JP2004257916A - Method and instrument for measuring total phosphorus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and instrument for measuring total phosphorus by means of ultraviolet oxidation-decomposition for quantitatively analyzing, with high reliability, total phosphorus in a specimen including condensed phosphoric acid. <P>SOLUTION: This total phosphorus measuring method, as well as its instrument, is provided comprises (1) an oxidation-decomposition process for adding an oxidant and sulfuric acid to specimen water, and then oxidating-decomposing a phosphorus compound including condensed phosphoric acid in the specimen water into orthophosphoric acid by irradiating the specimen water with ultraviolet rays under heated condition, (2) a neutralization process for neutralizing the specimen water including orthophosphoric acid obtained in the oxidation-decomposition process by thereto adding an alkali, and (3) a quantitative determination process for determining the quantity of the orthophosphoric acid based on an absorption photometry by adding a reducer, sulfuric acid, and a color former to the neutralized specimen water including the orthophosphoric acid. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a UV-oxidative decomposition method for reliably and quantitatively analyzing total phosphorus in sample water containing various forms of phosphorus such as orthophosphoric acid, condensed phosphoric acid (hydrolyzable phosphorus), and organic phosphorus. The present invention relates to a phosphorus measuring method and a total phosphorus measuring device. More specifically, the present invention relates to a total phosphorus measuring method and a total phosphorus measuring apparatus for performing ultraviolet oxidative decomposition and subsequent color development determination at an optimum sulfuric acid concentration.
[0002]
[Prior art]
Phosphorus compounds in water exist in various forms such as orthophosphoric acid, condensed phosphoric acid, and organic forms of phosphorus. To measure the total phosphorus in the sample water present in various forms, firstly, the condensed phosphoric acid in the sample water and the organic form of phosphorus are oxidatively decomposed to orthophosphoric acid, and then the orthophosphoric acid is converted to molybdenum spectrophotometry. Quantitative color development by the method.
[0003]
As a method of oxidatively decomposing a phosphorus compound in a sample water, an autoclave method in which an oxidizing agent is added to the sample water, and the sample water is held at 120 ° C. for 30 minutes under pressure in an autoclave hydrolysis tank, An automatic total phosphorus measuring device employing this method has been put to practical use. However, in this method, high heat resistance, pressure resistance, chemical resistance, etc. are required for the autoclave, and special materials such as ceramics and special metal alloy materials are used, so that the equipment becomes expensive and the life is short. is there.
[0004]
In addition, the phosphoric acid compound in the sample water was added to a 0.1 ppm solution suitable for color determination of orthophosphoric acid in the subsequent step. There is also a method of heating to 95 ° C. under normal pressure under 4N sulfuric acid acidity and irradiating with ultraviolet rays for 45 minutes to oxidatively decompose. A total phosphorus automatic measuring apparatus employing this method has been put to practical use. In this ultraviolet oxidative decomposition method, the load on the heat resistance and pressure resistance of the decomposition vessel is reduced as compared with the autoclave method, but the oxidative decomposition reaction of the condensed phosphoric acid requires a long time.
[0005]
[Patent Document 1]
Japanese Patent No. 3316664 [0006]
[Problems to be solved by the invention]
An object of the present invention is to provide a method and apparatus for measuring total phosphorus by ultraviolet oxidative decomposition, which can reliably and quantitatively analyze total phosphorus including condensed phosphoric acid in a sample.
[0007]
[Means for Solving the Problems]
The present inventors, the oxidative decomposition step of converting the phosphorus compound containing condensed phosphoric acid in the sample water to orthophosphoric acid, and the quantitative step of colorimetric determination of orthophosphoric acid by a spectrophotometric method, the optimal sulfuric acid concentration is different, Therefore, the present inventors have focused on the fact that by performing the neutralization of the sample water between the oxidative decomposition and the colorimetric determination, it is possible to perform both the oxidative decomposition and the colorimetric determination at the optimum sulfuric acid concentration, and arrived at the present invention.
[0008]
The present invention provides (1) an oxidative decomposition in which a phosphoric acid compound containing condensed phosphoric acid in a sample water is oxidatively decomposed into orthophosphoric acid by adding an oxidizing agent and sulfuric acid to the sample water and then irradiating the sample water with ultraviolet light under heating conditions. Process and
(2) a neutralization step of adding an alkali to the sample water containing orthophosphoric acid obtained in the oxidative decomposition step to neutralize the sample water;
(3) a step of adding a reducing agent, sulfuric acid, and a color former to the neutralized sample water containing orthophosphoric acid, and quantifying the orthophosphoric acid by a spectrophotometric method. Is the way.
[0009]
The present invention is the above method for measuring total phosphorus, wherein sulfuric acid is added in the oxidative decomposition step (1) such that the concentration of sulfuric acid in the sample water is 0.8 N or more.
[0010]
The present invention is the above-described total phosphorus measurement method, wherein ultraviolet light is irradiated for 20 to 30 minutes in the oxidative decomposition step (1).
[0011]
The present invention is the above method for measuring total phosphorus, wherein sodium hydroxide is added as an alkali in the neutralization step (2).
[0012]
The present invention is the above-described method for measuring total phosphorus, wherein sulfuric acid is added in the quantification step (3) such that the sulfuric acid concentration in the sample water is 0.2 to 0.6N.
[0013]
According to the present invention, in the quantification step (3), a reducing agent is added to sample water, and then a mixed solution of sulfuric acid and a color former is added so that the concentration of sulfuric acid in the sample water becomes 0.2 to 0.6N. And the method for measuring total phosphorus.
[0014]
Also, the present invention provides a means for adding an oxidizing agent and sulfuric acid to a sample water,
An oxidative decomposition reaction tank that irradiates the sample water with ultraviolet rays while heating the sample water to which the oxidizing agent and sulfuric acid have been added, and oxidatively decomposes a phosphorus compound containing condensed phosphoric acid in the sample water to convert it into orthophosphoric acid;
Means for neutralizing the sample water by adding an alkali to the sample water containing the oxidatively decomposed orthophosphoric acid,
Means for adding a reducing agent, sulfuric acid and a color former to a neutralized sample water containing orthophosphoric acid to cause a color reaction,
A total phosphorus measuring device, comprising: a measuring and quantifying means for measuring the absorbance of the colored sample water.
[0015]
Further, the present invention provides a syringe for adding predetermined various reagents to sample water,
A first port valve connected to the syringe by a flow path,
An oxidizing agent tank and a sulfuric acid tank connected to the first port valve by respective flow paths;
An alkali tank connected to the first port valve by a flow path;
A tank for the reducing agent and a tank for the mixed solution of sulfuric acid and the coloring agent, each connected to the first port valve by a flow path,
A second port valve connected to the first port valve by a flow path;
Oxidative decomposition, comprising a means for heating a sample water to which an oxidizing agent and sulfuric acid are added and an ultraviolet lamp for irradiating the sample water with ultraviolet light, the reaction tank being connected to a second port valve by a flow path. A reaction tank,
A measurement cell connected to the second port valve by a flow path, wherein the measurement cell measures the absorbance of a sample water colored by adding a reducing agent, sulfuric acid, and a coloring agent after alkali neutralization. Is a total phosphorus measuring device.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
An apparatus for automatically measuring total phosphorus that can be used in the method for measuring total phosphorus according to the present invention will be described with reference to FIG.
[0017]
FIG. 1 is a schematic configuration diagram of a total phosphorus automatic measuring device. In FIG. 1, a syringe 11 for adding predetermined reagents to a sample water is connected to a central port of a first port valve 10 by a flow path. The syringe 11 is provided with a stirring pump 18 via a flow path. The oxidizing agent tank 16 is provided at the sixth port of the first port valve 10, the sulfuric acid tank 17 is provided at the seventh port, the alkali tank 15 is provided at the fifth port, the reducing agent tank 14 is provided at the fourth port, and sulfuric acid is provided at the third port. The coloring agent mixed solution tanks 13 are connected by flow paths. Note that the second tank is connected to the spare tank 12 by a flow path.
[0018]
The first port of the first port valve 10 is connected to the center port of the second port valve 20 by a flow path 19. An oxidative decomposition reaction tank 30 is connected to a fourth port of the second port valve 20 by a flow path. The oxidative decomposition reaction tank 30 includes a temperature sensor, an ultraviolet lamp 31 for irradiating the sample water in the reaction tank with ultraviolet rays, and a heater 32 for heating the sample water outside. A discharge port is provided at the bottom of the reaction tank 30, and is connected to a waste liquid port 34 via a flow path and a discharge pump 33.
[0019]
An inlet 41 of the measurement cell 40 is connected to a seventh port of the second port valve 20 by a flow path, so that the absorbance of the colored sample water in the measurement cell 40 can be measured and quantified. The outlet 42 of the measurement cell 40 is connected to the waste liquid port 34 via a flow path, and the sample water after the measurement that has exited the measurement cell 40 is discharged.
[0020]
The first port of the second port valve 20 is connected to the off-line sample introduction port 21 by a flow path, so that an off-line sample is introduced, and the second port is connected to the on-line sample introduction port 22 by a flow path. And an on-line sample is introduced.
[0021]
A span liquid tank 23 is connected to a third port of the second port valve 20 by a flow path, and a dilution water tank 26 is connected to a sixth port by a flow path. The tanks 29A and 29B are connected by a flow path. A drain switching valve 25 is connected to a fifth port of the second port valve 20, two flow paths are connected to the valve 25, and one flow path is connected to a waste liquid port 34, and the other flow path is a drain port. It is connected to 35. The span solution in the tank 23 is a standard solution prepared according to the highest concentration in the measurement range of the device, and the span value of the device is calibrated using this span solution. The standard samples in the tanks 29A and 29B are used for checking the recovery rate of the apparatus, but are not necessarily used.
[0022]
In the apparatus illustrated in FIG. 1, various predetermined reagents are added to the sample water in each step, that is, an oxidizing agent and sulfuric acid are added in the oxidative decomposition step (1), an alkali is added in the neutralization step (2), and The addition of the reducing agent, sulfuric acid, and the coloring agent in the determination step (3) is all performed in the syringe 11. Of course, a different syringe or container may be used for each step.
[0023]
Next, the case of using the apparatus illustrated in FIG. 1 for the method for measuring total phosphorus according to the present invention will be described with reference to the flowchart for measuring total phosphorus according to the present invention in FIG.
[0024]
In the method for measuring total phosphorus of the present invention, first, an oxidative decomposition step (1) is performed. In the oxidative decomposition step, after adding an oxidizing agent and sulfuric acid to the sample water, the sample is irradiated with ultraviolet light under heating conditions to oxidatively decompose the phosphorus compound containing condensed phosphoric acid in the sample water to convert it to orthophosphoric acid.
[0025]
A certain amount of sample water is weighed and collected into the syringe 11 via the offline sample inlet 21 or usually the online sample inlet 22, the second port valve 20, the flow path 19 and the first port valve 10 in sequence, and if necessary. To dilute with dilution water 26. An oxidizing agent 16 (for example, potassium peroxodisulfate aqueous solution) and sulfuric acid 17 are added to the sample water in the syringe 11 to perform pretreatment. At this time, sulfuric acid is added so that the concentration of sulfuric acid in the sample water becomes 0.8N or more, preferably 0.8N or more and 2.0N or less, for example, about 1.0N. Therefore, the sulfuric acid 17 preferably has a high degree of normality, for example, 9N sulfuric acid.
[0026]
Next, the pretreated sample water is introduced into the oxidative decomposition reaction tank 30 via the first port valve 10, the flow path 19, and the second port valve 20 in order. In the reaction tank 30, the sample water is irradiated with ultraviolet rays from the ultraviolet lamp 30 for 5 to 30 minutes, for example, 20 minutes while the sample water is heated to 90 ° C. or more and less than 100 ° C., for example, 95 ° C. under normal pressure by the heater 32. In addition, various forms of phosphorus compounds such as condensed phosphoric acid and organic form phosphorus contained in sample water are changed to orthophosphoric acid.
[0027]
This process of oxidatively decomposing a phosphorus compound into orthophosphoric acid is hydrolysis. However, by adding sulfuric acid in the pretreatment stage, the sample water has a sulfuric acid concentration suitable for hydrolysis of 0.8N or more and 2.0N or less, for example, about 1.0N. Therefore, the decomposition rate is increased, and the oxidative decomposition of the phosphorus compound containing condensed phosphoric acid becomes possible by irradiation with ultraviolet rays for a short time of 20 to 30 minutes, for example, 20 minutes.
[0028]
FIG. 3 shows the total phosphorus (TP) recovery rate when the sulfuric acid concentration (normality: N) of the sample water was changed at the temperature of 95 ° C. and the ultraviolet irradiation time of 20 minutes in the oxidative decomposition step (1). %). According to this graph, by setting the sulfuric acid concentration of the sample water to 0.8N or more and 1.0N or less, the hydrolysis reaction is accelerated, and the total phosphorus recovery rate is increased to 92% or more. This revealed that the total phosphorus recovery rate was as high as 98.4%. Suitable for color determination of orthophosphoric acid in the subsequent step. At a 4N sulfuric acid concentration, the total phosphorus recovery is as low as 81.6%, and reliable quantification is not performed.
[0029]
FIG. 4 shows that in the oxidative decomposition step (1), the temperature was 95 ° C. and the sulfuric acid concentration of the sample water was 0. It is a graph which shows the total phosphorus (TP) recovery rate (%) at the time of changing the ultraviolet irradiation (oxidative decomposition) time on condition of 4N. According to this graph, the sulfuric acid concentration of the sample water was 0.1. At 4N, the total phosphorus recovery rate is only 92.0% even if the ultraviolet irradiation is performed for 45 minutes. Therefore, 0.1 suitable for the colorimetric determination of orthophosphoric acid in the subsequent step. At a 4N sulfuric acid concentration, even if the quantification is performed with a certain degree of reliability, a very high total phosphorus recovery rate cannot be obtained, and the hydrolysis reaction requires time.
[0030]
Next, a neutralization step (2) is performed. In the neutralization step (2), alkali is added to the sample water containing orthophosphoric acid obtained in the oxidative decomposition step (1) for neutralization.
[0031]
A predetermined amount of the sample water after the oxidative decomposition in the oxidative decomposition reaction tank 30 is measured and introduced into the syringe 11 via the second port valve 20, the flow path 19 and the first port valve 10 sequentially. An aqueous sodium hydroxide solution 15 is added as an alkali to the sample water in the syringe 11 to neutralize the sample water. The concentration of the aqueous sodium hydroxide solution is 5N.
[0032]
Next, a quantitative step (3) is performed by molybdenum blue absorptiometry. In the quantification step (3), a reducing agent, sulfuric acid and a coloring agent are added to the neutralized sample water containing orthophosphoric acid obtained in the neutralization step (2), and the orthophosphoric acid is quantified by an absorption spectrophotometry. .
[0033]
A reducing agent ascorbic acid aqueous solution 14 is added to the sample water in the syringe 11 after the neutralization, and subsequently, a mixed aqueous solution 13 of ammonium molybdate / antimony potassium tartrate / sulfuric acid is added to generate molybdenum blue. At this time, the mixed aqueous solution 13 is added so that the concentration of sulfuric acid in the sample water becomes 0.2 to 0.6N, preferably 0.3 to 0.5N, and most preferably about 0.4N. The sulfuric acid concentration of the mixed aqueous solution is, for example, 6N.
[0034]
Molybdenum blue absorption spectrophotometry is carried out by acidification with sulfuric acid. However, in the color reaction of molybdenum blue, the concentration of sulfuric acid and the concentration of ammonium molybdate affect each other. Is most preferable.
[0035]
The sample water in the syringe 11 to which the reducing agent, the coloring agent, and the sulfuric acid are added is introduced into the measurement cell 40 through the first port valve 10, the flow path 19, and the second port valve 20 in order. In the measurement cell 40, the absorbance at 880 nm of the sample water that has developed molybdenum blue is measured, and the total phosphorus concentration including condensed phosphoric acid is determined. After the absorbance measurement, the sample water is discharged from the waste liquid port 34.
[0036]
By the above measurement method, the oxidative decomposition step of converting the phosphorus compound containing condensed phosphoric acid in the sample water to orthophosphoric acid is performed at a high sulfuric acid concentration of 0.8 N or more, which is optimal for oxidative decomposition, so that quantification can be performed in a short time. Coloration determination of orthophosphoric acid, which is highly oxidatively decomposed and is easily affected by the sulfuric acid concentration, can be performed at a suitable sulfuric acid concentration of 0.2 to 0.6 N, thereby enabling highly accurate coloring determination.
[0037]
Using the apparatus shown in FIG. 1, the total phosphorus measurement of the present invention was carried out under the following conditions.
In the oxidative decomposition step (1), the sulfuric acid concentration of the sample water: 1.0 N, the temperature: 95 ° C., the ultraviolet irradiation time: 20 minutes In the quantitative step (3), the sulfuric acid concentration of the sample water: 0.4 N
[0038]
When the total phosphorus measurement was performed on the phenyl phosphate / ATP mixed solution having a phosphorus concentration of 10 mg / L, a total phosphorus measurement result: 9.7 mg / L (recovery rate: 97%) was obtained.
[0039]
【The invention's effect】
According to the present invention, since the ultraviolet oxidative decomposition and the subsequent color determination are each performed at the optimum sulfuric acid concentration, quantitative oxidative decomposition can be obtained in a short time, and high-precision color determination can be achieved. Therefore, a total phosphorus measuring method and a total phosphorus measuring apparatus by an ultraviolet oxidative decomposition method for reliably and quantitatively analyzing total phosphorus in a sample water containing various forms of phosphorus such as orthophosphoric acid, condensed phosphoric acid, and organic form phosphorus. Is provided. In the automatic total phosphorus measuring apparatus according to the present invention, the container does not need to have pressure resistance and the heat resistance is also alleviated, so that the cost is lower and the maintainability is higher than in the conventional apparatus based on the autoclave method.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an automatic total phosphorus measuring apparatus of the present invention.
FIG. 2 is a flowchart for measuring total phosphorus according to the present invention.
FIG. 3 is a graph showing a relationship between a sulfuric acid concentration of sample water and a total phosphorus recovery rate in an oxidative decomposition step. Sulfuric acid concentration (normality: N) VS Total phosphorus recovery rate (%)
FIG. 4 is a graph showing the relationship between the oxidative decomposition time and the total phosphorus recovery rate in the oxidative decomposition step. Oxidation decomposition time (min) VS Total phosphorus recovery rate (%)
[Explanation of symbols]
10: first port valve 11: syringe 12: reserve tank 13: tank for mixed solution of sulfuric acid and coloring agent 14: tank for reducing agent 15: tank for alkali 16: tank for oxidizing agent 17: tank 18 for sulfuric acid 18: stirring pump 19 : Flow path 20: 2nd port valve 21: Offline sample inlet 22: Online sample inlet 23: Span liquid tank 26: Dilution water tanks 29A, 29B: Standard sample tank 30: Oxidation decomposition reaction tank 31: Ultraviolet ray Lamp 32: heater 40: measuring cell

Claims (8)

(1) an oxidative decomposition step of adding an oxidizing agent and sulfuric acid to the sample water, and then irradiating ultraviolet rays under heating conditions to oxidatively decompose the phosphorus compound containing condensed phosphoric acid in the sample water to convert it to orthophosphoric acid;
(2) a neutralization step of adding an alkali to the sample water containing orthophosphoric acid obtained in the oxidative decomposition step to neutralize the sample water;
(3) a step of adding a reducing agent, sulfuric acid, and a color former to the neutralized sample water containing orthophosphoric acid, and quantifying the orthophosphoric acid by a spectrophotometric method. Method. The method for measuring total phosphorus according to claim 1, wherein in the oxidative decomposition step (1), sulfuric acid is added so that the concentration of sulfuric acid in the sample water is 0.8 N or more. The method for measuring total phosphorus according to claim 1, wherein ultraviolet light is irradiated for 20 to 30 minutes in the oxidative decomposition step (1). The method for measuring total phosphorus according to any one of claims 1 to 3, wherein sodium hydroxide is added as an alkali in the neutralization step (2). The method for measuring total phosphorus according to any one of claims 1 to 4, wherein in the quantification step (3), sulfuric acid is added so that the sulfuric acid concentration in the sample water is 0.2 to 0.6N. The quantification step (3), wherein a reducing agent is added to the sample water, and then a mixed solution of sulfuric acid and a color former is added so that the sulfuric acid concentration in the sample water is 0.2 to 0.6N. 5. The method for measuring total phosphorus according to any one of Items 4 to 4. Means for adding an oxidizing agent and sulfuric acid to the sample water;
An oxidative decomposition reaction tank that irradiates the sample water with ultraviolet rays while heating the sample water to which the oxidizing agent and sulfuric acid have been added, and oxidatively decomposes a phosphorus compound containing condensed phosphoric acid in the sample water to convert it into orthophosphoric acid;
Means for neutralizing the sample water by adding an alkali to the sample water containing the oxidatively decomposed orthophosphoric acid,
Means for adding a reducing agent, sulfuric acid and a color former to a neutralized sample water containing orthophosphoric acid to cause a color reaction,
A measuring and quantifying means for measuring the absorbance of the colored sample water; A syringe for adding predetermined various reagents to the sample water,
A first port valve connected to the syringe by a flow path,
An oxidizing agent tank and a sulfuric acid tank connected to the first port valve by respective flow paths;
An alkali tank connected to the first port valve by a flow path;
A tank for the reducing agent and a tank for the mixed solution of sulfuric acid and the coloring agent, each connected to the first port valve by a flow path,
A second port valve connected to the first port valve by a flow path;
Oxidative decomposition, comprising a means for heating a sample water to which an oxidizing agent and sulfuric acid are added and an ultraviolet lamp for irradiating the sample water with ultraviolet light, the reaction tank being connected to a second port valve by a flow path. A reaction tank,
A measurement cell connected to the second port valve by a flow path, wherein the measurement cell measures the absorbance of a sample water colored by adding a reducing agent, sulfuric acid, and a coloring agent after alkali neutralization. Total phosphorus measurement device.

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