JP2006201104A - Total nitrogen measuring method and system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly accurately determine the concentration of total nitrogen by easily reducing nitric acid to nitrous acid. <P>SOLUTION: In an oxidative degradation reaction part 12, a potassium peroxodisulfate solution 2 and a sodium hydroxide solution 3 are added to a nitrogen compound sample, then heated to approximately 120°, and oxidatively degraded to nitric acid ions. Sample water containing nitric acid ions is supplied for a reaction container 15 of a reduction reaction part 23. Potassium iodide is, for example, added to the sample water as a reduction accelerator 6. By irradiating ultraviolet rays by an ultraviolet lamp 14, the nitric acid ions are reduced to nitrous acid ions. Then a naphthyl ethylenediamine solution 5 is added to measure absorbance of the sample water of which colors have developed. An arithmetic processing part 18 converts the absorbance measured by a measuring part 16 into the concentration of total nitrogen and displays it on a display part 19. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method and apparatus for measuring total nitrogen contained in sample water such as waste water, sewage, environmental water, and plant water. In particular, the present invention relates to a total nitrogen measurement method in which a nitrogen compound in a sample water is oxidatively decomposed to nitrate ions, then reduced to nitrite ions, and total nitrogen is quantified by an absorptiometric method using a coloring reagent.

  In Japan, the method for measuring total nitrogen, which expresses the total amount of nitrogen compounds in wastewater from factories, etc. in terms of nitrogen concentration, is stipulated in the Japanese Industrial Standards (JIS) “Testing methods for wastewater discharged from factories”. The “ultraviolet absorptiometry” (see Non-Patent Document 1) is most commonly used because of its simplicity.

  In this nitrogen compound measurement method, the sample water to which alkaline potassium peroxodisulfate as an oxidizing agent is added is autoclaved, that is, the sample is thermally decomposed to nitrate ions at high temperature and high pressure, and then the pH is adjusted to 2 to 3. In this method, the total nitrogen concentration is quantified by measuring ultraviolet absorbance at a wavelength of 220 nm. An apparatus for realizing this method is required to have pressure resistance and heat resistance, and has a special material and design.

On the other hand, a total nitrogen measuring device adopting an “ultraviolet oxidative decomposition method” as a method for decomposing a sample into nitrate ions is also commercially available. In this method, improvement of lowering the temperature and pressure is being promoted and used. That is, the temperature required for the ultraviolet oxidation is lowered from 120 ° C. to about 60 ° C., and the pressure can also be performed under normal pressure.
In both cases, the nitrogen compound is oxidatively decomposed to nitrate ions by oxidative decomposition, and then an acid for measuring absorbance is added, and the total nitrogen in the sample is measured by measuring the absorbance near 220 nm.

  In the autoclave method and the total nitrogen measuring method by ultraviolet oxidative decomposition, it is common to measure the total nitrogen concentration by measuring the absorbance of ultraviolet rays near 220 nm. For this reason, samples containing metal ions and bromide ions that absorb in the ultraviolet range give an error in the measured value. At the same time, potassium peroxodisulfate used as an oxidizing agent also absorbs near 220 nm, so the remaining amount after oxidation is measured. The absorbance measurement at 220 nm has a problem that it is affected by substances having absorption in the ultraviolet region. In addition, regarding the measurement accuracy, it is difficult to quantify the highly processed sample in a low concentration range of 0.1 mg or less by the absorbance measurement method at 220 nm.

  To avoid this problem, an alkaline solution of potassium peroxodisulfate was added to oxidize the nitrogen compounds to nitrate ions. The oxidized sample was passed through a copper-cadmium column and reduced to nitrite ions, and then absorbed with naphthylethylenediamine. There is a copper-cadmium column reduction method in which the total nitrogen concentration is quantified from absorbance at around 540 nm by a photometric method (see Non-Patent Document 2).

As a method for reducing nitrate ions in water to nitrite ions, a method of irradiating ultraviolet rays has been proposed (see Non-Patent Document 3). In that case, the pH of the sample water irradiated with ultraviolet rays is said to give a good result of 8.0. In addition, since it is difficult to obtain a sufficient reaction rate only by ultraviolet irradiation, the irradiation time of ultraviolet rays is lengthened by winding the sample in a coil shape around the ultraviolet lamp.
JIS K0102 45.2 JIS K0102 45.4 K. Takeda and K. Fujiwara, Analytica Chimica Acta, 276 (1993) 25-32

  The copper-cadmium column reduction method is not suitable for on-line measurement because it requires the use of a copper-cadmium column, which is a hazardous substance, and the column must be regenerated frequently for activation. It was.

In addition, the method of reducing nitrate ions to nitrite ions only by ultraviolet irradiation not only has a low reaction rate, but also because the “ultraviolet oxidative decomposition method” is used to oxidize nitrogen compounds to nitrate ions. As can be seen, UV irradiation acts on both reduction and oxidation. Therefore, it is difficult to convert all the nitrogen compounds in the sample into nitrate ions or nitrite ions simply by irradiating the sample with ultraviolet rays, and there is a possibility that both ions are in an equilibrium state.
The present invention has been made in view of such a problem, and an object of the present invention is to provide a total nitrogen concentration determination method and apparatus that are simple, excellent in maintainability, and practical.

The total nitrogen measurement method of the present invention comprises a reduction step of reducing nitrate ions to nitrite ions after oxidative decomposition of nitrogen compounds in sample water to nitrate ions, and a spectrophotometric method using a coloring reagent for nitrite ions In the total nitrogen measurement method in which the total nitrogen is quantified by the above, in the reduction step, a reduction accelerator is added to the sample water and light in the ultraviolet region is irradiated while heating.
The reduction step may be performed under neutral conditions, but is preferably performed under alkaline conditions in order to increase the reaction rate.

  The total nitrogen measuring device of the present invention that realizes the total nitrogen measuring method of the present invention includes an oxidative decomposition reaction unit that oxidatively decomposes nitrogen compounds in sample water into nitrate ions, and an ultraviolet region while heating in the presence of a reduction accelerator. A reduction reaction unit that reduces nitrate ions to nitrite ions by irradiating the light, a measurement unit that measures the absorbance of the sample water from the reduction reaction unit by a spectrophotometric method using a coloring reagent, and a measurement unit And an arithmetic processing unit that obtains the total nitrogen concentration from the obtained absorbance.

The reduction reaction in the reduction reaction part is preferably carried out under alkaline conditions.
The oxidative decomposition reaction unit is, for example, an oxidant and an alkali added to sample water, and oxidatively decomposes nitrogen compounds to nitrate ions by an autoclave method or ultraviolet irradiation.
The measurement unit measures the absorbance in the visible region by coloring nitrite ions by an absorptiometric method such as ethylenediamine method.

The reduction accelerator used when reducing nitrate ions to nitrite ions by ultraviolet irradiation is preferably one containing iodine ions in order to increase the reaction rate, and potassium iodide, sodium iodide or other iodide salts are used. be able to.
The ultraviolet lamp used for ultraviolet irradiation may be a lamp that generates ultraviolet rays, such as a low-pressure mercury lamp, a high-pressure medium-pressure mercury lamp, or the like.

Addition of a reduction accelerator to the nitrogen compound sample water, and irradiation with ultraviolet light while heating to reduce nitrate ions to nitrite ions is highly sensitive and harmful to the environment, such as cadmium. Total nitrogen can be measured without using a simple reduction column. In this reduction process by ultraviolet irradiation, a reduction accelerator is added, so that the oxidation reaction is suppressed and the reduction reaction proceeds exclusively.
The reaction rate is increased by carrying out the reduction reaction under alkaline conditions.
When iodine ion is added as a reduction accelerator, the reduction reaction is completed in a short time.

  The total nitrogen measuring device includes an oxidative decomposition reaction unit that oxidatively decomposes nitrogen compounds to nitrate ions, a reduction reaction unit that reduces nitrite ions in the presence of a reduction accelerator, a measurement unit, and an arithmetic processing unit. A simple and highly maintainable high-precision measuring device can be configured.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic diagram showing the configuration of the total nitrogen measuring unit.
Reference numeral 1 denotes a sample adjustment tank, in which sample water is constantly flowing, and is connected to one port of the 8-port valve 10b via a tube 29, and sample water is collected during measurement.
The other port of the 8-port valve 10b includes a container for storing measurement calibration water (span solution) 8 and pure water 9, an oxidation decomposition reaction unit 12, a sample inlet / outlet port 25 of the reduction reaction unit 23, and a measurement unit. 16, the waste port 11 is connected, and the common port of the 8-port valve 10b is connected to one port of the other 8-port valve 10a.

A container for storing the reagents 2 to 6 and the air release port 7 are connected to each port of the 8-port valve 10a by piping.
In this example, reagent 2 is a potassium peroxodisulfate solution, reagent 3 is an aqueous sodium hydroxide solution, reagent 4 is a sulfanilamide / hydrochloric acid solution, reagent 5 is an N- (1-naphthyl) ethylenediamine solution, and reagent 6 is a reduction accelerator. Suppose that it is an agent.

  A syringe pump 17 is connected to a common port of the 8-port valve 10a. The syringe pump 17 is driven by a motor 27, and sample water, a reagent, and the like are taken into the syringe pump 17 via the 8-port valves 10a and 10b. In addition, the reagent can be sent to the reduction reaction unit 23 and the measurement unit 16 and a reagent can be added to the sample water in the syringe pump 17.

  Reference numeral 12 denotes an oxidative decomposition reaction unit that decomposes nitrogen compounds in the sample into nitrate ions. This is not particularly limited as long as it can oxidatively decompose nitrogen compounds to nitrate ions, and may be an autoclave (steam sterilizer) or an ultraviolet lamp.

  Reference numeral 23 denotes a reduction reaction part for reducing the nitrate ion solution after oxidative decomposition to nitrite ions. The reaction vessel 15 is provided with an ultraviolet lamp 14 such as a low-pressure mercury lamp at the center of the reaction vessel 15. Includes a heater 13 for adjusting the temperature. Heating by the heater 13 is desirably performed at 100 ° C. or lower.

  Nitrate ion-containing sample water is supplied from the oxidative decomposition reaction unit 12 into the reaction vessel 15 of the reduction reaction unit 23. For example, potassium iodide is added as a reduction accelerator 6 to the sample water, and ultraviolet rays are irradiated by an ultraviolet lamp 14. To reduce nitrate ions to nitrite ions.

The sample inlet / outlet port 25 of the reaction vessel 15 is connected to one port of the valve 10b.
The measuring unit 16 measures the absorbance of the coloring reaction solution by the N- (1-naphthyl) ethylenediamine solution 5 in the sample water after the completion of the reduction reaction. For example, a light source that irradiates the sample cell with light having a wavelength of 540 nm (for example, 540 nm), a sensor that detects the light transmitted through the sample cell, and the like.
The arithmetic processing unit 18 converts the absorbance measured by the measuring unit 16 into a total nitrogen concentration and displays it on the display unit 19.

  Reference numeral 22 denotes an input unit, and the operator inputs the reduction conditions in the reduction reaction unit 23 and the amount and concentration of the reagent added to the sample water from the input unit 22, so that the control unit 20 is based on the conditions input by the operator. Control. The control unit 20 is realized by a dedicated microcomputer or a general-purpose personal computer, and switches the 8-port valves 10a and 10b, operates the motor 27 that drives the syringe pump 17, adjusts the temperature of the reaction vessel 15 using the heater 13, The measurement operation of the measurement unit 16 and the on / off control of the ultraviolet lamp 14 are performed.

The measuring operation in this total nitrogen measuring device will be described with reference to the flowchart of FIG.
The sample water is measured from the sample preparation tank 1 to the syringe pump 17 through the 8-port valves 10b and 10a. If necessary, pure water 9 is sucked into the syringe pump 17 through the 8-port valves 10b and 10a, and diluted until the sample water becomes 2 mgN / L or less.

A solution obtained by adding the potassium peroxodisulfate solution 2 and the sodium hydroxide solution 3 to the sample water is introduced from the syringe pump 17 into the oxidative decomposition reaction vessel 12. And it heats to about 120 degreeC for 30 minutes with an internal heater, and oxidatively decomposes a nitrogen compound to nitrate ion ( ^NO3- ).

Subsequently, the nitrate ion-containing solution after oxidative decomposition is weighed while being diluted by the syringe pump 17, and after adding an aqueous sodium hydroxide solution and a potassium iodide solution thereto, the solution is introduced into the reduction reaction unit 23. Then, in an environment where the heater 13 is heated to 80 ° C. and irradiated with ultraviolet rays for 5 minutes, the nitrate ions in the sample are reduced to ultraviolet rays as shown in the equation (1) up to nitrite ions (NO ²⁻ ).

  After completion of the reduction reaction, a certain amount of the sample is weighed to the syringe pump 17 and the sulfanilamide / hydrochloric acid solution 4 and the naphthylethylenediamine solution 5 are added to produce a color reaction solution (light reddish brown solution) by the naphthylethylenediamine reaction.

The coloring reaction solution was introduced into the cell in the measurement unit 16, and after 3 minutes had passed, the colored sample was subjected to absorbance measurement at 540 nm, and the nitrogen concentration in the sample was calculated from the following formula (1).
{(Sample Absorbance−Pure Water Absorbance) / (Calibration Solution Absorbance−Pure Water Absorbance)} × (Calibration Solution Concentration) × Dilution Rate ………… (1)

As the calibration solution 8, for example, a 2 mg N / L potassium nitrate aqueous solution is used, and a reagent is added to the pure water 9 and the calibration solution 8 in the same manner as the sample water, and an oxidative decomposition reaction, a reduction reaction, and a color reaction are performed. Use.
The total nitrogen concentration may be obtained by taking the measurement result into the arithmetic processing unit 38 to which the dilution rate of the sample water and the calibration data are input, in addition to calculating from the equation (1).

Table 1 shows the measurement of total nitrogen by UV-reduced naphthylethylenediamine spectrophotometry of an actual wastewater sample after oxidative decomposition by the autoclave method using the apparatus of this example and reduction by irradiation with ultraviolet light in the presence of potassium iodide. Results are shown.

As shown in Table 1, in chemical industrial wastewater and sewage treatment plant wastewater (A) and (B), the measured values according to the method of the present invention are in good agreement with the JIS method, indicating that total nitrogen can be measured accurately. It was done.
Moreover, it was possible to reduce the nitrate ion to the nitrite ion by 90 to 100% in about 5 minutes, and the time until the measurement was completed was shortened.

  The heating temperature of the sample water, the ultraviolet irradiation time, the concentration of the reduction accelerator, etc. can be changed depending on the sample water. For example, the heating temperature during the reduction reaction is 20 to 100 ° C., the ultraviolet irradiation time is about 1 to 10 minutes, and the potassium iodide concentration of the reduction accelerator is suitably 0.01 to 1.0%.

  It can be used for reducing nitrate ions contained in sample water such as waste water, sewage, environmental water, plant water, etc., and total nitrogen contained in sample water can be measured by coloration reaction of nitrite ions. .

It is a block diagram which shows schematically the structure of the total nitrogen measuring apparatus of one Example. It is a flowchart which shows operation of the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sample preparation tank 2, 3, 4, 5, 6, 8, 9 Reagent or water 7 Atmospheric release port 10 Valve 11 Waste port 12 Oxidation decomposition reaction part 13 Heater 14 Ultraviolet lamp 15 Reaction container 16 Measurement part 17 Syringe pump 18 Calculation Processing unit 19 Display unit 20 Control unit 22 Input unit 23 Reduction reaction unit 25 Sample inlet / outlet 27 Motor

Claims (6)

After the oxidative decomposition of the nitrogen compound in the sample water to nitrate ions, a reduction process is provided for reducing the nitrate ions to nitrite ions, and total nitrogen is quantified by absorptiometry using a coloring reagent for the nitrite ions. In the nitrogen measurement method,
In the reduction step, a reduction accelerator is added to the sample water, and irradiation with ultraviolet light is performed. The total nitrogen measurement method according to claim 1, wherein the reduction step is performed under alkaline conditions. The total nitrogen measuring method according to claim 1 or 2, wherein iodine ions are added as the reduction accelerator. An oxidative decomposition reaction unit that oxidatively decomposes nitrogen compounds in the sample water into nitrate ions;
A reduction reaction part for reducing nitrate ions to nitrite ions by irradiating light in the ultraviolet region while heating the sample water that has passed through the oxidation decomposition reaction part in the presence of a reduction accelerator;
A measurement unit for measuring absorbance by a spectrophotometric method using a coloring reagent for the sample water from the reduction reaction unit;
An arithmetic processing unit for determining the total nitrogen concentration from the absorbance obtained by the measurement unit;
A total nitrogen measuring device. The total nitrogen measuring apparatus according to claim 4, wherein the reduction reaction in the reduction reaction part is performed under alkaline conditions. The total nitrogen measuring device according to claim 4, wherein the reduction accelerator is iodine ion.

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