JPS646694B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for measuring nitrate ion concentration in river water or treated sewage water.

Colorimetric methods, ion electrode methods, and polarographic methods are known as methods for analyzing nitrate ions. The colorimetric method uses brucine to directly develop color;
Widely used methods include a method in which a Cu--Cd alloy column is used to reduce No ₂ ^- to develop color, and a Devalta alloy is used to reduce it to NH ₃ and quantitative determination.
The ion electrode method is a simple quantitative method and is suitable for water quality analysis, but it is also heavily influenced by interfering substances and there are still problems with the stability of the electrode. The method using brucine is greatly affected by interfering substances, and the method using reduction is interfered with by No ₂ ^- and NH ₄ ⁺ , so these must be removed in pretreatment or analyzed in advance. The procedure is complicated and it is not suitable for continuous measurements.

The polarograph method utilizes the fact that NO ₃ ^- is electrolytically reduced in the coexistence of a catalyst and determines its concentration by measuring the increase in current value, but it takes time to completely remove oxygen. The problem is that it requires a lot of time, and that polarographic measuring devices are not common.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an automatic nitrate ion concentration measuring device that is less affected by interfering substances, is easy to operate, and does not require strict measurement conditions.

The present invention applies the principle of the polarographic method that is not affected by NH ₄ ⁺ ions, and specifically is as follows.

NO ₃ ^- ions in aqueous solution are not directly electrolytically reduced by the mercury electrode, but Cr()-hedta
(HEDTA=H ₃ hedta: N'-(2-hydroxyethyl)ethylenediamine-N,N,N'-triacetic acid)
When the complex coexists, Cr()--
hedta is generated, and this Cr() complex acts as a catalyst to reduce NO ₃ ^- ions. By utilizing this reaction, NO ₃ ^- ions can be determined from the amount of electricity required for electrolysis.

The reactions that occur during this experimental procedure are shown by the following equations (1) to (6) [Equations (1) and (2); pre-electrolysis; Equations (5) and (6);
NO ₃ ^-Reduction reaction] Cr ³⁺ +e→Cr ²⁺ (1) Cr ²⁺ +O→Cr ³⁺ +R (2) Cr ²⁺ +hedta→Cr()−hedta (3) Cr()−hedta+Cr ³⁺ → Cr()−hedta＋Cr2 ⁺
(4) Cr()-hedta+e→Cr()-hedta (5) 6Cr()-hedta+NO ₃ ^- +8H ⁺ →6Cr()-
hedta+NH ₃ OH ⁺ +2H ₂ O (6) Since the sample solution contains a substance (O) that is easily reduced such as oxygen, it is necessary to remove it. First, when pre-electrolysis is performed by adding only Cr ³⁺ ions in the absence of hedta, the reactions of equations (1) and (2) are repeated. When all oxygen etc. are reduced (2)
The reaction (1) disappears and only the reaction (1) proceeds, so Cr ²⁺ ions begin to accumulate in the solution. Note that R is a reduced substance. At this point, pre-electrolysis is finished,
When electrolysis is stopped and hedta is added, in the solution (3),
The reactions of equations (4) and (6) proceed, but since the reactions of equations (3) and (4) are fast, most of the chromium in the solution is Cr().
-becomes a hedta complex.

Next, when the initial voltage is set to reduce the Cr()-hedta complex and electrolysis is performed again, the reactions in equations (5) and (6) are repeated. When all NO ₃ ^- ions in the solution are reduced, only reaction (5) proceeds, and Cr()-hedta complex begins to accumulate in the solution. Therefore, the amount of electricity required from when Cr ²⁺ begins to accumulate during pre-electrolysis until the Cr()-hedta complex begins to accumulate corresponds to the amount of electricity required to reduce NO ₃ ^- . This is the NO ₃ ^- that was present in the solution.
It will be proportional to the amount of

Hereinafter, the present invention will be explained in detail based on illustrated embodiments.

FIGS. 1 and 2 show an embodiment of the present invention, with FIG. 1 showing the overall configuration and FIG. 2 showing the structure of an electrolytic cell. In the figure, 1 is the measurement/control unit, 2 is the buffer solution tank, 3 is the chromium solution tank, 4 is the hedta solution tank, and 5 is dilution water (distilled water).
tank, 6 is a test tank, 7 to 11 are measuring tubes, 12 and 1
3 is a mercury adsorption tower (aqueous solution tank filled with chelate resin), 14 is an N ₂ cylinder, 15 is an alkaline pyrogallol solution tank, 16 is a buffer tank, 17 is a waste liquid tank, 18 to 20 are air pumps, 21 to 2
5 is a three-way electromagnetic valve, 26 to 32 are electromagnetic valves, 33 is a manual valve, 34 is a magnetic stirrer equipped with a round stirrer 34A, and 40 is an electrolytic cell placed on this stirrer 34.

As shown in FIG. 2, the electrolytic cell 40 includes a mercury pool 4 as a working electrode at the bottom of a glass container 401.
02 is provided, and a lid 403 made of vinyl chloride is equipped with an anode 404 as a working electrode, a reference electrode 405, electrodes 406 and 407 for end point potential measurement, an N ₂ gas inlet 408,
Reagent/sample inlet 409, _N2 gas outlet 410,
It has a structure in which waste liquid discharge pipes 411 are respectively attached. A platinum wire is used as the anode 404,
Glass filter 412A and agar bridge 41 at one end
3 A is installed, and 0.5 mol/l K ₂ SO ₄ solution 4 is placed inside.
A platinum wire 40 is placed inside an insulating tube 415A containing 14A.
4 is inserted to isolate it from the sample solution. In addition, the reference electrode 405 is a saturated acetate electrode (saturated calomel electrode: SCE), and the anode 404 is
Similarly, it is isolated from the sample solution by an agar bridge 413B or the like.

The three-way solenoid valve 21 is connected to the buffer solution tank 2, the measuring tube 7, and the air pump 18, respectively, so that the measuring tube 7, the buffer solution tank 2, and the air pump 18 are connected to each other by switching. There is. Similarly, the three-way solenoid valve 22 is piped to the chromium solution tank 3, the metering pipe 8, and the air pump 18, respectively, and the three-way solenoid valve 23 is piped to the hedta solution tank 4, the metering pipe 9, and the air pump 18, respectively. has been done. Furthermore, the three-way solenoid valve 24 is connected to the dilution water tank 5, the metering tube 10, and the air pump 19, and the three-way solenoid valve 25 is connected to the water test tank 6, the metering tube 11, and the air pump 1.
9, respectively. Each measuring tube 7, 8,
9, 10, 11 are solenoid valves 26, 27, 28, respectively.
It is piped to the reagent/sample injection port 409 of the electrolytic cell 40 via 29 and 30. Said water test tank 6
A test water intake pipe is installed in the pipe, into which a manual valve 33 is inserted.

On the other hand, the N ₂ cylinder 14 is piped to the N ₂ gas inlet 408 of the electrolytic cell 40 via a solenoid valve 31 and an alkaline pyrogallol solution tank 15, and a mercury adsorption tower 1 is connected to the N ₂ gas outlet 410 of the electrolytic cell 40.
2 and 13 are connected in sequence to form an N ₂ gas flow path. In addition, a buffer tank 1 is provided in the waste liquid discharge pipe 411 of the electrolytic cell 40.
A waste liquid tank 17 is connected to the buffer tank 16 via a solenoid valve 32, and an air pump 20 is connected to the buffer tank 16 via a solenoid valve 32.

As shown by dotted lines, the measurement/control unit 1 includes an anode 404 of the electrolytic cell 40, a reference electrode 405, and electrodes 406 and 407 for end-point potential measurement (one of the end-point potential measurement electrodes 406 is at the same potential as the mercury pool 402). ) are connected to each other. Although not shown, each of the three-way solenoid valves 21 to 25 and the solenoid valve 2
6 to 32 and are also connected to air pumps 18 to 20. This measurement/control unit 1 measures the current value and time from the time when the hedta solution is injected to the time when the reduction of NO ₃ ^- ions is completed during electrolytic analysis, and reduces the NO ₃ ^- ions. It is equipped with a function to integrate and record the amount of electricity required, a function to detect the end point potential, and a sequence control function.

Next, the measurement operation will be described. The test water is always overflowed into the water test tank 6 by adjusting the opening degree of the manual valve 33. When measuring and injecting the test water,
First, connect the 3-way solenoid valve 25 to the metering pipe 11 and the air pump 1.
9 is switched to the communicating side, and the pressure inside the metering tube 11 is reduced by the action of the air pump 19. Thereafter, the three-way solenoid valve 25 is switched to the side where the measuring tube 11 and the water test tank 6 communicate with each other, and the test water is drawn into the measuring tube 11. After inhalation, the inside of the metering tube 11 is brought to atmospheric pressure and the metering level is determined. Next, the electromagnetic valve 30 is opened and sample water is injected into the container 401 of the electrolytic cell 40. At this time, for water testing, pressure is applied inside the measuring tube 11, and the solenoid valve 3
0. Make sure that no liquid remains in the piping. Measurement and injection of dilution water and reagents are performed in the same manner as for water testing.

After injecting the sample water into the electrolytic cell 40, the buffer solution and chromium are extracted from the buffer solution tank 2 containing an aqueous solution of sodium acetate, glycine, potassium chloride, copper sulfate, and acetic acid, and the chromium solution tank 3 containing an aqueous chromium alum solution. Inject the solution into a _N2 cylinder at room temperature 1
From step 4, _N2 gas is passed through the alkaline pyrogallol solution tank 15 while stirring with a magnetic stirrer 34, and pre-electrolysis is performed at a current value of 6 to 8 mA. When the solution potential suddenly changes, it is assumed that the pre-electrolysis has ended and the electrolysis is stopped. The reason for containing copper sulfate as a buffer is as follows. In other words, there are various substances that have coordination ability in actual samples, and they are generated by equation (1).
May form complexes with Cr ²⁺ ions, complicating reactions. Therefore, by allowing Cu ions to coexist, a complex is formed with various substances that have coordination ability, and the end point of the reaction is made clear.

Here, a hedta solution is injected from the hedta solution tank 4 containing an aqueous solution of trisodium N'-(2-hydroxyethyl)ethylenediamine-N,N,N'-triacetate. After the solution potential stabilizes, the initial electrolytic voltage (Ei) is set to a value close to the half-wave potential of the Cr()-hedta complex, and electrolysis is started again to reduce NO ₃ ^- ions. The point at which the solution potential suddenly changes during this reduction process is defined as the end point of the reduction. (hedta) The current and time from the time when the solution is injected to the time when the reduction of NO ₃ ^- ions is completed are measured in the measurement/control unit 1, and based on this, the NO ₃ ^- ions are reduced by the integrator. The amount of electricity required is integrated and recorded.

The above operating procedure is set by sequence control, and measurements are automatically performed. Further, subsequent liquid processing is similarly performed automatically by sequence control. That is, the waste liquid from the cell 40 is transferred to the air pump 2.
The liquid is sucked into the buffer tank 16 by the action of 0, and is sent to the waste liquid tank 17 from there. After this, the inside of the cell 40 and the electrodes are cleaned in the dilution water tank 5.
This is done by injecting more diluted water and discharging after washing. This process is performed three or more times to ensure the stability of the electrode.

Note that the N ₂ gas discharged from the electrolytic cell 40 may contain mercury vapor, albeit in a small amount, so it is exhausted from the N ₂ gas outlet 410 through the mercury adsorption towers 12 and 13 to remove mercury. It is being removed. In addition, the mercury pool 402 as an electrode is
Sometimes the sensitivity decreases, so it is necessary to leave it overnight in a 0.3N-HNO ₃ solution and clean it. Further, a blank set is performed in the above step using dilution water to set the end point potential of the pre-electrolysis. The span set is set by using a solution of NO ₃ ^- 5 μmol (NO ₃ ^- -N1.4 mg/l) and determining the initial electrolysis voltage (Ei) and electrolysis end point potential.

As described above, according to the present invention, Cr()--
When determining the nitrate ion concentration by electrolytic analysis using hedta complex as a catalyst, the sample/reagent supply section must have a negative pressure metering function using an air pump, measuring tube, solenoid valve, etc., and the _N2 gas flow path and cleaning・The amount of electricity required to automatically reduce NO ₃ ^- by performing sequence control including the drainage part (this is the amount of electricity required to reduce NO ₃ ^-
This method has the following advantages:

(1) Less influence of interfering substances, especially No ₂ ^- and
No influence of _NH4 ⁺ .

(2) Since the absolute amount of NO ₃ ^- is measured, there is no need for strict measurement conditions, and there is no need to draw a calibration curve each time a measurement is made.

(3) The electrode is isolated from the sample solution by an agar bridge and is washed with distilled water three or more times, so the electrode is sufficiently stable.

(4) Compared to colorimetric methods, it does not require pretreatment and is easy to operate.

(5) Buffer solution eliminates the influence of PH.

(6) By changing the initial electrolysis voltage and sample weight, it can be applied to more dilute systems such as seawater.

(7) Measurement time is about 20 minutes including cleaning time, making it possible to measure in a short time.

(8) Since it is metered and injected from the water test tank using the negative pressure metering method, it can be applied to both batch and continuous measurements.

(9) Sequence control allows measurement procedures to proceed in an orderly manner and maintains a good measurement environment.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an automatic nitrate ion concentration measuring device according to the present invention, and FIG. 2 is a block diagram of an electrolytic cell in the same embodiment. 1... Measurement/control unit, 2... Buffer solution tank, 3... Chromium solution tank, 4... Hedta solution tank, 5... Dilution water tank, 6
... water test tank, 7-11... measuring tube, 12 and 13... mercury adsorption tower, 14... _N2 cylinder, 15... alkaline pyrogallol solution tank, 16... buffer tank,
17... Waste liquid tank, 18-20... Air pump, 2
1 to 25... 3-way solenoid valve, 26 to 32... solenoid valve, 3
3...Manual valve, 34...Magnetic stirrer, 4
0... Electrolytic cell.

Claims (1)

[Claims] 1. An electrolytic cell equipped with a mercury pool, an anode, a reference electrode, an electrode for end-point potential measurement, an N ₂ gas inlet, a N ₂ gas outlet, a sample/reagent inlet, and a waste liquid discharge pipe, and a buffer solution tank. , each sample in the chromium solution tank, hedta solution tank, dilution tank, and sample tank containing trivalent chromium ions,
a sample/reagent supply unit that measures reagents under negative pressure using an air pump, a metering tube, a solenoid valve, etc. and supplies them to the electrolytic cells; an N ₂ gas flow path that circulates N ₂ gas to the electrolytic cells; The current value and time are measured between the waste liquid treatment section that discharges the waste liquid of the electrolytic cell and the time from the time when the hedta solution is injected during electrolytic analysis to the time when the reduction of NO ₃ ^- ions is completed, and NO ₃ ^- ions are reduced. A function to integrate the amount of electricity required for the reaction, a function to detect the solution potential and detect the end point of the reaction from a predetermined rate of change, each of the sample/reagent supply section, the N ₂ gas flow path, and the waste liquid treatment section. It is equipped with a measurement and control section that has a sequence control function that controls the operation according to a predetermined procedure, and reduces easily-reduced substances other than NO ₃ ^- ions in the sample by injecting a chromium solution into the electrolytic cell. The completion of the reduction is detected by the solution potential, and after the hedta solution is injected into the electrolytic cell, the Cr
( ) - An automatic nitrate ion concentration measuring device characterized by performing electrolysis at a potential that can reduce the hedta complex, thereby reducing NO ₃ ^- ions.