JP2008196873A - Phosphorus measuring method and apparatus thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To automatically measure PO<SB>4</SB>-P in a continuous, accurate and safe manner. <P>SOLUTION: A phosphorus measuring apparatus 1 electrochemically measures the concentration of PO<SB>4</SB>-P in sample water by a flow injection analysis means 2a, provided with a mixed solution of ammonium molybdate and sulfuric acid as a reagent solution. The flow injection analysis means 2a includes an injection valve 3 for injecting the reagent solution or sample water into a carrier solution; a mixer 4 for mixing the carrier solution, the reagent solution, and the sample water; and a flow cell 5 for detecting current changes based on the reaction between the reagent solution and the sample water supplied from the mixer 4. The ammonium molybdate concentration of the reagent solution or of the mixed solution is prepared to 8-10 g/L. The sulfuric acid concentration of the reagent solution or of the mixed solution is prepared to 16-24 mL/L. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a flow injection analysis method using an electrochemical measurement method of soluble phosphate ion phosphorus using a coulometric type flow cell as a detection system.

  The total water quality regulation system is inland in upstream prefectures, etc. that flow into the water area in order to secure environmental standards for wide-area closed water areas such as Tokyo Bay, which are highly polluted due to industrial concentration and population growth. It was established for the purpose of uniformly and effectively reducing the total amount of pollution load for pollution sources, including loads from the department and domestic wastewater.

  This system was introduced by the amendment of the Water Pollution Control Law in 1978, and has been implemented for four times with the subject of chemical oxygen demand (COD) since 1975.

  As a result, the pollution load related to Tokyo Bay has been steadily reduced, but the achievement rate of COD environmental standards is not satisfactory, and accompanying eutrophication caused by nitrogen and phosphorus such as red tide Due to problems, the fifth total amount regulation (target year: FY2004) was newly implemented in addition to the conventional COD, which also covers nitrogen and phosphorus contents.

  Phosphorus is an element that is widely present in the ground, so it is also contained in natural water. However, the amount of phosphorus in the water is increased in human waste, detergent, fertilizer, etc. In many cases, it is derived from contamination of factory effluent and agricultural effluent.

  Phosphorus plays an important role in the growth activity of organisms and is an essential element in the biological treatment of sewage. However, phosphorus is considered to be a cause of promoting eutrophication of lakes and marine areas, and an increase in phosphorus compounds in water is not preferable.

  Phosphorus in water is in various forms such as inorganic phosphates such as orthophosphate, metaphosphate, pyrophosphate and polyphosphate, and organic phosphorus compounds such as phosphate esters and phospholipids. Exists.

  When the forms of phosphorus are classified based on the analysis method, they are divided into three types: phosphate ion phosphorus, hydrolyzable phosphorus and total phosphorus. This is further classified as soluble and insoluble.

  In particular, as a method for measuring phosphate ion-type phosphorus, a non-patent document 1 edited by Japan Sewerage Association “Sewage Test Method” describes a molybdenum blue absorbance method.

  In this method, phosphate ions react with ammonium molybdate and potassium antimonyl tartrate to reduce the heteropoly compound produced by ascorbic acid. It is a method of quantification. It is suitable for samples containing a large amount of salts and samples that produced a large amount of salts by pretreatment.

  As shown in the formula (1), sample water (phosphorus) is reacted with a mixed solution in which the volume ratio of ammonium molybdate solution and ascorbic acid is 5: 1, and the absorbance at 880 nm is measured. The ammonium molybdate solution contains ammonium molybdate tetrahydrate, potassium antimonyl tartrate, sulfuric acid and ammonium amidosulfate. As a blank experiment, the absorbance at 880 nm is similarly measured for water instead of sample water. Then, after subtracting the absorbance value measured in the blank experiment from the absorbance value of the sample water and calculating the amount of phosphorus a (mg) in the sample water from the calibration curve, the sample water is calculated based on the equation (2). The phosphate ion phosphorus concentration P (mg / L) is calculated. “Phosphate ion phosphorus” is a phosphate ion in water expressed by the amount of phosphorus (P). (2) b in the formula means the sample amount (mL).

Phosphorus + (ammonium molybdate solution + ascorbic acid) → light (absorbance 880 nm) (1)
P = a × (1000 / b) (2)
On the other hand, the electrochemical measurement method is a method for measuring a current change and a voltage change associated with an oxidation-reduction reaction on an electrode, and is used in a wide range of fields such as inorganic chemistry, analytical chemistry, organic chemistry, biology, and medicine.

  The electrochemical measurement method is capable of high-sensitivity measurement, but has a problem that reproducibility is reduced due to contamination of the electrode surface. Since the coulometric measurement method detects the total amount of the target component in the sample water, it has a feature that the problem that the reproducibility is lowered is improved.

  In the flow injection analysis method, volume is measured by flowing a reagent solution at a constant flow rate, a fixed amount of sample water is injected into the flow, and both pipes such as Teflon (registered trademark) are regarded as reaction vessels such as flasks and beakers. This is a method of mixing and reacting liquids.

  A system in which a reagent solution and a carrier liquid such as distilled water that does not affect the measurement are provided with two flow paths and sample water is introduced into the carrier liquid flow is a common configuration.

  On the other hand, in the case of using a method called reverse flow injection analysis method in which sample water and carrier liquid are flowed at a constant flow rate instead of the reagent solution and the reagent solution is introduced into the carrier liquid flow, or an expensive reagent is used. After introducing the reagent solution into the carrier liquid flow, at the detector, provide a stopped-flow system that stops the flow, and a plurality of carrier liquid and reagent solution flow paths for a single sample water flow path. Various methods such as a method of analyzing multiple components have been proposed (Non-Patent Document 2).

The flow injection analysis method has few moving parts and is characterized by the fact that the solution moves more easily.
Edited by Japan Sewerage Association, “Sewage Test Method”, 1997, pp. 191 Rokuro Kuroda, Koichi Oguma, Hiroshi Nakamura, “Flow Injection Analysis”, Kyoritsu Publishing Co., Ltd., September 1990, pp. 50-117

  When measuring phosphate ion-type phosphorus by the absorbance method, ascorbic acid is unstable, and maintenance and maintenance for maintaining the quality of the reagent, such as storing it in a colored glass bottle, is troublesome. In addition, since a reaction time of about 15 minutes is required for the reaction between the sample water (phosphorus), the ammonium molybdate solution, and the ascorbic acid mixture, measurement cannot be performed unless a measurement interval of at least 15 minutes is secured. Furthermore, since it is influenced by nitric acid and nitrous acid, there are problems such as the need for highly toxic reagents such as potassium antimonyl tartrate and ammonium amidosulfate.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a phosphorus measuring method and apparatus capable of automatic measurement continuously and accurately and safely.

  Accordingly, the phosphorus measurement method of claim 1 is a phosphorus measurement method in which the phosphate ion-state phosphorus concentration in the sample water is electrochemically measured by flow injection analysis in which a mixed solution of ammonium molybdate and sulfuric acid is provided as a reagent solution. And the ammonium molybdate density | concentration of the said liquid mixture is 8-10 g / L, The sulfuric acid concentration of the said liquid mixture is 16-24 mL / L, It is characterized by the above-mentioned.

  The phosphorus measurement method according to claim 2 is the phosphorus measurement method according to claim 1, wherein the flow injection analysis includes an electrochemical detection step using coulometry, and an applied voltage of the electrochemical detection step is 290 to 320 mV. It is characterized by being.

  The phosphorus measuring method according to claim 3 is the phosphorus measuring method according to claim 2, wherein the working electrode used in the electrochemical detection step has a length of 20 mm or more.

  The phosphorus measurement method according to claim 4 is the phosphorus measurement method according to claim 3, wherein flow rates of the reagent solution, the sample water, and the carrier liquid are 0.05 to 0.5 mL / min.

  The phosphorus measurement method according to claim 5 is the phosphorus measurement method according to claim 4, characterized in that a sample amount of the flow injection analysis is 100 to 500 μL.

  The phosphorus measurement method according to claim 6 is characterized in that in the phosphorus measurement method according to any one of claims 1 to 5, the sample water is subjected to a flow injection analysis after reducing interference substances in the sample water by a coulometric type flow cell. To do.

  The phosphorus measurement method according to claim 7 is the phosphorus measurement method according to any one of claims 1 to 5, wherein the reagent solution is subjected to a flow injection analysis after reducing the interfering substance in the reagent solution by a coulometric type flow cell. Features.

  The phosphorus measuring method according to claim 8 is characterized in that the phosphorus measuring method according to any one of claims 1 to 5 is subjected to a flow injection analysis after reducing the interfering substance in the carrier liquid by a coulometric flow cell. To do.

  The phosphorus measuring device according to claim 9 is a phosphorus measuring device for electrochemically measuring a phosphate ion-type phosphorus concentration in a sample water by a flow injection analysis means provided with a mixed solution of ammonium molybdate and sulfuric acid as a reagent solution. The flow injection analysis means comprises: an injection means for injecting the reagent solution or sample water into a carrier liquid; a mixer for mixing the carrier liquid, the reagent solution, and the sample water; and A flow cell that detects a change in current based on a reaction between the supplied reagent solution and sample water, and the ammonium molybdate concentration of the reagent solution or mixed solution is 8 to 10 g / L. The sulfuric acid concentration is 16 to 24 mL / L.

  The phosphorus measuring apparatus according to claim 10 is the phosphorus measuring apparatus according to claim 9, wherein the flow injection analyzing means includes an electrochemical detecting means using coulometry, and an applied voltage of the electrochemical detecting means is 290 to 320 mV. It is characterized by being.

  The phosphorus measuring apparatus according to claim 11 is the phosphorus measuring apparatus according to claim 10, wherein the length of the working electrode according to the electrochemical detection means is 20 mm or more.

  The phosphorus measuring device according to claim 12 is the phosphorus measuring device according to claim 11, wherein flow rates of the reagent solution, the sample water and the carrier liquid are 0.05 to 0.5 mL / min.

  A phosphorus measuring apparatus according to a thirteenth aspect is the phosphorus measuring apparatus according to the twelfth aspect, wherein a sample amount of the flow injection analysis is 100 to 500 μL.

  A phosphorus measuring device according to a fourteenth aspect is the phosphorus measuring device according to any one of the ninth to thirteenth aspects, wherein a coulometric flow cell is provided in a flow path for supplying the sample water to the injection means, and the flow cell is the sample water. The interfering substance contained in is reduced.

  The phosphorus measuring device according to claim 15 is the phosphorus measuring device according to any of claims 9 to 13, wherein a flow cell for supplying the reagent solution to the mixer is provided with a coulometric flow cell, and the flow cell is the reagent solution. It is characterized by reducing the interfering substances therein.

  A phosphorus measuring device according to a sixteenth aspect is the phosphorus measuring device according to any one of the ninth to thirteenth aspects, wherein a coulometric flow cell is provided in a flow path for supplying the carrier liquid to the injecting means, and the flow cell is the carrier liquid. The interfering substance contained in is reduced.

  According to the inventions of claims 1 to 16, it has been confirmed that the soluble phosphate ion phosphorus in the sample water can be measured in the range of 0 to 100 mg / L without dilution. It has been confirmed that the soluble phosphate ion phosphorus in the sample water can be continuously measured at intervals of 1.3 to 2.3 minutes. It has been confirmed that the soluble phosphate ion phosphorus in the waste water can be measured with an accuracy of a variation coefficient within 2%. In particular, according to the inventions of claims 6 to 8 and 14 to 16, since the interfering substance is reduced, it can be measured with higher accuracy. In addition, the unstable ascorbic acid and the highly toxic ammonium amidosulfate reagent required in the official absorbance method are unnecessary. Furthermore, since it is not affected by nitric acid or nitrous acid, a reagent for ammonium amidosulfate, which is required in the official absorbance method, becomes unnecessary. It has also been confirmed that the measured value is stable even when the water temperature changes. This eliminates the troublesome labor involved in preparing the standard solution and calibration with the standard solution for each measurement.

  According to the first to sixteenth aspects, phosphate ion-type phosphorus can be continuously and accurately automatically measured with high accuracy.

  FIG. 1 is a schematic configuration diagram showing an embodiment of the phosphorus measuring method of the present invention.

  The phosphorus measuring apparatus 1 which is one embodiment of the present invention measures phosphate ion-type phosphorus by flow injection analysis. The flow injection analysis is a method in which a reagent solution and a carrier liquid are flowed in a certain direction, and sample water to be measured is introduced into the flow for measurement. Examples of sample water include wastewater discharged from manufacturing industries such as sewage treatment plants, food manufacturing industries, textile industries, and chemical industries.

  The phosphorus measuring apparatus 1 electrochemically measures the phosphate ion-type phosphorus concentration in the sample water by a flow injection analysis means 2a provided with a mixed solution of ammonium molybdate and sulfuric acid as a reagent solution. The flow injection analysis means 2 a includes an injection valve 3, a mixer 4, and a flow cell 5.

  The injection valve 3 is an injection means for injecting a carrier liquid and a reagent solution or sample water. The illustrated injection valve 3 is a six-way rotary valve type. Thin tubes 31 to 35 are connected to the injection valve 3 as flow paths. The narrow tube 31 is a tube constituting a flow path for injecting the carrier liquid supplied by the pump P2. The thin tube 32 is a tube constituting a flow path for injecting the sample water supplied by the pump P3. The thin tube 33 is a tube constituting a sample loop. The narrow tube 34 is a tube constituting a flow path for supplying a carrier liquid containing sample water to the mixer 4. The thin tube 35 is a tube for transferring the sample water overflowed from the sample loop to the drain bottle 7 which is a drain part.

  The injection valve 3 is configured to inject the carrier liquid and the sample water, but may be configured to inject the carrier liquid and the reagent solution. Further, the form of the injection means is not limited to the six-way rotary valve type such as the injection valve 3, and examples thereof include a syringe type and a proportional injector type.

  The mixer 4 mixes the carrier liquid, the reagent solution, and the sample water. As the mixer 4, a known mixer that is used for flow injection analysis using electrochemical detection may be used. A narrow tube 34 and thin tubes 41 and 42 are connected to the mixer 4. The narrow tube 41 is a tube constituting a flow path for injecting the reagent solution supplied by the pump P1. The narrow tube 42 is a tube constituting a flow path for injecting the carrier liquid containing the sample water and the reagent supplied from the mixer 4 into the flow cell 5.

  The flow cell 5 detects a current change based on the reaction between the reagent solution contained in the carrier liquid supplied from the mixer 4 and the sample water. Connected to the flow cell 5 is a thin tube 51 for transferring the carrier liquid supplied through the thin tube 42 to the drain bottle 7. An applied voltage for detecting a current change in the flow cell 5 is set to 290 to 320 mV, for example. The flow cell 5 includes a working electrode, a reference electrode, and a counter electrode. As the working electrode, the reference electrode, and the counter electrode, a known electrode provided in a flow cell used for a coulometric type (total amount detection) analysis may be employed. Examples of the working electrode include those made of carbon fiber. As the working electrode made of carbon fiber, for example, an electrode in which 100 or more bundles having a length of 20 mm or more are accommodated in a Vycor glass tube having an inner diameter of 5 mm is employed. Examples of the reference electrode include those made of Ag / AgCl. Examples of the counter electrode include those made of stainless steel (SUS316).

  The concentration of ammonium molybdate in the reagent solution is adjusted to 8 to 10 g / L. On the other hand, the concentration of sulfuric acid is adjusted to 16 to 24 mL / L. What is necessary is just to use what is inactive with respect to sample water and a reagent solution as said carrier liquid. An example is distilled water. The flow rates of the sample water, the reagent solution, and the carrier liquid may each be set to 0.05 to 0.5 mL / min. Moreover, the sample amount of the said flow injection analysis method is good to set to 100-500 microliters.

  An example of the operation of the phosphorus measuring device 1 will be described with reference to FIG. The reagent solution, the carrier liquid, and the sample water are respectively sent to the drain part (drain bottle 7) at a constant speed by pumps P1, P2, and P3. The sample water in the sample bottle 6 is supplied to the injection valve 3 through the thin tube 32 by the pump P3. The sample water quantified by the injection valve 3 rides on the flow of the carrier liquid provided via the narrow tube 31 and is supplied to the mixer 4 via the narrow tubes 33 and 34. At this time, the phosphorus component contained in the sample water reacts with ammonium molybdate in the reagent solution injected through the thin tube 41 to generate molybdophosphoric acid. When the generated molybdophosphoric acid reaches the flow cell 5 through the thin tube 42, the current change accompanying the reduction reaction of the molybdophosphoric acid is measured by the working electrode. The detected reduction current value is transmitted to the terminal (PC) via the potentiostat 8 and used for data processing. The carrier liquid containing the reagent solution and the sample water that has passed through the flow cell 5 is guided to the drain bottle 7 as a waste liquid through the thin tube 51.

  FIG. 2 is a characteristic diagram showing a reduction current pattern measured by a flow injection analysis method. FIG. 2 shows the results of measurement using a phosphorus standard solution (potassium dihydrogen phosphate aqueous solution) as sample water, and repeatedly measuring the same concentration of phosphorus standard solution (potassium dihydrogen phosphate aqueous solution) three times. The parameter of the measured value is the maximum current and the amount of electricity (current integrated value) of the measured reduction current.

  The reduction current pattern becomes sharp when the flow rate of the reaction solution is increased, and becomes broader when the flow rate of the reaction solution is decreased. Therefore, in the flow injection analysis method, the flow rate of the reaction solution generally affects the sensitivity of the measurement value and the like, and it is necessary to set the optimum flow rate of the reaction solution.

(1) Optimum Ammonium Molybdate Concentration FIGS. 3 to 8 show the results of studies on the optimum concentration of ammonium molybdate in the reagent solution. 3 to 8, the ammonium molybdate was adjusted so that the ammonium molybdate concentration was 5 to 10 g / L under the conditions shown in Table 1 in the experimental system comprising the components of the phosphorus measurement system 1 of FIG. A mixture of sulfuric acid and sulfuric acid was prepared as a reagent solution. As the sample water, a phosphorous standard solution (potassium dihydrogen phosphate aqueous solution) prepared to a phosphate ion phosphorus concentration of 60 mg / L was used. This sample water was injected into the carrier liquid from the injection valve of the phosphorus measurement system 1 in sample amounts of 200 μL and 400 μL. The quantity of electricity, maximum current, and background current were measured.

  FIG. 3 is a characteristic diagram showing the ammonium molybdate concentration dependence on the amount of electricity (sample amount 200 μm). FIG. 4 is a characteristic diagram showing the ammonium molybdate concentration dependence on the maximum current (sample amount 200 μm). FIG. 5 is a characteristic diagram showing the ammonium molybdate concentration dependence on the background current (sample amount 200 μm).

  As is clear from the characteristic diagram of FIG. 3, it was confirmed that when the sample amount was 200 μL, the amount of electricity was constant when the ammonium molybdate concentration was 6 μL or more. As apparent from the characteristic diagram of FIG. 4, the maximum current increases as the ammonium molybdate concentration increases, but as shown in the characteristic diagram of FIG. 5, the ammonium molybdate concentration starts from around 8 g / L. It can be confirmed that the background current increases rapidly. This suggests that the optimum concentration of ammonium molybdate is around 8 g / L.

  On the other hand, FIG. 6 is a characteristic diagram showing the ammonium molybdate concentration dependency (sample amount 400 μm) with respect to the amount of electricity. FIG. 7 is a characteristic diagram showing the ammonium molybdate concentration dependency (sample amount 400 μm) with respect to the maximum current. FIG. 8 is a characteristic diagram showing the ammonium molybdate concentration dependence on the background current (sample amount 400 μm).

  When the sample amount was 400 μL, as is clear from the characteristic diagram of FIG. 6, it was confirmed that the amount of electricity was constant when the ammonium molybdate concentration was 7 g / L or more. Further, as apparent from the characteristic diagram of FIG. 7, it was confirmed that the maximum current was constant from the vicinity of 8 g / L of ammonium molybdate, unlike the case where the sample amount was 200 μL. As apparent from the characteristic diagram of FIG. 8, the ammonium molybdate concentration rapidly increased from 7 to 8 g / L, indicating that an appropriate ammonium molybdate concentration is around 8 g / L.

  9 to 12 show a 0 to 100 mg / L phosphorus standard solution (potassium dihydrogen phosphate aqueous solution) measured under the conditions shown in Table 2 in the experimental system comprising the components of the phosphorus measurement system 1 of FIG. The results are shown.

  FIG. 9 is a characteristic diagram showing the relationship between the phosphorus standard solution concentration and the amount of electricity when the ammonium molybdate concentration of the reagent solution is 4 g / L. FIG. 10 is a characteristic diagram showing the relationship between the phosphorous standard solution concentration and the amount of electricity when the ammonium molybdate concentration of the reagent solution is 6 g / L. FIG. 11 is a characteristic diagram showing the relationship between the phosphorous standard solution concentration and the amount of electricity when the ammonium molybdate concentration of the reagent solution is 8 g / L. FIG. 12 is a characteristic diagram showing the relationship between the phosphorous standard solution concentration and the quantity of electricity when the ammonium molybdate concentration of the reagent solution is 10 g / L.

  As is clear from the characteristic diagrams of FIGS. 9 to 12, it can be confirmed that a phosphorous standard solution of 0 to 100 mg / L can be measured when the ammonium molybdate concentration is 8 to 10 g / L, but the reagent amount is small. In view of this, it is understood that the optimum concentration of ammonium molybdate is 8 g / L. In addition, the parameter y of the regression line described in FIGS. 9 to 12 represents the electric quantity (mC), and the parameter x represents the phosphorus standard solution concentration (mg / L).

(2) Optimum sulfuric acid concentration FIG. 13 shows the results of studies on the optimum concentration of sulfuric acid in the reagent solution.

  In the experimental system comprising the components of the phosphorus measuring system 1 in FIG. 1, a mixture of ammonium molybdate and sulfuric acid was prepared as a reagent so that the sulfuric acid concentration was 4 to 56 mL / L under the conditions shown in Table 3. As sample water, a 4 mg / L phosphorous standard solution (potassium dihydrogen phosphate aqueous solution) was injected from the injection valve, and the maximum current was measured.

  As is apparent from the characteristic diagram of FIG. 13, it is understood that the sulfuric acid concentration is optimal at 16 to 24 mL / L.

(3) Optimum applied voltage Since the applied voltage affects the background and sensitivity, the optimum applied voltage must be set. FIG. 14 shows the result of study on the optimum applied voltage.

  In the experimental system comprising the components of the phosphorus measuring system 1 in FIG. 1, a mixed solution of ammonium molybdate and sulfuric acid was used as a reagent solution under the conditions shown in Table 4, and a 10 mg / L phosphorus standard solution (as sample water from the injection valve) An aqueous potassium dihydrogen phosphate solution) was injected. The applied voltage was varied from 400 mV to 290 mV, and a hydrodynamic voltagram was obtained. FIG. 15 discloses a characteristic diagram showing the relationship between the applied voltage and the background current.

  As is apparent from the characteristic diagram of FIG. 14, it can be confirmed that the applied voltage has an appropriate value of 320 mV or less at which the fluctuation hardly occurs. Further, it can be confirmed from the characteristic diagram of FIG. 15 that the background current increases as the applied voltage decreases. From the above, it was shown that an applied voltage of 290 to 320 mV is suitable.

  FIGS. 16 to 19 show 10 to 50 mg / L phosphorus standard solution (phosphorus) at an applied voltage of 290 to 320 mV under the conditions shown in Table 5 in the experimental system comprising the components of the phosphorus measuring system 1 of FIG. The results of the measurement of (potassium dihydrogen aqueous solution) are shown.

  FIG. 16 is a characteristic diagram showing the relationship between the phosphorus standard solution concentration and the amount of electricity when the applied voltage is 290 mV. FIG. 17 is a characteristic diagram showing the relationship between the phosphorus standard solution concentration and the amount of electricity when the applied voltage is 300 mV. FIG. 18 is a characteristic diagram showing the relationship between the phosphorus standard solution concentration and the amount of electricity when the applied voltage is 310 mV. FIG. 19 is a characteristic diagram showing the relationship between the phosphorus standard solution concentration and the amount of electricity when the applied voltage is 320 mV.

Since the determination coefficients (R ² ) shown in FIGS. 16 to 19 are all R ² > 0.9, if the applied voltage is in the range of 290 to 320 mV under the conditions of Tables 4 and 5, it is accurate. It shows that it can be measured. The regression line parameters y shown in FIGS. 16 to 19 indicate the quantity of electricity (mC), and the parameter x indicates the phosphorus standard solution concentration (mg / L). Since the optimum applied voltage fluctuates when conditions such as reagent concentration differ, for example, it is necessary to obtain the optimum applied voltage by obtaining a hydrodynamic voltagram each time the conditions are changed.

(4) Effect of length of carbon fiber The length of carbon fiber affects the reduction reaction rate of molybdophosphoric acid produced by the reaction of a mixed solution of ammonium molybdate and sulfuric acid and sample water (phosphorus). Since the flow rate is high and the time during which molybdophosphoric acid stays in the flow cell is shortened, total electrolysis cannot be performed and the measured value may be low.

  In the experimental system comprising the components of the phosphorus measurement system 1 in FIG. 1, the electric quantity of a 50 mg / L phosphorus standard solution (aqueous potassium dihydrogen phosphate solution) was measured under the conditions shown in Table 6.

  Figure 20 shows a mixed solution of ammonium molybdate and sulfuric acid as a reagent solution, and 50 mg / L phosphoric acid standard solution (potassium dihydrogen phosphate aqueous solution) is injected from the injection valve as sample water, and the working electrode length and flow rate are changed. The result of measuring the amount of electricity is shown.

  According to the characteristic diagram of FIG. 20, a mixed solution of ammonium molybdate and sulfuric acid and a phosphoric acid standard solution (potassium dihydrogen phosphate aqueous solution) having a concentration of 50 mg / L or less have a flow rate if the length of the working electrode is 20 mm or more. It can be confirmed that complete electrolysis can be performed in the range of 0.2 to 1.0 mL / min.

(5) Effect of flow rate As is clear from the reduction current pattern in FIG. In the flow injection analysis method, since the flow rate generally affects the sensitivity of the measured value, an optimum flow rate must be set.

  The flow rate affects the rate of formation of molybdophosphoric acid produced by the reaction of a mixed solution of ammonium molybdate and sulfuric acid and sample water (phosphorus) in the mixer, and also affects the reduction reaction rate on the working electrode in the flow cell. .

  In the experimental system consisting of the components of the phosphorus measurement system 1 in FIG. 1, the amount of electricity of a 0-50 mg / L phosphorus standard solution (potassium dihydrogen phosphate aqueous solution) was measured under the conditions shown in Table 7.

  21 to 28, a mixed solution of ammonium molybdate and sulfuric acid is used as a reagent solution, and 0 to 50 mg / L phosphorus standard solution (potassium dihydrogen phosphate aqueous solution) is injected from the injection valve as sample water. The results are shown in which the amount of electricity was measured while changing from 0.05 to 0.5 mL / min.

  FIG. 21 is a characteristic diagram showing the relationship between the phosphorus standard solution concentration and the amount of electricity when the flow rate is 0.5 mL / min. FIG. 22 is a characteristic diagram showing the relationship between the phosphorus standard solution concentration and the amount of electricity when the flow rate is 0.4 mL / min. FIG. 23 is a characteristic diagram showing the relationship between the phosphorus standard solution concentration and the amount of electricity when the flow rate is 0.3 mL / min. FIG. 24 is a characteristic diagram showing the relationship between the phosphorus standard solution concentration and the amount of electricity when the flow rate is 0.25 mL / min. FIG. 25 is a characteristic diagram showing the relationship between the phosphorus standard solution concentration and the amount of electricity when the flow rate is 0.2 mL / min. FIG. 26 is a characteristic diagram showing the relationship between the phosphorus standard solution concentration and the amount of electricity when the flow rate is 0.15 mL / min. FIG. 27 is a characteristic diagram showing the relationship between the phosphorus standard solution concentration and the amount of electricity when the flow rate is 0.1 mL / min. FIG. 28 is a characteristic diagram showing the relationship between the phosphorus standard solution concentration and the amount of electricity when the flow rate is 0.05 mL / min. In addition, the parameter y of the regression line described in FIGS. 21 to 28 means the electric quantity (mC), and the parameter x means the phosphorus standard solution concentration (mg / L).

Since the determination coefficients (R ² ) shown in FIGS. 21 to 27 are all R ² > 0.9, the flow rate is in the range of 0.1 to 0.5 mL / min, and 0 to 50 mg / L. It turns out that the measurement of a phosphorus standard solution (potassium dihydrogen phosphate aqueous solution) is possible.

(6) Sample volume In the experimental system comprising the components of the phosphorus measurement system 1 in FIG. 1, 0 to 50 mg / L of phosphorus standard solution (potassium dihydrogen phosphate aqueous solution) was injected as sample water under the conditions shown in Table 8. The amount of electricity when the sample was injected from the valve at a sample amount of 100 μL, 200 μL, or 500 μL was measured.

  FIG. 29 is a characteristic diagram showing the relationship between the phosphorus standard solution concentration and the amount of electricity when the flow rate is 0.3 mL / min. FIG. 30 is a characteristic diagram showing the relationship between the phosphorus standard solution concentration and the amount of electricity when the flow rate is 0.6 mL / min. From these characteristic diagrams, it was shown that the sample amount can be completely electrolyzed by reacting with a reagent solution (mixture of ammonium molybdate and sulfuric acid) in the range of 100 to 500 μL.

(7) Effect of temperature FIG. 31 shows a sample system in which the temperature of the sample water is changed to 5 to 40 ° C. in a thermostatic bath under the conditions shown in Table 9 in the experimental system comprising the components of the phosphorus measurement system 1 of FIG. The result of measuring the amount of electricity when a 20 mg / L phosphorus standard solution (aqueous potassium dihydrogen phosphate solution) as water is injected from the injection valve 3 in a sample amount of 200 μL is shown.

  As is clear from the characteristic diagram of FIG. 31, it was confirmed that the sample water did not affect the measured value even when the water temperature changed in the range of 5 to 40 ° C.

(8) Measurement Sensitivity FIG. 32 shows a 0 to 4 mg / L phosphorous standard solution (potassium dihydrogen phosphate aqueous solution) under the conditions shown in Table 10 in the experimental system comprising the components of the phosphorus measuring system 1 in FIG. The result of measuring the quantity of electricity is shown. In addition, the parameter y of the regression line shown in the figure means the quantity of electricity (mC), and the parameter x means the phosphorus standard solution concentration (mg / L).

  As is clear from the characteristic diagram of FIG. 32, the difference between the amount of electricity when the phosphorous standard solution (potassium dihydrogen phosphate aqueous solution) concentration is 0.5 mg / L and the amount of electricity when the concentration is 0 mg / L is 1 mC or more. Therefore, it can be determined that at least the measurement sensitivity can be measured to 0.5 mg / L or less.

(9) Measurement range FIG. 33 shows a 0 to 100 mg / L phosphorous standard solution (potassium dihydrogen phosphate aqueous solution) under the conditions shown in Table 11 in the experimental system comprising the components of the phosphorus measuring system 1 in FIG. The result of measuring the quantity of electricity is shown. In addition, the parameter y of the regression line shown in the figure means the quantity of electricity (mC), and the parameter x means the phosphorus standard solution concentration (mg / L).

  As is apparent from the characteristic diagram of FIG. 33, it is shown that the concentration of the phosphor standard solution (aqueous potassium dihydrogen phosphate solution) can be measured up to 100 mg / L, and the measurement range is the phosphor standard solution (potassium dihydrogen phosphate). It can be judged that it is 0-100 mg / L in the aqueous solution concentration.

(10) Measurement accuracy FIG. 34 shows the concentration of phosphorus in the sewage treatment plant aeration tank sewage water at 15-minute intervals under the conditions shown in Table 12 in the experimental system comprising the components of the phosphorus measurement system 1 of FIG. The result of continuous measurement of mg / L) for 7 hours is shown.

  As apparent from the characteristic diagram of FIG. 34, the coefficient of variation of the 29 measurements was 1.4%, indicating that the measurement can be performed with good reproducibility.

  Moreover, the result of having continuously measured the filtered water of the aeration tank sewage of the sewage treatment plant sampled on another day under the conditions of Table 12 at intervals of 15 minutes is shown in FIG. As is clear from the characteristic diagram of FIG. 35, the coefficient of variation of the 25 measurements was 0.6%, indicating that measurement can be performed with good reproducibility.

(11) Measurement interval In FIG. 36, a reagent solution is prepared by mixing ammonium molybdate and sulfuric acid under the conditions shown in Table 13 in the experimental system comprising the components of the phosphorus measurement system 1 of FIG. The results are shown in which a 60 mg / L phosphorous standard solution (potassium dihydrogen phosphate aqueous solution) as sample water was injected into the carrier solution from the injection valve at intervals of 5 minutes and the reduction current was measured.

  As is clear from the characteristic diagram of FIG. 36, it was shown that even if the measurement interval was 5 minutes, measurement was possible without being affected by the sample measured immediately before.

  37 to 40, an ammonium molybdate and sulfuric acid are mixed under the conditions shown in Table 14 in the experimental system comprising the components of the phosphorus measurement system 1 of FIG. As a sample water, a 60 mg / L phosphorous standard solution (potassium dihydrogen phosphate aqueous solution) was injected into the carrier solution from the injection valve at intervals of 1.3 to 2.3 minutes, and the results of measuring the reduction current were shown. Yes.

  As is apparent from the characteristic diagrams of FIGS. 37 to 40, it was shown that measurement can be performed without being affected by the sample measured immediately before even at a measurement interval of 1.3 to 2.3 minutes.

  Further, in the experimental system comprising the components of the phosphorus measurement system 1 in FIG. 1, a reagent solution was prepared by mixing ammonium molybdate and sulfuric acid under the conditions shown in Table 15, and 60 mg / L of sample water was prepared. Phosphorus standard solution (potassium dihydrogen phosphate aqueous solution) 400 μL and distilled water 400 μL are alternately injected into the carrier solution through the injection valve three times at intervals of 2.3 minutes, and the 60 mg / L phosphorous standard solution measured immediately before is injected. It was tested whether the influence of (potassium dihydrogen phosphate aqueous solution) affects the measured value of distilled water or the so-called tailing effect.

  FIG. 41 shows the results of the test. As is clear from this characteristic diagram, it was shown that measurement can be performed without being affected by the sample measured immediately before.

(12) Correlation with the official method FIG. 42 shows the official method of the filtered water from the aeration tank sewage treatment plant under the conditions shown in Table 16 in the experimental system comprising the components of the phosphorus measurement system 1 in FIG. The correlation between the absorbance method) and the value measured by this measurement method is shown. In addition, the parameter y of the regression line shown in the figure means the quantity of electricity (mC), and the parameter x means the phosphorus standard solution concentration (mg / L).

As is clear from the characteristic diagram of FIG. 42, the coefficient of determination R ² is 0.9992 and the slope of the regression line is 0.9964, indicating a value close to 1, confirming that measurement accuracy equivalent to the official method is achieved. It was done.

(13) Standard curve (calibration curve)
FIG. 43 shows the amount of electricity of a phosphorous standard solution (potassium dihydrogen phosphate aqueous solution) of 0 to 50 mg / L four times under the conditions shown in Table 17 in the experimental system comprising the components of the phosphorus measuring system 1 of FIG. The results of measurement with different measurement dates are shown.

  Table 18 shows the regression equation of the measurement result and the correlation coefficient. The parameter y of the regression line shown in the table means the quantity of electricity (mC), and the parameter x means the phosphorus standard solution concentration (mg / L). Table 19 shows the coefficient of variation of the electric quantity when the electric quantity with respect to each concentration of the phosphorous standard solution (potassium dihydrogen phosphate aqueous solution) is calculated from each calibration curve.

  As shown in Table 19, the quantity of electricity with respect to the concentration of the phosphorus standard solution (potassium dihydrogen phosphate aqueous solution) has a coefficient of variation of about 1% even when the measurement date is different, and there is almost no change. It has been shown that the measurement need not be performed.

  As described above, since the calibration curve is stable, it has been shown that troublesome operations for the preparation of the standard solution and calibration of the standard solution are not required for each measurement.

  FIG. 44 is a schematic configuration diagram of a phosphorus measuring apparatus according to an embodiment of the phosphorus measuring method of the present invention.

  The flow injection analyzing means 2b of the phosphorus measuring device 10 is provided with a coulometric type flow cell 11 as a component of the flow injection analyzing means 2a according to the phosphorus measuring device 1. The flow cell 11 is provided in a narrow tube 32 connecting the pump P3 and the injection valve 3.

  Like the flow cell 5, the flow cell 11 includes a working electrode, a reference electrode, and a counter electrode. The flow cell 11 reduces the interfering substances exemplified by hypochlorite ions and the like contained in the sample water by an oxidation-reduction reaction that occurs between the working electrode, the reference electrode, and the counter electrode. The flow injection analysis means 2b exemplifies a system for measuring an interfering substance in the flow cell 11. However, when a reagent is required for measuring the interfering substance, a capillary tube connecting the pump P3 and the flow cell 11 is used. A mixing container may be provided between 32 so that the reagent can be introduced. When there is a possibility that an interfering substance is contained in the reagent solution, the capillary 41 is provided with a coulometric type flow cell of the same type as the flow cell 11. Furthermore, when there is a possibility that an interfering substance is contained in the carrier liquid, the capillary tube 31 is provided with a coulometric type flow cell of the same type as the flow cell 11. As described above, the interfering substances contained in the sample water, the reagent solution and the carrier liquid are reduced and removed before being supplied to the injection valve 3 or the mixer 4, and the phosphate ion-phosphorus concentration in the sample water is accurately measured. .

  An operation example of the phosphorus measuring apparatus 10 shown in FIG. 44 will be described. The reagent solution, the carrier liquid, and the sample water are respectively sent to the drain part (drain bottle 7) at a constant speed by pumps P1, P2, and P3. The sample water in the sample bottle 6 is supplied to the injection valve 3 through the thin tube 32 by the pump P3. In this process, the flow cell 11 reduces and removes interfering substances contained in the sample water. The sample water quantified by the injection valve 3 is supplied to the mixer 4 through the thin tubes 33 and 34 along the flow of the carrier liquid provided through the thin tube 31. At this time, the phosphorus component contained in the sample water reacts with ammonium molybdate in the reagent solution injected through the thin tube 41 to generate molybdophosphoric acid. When the generated molybdophosphoric acid reaches the flow cell 5 through the thin tube 42, the current change accompanying the reduction reaction of the molybdophosphoric acid is measured by the working electrode. The detected reduction current value is transmitted to the terminal (PC) via the potentiostat 8 and used for data processing. The carrier liquid containing the reagent solution and the sample water that has passed through the flow cell 5 is guided to the drain bottle 7 as a waste liquid through the thin tube 51.

The schematic block diagram which showed one Embodiment of the phosphorus measuring method of this invention. The characteristic view which showed the pattern of the reduction current measured by the flow injection analysis method. The characteristic view which showed the ammonium molybdate density | concentration dependence (sample amount of 200 micrometers) with respect to the amount of electricity. The characteristic view which showed the ammonium molybdate density | concentration dependence (sample amount of 200 micrometers) with respect to the largest electric current. The characteristic view which showed the ammonium molybdate density | concentration dependence (sample amount of 200 micrometers) with respect to background current. The characteristic view which showed the ammonium molybdate density | concentration dependence (sample amount of 400 micrometers) with respect to the amount of electricity. The characteristic view which showed the ammonium molybdate density | concentration dependence (sample amount of 400 micrometers) with respect to the largest electric current. The characteristic view which showed the ammonium molybdate density | concentration dependence (sample amount of 400 micrometers) with respect to background current. The characteristic view which showed the relationship between a phosphorus standard solution density | concentration in case the ammonium molybdate density | concentration of a reagent solution is 4 g / L, and an electric quantity. The characteristic view which showed the relationship between the phosphorus standard solution density | concentration in case the ammonium molybdate density | concentration of a reagent solution is 6 g / L, and an electric quantity. The characteristic view which showed the relationship between the phosphorus standard solution density | concentration in case the ammonium molybdate density | concentration of a reagent solution is 8 g / L, and an electric quantity. The characteristic view which showed the relationship between a phosphorus standard solution density | concentration in case the ammonium molybdate density | concentration of a reagent solution is 10 g / L, and an electric quantity. The characteristic view which showed the relationship between the sulfuric acid concentration of a reagent solution, and the maximum electric current value. The characteristic view which showed the relationship between an applied voltage and the amount of electricity. The characteristic view which showed the relationship between an applied voltage and background current. The characteristic view which showed the relationship between a phosphorus standard solution density | concentration in case an applied voltage is 290 mV, and an electric quantity. The characteristic view which showed the relationship between a phosphorus standard solution density | concentration in case an applied voltage is 300 mV, and an electric quantity. The characteristic view which showed the relationship between a phosphorus standard solution density | concentration in case an applied voltage is 310 mV, and an electric quantity. The characteristic view which showed the relationship between a phosphorus standard solution density | concentration in case an applied voltage is 320 mV, and an electric quantity. The characteristic view which showed the relationship between a working electrode and electricity. The characteristic view which showed the relationship between a phosphorus standard solution density | concentration in case a flow rate is 0.5 mL / min, and an electric quantity. The characteristic view which showed the relationship between a phosphorus standard solution density | concentration in case a flow rate is 0.4 mL / min, and an electric quantity. The characteristic view which showed the relationship between a phosphorus standard solution density | concentration in case a flow rate is 0.3 mL / min, and an electric quantity. The characteristic view which showed the relationship between a phosphorus standard solution density | concentration in case a flow rate is 0.25 mL / min, and an electric quantity. The characteristic view which showed the relationship between a phosphorus standard solution density | concentration in case a flow rate is 0.2 mL / min, and an electric quantity. The characteristic view which showed the relationship between a phosphorus standard solution density | concentration in case a flow rate is 0.15 mL / min, and an electric quantity. The characteristic view which showed the relationship between a phosphorus standard solution density | concentration in case a flow rate is 0.1 mL / min, and an electric quantity. The characteristic view which showed the relationship between a phosphorus standard solution density | concentration in case a flow rate is 0.05 mL / min, and an electric quantity. The characteristic view which showed the relationship between a phosphorus standard solution density | concentration in case a flow rate is 0.3 mL / min, and an electric quantity. The characteristic view which showed the relationship between a phosphorus standard solution density | concentration in case a flow rate is 0.6 mL / min, and an electric quantity. The characteristic view which showed the influence of the sample water temperature which acts on a measured value. The characteristic figure which showed the measurement sensitivity. The characteristic view which showed the relationship between a phosphorus standard solution density | concentration and the amount of electricity. A characteristic diagram showing measurement accuracy. A characteristic diagram showing measurement accuracy. The characteristic view which showed the result of having continuously measured the reduction current at intervals of 5 minutes. The characteristic view which showed the result of having continuously measured the reduction current at intervals of 1.3 minutes. The characteristic view which showed the result of having continuously measured the reduction current at intervals of 1.4 minutes. The characteristic view which showed the result of having continuously measured the reduction current at intervals of 1.6 minutes. The characteristic figure which showed the result of having continuously measured the reduction current at intervals of 2.3 minutes. The characteristic view which showed the electric quantity of distilled water and phosphorus standard solution. The characteristic view which showed the correlation with the measuring method and official method which concern on this invention. The characteristic view which showed the relationship between the phosphorus standard solution density | concentration measured repeatedly and the amount of electricity. The schematic block diagram which showed one Embodiment of the phosphorus measuring method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,10 ... Phosphorus measuring apparatus 2a, 2b ... Flow injection analysis means 3 ... Injection valve 4 ... Mixer 5,11 ... Flow cell 6 ... Sample bottle 7 ... Drain bottle 8 ... Potentiostat 9 ... Terminal (PC)
31-35, 41, 42, 51 ... capillary

Claims (16)

A phosphorus measurement method for electrochemically measuring a phosphate ion-phosphorus concentration in a sample water by flow injection analysis in which a mixed solution of ammonium molybdate and sulfuric acid is provided as a reagent solution,
The ammonium molybdate concentration of the mixed solution is 8 to 10 g / L,
The method for measuring phosphorus, wherein the mixed solution has a sulfuric acid concentration of 16 to 24 mL / L. The phosphorus measurement method according to claim 1, wherein the flow injection analysis includes an electrochemical detection step using coulometry, and an applied voltage in the electrochemical detection step is 290 to 320 mV. The phosphorus measuring method according to claim 2, wherein a length of the working electrode used for the electrochemical detection step is 20 mm or more. The phosphorus measurement method according to claim 3, wherein flow rates of the reagent solution, the sample water, and the carrier liquid are 0.05 to 0.5 mL / min. The phosphorus measurement method according to claim 4, wherein a sample amount of the flow injection analysis is 100 to 500 μL. The phosphorus measurement method according to any one of claims 1 to 5, wherein the sample water is subjected to a flow injection analysis after reducing interference substances in the sample water by a coulometric flow cell. The phosphorus measurement method according to any one of claims 1 to 5, wherein the reagent solution is subjected to flow injection analysis after reducing the interfering substances in the reagent solution by a coulometric flow cell. The phosphorus measurement method according to any one of claims 1 to 5, wherein the carrier liquid is subjected to a flow injection analysis after reducing interference substances in the carrier liquid by a coulometric flow cell. A phosphorus measuring device for electrochemically measuring a phosphate ion-phosphorus concentration in a sample water by a flow injection analysis means in which a mixed solution of ammonium molybdate and sulfuric acid is provided as a reagent solution,
The flow injection analysis means is supplied from an injection means for injecting the reagent solution or sample water into a carrier liquid, a mixer for mixing the carrier liquid, the reagent solution, and the sample water, and the mixer. A flow cell for detecting a change in current based on the reaction between the reagent solution and the sample water,
The ammonium molybdate concentration of the reagent solution or the mixed solution is 8 to 10 g / L,
The phosphoric acid measuring apparatus, wherein the reagent solution or the mixed solution has a sulfuric acid concentration of 16 to 24 mL / L. The phosphorus measuring apparatus according to claim 9, wherein the flow injection analysis means includes an electrochemical detection means using coulometry, and an applied voltage of the electrochemical detection means is 290 to 320 mV. The length of the working electrode which concerns on the said electrochemical detection means is 20 mm or more. The phosphorus measuring device of Claim 10 characterized by the above-mentioned. The phosphorus measuring apparatus according to claim 11, wherein flow rates of the reagent solution, the sample water, and the carrier liquid are 0.05 to 0.5 mL / min. The phosphorus measuring apparatus according to claim 12, wherein a sample amount of the flow injection analysis is 100 to 500 μL. A flow cell for supplying the sample water to the injection means is provided with a coulometric type flow cell,
The phosphorus measuring device according to any one of claims 9 to 13, wherein the flow cell performs a reduction treatment of an interfering substance contained in the sample water. The flow path for supplying the reagent solution to the mixer is provided with a coulometric type flow cell,
The phosphorus measuring device according to any one of claims 9 to 13, wherein the flow cell reduces the interfering substance in the reagent solution. A flow cell for supplying the carrier liquid to the injection means is provided with a coulometric type flow cell,
The phosphorus measuring apparatus according to any one of claims 9 to 13, wherein the flow cell performs a reduction treatment of an interfering substance contained in the carrier liquid.

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