eliminator, a coalescer and salt collector) and through a particle filter prior to passage into an infrared (IR) detector for the measurement of the concentration of carbon dioxide in the gas stream.
The methods and apparatus disclosed by Ejzak provide improvements over the teachings of Regan; however, the Ejzak device requires extensive manual operation and is also generally unsatisfactory. The Ejzak device requires three external chemical reagents;
oxygen gas, aqueous phosphoric acid and an aqueous solution of sodium persulfate. Hoth the phosphoric acid and persulfate solutions must be prepared at frequent intervals by the operator due to the relatively high rate of consumption. The Ejzak device requires dilution of the sample if the solution contains high concentrations of salts in order to ensure complete oxidation of the sample and to eliminate fouling of the particle filter located prior to the IR carbon dioxide detector. As with Regan, relatively large sample sizes are required- -typically 20 mL of sample for accurate measurement at 0.5 mg/L total organic carbon--and the carbon dioxide fomned in the oxidation G:\fOSL\ I I 2CP=CA\SCA N2. W PD 3 chamber is removed using a gravity dependent technique that cannot be easily used in space-based operations.
Another improved method and apparatus for the measurement of total organic carbon in water is disclosed in United States Patent lVo. 4,293,522 of Winkler. In Winkler, an oxidizing agent) molecular oxygen) is generated in-situ by the electrolysis of water.
Organic compounds are subsequently oxidized to form carbon dioxide by the combination of U.V.
radiation and the in-situ generated oxygen. The inradiation and electrolysis processes are both accomplished in a single oxidation chamber. Winkler does not teach that the aqueous sample stream be acidified to assist in the removal of carbon dioxide from solution, and in fact teaches against the use of acid.
Therefore, this method and apparatus cannot be used for the measurement of organic compounds in basic aqueous samples. The oxidation chamber of Winkler uses a solid electrolyte to separate the two electrodes employed for the electrolysis of water. The solid electrolyte described by Winkler is composed of an organic polymer which, under exposure to oxygen) ozone and U.V.
radiation, will undergo oxidation to form carbon dioxide, therefore resulting in unacceptable background levels of organic compounds in the sample stream, particularly at low organic compound concentrations.
Winkler also describes a conductometric carbon dioxide detection system wherein the sample stream exiting the oxidizing chamber is held in an equilibrating relationship to a stream of deionized water. The two flowing streams are separated by a gas permeable membrane that allows the concentration of carbon dioxide to equilibrate between the streams.
The concentration of the carbon dioxide is thereby determined by measuring the conductance of the deionized water stream. However, the use of two flowing streams introduces operating parameters into the detection process that require frequent calibration adjustments. The recirculation of deionized water with dissolved carbon dioxide can cause a diffusion of the carbon dioxide out of the deionized water into plastic components of the recireulation loop, and cause the introduction of ionic contamination into the deionized water. Further, the Winkler process is a very time-consuming batch process which is not commercially practical.
G ~IOSL\ I 12CP2CA\SCAN2. WPD 4 Another example of the prior art is disclosed in United States Patent No.
4,619,902 of Bernard, which teaches the oxidation of organic compounds to form carbon dioxide using persulfate oxidation at elevated temperatures- -typically 20 to 100° C--in the presence of a platinum metal catalyst. Bernard recognizes that the materials used in the construction of instrumentation for the determination of total organic carbon in water can contribute organic compounds to the sample during the measurement process, and teaches that inert materials such as PTFE must be used to reduce this background from the measurement. As with the previously mentioned disclosures) a gas stripping technique is employed to collect the formed carbon dioxide) and measurement is made using IR spectrometry. Bernard also recognizes that aqueous solutions of sodium persulfate are not stable due to auto-degradation of the reagent.
An improved system for the measurement of organic compounds in deionized water is disclosed in United States Patent No. 4,626,413 of Blades and Godec. The apparatus described by Blades and Godec is based on direct U.V. oxidation of organic compounds to form carbon dioxide which is measured by using conductometric detection. In the apparatus described in Blades and Godec, the oxidation of some organic compounds form strong acids such as HCI) HZSO, and HN03 which interfere with the conductometric method. The Blades device is also limited to the measurement of total organic compounds in deionized water and cannot be used for samples containing ionic compounds other than bicarbonate ion.
In United States Patent No. 4,209,299 of Carlson, it is disclosed that the concentration of volatile materials in a liquid can be quantitively determined by transferring the desired material through a gas permeable membrane into a liquid of known conductivity, such as deionized water.
The Carlson device is demonstrated for the measurement of a number of volatile organic and inorganic compounds, but Carlson does not suggest the combination of this process in conjunction with a carbon dioxide producing reactor.
In electrochemical reactions in aqueous solutions) a common reduction product is hydrogen gas. Because of its flammability, the hydrogen presents a potential hazard in devices using electrochemical techniques. Hydrogen gas in solution with water in the presence of U.V.
light will reduce organics; thus, the hydrogen must be removed in some manner to ensure the oxidation of organics in the presence of U.V. light. The interaction of hydrogen gas in aqueous G:',IOSL~I I :CP1CA~SCAN2.WPD S

solutions and palladium metal is well known (e.g., F.A. Lewis) "The Palladium Hydrogen System," Academic Press) 1967, London) and the use of palladium offers a potential solution to the generation of hydrogen in electrochemical reactions by selective removal and disposal of the hydrogen.
An improved carbon analyzer is disclosed in U.S. Patent No. 5,132,094 by Godec et al., of which the present is a continuation-in-part. Originally developed for NASA, the Godec device uses W/persulfate oxidation and a new COi detection technique utilizing a gas-permeable membrane and a temperature and conductivity cell. A gas-permeable membrane is used to separate the acidified sample stream (pH<4) from a thin layer of deionized water. A solenoid valve is opened to allow fresh DI water to flow into the membrane module and the solenoid valve is closed. Carbon dioxide formed from the oxidation of organic compounds will diffuse across the membrane into the deionized water, where a portion of the C0: will ionize to produce H+ and HC03-ions. After an equilibration period, the solenoid valve is opened to flush the ions into a conductivity and temperature measurement cell) and the concentration of C0: in the deionized water is determined from the conductivity and temperature.
Membrane-based conductivity detection of C0~ offers several advantages.
Calibration is extremely stable, and the calibration can be easily performed by the analyst.
No purge gases are required. The technique is highly selective for C0~ and is extremely sensitive, permitting detection of TOC down to sub-parts per billion levels. It also has a wide dynamic range) permitting measurement up to at least 100 ppm TOC.
In operation the sample is drawn into the analyzer by means of a peristaltic pump, and two reagents are added via syringe pumps. Acid (6 M H3P0~) is added to reduce the pH of the sample stream and persulfate (IS% (NH, )z S~Og) is added for the oxidation of organic compounds. The sample stream is split for measurement of inorganic carbon (IC) concentration (IC=[HCO~-] + [C03?]+[COz]) without oxidation, and measurement of total carbon (TC) concentration after oxidation. TOC is then computed from the difference (TOC=TC-IC). For samples containing high levels of inorganic carbon and lower levels of TOC, an IC removal module may be used to remove the inorganic carbon and permit accurate TOC
measurements. A
supply of the acid and oxidizer may be pre-packaged and stored in the analyzer, eliminating the G:~IOSL\1 I 2CP?CA\SCAN2.~VPD

preparation by the analyst. Deionized water is continuously produced in the analyzer using a mixed-bed ion exchange resin with a capacity for several years of operation.
The maintenance required is replacement of the reagent containers several times a year, replacement of the W
lamp and replacement of the pump tubing. The ease of use, low maintenance requirements and dependable performance have made this device the TOC analyzer of choice for monitoring water purification systems in semiconductor manufacturing) the pharmaceutical industry and both conventional and nuclear power plants.
It is important that the amount of persulfate or other oxidizer added to the sample be sufficient to fully oxidize the sample. However, it is also important not to add excess oxidizer to the point that gas bubbles form in the sample. Gas bubbles are undesirable because the carbon dioxide dissolved in the sample will diffuse into the oxygen bubbles. Further, if the oxygen bubble diffuses through the membrane and into the deionized water stream, the result will be a negative spike in the measured conductivity as the bubble passes through the conductivity cell and partially or wholly insulates the conductivity electrode from the water stream.
This has been addressed in the past by controlling the addition of oxidizer based on the expected approximate range of carbon concentration. For example, the oxidizer flow rate would be set relatively low if the expected carbon concentration were in the 1 to 5 ppm range, and the oxidizer flow rate would be set higher if the expected carbon concentration were in the 25 to 50 ppm range. This is a simple and very effective approach. However, it would be desirable for the device to produce accurate readings across a broad range of carbon concentrations with a minimum of experimentation or prior knowledge about the approximate expected carbon concentrations.
It has also been found in utilizing prior devices that chloride in the sample tends to lead to inaccurate measurements of carbon concentrations, because the chloride preferentially interacts with hydroxyl radicals to the exclusion of organics, thus exhausting the oxidizer before the organics are fully oxidized.
G:\IUSL\ 1 1 ~C:PICA4SCAN2.WPD 7 gummam of the Invention An important aspect of the invention which is common to each of the preferred embodiments is varying over a period of time the oxidation potential used to oxidize a sample.
By so varying the oxidation potential) there is assurance that at some point in the oxidation potential period the sample becomes substantially completely oxidized without the formation of oxygen bubbles. The measured conductivity of the sample is at a peak at that point and can be accurately related to the true carbon concentration.
In one embodiment of the present invention, an aqueous sample stream is passed through a filter to remove any particulate matter. Acid is added to produce a pH of less than 4. Inorganic carbon species--primarily carbonate and bicarbonate ions- -are reacted with the acid to form carbon dioxide, while organic compounds remain unreacted. Also added is an oxidizer such as persulfate.
The sample is then split into a first stream for measurement of total carbon and a second stream for measurement of inorganic carbon. The first stream is directed into an oxidation module for oxidation of organic compounds into carbon dioxide. The oxidation module may incorporate either direct U.V. oxidation using short wavelength U.V. radiation such as an exeimer source or a mercury vapor lamp, semiconductor catalyzed U.V. oxidation using short wavelength U.V. radiation, or U. V. oxidation in the presence of oxygen and or other oxidizing agents. The U.V. radiation may be generated particularly well using a narrow band excimer source.
The degree of oxidation potential in the oxidation module is not constant over time.
Instead, the oxidation is done in cycles in which the oxidation potential changes from near zero to a maximum, gradually over a period of time such as three or four minutes.
By gradually increasing the oxidation potential over a timed cycle, there is assurance that the optimum oxidation potential, and thus the optimum overall oxidation, is achieved at some point in the cycle. The term "oxidation potential" is used herein to mean the potential for oxidation of a compound due to the presence of an oxidation source. The oxidation source may be a chemical reagent such as persulfate and/or other means such as an electrolysis cell or U.V. light. The G:\IUSL\I 12CP2CA\SCAh2.WPD

oxidation potential is varied by increasing or decreasing the concentration of a chemical oxidizer) or increasing or decreasing the activity of the other possible means such as the rate of oxygen generation in an electrolysis cell or the intensity of a U.V. light source or the duration of the U.V.
light exposure.
The carbon dioxide formed in the oxidation module is sensitively measured using a carbon dioxide sensor. The sensor includes a first gas-transfer module which is comprised of a carbon dioxide selective gas-permeable membrane which separates the first stream from a deionized water stream. The deionized stream is in a closed loop and is continuously regenerated by means of a mixed bed ion exchange resin. Alternatively, deionized water can be supplied from a source external to the apparatus described in the present invention.
The deionized water in one embodiment may be maintained at a positive pressure such as approximately 5-6 PSI
higher than the first stream pressure to inhibit bubble formation in the deionized water.
As the carbon dioxide enters the deionized water) the carbon dioxide will dissolve in the water and cause an increase in the conductivity of the aqueous solution. The stream of deionized water with dissolved carbon dioxide then flows out of the first gas transfer module and into a temperature and conductivity cell in order to measure the increase in the concentration of ionic species. There is a passive deoxygenation module in the deionized water loop to remove oxygen gas from the water after it passes through the temperature and conductivity cell on its way to the next pass into the first gas transfer module.
The peak conductivity observed in the deionized water with dissolved carbon dioxide during any given oxidation potential cycle can be directly related to the concentration of carbon dioxide in the first stream. The concentration of carbon dioxide in the first stream can, in turn, be directly related to the level of organic compounds originally present in the sample.
The second stream flows simultaneous with the flow of the first stream. The second stream first flows through a delay tubing to compensate for the period of time the first stream is in the oxidation module. The second carbon stream then flows through its own separate carbon dioxide sensor which functions similarly to the carbon dioxide sensor for the first stream.
However, because there is no oxidation step in the second stream, organic carbon remains (i:~IOSL\ I 12CP2CA1SCAN2. WPD

unoxidized and therefore undetected. The entire detected carbon in the second stream can be presumed to be inorganic carbon. The device thus accurately measures both total carbon and inorganic carbon. Total organic carbon can be determined by subtracting the inorganic carb6n measurement from the peak total carbon measurement in a given oxidation potential cycle.
In the preferred embodiment, the device utilizes components with very small volumes and water layer thicknesses. This is important in facilitating rapid response times and sensitivities.
Other embodiments are possible utilizing the approach of varying the oxidation potential over an oxidation potential period. In an exemplary alternative embodiment, inorganic carbon is measured in an inorganic carbon measurement step, and then organic carbon is measured in an organic carbon measurement step. The inorganic carbon measurement step includes acidifying the sample stream to convert inorganic carbon to carbon dioxide. The sample stream with dissolved carbon dioxide then flows into a first gas transfer module for the transfer of carbon dioxide to a deionized water stream and measurement of conductivity in a first temperature and conductivity cell. That measurement can be related to the inorganic carbon concentration in the sample.
The stream then flows into a carbon dioxide degassification module or other carbon dioxide removal device, in which the stream is contained within a gas-permeable conduit or container surrounded by a vacuum. The dissolved carbon dioxide produced by earlier acification of the stream is thus removed from the stream.
The organic carbon in the stream is then oxidized using an oxidation potential that vanes over an oxidation potential cycle. As in the other embodiments) the variation in the oxidation potential can be accomplished by varying the rate of introduction of a chemical reagent) or by other means as described herein. The stream then flows into a second gas transfer module for the transfer of carbon dioxide into a deionized water stream and measurement of conductivity in a second temperature and conductivity cell. This measurement can be related to the organic carbon concentration in the sample.
G:UOSL\I 12CP2CA\SCAN2.WPD 1 ~

This alternative embodiment thus provides a means to measure both inorganic carbon and organic carbon. Total carbon can be determined by adding the two measurements.
Accordingly, in one aspect, the present invention provides an apparatus for the measurement of carbon in an aqueous sample, comprising: an oxidation reactor that varies an oxidation potential during an oxidation potential period to produce carbon dioxide concentrations that vary during the oxidation potential period; and a first carbon dioxide sensor to measure the amount of carbon dioxide in the sample at a plurality of times during the oxidation potential period.
In a further aspect) the present invention provides an apparatus for determining carbon concentration in aqueous samples) said apparatus comprising in combination:
(a) a reactor having fluid inlet and fluid outlet means and associated variable oxidation means; (b) liquid-phase measurement means at least in part located in or downstream of said reactor, said measurement means being responsive to liquid-phase concentrations of organic carbon oxidation products including carbon dioxide; (c) flow control means for continuously flowing an aqueous fluid through said reactor and in fluid contact with at least a portion of said measurement means at a controlled flow rate; and (d) reaction control means for varying said variable oxidation means in a controlled and reproducible manner during a predetermined oxidation period so as to vary the potential in said reactor for oxidation of organic carbon in said aqueous fluid flowing through said reactor over a range comprising at least two oxidation potentials so as to generate a profile of differing concentrations of organic carbon oxidation products including carbon dioxide in the aqueous fluid corresponding to the different oxidation potentials in said reactor.
In a still further aspect, the present invention provides in an apparatus for measuring carbon concentration in a flowing aqueous sample, said apparatus comprising a reactor for reacting at least a portion of a first organic compound in said sample from a first oxidation state to one or more second compounds each at an oxidation state different from said first oxidation state; means for flowing the aqueous sample continuously into, through, and out of said reactor at a controllable, non-zero flow rate; and means for sensing the concentration of said second compounds in said flowing aqueous sample; the improvement comprising:
reactor control means in combination with variable oxidation means for varying in a controlled and reproducible manner the reaction conditions in said reactor so as to generate a sensing profile that defines a peak value based on at least two different concentrations of said second compounds in said sample corresponding to each of at least two different reaction conditions in said reactor.
In a further aspect, the present invention provides a process for determining carbon concentration in an aqueous sample, said process comprising the steps of: (a) flowing a fluid including at least said aqueous sample at a controlled flow rate; (b) reacting carbon in said aqueous sample to produce organic carbon oxidation products by providing and varying oxidizing conditions in said fluid which are varied in a controlled and reproducible manner during a predetermined oxidation period over a range comprising at least two oxidation potentials so as to generate a profile of differing concentrations of organic carbon oxidation products in said fluid corresponding to the different oxidation potentials;
(c) measuring the concentration of organic carbon oxidation products in said fluid at said at least two oxidation potentials; and, (d) determining the carbon concentration in said aqueous sample from the measures of organic carbon oxidation products in said fluid at said at least two oxidation potentials.
Brief Description of the Drawings FIG. 1 is a block diagram depicting an embodiment of the present invention for the on-line measurement of carbon concentrations in accordance with the present invention.
FIG. 2 is a representation of the measured carbon in a sample using variable oxidation potential.
FIG. 3 is a graph of measured carbon and persulfate oxidizer flow rate versus time for a preferred embodiment of the invention.
FIG. 4 is a block diagram depicting an alternative embodiment of the present invention for the on-line measurement of carbon concentrations.

Detailed Description of the Preferred Embodiment The measurement of the total organic content of aqueous samples has become a standard technique for determining the quality of potable water, industrial process water and industrial and municipal waste waters. The determination of the organic content of water samples is most commonly achieved by oxidation of the carbon constituents to carbon dioxide using chemical oxidizing agents, U.V. radiation, electrolysis, high temperature combustion, or a combination of these methods and subsequent detection of the carbon dioxide using IR spectroscopy or by membrane/conductometric or potentiometric techniques.
The present invention is an improved process and apparatus for determining concentration levels of total organic and inorganic carbon compounds in aqueous samples.

A block diagram of one embodiment of the present invention is shown in FIG. I.
An aqueous sample inlet 10 is in communication with a particle filter 12 for the removal of particulate matter that may be suspended in the aqueous sample stream. A
filter outlet conduit 14 joins a fitting 16. An acid reagent (6 M HYPO, in the preferred embodiment) is delivered to the fitting l6 via a pump such as the acid syringe pump 20 shown in FIG. 1 through an acid line 22.
The acid syringe pump 20 is driven by a motor 24 and worm gear 26 in the manner well known in the field of syringe pumps. An oxidizer reagent ( 15% (NH4)iSZOp) is delivered to the fitting 16 via another pump such as the oxidizer syringe pump 28 shown in FIG. l through an oxidizer line 30. The oxidizer syringe pump 28 is also driven by a motor 32 and worm gear 34 in the conventional manner. The apparatus may include an acid reservoir (not shown) for periodic replenishment of the acid syringe pump 20 and an oxidizer reservoir (not shown) for periodic replenishment of the oxidizer syringe pump 28.
The aqueous outlet conduit 40 from the fitting 16 is split into a conduit l42 for the measurement of inorganic carbon and a conduit 42 for the measurement of total carbon. It is noted that a vacuum degasser or other carbon dioxide removal device may be placed in or near the conduit 40 to remove gas from the sample stream which may interfere with the downstream carbon measurements. The conduit 42 leads to a U.V. oxidation reactor 46.
Several U.V.
oxidation reactors are described in detail in U.S. Patent No. 5,132,094 by Godec, ofwhich the present is a continuation-in-part and the contents of which are hereby incorporated by reference.
Briefly) the aqueous sample inlet of the U.V. oxidation module is in communication with a coiled fused silica tube with an internal diameter of approximately lmm. The radius of the coil is such that a U.V. radiation source can be positioned in the annular region of the fused silica coiled tube. A suitable power supply and electrical connections (not shown) are used for the operation of the U.V. radiation source, which may consist of any known device which emits U.V.
radiation, such as an excimer lamp) a gas discharge tube or a mercury vapor discharge tube. An excimer lamp emitting light concentrated around 172 nm or other desired excimer-emitting frequencies may be particularly useful. The design of the U.V. oxidation module has been demonstrated to provide high efficiency conversion of organic compounds to form carbon dioxide from aqueous samples at concentrations up to about at least 100 mg,'L
total organic carbon without sample dilution, with the addition of oxygen or other chemical oxidizing reagents such as persulfate.
G:\IOSL\I 12CP2CA\SCAN2.WPD 12 The U.V. oxidation module outlet conduit 52 is in communication with the aqueous sample inlet of the first gas transfer module 56. The first gas transfer module contains a carbon dioxide gas permeable membrane 58 positioned such that the flowing aqueous sample stream passes on one side. On the other side flows deionized water. The deionized water on the deionized water side of the membrane 58 preferably is in a thin layer of approximately 0.01 to 0.02 inch and has a total volume of less than 150 ul in the preferred embodiment. Although somewhat thicker layers and larger volumes may be used) this thin layer and small volume are important in facilitating rapid analysis and response times.
The deionized water portion consists of a mixed bed 66 of anion and canon ion exchange resins in communication via a conduit 68 with a circulating pump 70 which is in communication via a conduit 72 to a joint 74. One outlet of the joint 74 is in communication via conduit 76 with the deionized water inlet of the first gas transfer module 56. Another outlet of the joint 74 is in communication with the ion exchange resin bed 66 through conduit 78, restrictor 104 and conduit 82. Restrictor 104 is used to maintain a pressure differential of 6-7 psi on the side of the first and second gas transfer modules 56 and 156. The last outlet of the joint 74 is in communication via conduit 80 with the deionized water inlet of the second gas transfer module 156 as described below.
The deionized water outlet of the first gas transfer module 56 is in communication via a conduit 92 to the inlet of a first temperature and conductivity cell 94. As in the case of the first and second gas transfer modules 56 and 156) the dimensions and liquid volume of the first and second temperature and conductivity cells 94 and l94 are very small in the preferred embodiment -- less than 10 ul - - to ensure rapid analysis and response times.
The outlet of the first temperature and conductivity cell 94 is in communication via a conduit 96 to a restrictor/deoxygenation module 98.
The restrictor/deoxygenation module 98 is a length of gas-permeable tubing.
Any gas in the deionized water tends to permeate through the tubing and out of the water.
The tubing also serves as a restrictor to maintain a pressure differential of 6-7 psi between the deionized water and the sample in first and second gas transfer modules 56 and 156 and to control the flow of deionized water in the deionized water loop. Therefore) gas that may tend to be in bubble form r.:nos~w zcN:cn~scnNZ.wP~

in the sample is more likely to remain dissolved in the deionized water stream. A pressure source may also be added to the deionized water stream to maintain this pressure di fferential, although the circulating pump 70 alone may be sufficient by properly sizing restrictor 104.
The aqueous sample outlet conduit 108 of the first gas transfer module 56 is in communication with the inlet of a peristaltic sampling pump l 10, and the outlet of the sampling pump is connected via a conduit l 12 to a suitable waste container (not shown).
The conduit 142 far the measurement of inorganic carbon leads to a coil of delay tubing 146. The purpose of the delay tubing 146 is to delay the sample flow for a period equal to the delay produced by the sample flowing through the U.V. oxidation reactor 46 on the total carbon side of the device. Therefore) the delay tubing 146 is simply a coil of inert tubing. The outlet of the delay tubing l46 is in communication with a conduit 152 leading to the second gas transfer module 156. The second gas transfer module 156 is similar to the first gas transfer module 56.
A gas permeable membrane 158 is positioned such that the flowing aqueous sample stream passes on one side, and deionized water passes in the opposite direction on the other side. Again, the deionized water is in a thin layer of approximately O.OI to 0.02 inches) and the chamber volume is less than 150 ul, to facilitate rapid analysis times in the preferred embodiment. Upon leaving the second gas transfer module 156 via conduit 208, the sample is drawn into sample pump 110 and discarded to a waste container via conduit 112.
The deionized water loop for the inorganic carbon side is similar to the deionized water loop for the total carbon side. It includes the same ion exchange resin bed 66, circulating pump 70, and joint 74. The last outlet conduit 80 from the joint 74 is in communication with the deionized water inlet of the second gas transfer module 156. From the second gas transfer module 156) the deionized water flows through a conduit 192 and into a second temperature and conductivity cell 194. The deionized water then flows through a conduit 196, through a restrictor 198 or, if desired, restrictor/deoxygenator, and joins the other deionized water loop for return to the mixed bed 66.
G:110SU.112CP2CA~SCAY2.W PD 14 The temperature and conductivity cells 94 and 194 are connected to a suitable power supply (not shown) and the electrical output from the temperature and conductivity cells 94 and 194 are connected to a control and signal electronics module (not shown). The control and electronic module is comprised of a computer or other electronic device which is capable of controlling the voltages and currents to all of the electrical components, actuating valves and switches in a predetermined timed sequence, processing the electrical signal from the temperature and conductivity cells, and calculating total organic carbon concentration, total carbon concentration and total inorganic carbon concentration from the output of the temperature and conductivity cells.
Next described is the typical operation of the present invention as diagrammed in FIG. 1.
The peristaltic sampling pump 110 withdraws an aqueous sample via the sample inlet conduit 10, at a desired flow rate of 340 microliters per minute through the particulate filter 12. Aqueous acid, such as phosphoric acid or sulfuric acid, is introduced into the sample at the fitting IG at a controlled rate of approximately 1 uL/min by the acid syringe pump 20. The desired pH of the aqueous sample after acidification is about Z.
The acidification of the sample stream will convert inorganic species to carbon dioxide, but will not convert organic species to carbon dioxide. The conversion of organic species to carbon dioxide requires the U.V. (or other type) oxidation module.
Also introduced at the fitting 16 in the preferred embodiment is an oxidizer such as persulfate as discussed above) via the oxidizer syringe pump 28 and oxidizer line 30. Rather than introducing oxidizer at a constant rate, however) oxidizer is introduced at rates that vary over an oxidation potential cycle as shown in FIG. 3. At the start of a riven oxidation potential cycle, the oxidizer is introduced at a very low rate or at a zero rate. The rate gradually increases over the period of the cycle (210 seconds in the preferred embodiment) until reaching a maximum rate.
The cycle then repeats.
The reason for varying the oxidation potential is to ensure that the optimum oxidation is achieved at some point in the cycle to produce the highest carbon measurement downstream. If too little oxidation potential is provided) the carbon could be incompletely oxidized. In that G:\IOSL\I 12CP2CA\SCAN2. W PD Z S

event) insufficient carbon in the form of carbon dioxide could pass through the semipermeable membrane 58 in the gas transfer module 56 for downstream measurement in the temperature and conductivity cell 94. The result will be an inaccurately low total carbon measurement.
Conversely, if too much oxidation potential is provided, oxygen bubbles will farm which will interrupt or lower the conductivity measurement in the temperature and conductivity cell 94, also resulting in an inaccurately low total carbon measurement. Thus the accurate carbon measurement will be the one resulting from the highest conductivity measurement in the conductivity cells over the oxidation potential cycle.
As explained above, the variation in oxidation potential can be achieved in several ways, in addition to varying the rate of introducing chemical oxidizers such as persulfate. Other approaches include varying the intensity of a U.V. radiation source used as an oxidizer, varying the residence time of the sample in a U.V. radiation source, or varying the rate of electrolysis in an electrolysis cell used to produce oxygen for oxidation. The point of this step, regardless of the approach chosen, is to vary the degree to which oxygen is reacted with the sample or, in other words, to vary the "oxidation potential."
The aqueous sample stream is split at fitting 18 into the first stream for the measurement of total carbon and the second stream for the measurement of inorganic carbon.
The first stream enters the U.V. oxidation reactor 46 where organic compounds are converted to carbon dioxide and other products. Simultaneously, the second stream enters the delay tubing 146. The rivo streams then enter their respective gas transfer modules 56 and 156 simultaneously; that is, the portion of the sample entering the first gas transfer module 56 at a given moment was separated from the portion of the sample entering the second gas transfer module 156 at that same moment.
The effluent of the U.V. oxidation reactor 46 is directed via conduit 52 into the inlet of the first gas transfer module 56, out through the outlet of the first gas transfer module 56 through the peristaltic sample pump 110 to a suitable waste container. Similarly, the effluent of the delay tubing 146 is directed via conduit 152 into the aqueous sample inlet of the second gas transfer module 156, out through the outlet of the second gas transfer module 156 through the peristaltic sample pump I 10 to the waste container.
G:'.IOSL\I I 2C'P_C'A\SCAN2.~VPD 16 A continuous supply of deionized water is produced in the deionized water portion by passing an aqueous stream of water through the mixed bed ion exchange resins 66 by means of the circulating pump 70. The deionized water flows in two loops: one is the total carbon loop and the other is the inorganic carbon loop. In the total carbon loop, deionized water flows from fitting 74 via conduit 76 into the deionized water inlet of the first gas transfer module 56. As the sample stream passes on one side of the gas permeable membrane 58 of the gas transfer module 56, the carbon dioxide formed upstream will diffuse across the gas permeable membrane 58 into the deionized water sample on the opposite side of the membrane 58) where the carbon dioxide will be converted into ionic species. In the inorganic carbon loop, deionized water flows from fitting 74 via conduit 80 into the deionized water inlet of the second gas transfer module I 56. As the sample stream passes on one side of the gas permeable membrane 158 of the second gas transfer module 156, the carbon dioxide formed upstream by conversion of the inorganic carbon to carbon dioxide in the acification step will diffuse across the gas permeable membrane 158 into the deionized water sample on the opposite side of the membrane 158, where the carbon dioxide will be converted into ionic species.
The carbon dioxide membrane 58 or 158 employed in the carbon dioxide sensors in one embodiment of the present invention may advantageously be constructed from a Teflon-like material, pertluoroalkoxy resin ("PFA"). As shown in Table l, the use of this material in the carbon dioxide sensor provides significantly higher selectivity for the passage of carbon dioxide compared with other compounds which may be present in aqueous samples and potentially interfere in the measurement of carbon dioxide using the conductomeric technique described in U.S. Patent Nos. 5,132,094 and 5,443,991. For comparison purposes, data reported by Kobos et al. in 54 Anal. Chem. 1976-1980 (1982) are included in Table 1.

Selectivity of permeable membranes:
potential interferences in CO? measurements DETECTOR RESPONSE

mC

Porous Compound Spike Concentration PFA PTFE Tefzel Iz 13 ppm ND -__ __-HNO~ 1000 ppm ND --- ---Na2S04 1000 ppm ND --- ---Na2S0~ 21 ppm ND 1 0.4 NaN02 11 ppm 0.2 5 0.6 NaCI 1000 ppm ND --- ---NaOCI 10 ppm ND --- ---Na2S l5 ppm 0.05 6 0.4 Na2S 150 ppm 2.0 30 2.0 Formic Acid 10 ppm ND 1 0.7 Acetic Acid 10 ppm ND I 0.

From Kobos et al.
ND: no detectable increase -- : data not reported The increase in conductivity caused by the presence of ionic species formed from carbon dioxide is measured by the temperature and conductivity cells 94 and 194. The measured conductivity of the deionized water sample can be directly related to the concentration of carbon dioxide, and hence, the level of total carbon and inorganic carbon compounds present in the aqueous sample stream. Temperature measurements are also taken at or proximate to the temperature and conductivity cells 94 and 194 so that the carbon determinations can take into consideration the temperatures. The measurements at the temperature and conductivity cells 94 and 194 can take place virtually continuously or at periodic intervals over the course of an oxidation potential cycle.

Once an oxidation potential period is completed, the highest measured carbon is deemed the correct measurement, and the other measurements are deemed flawed due to insufficient oxidation or oxygen gas production resulting in bubble formation.
Thus a single correct measurement is obtained for each cycle. Sequential correct measurements are obtained in sequential cycles. Thus a device utilizing 210 second cycles can obtain a correct measurement approximately every 210 seconds.

After the deionized water streams leave the temperature and conductivity cells 94 and 194, they pass through the restrictors 98 and 198. The restrictors 98 and 198 maintain a pressure differential. In a preferred embodiment, they also function as deoxygenetion modules by allowing oxygen to diffuse through a gas permeable wall to the atmosphere. The two deionized water streams then join and flow into the ion exchange resin bed 66 via the conduits 102 and 82, then to the pump 70, and back to the splitting fitting 74 to complete the cycle. The deionized water continuously circulated through the exchange resin bed 66. Only a small fraction of that circulation is tapped for circulation through the total carbon loop and inorganic carbon loop.

EXAMPLE

In the depiction of FIG.2, a 25 ppm KHP standard solution was analyzed using several different persulfate rates in a standard sample, using a Sievers Model 800 device as described in U.S. Patent Nos.5,132,094 and 5,443,991. That device is similar in principle to the present invention, but it does not automatically vary the oxidation potential over an oxidation potential cycle. Therefore, the experiment was conducted by using several different persulfate rates sucessively, as shown in FIG.2.

Because the U.V. light source in the oxidation reactor is on during the entire cycle, some oxidation takes place even when the oxidizer rate is 0, which is reflected in the carbon determination shown in FIG.2 of almost 10 ppm at the 0 oxidizer rate. The rate of persulfate being added is then adjusted to 1 ul/min, 2 ul/min, and so on. The measured TOC increases, reaching a maximum value when the persulfate rate is 4 ul/min. Greater persulfate rates result in the formation of oxygen bubbles in the sample stream and a depression in the measured TOC.
The cycle is then repeated, and again the measured TOC increases to a maximum value and then decreases as excess persulfate is added. The maximum TOC value obtained during a cyle is used to calculate the TOC of the sample stream.

EXAMPLIr FIG. 3 shows a graph of measured carbon and persulfate flow rate versus time for a preferred embodiment of the present invention, utilizing automatic variable oxidation potential.
The graph extends over several oxidation potential cycles. It can be seen that the persulfate flow rate in each cycle increases from zero to approximately 6 ul/min. At the zero rate, there is some carbon detected due to the oxidizing effect of the U.V. radiation even in the absence of added persulfate. As the oxidation potential is increased by increasing the rate that persulfate is added to the sample stream, the oxidation of the sample also increases. This increasing oxidation results in increasing organic carbon measurements, as more organic carbon is converted to carbon dioxide. The peak organic carbon measurement occurs at about 24 ppm, corresponding to a persulfate flow rate of about 5.2 ul/min.
As the persulfate flow rate is increased further, the increased oxidation potential results in the formation of oxygen gas bubbles. Those bubbles may dilute the net average carbon dioxide concentration in the same. In addition, they could diffuse through the gas permeable membrane of the gas transfer module into the deionized water stream and then into the temperature and conductivity cell where they briefly partially or wholly insulate the conductivity electrodes from the deionized water stream, thereby interfering with the conductivity measurement to produce an erroneously low measurement. The erroneously low measurements are reflected in the fall-off in the measured organic carbon as the persulfate flow rate is increased from 5.2 to G ul/min, as shown in FIG. 3. The several cycles depicted in FIG. 3 illustrate that these phenomena are quite predictable and repeatable. In fact, for a given sample, the cycles are virtually identical.
The embodiment described in the preceding paragraphs contemplates an oxidizer rate that starts at a minimum and gradually increases to a maximum over the oxidizer cycle. However, it will be apparent that the invention could as easily utilize some other oxidizer rate profile such as a profile in which the rate starts at a maximum and gradually declines to a minimum or the rate varies in some other fashion. The important concept is that the oxidizer rate does vary within a predetermined range, to ensure that it is at the optimum range at some point in the cycle.
The device as described herein may also incorporate components for the removal of inorganic carbon from the sample stream utilizing a membrane-based carbon dioxide removal G ~IUSL~I I2CP?CA~SCAV2.WPD 19 module in the sample stream. The removal of inorganic carbon is beneficial in measuring organic carbon in samples that contain a large amount of inorganic carbon in relation to organic carbon, so that the level of organic carbon determined by subtracting the measured inorganic carbon from the measured total carbon is not lost in the variability of the total carbon measurement. This approach is described in some detail in U.S. Patent No.
5,443,991 by Godec, et al.
It can be appreciated that the device and method of the present invention can be used to make one or more of several determinations. Total carbon can be determined.
Inorganic carbon can be determined. Finally, organic carbon can be determined by subtracting the inorganic carbon determination from the total carbon determination.
The aspect of the invention in which the oxidation potential applied to a sample varies over an oxidation potential period can be utilized in other embodiments. One such other embodiment is shown in the block diagram of FIG. 4. An aqueous sample inlet 210 is in communication with a particle filter 212 for the removal of particulate matter that may be suspended in the aqueous sample stream. A filter outlet conduit 214 joins a fitting 216. An acid reagent (6MH~P0, in the preferred embodiment) is delivered to the fitting 216 via a pump such as the acid syringe pump 220 through an acid line 222. The acid syringe pump 220 is driven by a motor 224 and worm gear 226 in the manner well known in the field of syringe pumps. The apparatus may also include an acid reservoir (not shown) for periodic replenishment of the acid syringe pump 220. Acidification of the sample stream by the introduction of acid at the fitting 216 serves to convert inorganic carbon compounds to carbon dioxide.
The outlet conduit 240 from the fitting 216 leads to a first gas transfer module 256. Like the gas transfer modules 56 and 156 of the embodiment of FIG. 1, the first gas transfer module 256 of FIG. 4 includes a carbon dioxide permeable membrane Z58 positioned between the sample stream and a deionized water stream. The deionized water on the deionized water side is in a thin layer of approximately 0.01 to 0.02 inches and has a total volume of less than 150 ul to facilitate rapid response times. The deionized water can be from any of several sources. in the preferred embodiment of FIG. 4, the deionized water source 300 is a closed loop with a circulating pump and a mixed bed of anion and cation ion exchange resins similar to the G:11l7SLll 1?CP2(; A\SCAN2. WPU 2 O

deionized water closed loop shown in the embodiment of FIG. 1.
Deionized water flows from the deionized water source 300 into the first gas transfer module 256, receives carbon dioxide permeating through the carbon dioxide permeable membrane 258, and then flows to the first temperature and conductivity cell 294. The first temperature and conductivity cell 294 measures both the temperature and conductivity cell of the stream of deionized water with dissolved carbon dioxide, from which the inorganic carbon concentration can be derived. The first temperature and conductivity cell 294, as well as the second temperature and conductivity cell 394 described below, have very small liquid volumes of less than l0 ul. This very small liquid volume produces rapid liquid turnover in the cell and consequently rapid analysis and response times.
The stream leaves the first gas transfer module 256 and flows to a carbon dioxide degassification module 290 via conduit 295. The carbon dioxide degassification module 290 preferably includes a length of carbon dioxide permeable tubing positioned in a vacuum container. Carbon dioxide permeates from the flowing stream through the carbon dioxide permeable tubing into the vacuum container. The vacuum is continuously or periodically renewed by a vacuum pump (not shown) or other vacuum producing source in communication with the container interior. The exact dimensions and materials appropriate for the carbon dioxide degassification module 290 depend on the flow rate of the stream and the carbon concentration in the stream. In the preferred embodiment, utilizing a flow rate of approximately 500 ul/min, the carbon dioxide permeable tubing is a microporous material having an inside diameter of 280 microns and a length subjected to the vacuum of approximately three inches.
It can be appreciated that the stream leaving the gas transfer module 290 is essentially free of inorganic carbon. Substantially all the inorganic carbon was converted to carbon dioxide in the upstream acidification step, and the carbon dioxide was then removed in the carbon dioxide degassification module 290. At this point - - the conduit 250 from the outlet of the carbon dioxide degassification module 290 -- the stream still contains organic carbon, and the organic carbon has not yet been measured.
G:~IOSL'.11.'.CP2CA~.SCAN2.WPD 2 1 The conduit 250 from the outlet of the carbon dioxide degassification module leads to a fitting 260 for the introduction of a chemical reagent to oxidize organic carbons in the stream.
The chemical reagent in the preferred embodiment is 15 percent (NHd)iSiOa and is delivered to the fitting 260 via an oxidizer syringe pump 228 through an oxidizer line 230.
The oxidizer syringe pump 228 is driven by a motor 232 and worm gear 234 in the conventional manner. The apparatus may also include an oxidizer reservoir (not shown) for periodic replenishment of the oxidizer syringe pump 228. The stream then enters a U.V. oxidation reactor 246. The U.V.
oxidation reactor 246 is preferably similar to the U. V. oxidation reactor 46 described above in connection with the embodiment of FIG. 1.
As in the embodiment described above, this embodiment oxides the stream using an oxidizer potential that varies over an oxidation potential period. One approach to varying the oxidization potential is to vary the rate of introducing a chemical reagent oxidizer through the oxidizer syringe pump 228 described in the preceding paragraph. Other approaches to achieving that objective in this embodiment, as in the other embodiments) is to vary the rate of oxygen production in an electrolysis cell, to vary the intensity of a U. V. radiation oxidizer, or to vary the duration of exposure of the stream to a U.V, radiation oxidizer.
The oxidation step, whether accomplished by a chemical reagent oxidizer or by other means, oxidizes organic carbon in the sample to produce dissolved carbon dioxide. The concentration of the dissolved carbon dioxide varies aver the oxidation potential period because the oxidation potential in the stream varies over the oxidation potential period. The point of varying the oxidation potential over the oxidation potential period is to ensure that the oxidation potential reaches an optimum at some point during the oxidation potential period. That optimum is when the organic carbon is substantially completely oxidized, but no significant oxygen bubbles have been formed. At that optimum, the maximum possible carbon dioxide is produced without the formation of interfering bubbles.
The stream, now with dissolved carbon dioxide produced by the oxidation of organic carbon, flows through conduit 270 into the second gas transfer module 356 similar to the first gas transfer module 256. The second gas transfer module includes a carbon dioxide permeable membrane 358 positioned between the sample stream and another deionized water stream. This G:\IOSI.\112CP2CA\.S('AN2.WPD 22 deionized water stream may be from the same source 300 as the deionized water stream used with the first gas transfer module 256) as shown in FIG. 4) or may be from a separate source.
Deionized water flows from the deionized water source 300 into the second gas transfer module 356, receives carbon dioxide permeating through the carbon dioxide permeable membrane 358 of the second gas transfer module 356, and then flows to the second temperature conductivity cell 394.
The measured conductivity of the stream will vary over the oxidation potential period due to the variable oxidation over the oxidation potential period. That peak measured conductivity is deemed the accurate indicator of organic carbon concentration in the sample.
Any lower measured conductivity in the presence of an oxidation potential lower than the oxidation potential that produced the peak is deemed due to incomplete oxidation of organic carbon in an insufficient oxidation potential. Any lower measured conductivity in the presence of an oxidation potential higher than the oxidation potential that produced the peak is deemed due to production of oxygen gas bubbles that interfere with the carbon dioxide measurement.
After leaving the second temperature and gas transfer module 356, the stream flows through pump 310 and into disposal line 312.
It can be appreciated that still other embodiments are possible utilizing the general approach of varying the oxidation potential over an oxidation potential period. For example, the degassification module could utilize membrane separation of the stream from a basic stream as taught by U.S. Patent No. 5,132,094 by Godec, et al.
The apparatus thus makes a measurement of inorganic carbon concentration and a measurement of organic carbon concentration using a single stream. Total carbon can also be determined by adding the measured inorganic carbon and measured organic carbon.
The present invention represents a signiftcant improvement over the methods and apparatus existing for the measurement of total organic carbon, total inorganic carbon, and total carbon content of aqueous samples. The present invention can be used for these rapid determinations in a wide range of samples, with minimal use of external chemical reagents, and G:NOSL1112CP2CA'.SCAN:.WYU 2 3 without prior knowledge of the approximate carbon range in the sample. The use of a carbon dioxide selective membrane and conductometric detection applied to the measurement of total organic carbon and total inorganic carbon concentrations in aqueous samples offers several advantages: 1 ) no purge gas, gas/liquid purge apparatus or drying system is required, 2) the conductometric detection system provides excellent long-term calibration stability (over one year between calibrations) and minimal fouling or contamination since the sensor is only exposed to carbon dioxide in deionized water, 3) the size of the conductivity sensor can be sufficiently small that accurate measurement in samples as small as 0.1 ml can be achieved, 4) membrane/conduetometric detection provides a large linear dynamic range, typically one to three orders of magnitude greater than other techniques utilized for the measurement of carbon dioxide in aqueous samples) 5) the sensitivity of the carbon dioxide sensor and conductivity detector is substantially better than in other techniques, 6) no sample clean-up or dilution is required, 7) if used with an inorganic carbon removal module the device can accurately measure very low concentrations of organic carbon even in the presence of relatively high concentrations of inorganic carbon, 8) the membrane-based sensing system minimizes interference from other gasses, and 9) the use of thin sample layers and low volume components facilitates rapid response to allow practical use in commercial applications.
G:~IOSf.V I'_CP2CA~,SCANZ.W'PD 24

Claims

1. An apparatus for the measurement of carbon in an aqueous sample, comprising: an oxidation reactor that varies an oxidation potential during an oxidation potential period to produce carbon dioxide concentrations that vary during the oxidation potential period; and a first carbon dioxide sensor to measure the amount of carbon dioxide in the sample at a plurality of times during the oxidation potential period.

2. The apparatus of claim 1, wherein the oxidation reactor includes a reagent pump to pump an oxidizing reagent into the sample stream at a rate that varies over the oxidation potential period.

3. The apparatus of claim 1, further comprising an ultraviolet light source to irradiate the sample to assist in the oxidation of the sample.

4. The apparatus of claim 1, wherein the first carbon dioxide sensor includes a carbon dioxide permeable membrane separating the sample from deionized water, and a conductivity cell, whereby carbon dioxide may permeate from the sample through the membrane and into the deionized water to be measured in the conductivity cell at a known temperature.

5. The apparatus of claim 4, wherein the carbon dioxide permeable membrane defines on one side of the carbon dioxide permeable membrane a sample layer less than 0.06 inches thick and less than 1,000 ul in volume.

6. The apparatus of claim 4, wherein the conductivity cell includes a temperature sensor and has a volume of less than 500 ul.

7. The apparatus of claim 4, wherein the first carbon dioxide sensor includes a closed loop for said deionized water, whereby the deionized water flows past the carbon dioxide permeable membrane, into the conductivity cell, and returns to the carbon dioxide permeable membrane.

8. The apparatus of claim 7, wherein the loop includes a deionizer.

9. The apparatus of claim 7, further comprising an acidifier for acidifying the sample to covert inorganic carbon to carbon dioxide.

10. The apparatus of claim 1, wherein the first carbon dioxide sensor includes a gas transfer module to transfer carbon dioxide from the sample to deionized water and a conductivity cell to measure the conductivity of the deionized water with carbon dioxide.

11. The apparatus of claim 1, further comprising a set of conduits to contain a flowing stream of the sample, the oxidation reactor and first carbon dioxide sensor being in fluid communication with the set of conduits.

12. The apparatus of claim 10, further comprising an acidifier in fluid communication with the set of conduits to add acid to the stream to convert inorganic carbon to carbon dioxide.

13. The apparatus of claim 12, further comprising a second carbon dioxide sensor to measure carbon dioxide in the stream, the second carbon dioxide sensor being in fluid communication with the set of conduits downstream from the acidifier.

14. The apparatus of claim 13, wherein the second carbon dioxide sensor includes a gas transfer module to transfer carbon dioxide from the sample to deionized water and a conductivity cell to measure the conductivity of the deionized water with carbon dioxide.

15. The apparatus of claim 13, further comprising a carbon dioxide remover, the carbon dioxide remover being in fluid communication with the set of conduits between the first carbon dioxide sensor and the second carbon dioxide sensor.

16. The apparatus of claim 15, wherein the second carbon dioxide sensor is downstream from the acidifier, the carbon dioxide remover is downstream from the second carbon dioxide sensor, the oxidation reactor is downstream from the carbon dioxide remover, and the first carbon dioxide sensor is downstream from the oxidation reactor

17. The apparatus of claim 1, further comprising a first set of conduits to contain a first flowing stream of the sample; a second set of conduits to contain a second flowing stream of the sample in parallel with the first stream; the first carbon dioxide sensor being in fluid communication with the first set of conduits; and further comprising a second carbon dioxide sensor in fluid communication with the second set of conduits.

18. The apparatus of claim 17, further comprising an ultraviolet light source to irradiate the first stream downstream from the oxidation reactor.

19. The apparatus of claim 18, wherein the first carbon dioxide sensor includes a first carbon dioxide permeable membrane to separate the first stream from deionized water, and a first conductivity cell, whereby carbon dioxide may permeate from the first stream through the second membrane and into the deionized water to be measured in the first conductivity cell at a known temperature.

20. The apparatus of claim 19, wherein the second carbon dioxide sensor includes a second carbon dioxide permeable membrane to separate the second stream from deionized water, and a second conductivity cell, whereby carbon dioxide may permeate from the second stream through the second membrane and into the deionized water to be measured in the second conductivity cell at a known temperature.

21. The apparatus of claim 20, further comprising a set of deionized water conduits to contain the deionized water into which carbon dioxide permeates from the first stream and the deionized water into which carbon dioxide permeates from the second stream.

22. The apparatus of claim 21, further comprising a deionized water source in communication with said deionized water set of conduits.

23. The apparatus of claim 22, wherein said deionized water source includes a water deionizer, and further comprising a circulating pump to circulate water through the deionizer and through the first carbon dioxide sensor and second carbon dioxide sensor.

24. The apparatus of claim 23, wherein said first set of conduits and said second set of conduits split a main sample stream, and said oxidation reactor includes an oxidizer reagent pump in communication with the main sample stream.

25. The apparatus of claim 24, further comprising an acid source in communication with the main sample stream.

26. The apparatus of claim 25, wherein the second set of conduits includes a set of delay tubing to delay the flow of the second stream for a period of time substantially equal to a period of time for the first stream to flow past the ultraviolet light source.

27. An apparatus for determining carbon concentration in aqueous samples, said apparatus comprising in combination: (a) a reactor having fluid inlet and fluid outlet means and associated variable oxidation means; (b) liquid-phase measurement means at least in part located in or downstream of said reactor, said measurement means being responsive to liquid-phase concentrations of organic carbon oxidation products including carbon dioxide;
(c) flow control means for continuously flowing an aqueous fluid through said reactor and in fluid contact with at least a portion of said measurement means at a controlled flow rate; and (d) reaction control means for varying said variable oxidation means in a controlled and reproducible manner during a predetermined oxidation period so as to vary the potential in said reactor for oxidation of organic carbon in said aqueous fluid flowing through said reactor over a range comprising at least two oxidation potentials so as to generate a profile of differing concentrations of organic carbon oxidation products including carbon dioxide in the aqueous fluid corresponding to the different oxidation potentials in said reactor.

28. An apparatus according to claim 27 wherein said reaction control means can vary the potential in said reactor for oxidation of organic carbon from a first oxidation potential to at least a second, higher oxidation potential.

29. An apparatus according to claim 27 wherein said reaction control means can vary the potential in said reactor for oxidation of organic carbon from a first oxidation potential to at least a second, lower oxidation potential.

30. An apparatus according to claim 27 wherein said reaction control means is capable of establishing and maintaining each of said at least two oxidation potentials at a substantially constant level for a controlled period of time.

31. An apparatus according to claim 30 wherein said oxidation potentials can be maintained for substantially equal controlled periods of time.

32. An apparatus according to claim 30 wherein said oxidation potentials can be maintained for differing controlled periods of time.

33. An apparatus according to claim 27 wherein at least one of said oxidation potentials can be established at a level greater than that necessary to substantially completely react the organic carbon in the aqueous fluid in said reactor to carbon dioxide.

34. An apparatus according to claim 27 wherein at least one of said oxidation potentials can be established at a level substantially greater than that necessary to substantially completely react the organic carbon in the aqueous fluid in said reactor to carbon dioxide.

35. An apparatus according to claim 27 wherein at least one of said oxidation potentials can be established at a level above oxygen saturation conditions for said aqueous fluid in said reactor.

36. An apparatus according to claim 27 wherein at least one of said oxidation potentials can be established at a level sufficient to substantially completely react the organic carbon in the aqueous fluid in said reactor to carbon dioxide independently of the concentrations of organic carbon and initial dissolved oxygen gas in said aqueous fluid.

37. An apparatus according to claim 27 wherein said reaction control means comprises material regulation means for regulating the addition of an oxidizer to the aqueous fluid.

38. An apparatus according to claim 37 wherein said oxidizer is an electrolyte.

39. An apparatus according to claim 37 wherein said oxidizer comprises at least a persulfate.

40. An apparatus according to claim 37 wherein said oxidizer is a non-electrolyte.

41. An apparatus according to claim 37 wherein said material regulation means comprises syringe pump means.

42. An apparatus according to claim 27 wherein said reaction control means comprises electrolysis regulation means for regulating the rate of generation of an oxidizer in an electrolysis cell which is in association with said reactor.

43. An apparatus according to claim 27 wherein said reaction control means comprises: (a) U.V. regulation means for regulating the exposure of the aqueous fluid to a U.V. light source which is in association with said reactor; and (b) oxidizer supply means to insure sufficient oxidizer in said aqueous fluid to substantially completely react the organic carbon in said aqueous fluid to carbon dioxide.

44. An apparatus according to claim 43 wherein said oxidizer supply means comprises an aqueous fluid containing sufficient dissolved oxygen to substantially completely react the organic carbon in said aqueous fluid to carbon dioxide.

45. An apparatus according to claim 43 wherein said U.V. regulation means comprises intensity variation means for varying the intensity of said U.V.
light source.

46. An apparatus according to claim 43 wherein said U.V. regulation means comprises duration variation means for varying the duration of exposure of the aqueous fluid to said U.V. light source.

47. An apparatus according to claim 46 wherein said duration variation means comprises flow-rate variation means for varying the flow rate of the aqueous fluid past said U.V. light source.

48. An apparatus according to claim 43 wherein said oxidizer supply means comprises a source of an oxidizer other than dissolved oxygen in said aqueous fluid.

49. An apparatus according to claim 48 wherein said oxidizer is an electrolyte.

50. An apparatus according to claim 48 wherein said oxidizer comprises at least a persulfate.

51. An apparatus according to claim 48 wherein said oxidizer is a non-electrolyte.

52. An apparatus according to claim 48 wherein said reaction control means further comprises material regulation means for regulating the addition of said oxidizer to the aqueous fluid.

53. An apparatus according to claim 52 wherein said material regulation means comprises syringe pump means.

54. An apparatus according to claim 43 wherein said oxidizer supply means comprises electrolysis means for generating an oxidizer in an electrolysis cell which is in association with said reactor.

55. An apparatus according to claim 27 wherein said reaction control means is capable of establishing at least three distinct and separate oxidation potentials in said reactor, each of said distinct and separate oxidation potentials being maintainable at a substantially constant level for a controlled period of time.

56. An apparatus according to claim 55 wherein said distinct and separate oxidation potentials can be maintained for substantially equal controlled periods of time.

57. An apparatus according to claim 55 wherein said distinct and separate oxidation potentials can be maintained for differing controlled periods of time.

58. An apparatus according to claim 27 wherein said reaction control means comprises means for smoothly and continuously varying the oxidation potential in said reactor from a level below that necessary to substantially completely react all of the organic carbon in the aqueous fluid in said reactor to carbon dioxide to an oxidation potential level above that necessary to substantially completely react all of the organic carbon in the aqueous fluid in said reactor to carbon dioxide.

59. An apparatus according to claim 27 wherein said reaction control means comprises means for smoothly and continuously varying the oxidation potential in said reactor from an oxidation potential level above that necessary to substantially completely react all of the organic carbon in the aqueous fluid in said reactor to carbon dioxide to an oxidation potential level below that necessary to substantially completely react all of the organic carbon in the aqueous fluid in said reactor to carbon dioxide.

60. An apparatus according to claim 42 further comprising means to remove hydrogen from said electrolysis cell.

61. An apparatus according to claim 54 further comprising means to remove hydrogen from said electrolysis cell.

62. An apparatus according to claim 27 wherein said measurement means comprises first CO2-permeable membrane separation means separating said flowing aqueous fluid from contact with a second fluid.

63. An apparatus according to claim 62 wherein said first CO2-permeable membrane separation means comprises a CO2-selective membrane.

64. An apparatus according to claim 63 wherein said CO2-selective membrane consists essentially of perfluoroalkoxy resin.

65. An apparatus according to claim 62 wherein said measurement means further comprises at least temperature or conductively sensing means for sensing changes in temperature or conductivity respectively of said second fluid.

66. An apparatus according to claim 62 wherein said second fluid is deionized water.

67. An apparatus according to claim 27 further comprising inorganic carbon sensing means for also determining the inorganic carbon content of said aqueous fluid.

68. An apparatus according to claim 67 wherein said inorganic carbon sensing means comprises acidification means for converting inorganic carbon in said aqueous fluid to carbon dioxide.

69. An apparatus according to claim 68 wherein said inorganic carbon sensing means further comprises CO2-sensing means for sensing the concentration of carbon dioxide in said aqueous fluid downstream of said acidification means.

70. An apparatus according to claim 69 wherein said CO2-sensing means comprises CO2-permeable membrane separation means separating said aqueous fluid from contact with a second fluid.

71. An apparatus according to claim 70 wherein said CO2-permeable membrane separation means comprises a CO2-selective membrane.

72. An apparatus according to claim 71 wherein said CO2-selective membrane consists essentially of perfluoroalkoxy resin.

73. An apparatus according to claim 70 wherein said CO2-sensing means further comprises at least temperature or conductivity sensing means for sensing changes in temperature or conductivity respectively of said second fluid.

74. An apparatus according to claim 70 wherein said second fluid is deionized water.

75. An apparatus according to claim 27 wherein said reaction control means comprises high temperature combustion means.

76. An apparatus according to claim 43 wherein said U.V. light source comprises at least a U.V. light source selected from gas discharge tubes, mercury vapor discharge tubes, and excimer lamps.

77. An apparatus according to claim 27 wherein said measurement means comprises at least a means selected from IR spectroscopy, conductometric, and potentiometric measurement means.

78. In an apparatus tier measuring carbon concentration in a flowing aqueous sample, said apparatus comprising a reactor for reacting at least a portion of a first organic compound in said sample from a first oxidation state to one or more second compounds each at an oxidation state different from said first oxidation state; means for flowing the aqueous sample continuously into, through, and out of said reactor at a controllable, non-zero flow rate; and means for sensing the concentration of said second compounds in said flowing aqueous sample; the improvement comprising: reactor control means in combination with variable oxidation means for varying in a controlled and reproducible manner the reaction conditions in said reactor so as to generate a sensing profile that defines a peak value based on at least two different concentrations of said second compounds in said sample corresponding to each of at least two different reaction conditions in said reactor.

79. An apparatus according to claim 78 further comprising calculation means for calculating from said sensing profile the carbon concentration in said sample.

80. An apparatus according to claim 78 wherein said reactor control means comprises means for establishing at least two distinct and separate levels of reaction potential in said reactor, each of said levels of reaction potential being maintainable for substantially equal lengths of time.

81. An apparatus according to claim 78 wherein said reactor control means comprises means for establishing at least two distinct and separate levels of reaction potential in said reactor, each of said levels of reaction potential being maintainable for unequal lengths of time.

82. An apparatus according to claim 78 wherein said reactor control means comprises means for establishing at least two levels of reaction potential in said reactor wherein at least one of said levels corresponds to a concentration of said second compounds below said peak value and at least one of said levels corresponds to a concentration of said second compounds above said peak value.

83. An apparatus according to claim 78 wherein said reactor control means comprises means for varying the level of reaction potential in said reactor between a level corresponding to a concentration of said second compounds below said peak value and a level corresponding to a concentration of said second compounds above said peak value.

84. An apparatus according to claim 78 wherein said reactor control means comprises oxidizer regulation means for controlling the addition of oxidizer to said sample.

85. An apparatus according to claim 84 wherein said oxidizer is an electrolyte.

86. An apparatus according to claim 84 wherein said oxidizer comprises a persulfate.

87. An apparatus according to claim 84 wherein said oxidizer is a non-electrolyte.

88. An apparatus according to claim 78 wherein said reactor control means comprises electrolysis regulation means for controlling the rate of generation of oxidizer in an electrolytic cell associated with said reactor.

89. An apparatus according to claim 78 wherein said reactor control means comprises U.V. intensity regulation means for controlling the intensity of at least a U.V. light source in association with said reactor.

90. An apparatus according to claim 78 wherein said reactor control means comprises U.V. duration regulation means for controlling the duration of exposure of said flowing sample to U.V. light in said reactor.

91. An apparatus according to claim 90 wherein said U.V. duration regulation means comprises means for varying the flow rate of said sample through said reactor.

92. An apparatus according to claim 78 wherein said means for sensing the concentration of said second compounds comprises means for liquid-phase sensing of carbon dioxide.

93. An apparatus according to claim 92 wherein said means for sensing of carbon dioxide comprises a membrane permeable to carbon dioxide.

94. An apparatus according to claim 92 wherein said means for sensing of carbon dioxide comprises a membrane selectively permeable to carbon dioxide.

95. An apparatus according to claim 78 wherein said means for sensing the concentration of said second compounds comprises electrical conductivity sensing means.

96. An apparatus according to claim 95 wherein said electrical conductivity sensing means comprises a membrane permeable to carbon dioxide

97. An apparatus according to claim 95 wherein said electrical conductivity sensing means comprises a membrane selectively permeable to carbon dioxide.

98. An apparatus according to claim 97 wherein said membrane consists essentially of perfluoroalkoxy resin.

99. A system for sensing and monitoring the carbon content of an aqueous sample, said system comprising: (a) at least a reaction zone through which to pass a flowing aqueous sample at a controlled flow rate; (b) fluid flow means for flowing said aqueous sample through said reaction zone; (c) variable oxidation means for establishing varying oxidation conditions in said flowing aqueous sample while in said reaction zone at a level sufficient to react at least a portion of any organic carbon in said sample to carbon dioxide; (d) CO2-sensing means for sensing carbon dioxide in said flowing aqueous sample following its exposure to said reaction conditions thereby to generate CO2 response data;
and, (e) reaction condition control means for controlling said variable oxidation means to establish a controllable program of differing reaction conditions in said reaction zone during each of a plurality of timed reaction cycles, wherein said reaction conditions for each said cycle comprise at least a sufficient number of different reaction conditions over a sufficient range, including at least one reaction level below that necessary to substantially completely react the organic carbon in the sample to carbon dioxide and at least a second reaction level which is close to or greater than that necessary to substantially completely react the organic carbon in the sample to carbon dioxide, so as to mathematically identify from said CO2 response data the peak CO2 response level corresponding to the concentration of organic carbon in said sample.

100. A process for determining carbon concentration in an aqueous sample, said process comprising the steps of:
(a) flowing a fluid including at least said aqueous sample at a controlled flow rate;
(b) reacting carbon in said aqueous sample to produce organic carbon oxidation products by providing and varying oxidizing conditions in said fluid which are varied in a controlled and reproducible manner during a predetermined oxidation period over a range comprising at least two oxidation potentials so as to generate a profile of differing concentrations of organic carbon oxidation products in said fluid corresponding to the different oxidation potentials;
(c) measuring the concentration of organic carbon oxidation products in said fluid at said at least two oxidation potentials; and, (d) determining the carbon concentration in said aqueous sample from the measures of organic carbon oxidation products in said fluid at said at least two oxidation potentials.

101. A process according to claim 100 wherein said oxidizing conditions in said fluid are varied in a controlled and reproducible manner using at least one process selected from the group comprising:
(a) varying the flow rate of said fluid;
(b) varying the rate of addition of an oxidizer to said fluid;
(c) varying the flow rate of said fluid past a location where the fluid is exposed to ultraviolet light;
(d) flowing said fluid past a location where the aqueous sample is exposed to ultraviolet light while varying the intensity of the ultraviolet light; and (e) varying the rate of generation of an oxidizer in an apparatus which is in fluid communication with said fluid.

102. A process according to claim 100 wherein at least one of said at least two oxidation potentials in said fluid is selected from the following:
(a) an oxidation potential that is sufficient to substantially completely react the organic carbon in said aqueous sample;
(b) an oxidation potential greater than that necessary to substantially completely react the organic carbon in said aqueous sample;
(c) an oxidation potential that is above oxygen saturation conditions for said fluid;
and, (d) an oxidation potential that is maintained at a substantially constant level for a controlled period of time.

103. A process according to claim 100 wherein the oxidizing conditions in said fluid are smoothly and continuously varied from a first oxidation potential to a second oxidation potential, one of said first and second oxidation potentials being below that which is necessary to substantially completely react all of the carbon in said aqueous sample, the other of said first and second oxidation potentials being above that which is necessary to substantially completely react all of the carbon in said aqueous sample.

104. A process according to claim 100 wherein the concentration of carbon dioxide in said organic carbon oxidation products in said aqueous sample is measured utilizing a carbon dioxide gas permeable membrane and further comprising the step of flowing said fluid on one side of the membrane which separates said fluid from contact with a second fluid.

105. A process according to claim 101 wherein at least one of said at least two oxidation potentials in said fluid is selected from the following:
(a) an oxidation potential that is sufficient to substantially completely react the organic carbon in said aqueous sample;
(b) an oxidation potential greater than that necessary to substantially completely react the organic carbon in said aqueous sample;
(c) an oxidation potential that is above oxygen saturation conditions for said fluid;
and, (d) an oxidation potential that is maintained at a substantially constant level for a controlled period of time.

106. A process according to claim 100 wherein the oxidizing conditions provided in said fluid are varied from a first oxidation potential to at least a second, higher oxidation potential.

107. A process according to claim 100 wherein the oxidizing conditions provided in said fluid are varied from a first oxidation potential to at least a second, lower oxidation potential.

108. A process according to claim 100 wherein providing oxidizing conditions in said fluid includes the step of establishing and maintaining each of said at least two oxidation potentials at a substantially constant level for a controlled period of time.

109. A process according to claim 108 wherein said at least two oxidation potentials are maintained at constant levels for substantially equal periods of time.

110. A process according to claim 108 wherein said at least two oxidation potentials are maintained at constant levels for differing periods of time.

111. A process according to claim 100 wherein providing oxidizing conditions in said fluid includes the step of smoothly and continuously varying the oxidation potential from a level below that necessary to substantially completely react all of the organic carbon in the aqueous sample to carbon dioxide to an oxidation potential level above that necessary to substantially completely react all of the organic carbon in the aqueous sample to carbon dioxide.

112. A process according to claim 100 wherein providing oxidizing conditions in said fluid includes the step of smoothly and continuously varying the oxidation potential from a level above that sufficient to substantially completely react all of the organic carbon in the aqueous sample to carbon dioxide to an oxidation potential level below that sufficient to substantially completely react all of the organic carbon in the aqueous sample to carbon dioxide.

113. A process according to claim 100 wherein said oxidizing conditions in said fluid are varied in a controlled and reproducible manner by varying the rate of generation of one or more oxidizers in an electrolysis cell which is in association with said fluid.

114. A process according to claim 113 further including the steps of removing at least some hydrogen from said fluid.

115. A process according to claim 100 wherein said oxidizing conditions in said fluid are varied in a controlled and reproducible manner by flowing said fluid containing at least sufficient oxidizer for substantially complete reaction of organic compounds in said aqueous sample to carbon dioxide, past a location where the aqueous sample is exposed to ultraviolet light while varying the exposure of the sample to ultraviolet light.

116. A process according to claim 115 wherein said aqueous fluid contains sufficient dissolved oxygen relative to the content of organic carbon in said sample for substantially complete reaction of organic compounds to carbon dioxide.

117. A process according to claim 115 wherein exposure of the sample to ultraviolet light is varied by varying the intensity of the ultraviolet light.

118. A process according to claim 115 wherein exposure of the sample to ultraviolet light is varied by varying the duration of the exposure.

119. A process according to claim 115 wherein exposure of the sample to ultraviolet light is varied by varying the flow rate of the sample past the ultraviolet light.

120. A process according to claim 115 further including the step of adding an oxidizer to said fluid.

121. A process according to claim 120 wherein said oxidizer is an electrolyte.

122. A process according to claim 120 wherein said oxidizer comprises at least a persulfate.

123. A process according to claim 120 wherein said oxidizer is a non-electrolyte.

124. A process according to claim 120 wherein the step of adding an oxidizer to said fluid includes generating an oxidizer in an electrolysis cell which is in association with said fluid.

125. A process according to claim 124 further including the step of removing at least some hydrogen from said fluid.

126. A process according to claim 100 wherein step of measuring organic carbon oxidation products in said fluid includes flowing said fluid into contact with one side of a first CO2-permeable membrane, the opposite side of which is in contact with a second fluid.

127. A process according to claim 126 wherein said first CO2-permeable membrane is a CO2-selective membrane.

128. A process according to claim 127 wherein said CO2-selective membrane consists essentially of perfluoroalkoxy resin.

129. A process according to claim 126 further including the step of sensing changes in the carbon dioxide content of said second fluid.

130. A process according to claim 126 further including the step of sensing changes in temperature of conductivity of said second fluid.

131. A process according to claim 126 wherein said second fluid is deionized water.

132. A process according to claim 100 further including the step of determining the inorganic carbon content of said aqueous sample.

133. A process according to claim 132 wherein said step of determining the inorganic carbon content includes converting inorganic carbon in said aqueous sample to carbon dioxide.

134. A process according to claim 133 further including the step of measuring the concentration of carbon dioxide in said fluid downstream from said converting step.

135. A process according to claim 134 wherein said step of measuring the concentration of carbon dioxide in said fluid downstream from said converting step includes flowing said fluid into contact with one side of CO2-permeable membrane, the opposite side of which is in contact with a second fluid.

136. A process according to claim 135 further including the step of sensing changes in the carbon dioxide content of said second fluid.

137. A process according to claim 135 wherein said CO2-permeable membrane is a CO2-selective membrane.

138. A process according to claim 137 wherein said CO2-selective membrane consists essentially of perfluoralkoxy resin.

139. A process according to claim 135 further including the step of sensing changes in temperature or conductivity of said second fluid.

140. A process according to claim 135 wherein said fluid is deionized water.

141. A process according to claim 115 wherein said ultraviolet light is generated by gas discharge tubes, mercury vapor discharge tubes, or excimer lamps.

142. A process for determining the carbon content of each of a series of water samples containing organic compounds comprising the following steps:
(a) introducing one of said water samples into a first fluid flow path and moving said sample from an upstream location along said flow path at a controlled flow rate to a downstream location along said flow path;
(b) passing said sample through a first reaction zone along said flow path, said first reaction zone being between said upstream and downstream locations, and exposing different portions of said sample to controllable, differing oxidizing conditions at said first reaction zone, said oxidizing conditions for each sample passing through said first reaction zone including at least a first reproducible oxidizing condition which is insufficient to oxidize substantially all of the organic compounds in the sample to carbon dioxide and at least a second reproducible oxidizing condition which is sufficient to oxidize substantially all of the organic compounds in the sample to carbon dioxide;
(c) sensing the carbon dioxide content of the different portions of said sample at a first sensing zone along said flow path downstream from said first reaction zone; and, (d) repeating steps (a) to (c) for subsequent water samples in the series utilizing substantially identical first and second oxidizing conditions.

143. A process according to claim 142 wherein said oxidizing conditions at said first reaction zone are varied in a controlled and reproducible manner using at least one process selected from the group comprising:
(a) varying the flow rate of said sample;
(b) varying the rate of addition of an oxidizer to said sample;
(c) varying the flow rate of said sample through said first reaction zone where the sample is exposed to ultraviolet light;
(d) flowing said sample through said first reaction zone where the sample is exposed to ultraviolet light while varying the intensity of the ultraviolet light; and, (e) varying the rate of generation of an oxidizer in an apparatus which is in fluid communication with said sample.

144. A process according to claim 142 wherein at least one said oxidation conditions at said first reaction zone is selected from the following:
(a) an oxidizing condition that is above oxygen saturation conditions for said sample;
(b) an oxidizing condition that is maintained at a substantially constant level for a controlled period of time;
(c) an oxidizing condition that is established by applying electrolysis to said sample while it is passing through said first reaction zone; and, (d) an oxidizing condition that is established by applying electrolysis and ultraviolet light to said sample while it is passing through said first reaction zone.