JP2005140643A - Method and detector for detecting toc - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a TOC measuring method and instrument of high sensitivity hardly affected by temperature fluctuation. <P>SOLUTION: CO<SB>2</SB>in sample water generated in an oxidation reaction part 6 is absorbed into ethanol amine filled in a chamber 14 via a gas permeable film 12 in a CO<SB>2</SB>migration part 8. After a set time lapses, a valve 18 is switched to a drain side to block flow-in of the sample water into the CO<SB>2</SB>migration part 8. A potential set for electrolyzing only a reaction product of the CO<SB>2</SB>and the ethanol amine is imparted to a working electrode of an electrode 11 for coulometry to conduct the coulometry for the ethanol amine. A CO<SB>2</SB>amount accumulated in the ethanol amine is measured as a molar quantity. Since the CO<SB>2</SB>molar quantity corresponds to a molar quantity of the TOC, a TOC concentration is found easily, and the TOC concentration is determined based on a flow rate of the sample water flowing within the set time and the measured TOC molar quantity. The ethanol amine is reproduced because the CO<SB>2</SB>accumulated in the ethanol amine is discharged by the execution of the coulometry. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a TOC (total organic carbon) measurement method and apparatus used as a means for measuring the degree of contamination of environmental water, tap water, pure water or ultrapure water.

One method for measuring TOC is, for example, adding potassium peroxodisulfate to a sample solution and heating to convert the organic matter to CO _2, and then converting the sample solution into CO deionized water through a gas permeable membrane. ₂ is shifted to, to quantify the amount of CO ₂ from a change in the electrical conductivity of the deionized water, there is a method of determining the TOC value (see Patent Document 1.).

As a specific example, for example, a sample containing an organic compound is oxidized, and the difference between the electrical conductivity before oxidation and the electrical conductivity after oxidation of the sample is measured for electrical conductivity having at least two electrodes. By placing the cell in the pre-oxidation position and the post-oxidation position and detecting it using a differential conductivity meter that outputs the difference in the electrical conductivity of the sample between the positions of both conductivity measuring cells, There is a method of measuring the amount of increase in electrical conductivity caused by oxidative decomposition and quantifying the amount of TOC in the sample from the amount of increase in electrical conductivity (see Patent Document 2).
Japanese Patent No. 2510368 JP 2001-281189 A

In the case of measuring the TOC value by transferring CO ₂ produced by conversion from organic substances from sample water to deionized water, if the CO ₂ concentrations of the sample water and deionized water are equal, an equilibrium state occurs, and the produced CO ₂ There is a problem that a part of is not used for electrical conductivity measurement and the maximum sensitivity of TOC measurement is limited.
Moreover, since electrical conductivity has large temperature dependence, the lower limit of quantification in the case of measuring a trace amount TOC value is restricted.
Furthermore, since the electrical conductivity measurement does not directly measure CO ₂ in principle, it is necessary to perform span calibration using a standard solution, and it is difficult to produce a standard solution having a very low concentration.

  Accordingly, an object of the present invention is to provide a TOC measurement method and apparatus that are highly sensitive and less affected by temperature fluctuations.

Measuring method of the present invention, the organic matter oxidative decomposition to convert the CO _2, after which the resulting CO ₂ and transferred to the CO ₂ absorbent, the CO ₂ absorbing agent is quantified by absorbed CO ₂ amount coulometric method Thus, the TOC measurement method is characterized in that TOC measurement is performed.
A solution of amines can be used as the CO ₂ absorbent.

Coulometry (coulometric analysis) will be described.
Coulometry used in the present invention is constant potential coulometry. The apparatus used for constant potential coulometry is a constant potential electrolysis apparatus with a coulometer (coulometer) attached. The electrode of the device includes an electrode for oxidation and a working electrode, and the potential of the working electrode is controlled by a potentiostat.
In coulometric electrolysis, the concentration and current value logarithmically decrease with time during electrolysis, and finally a residual current resulting from the indicator electrolyte. The limit of detection is 2 milliequivalent to 0.5 milliequivalent although it depends on the residual current level.
The potential of the working electrode is set to such a potential that only the component to be quantified is electrolyzed.

The measuring apparatus of the present invention comprises an oxidation reaction part that oxidizes and decomposes organic matter in sample water to convert it into CO ₂ , and a sample water introduced from the oxidation reaction part is brought into contact with a CO ₂ absorbent through a gas permeable membrane. comprises a CO ₂ transition to shift the CO ₂ in the sample water in the CO ₂ absorber, an electrode for coulometry provided in CO ₂ absorbent side of the CO ₂ transition portion, quantified CO ₂ by coulometry method A CO ₂ quantification unit.

Since the organic matter in the sample is absorbed in the oxidative decomposition to convert the CO ₂ CO ₂ absorbent has to perform the TOC measurement can utilize generated CO ₂ for all measurements. In addition, coulometry, combined with its low temperature dependence, enables highly sensitive measurements.
In addition, coulometry does not require span calibration in principle, and therefore adjustment, storage, and evaluation of standard solutions can be omitted.

As shown in FIG. 1, the TOC measuring apparatus according to the present invention includes a pH adjusting unit 2 that adjusts the pH of sample water to acid, and an IC removing unit that removes IC (inorganic carbon) in the acidified sample water. 4, and the oxidation reaction unit 6 for converting the water sample of organics after IC is removed by oxidative decomposition to CO _2, CO ₂ proceeds to shift the CO ₂ produced by the oxidation reaction unit 6 in the CO ₂ absorbent a part 8, and a coulometric circuit section 10 for quantifying the coulometric method absorbed CO ₂ amounts to CO ₂ absorbent.

[Example]
Hereinafter, an embodiment will be described in detail with reference to FIG.
As a configuration of the apparatus, a pH adjustment unit 2, an IC removal unit 4, an oxidation reaction unit 6, a CO ₂ transfer unit 8 and a coulometry circuit unit 10 are arranged from the upstream side (the left side in the figure) along the flow of the sample water. Yes.
For example, the pH adjuster 2 adjusts the pH of the sample water to be acidic by adding a certain proportion of an inorganic acid, for example, phosphoric acid, as a pH adjuster to the collected sample water.
The IC removing unit 4 is connected to the outlet channel of the pH adjusting unit 2, and the sample water and distilled water are in contact with each other through the gas permeable membrane. By bubbling air in the distilled water, the IC in the sample water is transferred to air, and the IC in the sample water is removed. The CO ₂ transferred to the air is adsorbed and removed by the CO ₂ absorber 5. The CO ₂ absorber 5 contains an amine solution such as ethanolamine.
The oxidation reaction unit 6 is connected to the outlet channel of the IC removal unit 4, and potassium peroxodisulfate is used as an oxidizing agent for promoting the oxidation of organic substances in the sample water in the channel of the IC removal unit 4 and the oxidation reaction unit 6. Is added to the sample water. The oxidation reaction unit 6 has a structure in which a tube through which sample water flows is wound around a UV lamp 7, and by reacting dissolved oxygen and organic matter by irradiating the sample water with ultraviolet rays, the organic matter is converted into CO ₂ . To do.

The CO ₂ transfer section 8 is composed of a sample water chamber 16 and a CO ₂ absorbent chamber 14, which are partitioned by a gas permeable membrane 12 indicated by a broken line. Although the material of the gas permeable film 12 is not limited, for example, it is an organic resin film such as polytetrafluoroethylene having continuous pores. Chamber 14 for CO ₂ absorber is filled with ethanolamine solution as a CO ₂ absorbent. The concentration of the ethanolamine solution is, for example, 5%.
In the CO ₂ transfer unit 8, CO ₂ generated in the oxidation reaction unit 6 is absorbed by the CO ₂ absorbent through the gas permeable membrane 12. In the CO ₂ transfer section 8, only CO ₂ in the sample water flowing into the sample water chamber 16 permeates the gas permeable membrane 12 and moves to the chamber 14 side, and is absorbed by the ethanolamine solution filled in the chamber 14. Is done. The sample water from which CO ₂ has been removed is discharged to the outside. Ethanolamine has a strong CO ₂ absorption capacity and can quickly shift CO ₂ .
A valve 18 is provided on the flow path between the oxidation reaction unit 6 and the CO ₂ transfer unit 8 so that the flow of sample water into the CO ₂ transfer unit 8 can be arbitrarily interrupted.

The CO ₂ absorbent chamber 14 is provided with a coulometric electrode 11 connected to the coulometric circuit 10. By applying a potential to the working electrode (not shown), the ethanolamine in the chamber 14 is supplied. Coulometry can be performed. The working electrode is connected to a potentiostat so that the potential can be adjusted arbitrarily.

The operation of this embodiment will be described below.
The sample water supplied to the TOC measuring device is adjusted so that the pH becomes acidic by adding a pH adjusting agent such as phosphoric acid in the pH adjusting unit 2, and then the IC is removed by the IC removing unit 4. After that, an oxidizing agent is added and introduced into the oxidation reaction unit 6. In the oxidation reaction unit 6, the sample water is irradiated with ultraviolet rays from a UV lamp 7, whereby organic substances are oxidized and decomposed and converted to CO ₂ .

Sample water containing CO ₂ generated in the oxidation reaction unit 6 is introduced into the chamber 16 of the CO ₂ transfer unit 8 for a certain period of time. This introduction time is set in advance by the operator. During the set time, CO ₂ in the sample water permeates the gas permeable membrane 12 and is absorbed and accumulated in the ethanolamine in the chamber 14.

After the set time elapses, the valve 18 is switched to the drain side to block the sample water from flowing into the CO ₂ transition section 8. Then, coulometry of ethanolamine is performed by applying a potential set to electrolyze only the reaction product of CO ₂ and ethanolamine to the working electrode of the electrode 11 for coulometry. The amount of CO ₂ accumulated in ethanolamine is measured as a molar amount. Since the molar amount of CO ₂ corresponds to the molar amount of TOC, the TOC concentration can be easily determined. The TOC concentration is determined from the flow rate of the sample water flowing within the set time and the measured TOC molar amount. Is done. Since CO ₂ accumulated in ethanolamine is discharged by performing coulometry, ethanolamine is regenerated.
Thus, the measurement for one cycle is completed, and the measurement for the next cycle is started.

According to this embodiment, since CO ₂ is accumulated in ethanolamine, the quantitative error of CO ₂ can be reduced by increasing the sample water flow rate (measurement time) for one set measurement cycle, and the sensitivity of measurement. Can be increased.
In CO ₂ transition 8, since through the gas permeable membrane 12 and the sample water and CO ₂ absorbent is in contact, can be efficiently shifting the CO ₂ in the CO ₂ absorbent, CO ₂ transition 8 The volume of can be reduced.

As another measurement method of this embodiment, there is a method in which the amount of CO ₂ is quantified by performing coulometry of the chamber 14 containing ethanolamine while flowing sample water through the CO ₂ transition section 8 and integrating the current value. It is done. Then, after the preset time has elapsed, if the sample water is blocked from flowing into the CO ₂ transition section 8 and the coulometry is continued as it is, all of the CO ₂ absorbed by the ethanolamine is removed, and the current value is almost equal. It becomes a constant value close to zero. By integrating the current value until the current value becomes a constant value close to almost zero, the amount of CO ₂ contained in the sample water that has flowed within the set time can be quantified. If the current value becomes a constant value close to zero, all the CO ₂ absorbed by ethanolamine has been removed, and ethanolamine has been regenerated.

The mounting position of the valve 18 is not particularly limited, such as upstream of the pH adjusting unit 2 or between the pH adjusting unit 2 and the IC removing unit 4.
As an organic oxidation method, known oxidation methods other than those by ultraviolet irradiation may be used alone or in combination.
As an IC removal method of the IC removal unit 4, a method in which an IC is absorbed by an IC absorbent using a gas permeable film can also be used.

It is a channel figure showing the composition of the present invention roughly. It is a flow chart which shows the composition of one example.

Explanation of symbols

2 pH adjustment unit 4 IC removal unit 5 CO ₂ absorber 6 Oxidation reaction unit 7 UV lamp 8 CO ₂ transition unit 10 Coulometry circuit unit 11 Coulometry electrode 12 Gas permeable membrane 14 CO ₂ absorbent chamber 16 Sample water chamber 18 Open / close valve

Claims (3)

The organics water sample oxidative decomposition to convert the CO _2, after which the resulting CO ₂ and transferred to the CO ₂ absorbent, TOC measured by quantifying the coulometric method the amount of CO ₂ CO ₂ absorbent has absorbed A method for measuring TOC, wherein: The TOC measurement method according to claim 1, wherein the CO ₂ absorbent is a solution of amines. An oxidation reaction part that oxidatively decomposes organic matter in the sample water to convert it into CO ₂ ;
A sample water led from the oxidation reaction part is brought into contact with a CO ₂ absorbent through a gas permeable membrane, and a CO ₂ transfer part for transferring CO ₂ in the sample water to the CO ₂ absorbent;
A TOC measuring apparatus comprising a coulometric electrode provided on the CO ₂ absorbent side of the CO ₂ transfer part, and a CO ₂ quantifying part for quantifying CO ₂ by a coulometric method.

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