JPH10274648A - Total carbon measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a total carbon value accurately by adding one salt out of a group of NH4 Cl, (NH4 )2 SO4 , and NH4 NO3 to a sample. SOLUTION: A TC combustion pipe 4 where an oxidation catalyst is filled in a TC oxidation reaction part 2 and a heating oven 5 are provided and a sample is injected from a TC sample injection port 3 to the TC combustion pipe 4. The outlet of the TC oxidation reaction part 2 is connected to a CO2 detection part 20 of a non-dispersion-type infrared spectrophotometer through an IC reaction part 6. At this time, one solution out of NH4 C1 , (NH4 )2 SO4 , and NH4 NO3 being added to a sample is neutral at normal temperatures and an inorganic body carbon in a sample cannot be decomposed due to it. The salts discharge NH3 at a high temperature and become acid, thus preventing an alkaline oxide being adhered on the catalyst from being built up and hence preventing the shape of a measurement peak from deteriorating and preventing sensitivity and reproducibility from decreasing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring TC (total carbon) in a liquid sample such as waste water, water, environmental water, and the like.
It is about measurement.

[0002]

2. Description of the Related Art In the conventional TOC measurement, the T
C and IC (inorganic carbon) are measured, and I
The TOC is determined by subtracting the C measurement. In the TC measurement, a sample having a high concentration of an alkali metal salt or an alkaline earth metal salt or an alkaline component (NaOH, Ca
It has been reported that measurement of a sample containing a large amount of (OH) ₂ ) causes a decrease in TC measurement sensitivity and a decrease in reproducibility of the sample. This is because when measuring a sample with a high concentration of an alkali metal salt or an alkaline earth metal salt, alkaline oxides such as Na ₂ O and CaO accumulate on the catalyst in the TC combustion tube, and when the accumulation amount increases, It is considered that this is because a part of CO ₂ generated by the combustion reaction of the organic matter in the sample reacts with those alkaline oxides.

[0003]

As a method for preventing such a problem, a method of neutralizing and decomposing the alkaline oxide accumulated on the catalyst by premixing an acid such as hydrochloric acid with the sample is considered. However, if the sample is mixed with an acid, the IC is decomposed to generate CO ₂ before the sample is injected into the TC combustion tube, and there is a problem that the IC is lost and the TC value decreases.

[0004] A method of regenerating the catalyst by frequently injecting an acid into the TC combustion tube during the measurement may be considered, but such a process requires much time and effort. There is such an annoyance. The present invention
It is an object of the present invention to provide a method for accurately measuring a TC value even for a sample having a high concentration of an alkali metal salt or an alkaline earth metal salt or a sample containing a large amount of alkaline components.

[0005]

According to the present invention, all carbon compounds in a liquid sample are converted to carbon dioxide by combustion and oxidation using a catalyst, and the total carbon content is measured by measuring the carbon dioxide content. In the total carbon measurement method to be determined, the sample is provided with at least one salt selected from the group consisting of ammonium chloride (NH ₄ Cl), ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) and ammonium nitrate (NH ₄ NO ₃ ). Is added. The amount of salt added such as ammonium chloride is preferably equal to or higher than the alkali concentration of the sample.

Since the solution of NH ₄ Cl or (NH ₄ ) ₂ SO ₄ is almost neutral at room temperature, the IC in the sample has NH ₄ Cl or (N
It is not decomposed by mixing H ₄ ) ₂ SO ₄ . NH ₄
Cl and (NH ₄ ) ₂ SO ₄ release NH ₃ in a high-temperature heating furnace to become acids such as HCl and H ₂ SO ₄ . These acids neutralize the alkaline oxides generated or deposited on the catalyst, thus preventing the accumulation of alkaline oxides on the catalyst.

[0007]

1 shows an example of a TOC meter to which the present invention is applied.
It is shown in (A). In the TOC meter, a non-dispersive infrared gas analyzer is connected to the TOC meter main body 1 as a detector 20. The TC of the aqueous solution in the sample in the TOC meter body 1 CO ₂
A TC oxidation reaction section 2 for converting the IC into CO ₂ and an IC reaction section 6 for converting the IC in the aqueous solution sample to CO ₂ are provided. An automatic sample injector 15 is provided to collect a certain amount of the aqueous solution sample and guide the sample to the TC oxidation reaction section 2 or the IC reaction section 6. The automatic sample injector 15 includes a 4-port valve 16 and a micro syringe 17. Have. A sample container 18 for the TOC meter is connected to the 4-port valve 16, and a certain amount of the aqueous solution sample in the sample container 18 is collected by the micro syringe 17 and guided to the TC oxidation reaction unit 2 or the IC reaction unit 6.

The TC oxidation reaction section 2 is provided with a TC combustion tube 4 filled with an oxidation catalyst and a heating furnace 5, and a sample is injected into the TC combustion tube 4 through a TC sample inlet 3. The outlet of the TC oxidation reaction section 2 is connected via an IC reaction section 6 to a CO ₂ detection section 20 of an NDIR (non-dispersive infrared spectrophotometer). The IC reaction section 6 is provided with an IC reactor filled with an IC reaction solution, and a liquid sample is injected from the automatic sample injector 15 via the IC sample inlet 7. IC reaction part 6
A dehumidifying and dust-removing unit 11 is provided in a flow path between the unit and the CO ₂ detecting unit 20.

In the CO ₂ detecting section 20, the sample cell 22 and the comparison cell 23 are set so that the same amount of light from the light source 21 is incident thereon.
Are arranged in parallel with each other.
CO ₂ corresponding to TC from the oxidation reaction section 2 is introduced together with the carrier gas, or IC 2 from the IC reaction section 6
CO ₂ is introduced by a carrier gas, which corresponds to. The comparison cell 23 is filled with an inert gas such as nitrogen or air that does not absorb infrared rays. The chopper 24 alternately interrupts light incident on the sample cell 22 and the comparison cell 23 from the light source 21, and adjusts the amount of light transmitted through the cells 22 and 23 and incident on the detector 27. Cells 22, 2
3 and the detector 27 are provided with light amount adjusters 25 and 26, respectively.
Is arranged. The detector 27 is a condenser microphone type detector, and an output signal of the detector 27 is obtained as an AC signal by rotation of the chopper 24, and its amplitude becomes an output value.

[0010] To obtain the TOC with this TOC meter, TC
Measurement and IC measurement are performed at staggered times. For example, if a certain amount of sample is first introduced into the TC oxidation reaction section 2 by the sample injection section 15, the signal obtained by smoothing the NDIR detection signal is a peak signal shown as "TC" in FIG. When the same fixed amount of the sample is injected into the IC reaction unit 6 by the sample injection unit 15, "
A signal having a peak as shown as IC "is obtained.
The TOC value is obtained by calculating the difference between the integrated values of the two peaks.

In the TC measurement in the TOC measurement, as an example of a measurement result of a sample having a high concentration of an alkali metal salt or an alkaline earth metal salt or a sample containing a large amount of an alkaline component, a 500 ppm C aqueous solution of sodium carbonate was used as a sample. The results are shown in FIG.

FIG. 2 (A) corresponds to a conventional measuring method, and shows the peaks of TC measured when the sample aqueous solution is repeatedly measured at intervals of 2 to 3 minutes.
Following the six measurements of (a-1), six measurements of (a-2) were performed, followed by the six measurements of (a-3). As the number of measurements increases, the shape of the measurement peak deteriorates. However, the area has not yet decreased much. This is because as the measurement is continued, alkaline oxides such as Na ₂ O accumulate on the catalyst, and part of the CO ₂ generated by the combustion reaction of TC in the sample decomposes after reacting with the alkaline oxides. It is thought that it is to come out. In the measurement performed here for about one hour, CO ₂
Although the sensitivity does not decrease, the C that reacted with the alkaline oxide accumulated in the catalyst form when the measurement was continued for a longer time
It is expected that O ₂ will be trapped, leading to a decrease in sensitivity. In fact, it has been pointed out that long-term measurement causes a decrease in sensitivity.

On the other hand, FIG. 2B shows the same sample (5
(00 ppm C aqueous solution of sodium carbonate), and the results were obtained by mixing 2000 ppm of NH ₄ Cl. In this case, even if the measurements (b-1), (b-2), and (b-3) are continued for approximately the same time as in FIG. Thus, by adding NH ₄ Cl to the sample, Na ₂ Cl was added on the oxidation catalyst.
It is considered that the accumulation of alkaline oxides such as O is suppressed.

[0014]

According to the present invention, when measuring a sample having a high concentration of an alkali metal salt or an alkaline earth metal salt or a sample containing a large amount of alkaline components, NH ₄ Cl, (NH ₄ ) ₂ S
By adding a compound that generates an acid by thermal decomposition, such as O ₄ or NH ₄ NO ₃ , alkali oxides are prevented from adhering to the oxidation catalyst during TC measurement, and the shape of the measurement peak is deteriorated. This can prevent a decrease in sensitivity and reproducibility. In addition, by preventing the adhesion of alkali oxides to the oxidation catalyst,
It is possible to save the trouble of performing the oxidation catalyst regeneration treatment using an acid, which has been conventionally performed.

[Brief description of the drawings]

FIG. 1A is a configuration diagram showing a TOC meter as an example of a measuring apparatus to which the present invention is applied, and FIG. 1B is a diagram showing TC and IC measurement peaks when measuring TOC using the TOC meter. FIG.

FIG. 2 is a diagram showing measurement peaks as a result of TC measurement of a sample having a high alkali salt concentration (a 500 ppm C aqueous solution of sodium carbonate). FIG. (B) indicates that the sample
The present invention corresponds to the case where the measurement is performed by adding 00 ppm of (NH ₄ ) ₂ SO ₄ .

[Explanation of symbols]

2 TC oxidation reaction section 6 IC reaction section 15 Automatic sample injector 18 Sample container 20a NDIR 32,33 cell of CO ₂ detection section

Claims (1)

[Claims] 1. A total carbon measurement method for converting all carbon compounds in a liquid sample to carbon dioxide by burning and oxidizing the mixture using a catalyst and measuring the carbon dioxide amount to obtain the total carbon amount. Total carbon measurement method, wherein at least one salt selected from the group consisting of ammonium chloride, ammonium sulfate and ammonium nitrate is added to the mixture.