JPH10160668A - Method and device for measuring nitric acid concentration by continuous flow analysis method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rapidly and accurately measure the concentration of not only a high-concentration nitric acid solution but also a low-concentration nitric acid solution by using measurement light including a plurality of wavelengths with an absorption region for a nitric acid ion and selecting the wavelength of measurement light according to the nitric acid concentration of a sample liquid and measuring absorbance. SOLUTION: A target sample liquid is selected by a switching valve 12 and the sample loop of an injection valve 11 is filled with the sample liquid by a suction pump 14. Then, the injection valve 11 is opened, the sample liquid is fed to a pipeline 40 and is fed to a measurement part 30 via a dilution part 20 by a carrier liquid that flows in the pipeline 40, and the absorbance is measured. When the nitric acid concentration level of the sample liquid is known in advance, the wavelength of the measurement light is selected according to the nitric acid concentration level and an absorbance is measured by the measurement light with a proper wavelength. Concretely speaking, light with a wavelength of 280nm-330mm has an absorption liquid for nitric acid ion so that it is used for measurement. The wavelength of the measurement light is selected after measuring the nitric acid concentration level of the sample liquid in advance by preliminary measurement when the level of the nitric acid concentration is known.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a nitric acid concentration in a continuous flow analysis by accurately selecting a nitric acid concentration in a sample solution by selecting a wavelength according to the concentration and using an optimum measuring wavelength. Regarding the device.

[0002] In a denitration facility provided for removing harmful substances that cause environmental pollution from a gas containing nitrogen oxides and the like, it is essential to control the concentration of nitric acid in the liquid. For example, in the silver dissolution process performed in the fields of photographic processing and mint, nitrogen oxides generated when metal silver is dissolved are absorbed in an acid solution. Concentration control is important. The present invention is useful for such a nitric acid concentration measurement.

[0003]

2. Description of the Related Art As a method for measuring the concentration of nitric acid, conventionally, a measurement using a specific gravity, a measurement using an ultrasonic wave, a measurement using an absorptiometer, and the like are known. Among these methods, (1) the specific gravity measurement method is a method of measuring the specific gravity of a sample solution and converting it into a nitric acid concentration, but has a problem that a measurement error due to the temperature of the sample solution is large. Further, since the change in specific gravity due to the density difference is small, the detection sensitivity is low, and accurate density measurement cannot be performed. (2) The ultrasonic measurement method is a method of converting a concentration from the density of a sample liquid, and the range that can be quantified is limited, and a concentration of 10 M or more cannot be measured. (3) Absorbance method and differential spectrophotometry based on it are well water, river water,
Applicable to measurement of freshwater surface water such as tap water.
Level) of nitrogen oxide ions.
In order to apply to a highly concentrated solution such as a process solution, a dilution operation by 10,000 times is necessary, and an error in the dilution operation becomes a problem.
In addition, examples of quantification of nitrogen oxide ions by continuous flow analysis have been reported, but this is an example of application to well water, rainwater, etc., and is not intended for solutions with a high nitric acid concentration such as process liquids. Absent.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the conventional measuring method, and is intended to solve such a problem as a nitric acid absorbing solution used in a denitration facility for removing nitrogen oxides generated from a silver dissolving step. An object of the present invention is to provide a method and an apparatus for measuring the concentration of nitric acid which can quickly and accurately measure the concentration of a nitric acid solution of a low concentration as well as a high concentration of a nitric acid solution.

[0005]

The present invention (1) measures the nitric acid concentration from the absorbance of a sample solution based on a continuous flow analysis method in which the sample solution is adjusted and the absorbance is measured while flowing the sample solution through a pipe line. In the method, using a measurement light including a plurality of wavelengths having an absorption range for nitrate ions, measuring the absorbance by selecting a wavelength of the measurement light according to the nitric acid concentration of the sample solution. Is a measuring method.

The above-mentioned measuring method of the present invention comprises the following steps: (2) using a measuring light having a wavelength of 330 nm for a sample solution having a high nitric acid concentration;
A method using a measurement light having a wavelength of 280 nm for a sample solution having a low nitric acid concentration. (3) The nitric acid concentration level of the sample solution is first measured by preliminary measurement, and the wavelength of the measuring light is determined based on the nitric acid concentration level. (4) In the pre-measurement, using a measurement light on the 330 nm side for a sample solution with a nitric acid concentration of 10 M or more within the measurable range, using a sample light of less than 10 M (5) In preliminary measurement, dilute a sample solution whose nitric acid concentration is out of the measurable range to make the measurable range, and then measure the nitric acid concentration. And (6) a method of diluting a sample solution in a measurable range of nitric acid concentration and measuring nitric acid concentration using measuring light on the 280 nm side.

The present invention also provides (7) a sample liquid introduction section, a diluted section of the introduced sample liquid, a measurement section for measuring the absorbance of the diluted sample liquid due to nitrate ions, and a pipeline connecting these sections in series. Thus, a measurement system for continuous flow analysis is formed, and the measurement section has measurement light including a plurality of wavelengths having an absorption range for nitrate ions, and the wavelength of the measurement light can be selected according to the nitric acid concentration. This is a nitric acid concentration measuring device provided with a spectrophotometer.

(8) An apparatus according to the present invention, wherein (8) a selective liquid supply means for holding a plurality of sample liquids and selectively introducing the sample liquids into the conduit of the measurement system is provided in the sample liquid introduction section.
(9) An injection valve interposed in the above-mentioned conduit of the measurement system, a switching valve connected to the injection valve, a plurality of sample liquid holding portions connected to the switching valve, and suction for guiding the sample liquid to the conduit of the measurement system. It includes a pump and an apparatus in which the above-mentioned selective supply means is formed by an injection line connecting them.

Further, the measuring device of the present invention comprises (10) a device in which a sedimentation / separation unit is provided between the sample liquid introduction part and the measuring unit, and (11) a switching valve provided in the measuring system pipe. A precipitant addition pipe line provided on the sample liquid inflow side of the switching valve, a mixing coil section for mixing the precipitant with the sample liquid, a filtration loop attached to the switching valve, and a washing connected to the switching valve. An apparatus in which a sedimentation separation section is formed by a pipe line, and the connection of a filtration loop is switched to a measurement system pipe line or a washing pipe line by a switching valve. (12) Selective supply means of a sample liquid introduction section, a dilution section, a sedimentation separation section Section and the measuring section are connected to the central controller, a series of operations from the introduction of the sample solution to the measurement of the absorbance are automatically controlled by the central controller, and the calibration curve data of the absorbance recorded in the central controller Try based on Include devices nitric acid concentration of the solution is measured automatically.

[0010]

(I) Measuring Apparatus FIG. 1 shows an example of a measuring apparatus according to the present invention. The measuring apparatus has a sample liquid inlet 10 and a measuring unit 30 for measuring the absorbance of the sample liquid due to nitrate ions.
A sample liquid diluting section 20 is provided between the sample section and the measuring section 30, and a pipe line 40 connecting the respective sections in series in order is provided, thereby forming a measuring system for continuous flow analysis.

At the beginning of the conduit 40, a carrier liquid (water)
A pump 42 and a degassing device 41 for flowing the carrier liquid are provided, and a supply source (not shown) of the carrier liquid is connected through these. Since bubbles are removed from the carrier liquid by the deaerator 41, measurement errors due to bubbles in the liquid hardly occur. A back pressure adjusting coil 43 for adjusting the flow pressure in the pipe is provided at the end of the pipe 40.

The sample liquid inlet 10 is provided with an injection valve 11 interposed in the pipe 40. The injection valve 11 is a part for introducing the sample liquid into the conduit 40, and a six-way valve or the like is used. The 6-way valve has a pipe communicating with the pipe 40, a pipe (loop) for holding the sample liquid, and a pipe through which the washing liquid flows. By switching the connection of these pipes to the pipe 40, the sample liquid is supplied. It is introduced into conduit 40.

The introduction section 10 is preferably provided with a selective supply means for holding a plurality of sample liquids and selectively introducing the sample liquids into the conduit 40 of the measurement system. In the illustrated apparatus example, the selective supply means includes a switching valve 12 connected to an injection valve (six-way valve) 11, a plurality of sample liquid holding units 13 connected to the switching valve 12, a sample liquid suction unit, and a measuring system. It is formed by a suction pump 14 to be introduced into the pipeline and an injection pipeline 15 connecting them. A cleaning liquid line 17 is connected to a discharge end of the injection line 15 via a pump 16.

In the illustrated apparatus example, a four-way valve is used as the switching valve 12, and pipe lines 13 a to 13 d holding four kinds of sample liquids are connected to respective openings of the switching valve 12. The switching valve 12 is connected to the sample liquid holding section (sample loop) of the injection valve 11 through the pipe 15, and each sample liquid is selected by switching the connection of the valve 12 to the pipe 15. In addition, a suction pump 14 is provided at the back (discharge side) of the injection valve 11 as a means for applying a fluid pressure to these sample liquids and guiding them to the conduit 40. The sample liquid selected by switching the valve 12 is sucked by the suction pump 14 through the pipe 15 and filled in the sample loop. This sample liquid is sent into the conduit 40 by opening and closing the injection valve 11. This injection valve 1
By adjusting the connection time with the pipe line 40 according to 1, the amount of sample liquid introduced can be accurately controlled.

A washing liquid pipe line 17 is connected to the injection pipe line 15 via a pump 16, and sucks the sample liquid to be connected to the pipe line 4.
After the cleaning liquid has been introduced into the pipe 1
Send to 5. At this time, it is preferable to use a suction pump 14 that can reversely flow the solution and guide the cleaning liquid to the injection valve 11 and the switching valve 12 to clean the pipeline.

The sample liquid introduced into the pipe 40 is
Is sent to the measuring unit 30 via the diluting unit 20 by the carrier liquid (water) flowing therethrough. The diluting section 20 is a section in which the pipe 40 is formed in a coil shape, and the sample liquid is diluted by the carrier liquid while flowing through this section. The dilution rate can be adjusted by changing the amount of the sample solution introduced. The measuring section 30 is provided with a spectrophotometer for measuring the absorbance according to the nitrate ion concentration of the sample solution. The spectrophotometer uses a plurality of wavelengths having an absorption range for nitrate ions as measurement light, and the wavelength of the measurement light can be selected according to the nitrate ion concentration. Specifically, at least 280 nm
A spectrophotometer capable of changing the measurement wavelength in a wavelength range from to 330 nm is used. As such measurement light including a plurality of wavelengths, continuous light in the above wavelength range by a D2 lamp or the like can be used, but a plurality of light sources may be used.

Further, the measuring apparatus of the present invention includes an apparatus in which a sedimentation / separation section is provided between the sample liquid introduction section and the measurement section. If the measurement sample solution contains chloride ions, etc., absorption of chloride ions is observed in the measurement wavelength region (280 to 330 nm) of nitrate ions, which hinders measurement of nitrate ion concentration. Therefore, a precipitation separation section is provided to precipitate and remove chloride ions and the like. One example of the precipitation separation section is shown in FIGS. The sedimentation / separation unit 60 is provided between the introduction unit 10 and the measurement unit 30, and when the dilution unit 20 is provided, the dilution unit 20 and the measurement unit 30 are provided.
Is provided in between.

A sedimentation separation section 60 shown in FIG. 2 includes a switching valve 61 provided in the measurement system pipe 40, a precipitant addition pipe 62 provided on the sample liquid inflow side of the switching valve 61, and a precipitant. It is formed by a mixing coil unit 63 for mixing the sample liquid, a filtration loop 64 attached to the switching valve 61, and a washing conduit 65 communicating with the switching valve 61. The precipitant is added to the sample liquid flowing through the measuring system line 40 through the line 62 and guided to the mixing coil unit 63. The mixing coil portion 63 is a portion in which the conduit is formed in a coil shape,
The precipitant and the sample solution are mixed during the flow, and a precipitate is formed due to chloride ions and the like. The sample liquid containing the precipitate is guided to the filtration loop 64 of the switching valve 61. Filtration loop 6
The inside of 4 is filled with a filter medium for separating the precipitate in the center.

FIG. 2 shows an example in which an automatic hexagonal valve is used as the switching valve 61.
a to 61f are provided.
The measuring system pipeline 40 on the (entrance side) is connected to the measuring system pipeline 40 on the measuring unit side (exit side). Through hole 61
b and 61e are connected by a filtration loop 64;
A cleaning conduit 65 is connected to the through holes 61c and 61d. In the measurement state, the through holes 61a and 61b, the through hole 6
1e and 61f are in communication with each other, and the sample liquid in which the precipitate has formed is led to the filtration loop 64 from the inlet line 40, the precipitate is filtered while passing therethrough, and the measuring unit 30 is passed through the outlet line 40. Sent to On the other hand, in the cleaning state, the connection between the through holes 61a and 61b and the connection between the through holes 61e and 61f are released by rotating the valve 61 so that the through hole 61
b and 61c and the through-holes 61d and 61e are communicated with each other, and the washing liquid is introduced from the pipe 65 into the filtration loop 64 to elute the precipitate, and is discharged outside through the outlet pipe 65.

The above components are preferably controlled by a central control unit 50 and automatically operated. The controller 50 incorporates a program for managing the flow rate and operation of each pump, the operation of the injection valve and the switching valve and the photometer, and calibration curve data for deriving the nitrate concentration from the absorbance, thereby automatically performing a series of concentration measurements. Can be done.

(II) Measuring Method The measuring method of the present invention is based on a continuous flow analysis method in which a sample solution is adjusted and an absorbance is measured while flowing the sample solution through a pipe, and a plurality of samples having an absorption region for nitrate ions are provided. Is a method of measuring the absorbance by selecting the wavelength of the measurement light in accordance with the nitric acid concentration of the sample solution using the measuring light having the wavelength, and measuring the nitric acid concentration from the absorbance.

In the measuring system shown in FIG.
The target sample solution is selected by 2 and the sample solution is filled into the sample loop of the injection valve 11 by the suction pump 14. Next, the injection valve 11 is opened and the sample solution is
To the measuring unit 30 via the diluting unit 20 with the carrier liquid flowing through the conduit 40, and the absorbance thereof is measured.

In this case, when the nitric acid concentration level of the sample solution is known in advance, the wavelength of the measuring light is selected according to the level of the nitric acid concentration, and the absorbance is measured using the measuring light having an appropriate wavelength. Specifically, light having a wavelength of 280 nm to 330 nm has an absorption range for nitrate ions, and thus can be used for measuring absorbance due to nitrate ions. In this case, since the absorbance per unit concentration (detection sensitivity or molar extinction coefficient) based on the absorption spectrum of nitric acid is higher on the shorter wavelength side, when the nitric acid concentration of the sample solution is lower, a wavelength having a higher detection sensitivity around 280 nm is suitable. On the other hand, if the wavelength on the short wavelength side is used for a sample solution having a high nitric acid concentration, the gradient of the calibration curve of absorbance is large, so that a reading error tends to be large. In this case, the gradient of the calibration curve is relatively small. (33
(0 nm side) is suitable.

Usually, the wavelength is preferably selected based on a nitric acid concentration of 10M. Spectrophotometers used for detecting nitrate ions generally have an absorbance of -0.5 to 3 Abs. (Abs.
(Arbitrary unit), the sample injection amount and the measurement wavelength must be adjusted so that the absorbance falls within this measurement range. With a commonly used spectrophotometer, if the nitric acid concentration is up to 10M, the nitric acid concentration of the sample can be measured only by changing the measurement wavelength to the longer wavelength side without changing the injection amount of the sample. When the nitric acid concentration exceeds 10 M, it is necessary to change the measurement wavelength to the longer wavelength side and to adjust the sample injection amount. Unless the sample injection amount is adjusted, measurement in a measurable range (absorbance of -0.5 to 3 Abs.) Cannot be performed with a general spectrophotometer. Since the measurable range differs depending on the spectrophotometer used, the reference nitric acid concentration for switching the measurement wavelength may be determined according to the spectrophotometer used in the measurement system.

When the level of the nitric acid concentration of the sample solution is unknown, the level of the nitric acid concentration of the sample solution is first measured by preliminary measurement, and the wavelength of the measuring light is selected based on the level of the nitric acid concentration. The main measurement may be performed using the measurement light. For example, the main measurement is performed using the measurement light on the 330 nm side for a sample solution having a nitric acid concentration of 10 M or more in the preliminary measurement, and using the measurement light on the 280 nm side for a sample solution having a nitric acid concentration of less than 10 M.

If the nitric acid concentration of the sample solution is out of the measurable range, the sample solution is further diluted and the wavelength is selected to measure the nitric acid concentration. That is, depending on the nitric acid concentration of the sample solution, the measured absorbance may be out of an appropriate range. At this time, the flow rate (Xμl / sec) of the carrier liquid at the time of sample injection and the opening and closing time of the injection valve are set so that they are within the appropriate range.
(Ysec) is adjusted to control the injection amount (X · Yμl) of the sample solution. For example, when the nitric acid concentration of the sample solution is 14M or more, 3
Since the measurement error is large even with the measurement light of 30 nm wavelength,
After decreasing the injection amount of the sample solution to increase the dilution rate and adjusting the concentration to a concentration level of less than 14M, the wavelength according to the concentration level is selected and the absorbance is measured. Even when the nitric acid concentration level is within the measurable range, the dilution ratio of the sample solution is increased, and the absorbance is measured using the highly sensitive short-wavelength side (280 nm side) measurement light to obtain highly accurate measurement results. Some are done.

For a sample solution containing chlorine ions and the like, this causes a measurement error, so that the chlorine ions are removed through the filtration / separation unit 60. That is, a precipitant such as a silver sulfate solution is added to the sample solution flowing through the pipe 40 through the pipe 62. The sample solution containing the silver sulfate solution is guided to the mixing coil unit 63, where the reaction between the chloride ions in the solution and silver sulfate proceeds, and silver chloride precipitates. The sample solution containing the precipitate is led to a filtration loop 64, and the precipitate is separated by filtration. The sample liquid from which the precipitate has been removed is led to the measuring section 30 through the conduit 40, and the absorbance of nitrate ions in the liquid is measured.

To determine the nitric acid concentration from the measured absorbance, a calibration curve may be used. The calibration curve is prepared as a graph that uses the nitrate ion standard solution of various concentrations (0 to 14 M), the maximum absorbance obtained by actually measuring this as the absorbance of the concentration, and the absorbance of each concentration. . In order to change the measurement wavelength and the sample injection amount, a calibration curve taking these conditions into consideration is used.

Specifically, a calibration curve obtained by the following equation is used as an example. X = (A−b) / a (1) X: nitrate ion concentration (M) A: measured absorbance (maximum absorbance, Abs.) A: detection sensitivity per 1 M nitrate ion concentration (Abs./M) B) Blank absorbance (absorbance measured when nitric acid concentration is 0 M, Abs.) Here, detection sensitivity a changes depending on the measurement wavelength and the sample injection amount. Therefore, the detection sensitivity to nitrate ion at each measurement wavelength used in advance for measurement (Δλ: set by the molar absorption system number and wavelength at a specific wavelength) and the sample injection amount V
(Μl: carrier flow rate C (μl / sec) and sample injection time t (s
ec) and the relationship between detection sensitivity K (K = V × f, f: detection sensitivity change rate when the sample injection amount is changed)
The detection sensitivity a is experimentally obtained based on the following equation, and the setting is made so that the optimum value is used when the measurement conditions are changed. a = Τλ × K, that is, X = (A−b) / Τλ × K (2)

By using this equation as a calibration curve, for example, if a calibration curve is created for a nitric acid concentration up to 1 M using a wavelength of 280 nm, the measurement conditions can be changed even if the measurement wavelength and the sample injection amount are changed. , The change in detection sensitivity to nitrate ion accompanying the calculation can be used to determine the nitrate ion concentration. The calibration curve data can be automatically measured by storing it in the central control device of the measuring device.

[0031]

Examples of the present invention will be described below. As the measuring apparatus, an apparatus having the measuring system shown in FIG. 1 was used. As a measurement system conduit, a PTFE (polytetrafluoroethylene) tube having an inner diameter of 1 mm and an outer diameter of 2 mm was used. The back pressure coil 43 has an inner diameter of 0.5 mm,
PTFE having an outer diameter of 1.7 mm was used. Further, it was led to a dilution section and a precipitation separation section as needed to dilute and remove chloride ions. A filtration membrane such as a hydrophilic PTFE membrane (diameter 25 mm, membrane pore diameter 0.45 μm or less) or the like was used as a filter medium of the filtration separation unit 60. Silver chloride solution (100 ppm aqueous solution
5% / min), and 10% aqueous ammonia or a 0.5M thiourea solution (flow rate: 1 ml / min) was used as the precipitate dissolving solution introduced from the washing line 65.

Example 1 (Measurement of nitric acid concentration of less than 10 M) A sample solution (0.1 M nitric acid solution) was introduced into the measuring system under the initial measuring conditions shown in Table 1, and then guided to the measuring section, and the absorbance based on the nitrate ion concentration was measured. Was measured. If the maximum measured value was less than the maximum absorbance measurable by the photometer (generally 3 Abs. Or less), the nitrate concentration corresponding to the measured maximum absorbance was determined from a comparison with a previously prepared calibration curve ( Table 1 Sample No. 1). If the nitrate ion concentration in the sample solution is high and the maximum absorbance measured under the initial setting conditions exceeds the maximum absorbance measurable by the photometer,
The measurement wavelength was changed to 300 nm, and the measurement was performed again to measure the nitric acid concentration (Table 1 sample No. 2). If the maximum absorbance due to this re-measurement also deviated from the measurable range, the measurement wavelength was further changed to 330 nm, the measurement was performed again, and the nitrate concentration was measured based on the maximum absorbance falling within the measurable range (Table 1 sample No. .3). Further, the dilution ratio of the sample solution in the measurable region was increased, and the nitric acid concentration was measured using the measurement light on the short wavelength side (Table 1 sample No. 7).

(Measurement of nitric acid concentration of 10 M or more)
Even if a measurement routine of a concentration of less than M is performed, if the measured maximum absorbance exceeds the measurable range, the measurement is performed by increasing the dilution rate of the sample liquid by controlling the sample injection amount while setting the measurement wavelength to 330 nm. . For example, for a sample solution having a nitric acid concentration of 11 M, absorbance was measured by changing the sample injection amount to 33 μl and the sample injection time to 1 second among the above initial measurement conditions, and the nitrate concentration was determined based on the calibration curve from the maximum absorbance. (Sample No. 4 in Table 1). For a sample solution with a nitric acid concentration of 13 M, absorbance was measured under the conditions of a flow rate of 1.0 ml / min, a sample injection amount of 17 μl, a sample injection time of 1 second, and a measurement wavelength of 330 nm. The nitric acid concentration was determined based on the line (Table 1, Sample No. 5). Sample No.1 ~
Table 1 shows the measurement results of No. 7 together with the measurement conditions.

[0034]

[Table 1]

Example 2 Using the measuring apparatus shown in FIG. 1, the nitrogen gas absorbing liquid in the denitration equipment was used as a sample liquid, and the absorbance was measured under the measuring conditions shown in Table 2.
The nitrate ion concentration was determined from the maximum absorbance based on a calibration curve. The results are shown in Table 2 together with the measurement conditions. Separately, the results of measuring the nitric acid concentration of the same sample solution by the neutralization titration method are shown in Table 2. The measurement results of the present invention were in good agreement with the concentrations measured by the commonly used neutralization titration method.

[0036]

[Table 2]

[0037]

According to the measurement method and apparatus of the present invention described above, the wavelength is selected according to the concentration and the optimum measurement wavelength is used based on the continuous flow analysis, so that the nitric acid absorbing solution in the denitration equipment can be used. It is possible to quickly and accurately measure the concentration of a nitric acid solution having a low concentration as well as a nitric acid solution having such a high concentration.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a measurement system of a measurement device according to the present invention.

FIG. 2 is a conceptual diagram of a settling / separation unit in the measuring device.

[Explanation of symbols]

10: sample liquid introduction part, 11: injection valve, 12: switching valve, 13: sample holding part, 14: suction pump,
15: line, 16: pump, 17: washing liquid line,
20: dilution section, 30: measurement section, 40: pipeline, 4
1: deaerator, 42: pump, 43: back pressure coil,
50: Central control unit

Claims (12)

[Claims] 1. A continuous flow analysis method for adjusting a sample solution and measuring absorbance while flowing the sample solution through a pipe,
In the method of measuring the nitric acid concentration from the absorbance of the sample solution,
A method for measuring a nitric acid concentration, comprising using a measuring light including a plurality of wavelengths having an absorption range for nitrate ions and selecting a wavelength of the measuring light according to a nitric acid concentration of a sample to measure an absorbance. 2. A sample solution having a high nitric acid concentration is 330 nm.
The measurement method according to claim 1, wherein the measurement light having a wavelength of 280 nm is used for a sample solution having a low nitric acid concentration, using the measurement light having a wavelength of about 280 nm. 3. The method according to claim 1, wherein the nitric acid concentration level of the sample liquid is first measured by preliminary measurement, the wavelength of the measuring light is selected based on the nitric acid concentration level, and the main measurement is performed using the measuring light of this wavelength. The measurement method described. 4. In a preliminary measurement, a measurement light on the 330 nm side is used for a sample solution having a nitric acid concentration of 10 M or more in a measurable range, and a measurement light on the 280 nm side is used for a sample solution having a nitric acid concentration of less than 10 M. The measurement method according to claim 3, wherein the main measurement is performed. 5. The method according to claim 1, wherein, in the preliminary measurement, the nitric acid concentration is measured after diluting a sample solution having a nitric acid concentration outside the measurable range to a measurable range. 6. The method according to claim 1, wherein the sample solution in which the nitric acid concentration can be measured is diluted, and the nitric acid concentration is measured using a measuring light on the 280 nm side. 7. A continuous flow analysis measurement using a sample liquid introducing section, a diluted section of the introduced sample liquid, a measuring section for measuring the absorbance of the diluted sample liquid due to nitrate ions, and a pipe connecting these sections in series. A system is formed, and the measuring unit is provided with a spectrophotometer that has measurement light including a plurality of wavelengths having an absorption range for nitrate ions and that can select the wavelength of the measurement light according to the nitric acid concentration. A nitric acid concentration measuring device. 8. The measuring apparatus according to claim 6, wherein a selective supply means for holding a plurality of sample liquids and selectively introducing the sample liquids into the conduit of the measurement system is provided in the sample liquid introduction section. 9. An injection valve interposed in the pipe of the measurement system, a switching valve connected to the injection valve, a plurality of sample liquid holding portions connected to the switching valve, and a sample liquid supplied to the pipe of the measurement system. 8. The measuring device according to claim 7, wherein said selective supply means is formed by a guiding suction pump and an injection line connecting them. 10. The measuring apparatus according to claim 6, wherein a precipitation separating section is provided between the sample liquid introducing section and the measuring section. 11. A switching valve interposed in a measurement system pipe, a precipitant addition pipe provided on a sample liquid inflow side of the switching valve, and a mixing coil section for mixing the precipitant with the sample liquid.
The filter loop mounted on the switching valve and a washing line communicating with the switching valve form a sedimentation separation section, and the connection of the filtration loop is switched to a measurement system line or a washing line by the switching valve. 10. The measuring device according to 9. 12. A means for selectively supplying a sample liquid introduction section, a dilution section, a precipitation separation section, and a measurement section are connected to a central controller, and a series of operations from introduction of the sample liquid to measurement of absorbance are performed by the central controller. The measuring device according to claim 10, wherein the nitric acid concentration of the sample solution is automatically measured based on the calibration curve data of the absorbance recorded in the central controller.