JPH10160675A - Underwater nitrogen measurement device - Google Patents

Abstract

(57) [Problem] To enable the correction of interference due to CO ₂ when measuring by converting total nitrogen in an aqueous solution sample to NO. SOLUTION: Detection outputs of an NDIR 8 and a NO detection unit 10 are amplified by an analog amplifier 12 respectively, and then A / A
The signal is converted into a digital signal by the D
It is taken into 6. The CPU 16 uses the NDIR8 CO
₂ Calculate the CO ₂ interference amount based on the measured value, and
To correct the CO ₂ interference of the NO measurement value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an underwater nitrogen measuring apparatus for measuring total nitrogen (TN) in an aqueous solution sample.

[0002]

2. Description of the Related Art An underwater nitrogen measuring device collects a certain amount of an aqueous solution sample, injects it into an oxidation reaction section and vaporizes it, and in the oxidation reaction section, removes all nitrogen contained in the sample into NO.
Convert to The vaporized sample gas is converted into N by the carrier gas.
It leads to the O detection section and performs NO detection. As the NO detection unit, a chemiluminescence detection system is generally used, but it can also be detected by a non-dispersive infrared spectroscopy system.

[0003]

An aqueous solution sample often contains a carbon component. The oxidation reaction section that converts the nitrogen component to NO converts the nitrogen component into NO by bringing the sample water into contact with the oxidation catalyst heated by the electric furnace, but also converts the carbon component into CO ₂ . NO detector of chemiluminescent is advantage of the chemiluminescence by the reaction of NO with ozone, if this time CO ₂ coexist, CO ₂ inhibits the reaction between NO and ozone, NO
CO ₂ so that the measured value is smaller than the actual NO concentration
Receive interference.

[0004] Non-dispersive infrared spectroscopy can also be used to detect NO. This utilizes the absorption of NO in the infrared region. However, since the absorption band of NO and the absorption band of CO ₂ overlap, this time the measured NO
Subject to CO ₂ interference to be greater than the concentration. Therefore, an object of the present invention is to make it possible to correct interference due to CO ₂ when measuring by converting all nitrogen in an aqueous solution sample to NO.

[0005]

The underwater nitrogen measuring apparatus of the present invention is provided with a heated oxidation catalyst, catalytically pyrolyzes an aqueous solution sample to vaporize it, and converts all the nitrogen in the sample to NO.
An oxidation reaction section that converts all carbon to CO ₂ , a sample injection section that collects a certain amount of an aqueous solution sample and injects the same into the oxidation reaction section,
A carrier gas supply unit for supplying a carrier gas to the oxidation reaction unit; a NO detection unit for detecting NO in the sample vaporized gas sent together with the carrier gas from the oxidation reaction unit;
C that detects CO ₂ in the sample vaporized gas detected by the detector
O ₂ detection unit and C for NO detection in NO detection unit
A data processing device that calculates the amount of O ₂ interference based on the detection value of the CO ₂ detection unit, corrects the NO detection value, and outputs the corrected NO detection value. As the oxidation catalyst used in the oxidation reaction section, a metal oxide or a noble metal catalyst can be used.

[0006] When the NO detector is of a chemiluminescent type, CO
_{Although the} NO measurement value appears smaller than the actual NO concentration due to the _two interferences, the data processing device corrects the CO ₂ interference amount based on the detection value of the CO ₂ detection unit. If NO detector is a non-dispersive infrared analysis method, NO by CO ₂ interference
Although the measured value appears larger than the actual NO concentration, the CO ₂ interference is also corrected based on the detected value of the CO ₂ detector.
By performing the data processing in this manner, the correct total nitrogen concentration is obtained by correcting the CO ₂ interference.

[0007]

FIG. 1 shows an embodiment. Reference numeral 2 denotes an oxidation reaction section, and a reaction tube 4 filled with an oxidation catalyst of a metal oxide or a noble metal catalyst is heated to a predetermined temperature by an electric furnace 6. A certain amount of an aqueous solution sample is collected by a sample injection unit (not shown) and injected into the reaction tube 4 from above. The aqueous solution sample injected into the reaction tube 4 is thermally decomposed and vaporized by contact with the heated oxidation catalyst, and the nitrogen component in the sample is converted into NO, and at the same time, the carbon component is converted into CO ₂ . Air from which nitrogen and carbon are removed is supplied as a carrier gas from the upper part of the reaction tube 4.
The sample gas vaporized in the reaction tube 4 is sent by a carrier gas, and guided to an NDIR (non-dispersive infrared spectrophotometer) 8 as a CO ₂ detecting unit, where the CO ₂ concentration is measured. NDI
The sample gas that has passed through R8 is led to the chemiluminescence NO detection unit 10, where the chemiluminescence due to the reaction between NO and ozone is detected, and the NO concentration is measured. The sample gas that has passed through the NO detection unit 10 is exhausted.

The detection outputs of the NDIR 8 and the NO detection unit 10 are amplified by an analog amplifier 12,
The data is converted into a digital signal by the D converter 14, and is taken into the CPU 16 for realizing the function of the data processing device of the present invention. The CPU 16 calculates the amount of CO ₂ interference based on the measured value of CO ₂ by the NDIR 8,
Correct the measured value for CO ₂ interference.

[0009] CO ₂ interference is that the CO ₂ concentration in the sample gas is 3
Up to about 0% by volume is proportional to the CO ₂ concentration as shown in FIG. The higher the CO ₂ concentration, the smaller the measured interference NO. If the NO detector is a chemiluminescent detector, the total nitrogen concentration measured by the NO detector 10 is calculated as T
Np (ppm), the measured CO ₂ concentration by _NDIR8 is D _CO2M , and the correction coefficient is α, the corrected T
The N concentration TNr (ppm) is as follows: TNr = (1 + α · D _CO2M ) · TNp (1) Here, the correction coefficient α is as follows: α = {(N + 1) / N} · (1 / D _CO2 ) · {(TN ₁ −TN ₂ ) / TN ₂ } (2) Here, N is a dilution ratio, TN ₁ is a TN measurement value when diluted with N ₂ , TN ₂ is a TN measurement value when diluted with a diluent gas containing CO ₂ , and D _CO2 is CO ₂ used for dilution. This is the CO ₂ concentration of the diluent gas contained.

The equations (1) and (2) used for this correction are derived as follows. Until the CO ₂ concentration in the sample gas is about 30% (most samples fall within this range)
Since there is a proportional relationship between the CO ₂ interference and the TN measurement value, TNc = α · D _CO2M (3) where TNc is the ratio of the CO ₂ interference to the TN measurement value. At this time, the actual concentration of TN is set to TN
r, where TNp is the measured value, TNc = (TNr−TNp) / TNp (4) Substituting equation (4) into equation (3) gives the above (1)
An expression is obtained.

On the other hand, when equation (1) is solved for α, α = (1 / D _CO2M ) · {(TNr−TNp) / TNp} (5) Here, the concentration D _CO2 of the dilution gas and the measured value D
_CO2M the dilution ratio is N: Since (N + 1) is, the _{D CO2M = {N / (N} + 1)} · D CO2 (6). Since TNr is replaced by TN concentration TN ₁ when diluted with N ₂ and TNp is replaced with TN concentration TN ₂ when diluted with a gas containing CO ₂ , the above equation (2) is obtained from equations (5) and (6). Can be

Next, the operation of this embodiment will be described with reference to FIG. FIG. 3A shows an operation for deriving the correction coefficient α. A sample gas obtained by diluting a standard gas having a known NO concentration at a fixed ratio with N ₂ gas is introduced into a detector of the analyzer, and the TN measurement value (TN ₁ ) at that time is recorded in a nonvolatile memory by a CPU. .

[0013] The same standard gas is replaced with a gas having a known CO ₂ concentration instead of N ₂ gas as a diluting gas, and the same measurement is performed. The TN measurement value (TN ₂ ) at that time is measured by a CPU in a nonvolatile memory. To record. CO _{2 of} the gas used for dilution
The concentration D _CO2 and the dilution ratio N are input to the CPU, and the correction coefficient α is calculated by the equation (2) using the measured values TN ₁ and TN ₂ of the standard gas.

FIG. 3B shows an operation of measuring an unknown sample and correcting CO ₂ interference. A certain amount of the unknown sample is injected into the oxidation reaction section, and the CO ₂ measurement value D _CO2M measured by the NDIR ₈ and the measurement value TNp measured by the NO detection section 10 are transferred to the CP via the analog amplifier 12 and the A / D converter 14, respectively.
The correction TN concentration TNr is obtained and output by performing a correction calculation according to the equation (1) using the correction coefficient α previously obtained in FIG.

[0015] Similar to the CO ₂ detector is a NO detection unit N
DIR can be used. In that case, the CO ₂ interference works in the direction of increasing the NO measurement value. In such a case, the correction is performed by subtracting from the NO measurement value corresponding to the CO ₂ measurement value. Since the CO ₂ interference in is not linear with respect to CO ₂ concentration, may be recorded as data in advance measures the relationship between the CO ₂ concentration and the amount of interference, CO ₂
The amount of interference is derived from the recorded data and corrected according to the measured value. The CO ₂ measurement is performed simultaneously with or at a different time from the NO measurement, but in any case, the CO ₂ measurement is performed using the same sample vaporized gas as used for the NO measurement.

[0016]

According to the present invention, the CO ₂ measurement is performed together with the NO measurement on the same sample, and the CO ₂ interference in the NO measurement value is corrected according to the CO ₂ concentration. You can ask.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment.

FIG. 2 is a diagram showing a relationship between a CO ₂ concentration and an interference amount.

3A and 3B are flowcharts showing the operation, in which (A) shows a procedure for obtaining a correction coefficient α, and (B) shows a procedure for measuring and correcting an unknown sample.

[Explanation of symbols]

2 Oxidation reaction unit 8 NDIR for detecting CO ₂ 10 Chemiluminescence detecting unit for detecting NO 16 CPU

Claims (1)

[Claims] 1. An oxidation reaction section comprising a heated oxidation catalyst, catalytically decomposing and vaporizing an aqueous solution sample, converting all nitrogen in the sample to NO and converting all carbon to CO ₂ , A sample injection section for collecting a certain amount and injecting the sample into the oxidation reaction section; a carrier gas supply section for supplying a carrier gas to the oxidation reaction section; and a sample vaporized gas sent together with the carrier gas from the oxidation reaction section. and NO detector for detecting the NO of the NO and CO ₂ detector for detecting the CO ₂ in the sample vaporization gas to be detected by the detecting unit, wherein the interference amount of CO ₂ to NO detection in NO detection unit CO ₂ Calculated based on the detection value of the detection unit, NO
An underwater nitrogen measuring device comprising: a data processing device that corrects and outputs a detected value.