JP5467266B2 - Method for measuring solution components using absorbance method and measuring apparatus using the method - Google Patents

Description

  The present invention relates to a measurement method capable of measuring values of solution components, in particular, measurement items of carbonic acid in seawater, and a measurement apparatus using the measurement method.

  Alkalinity is obtained by subtracting the number of equivalents of strong electrolyte anions from the number of equivalents of strong electrolyte cations. There are multiple detailed definitions including land water, and those suitable for each water survey. Used. In the case of seawater, there are about 600 mmol / kg of strong electrolyte cations and anions, respectively, which are almost balanced, but only about 2 mmol / kg of cations. This difference is the alkalinity, which is occupied by weak acid ions such as bicarbonate ions, carbonate ions, and borate ions, and the carbon dioxide storage capacity of the ocean is determined by the alkalinity.

Conventionally, the alkalinity titration method is used as one of the methods for measuring the total alkalinity _AT of a solution. Specifically, the total alkalinity _AT indicates how much an acid consuming component is contained in the solution. For example, when the total alkalinity _AT of a solution is measured by the alkalinity titration method, acid is dropped into the solution so that the solution has a predetermined hydrogen ion concentration. The total alkalinity _AT of the solution is measured as the number of acid equivalents required for the titration.

As described above, the total alkalinity _AT of the solution indicates how much a component that consumes acid is contained in the solution. For example, even if the hydrogen ion concentration of the solution is the same, Depending on the amount and type of dissolved salt, the total alkalinity _AT of the solution will vary. Specifically, for example, in the case of a solution (for example, saline) in which a neutral compound such as sodium chloride (NaCl) is dissolved, the total alkalinity _AT is zero. On the other hand, if the solution is not only sodium chloride (NaCl) but also a salt such as carbonic acid (H ₂ CO ₃ ) or phosphoric acid (H ₃ PO ₄ ), such as seawater, the total alkalinity A _T Exist for that amount. Also, carbonate alkalinity A _C is ^{_{A C = [HCO 3 -]}} +2 and [CO ₃ ^2-] is defined, it is possible to calculate the carbonate alkalinity A _C from salinity total alkalinity A _T and seawater .

For example, as a method for measuring the total alkalinity _AT of a solution, there is a method disclosed in Non-Patent Document 1.

DOE (1994) Handbook of methods for the analysis of the various parameter of the carbon dioxide system in sea water.Version 2, A.G.Dickson & C. Goyet, eds.ORNL / CDIAC-74

The method disclosed in Non-Patent Document 1 includes carbonate ions (CO ₃ ²⁻ ) and hydrogen carbonate ions (HCO ₃ ⁻ ) as represented by seawater, for example, and has a total alkalinity _AT . This is a method carried out by dropping an acid into a solution (hereinafter sometimes simply referred to as a solution). Specifically, the pH of the solution is measured with a pH electrode while acid is dropped into the solution. Then, the total alkalinity _{AT of the} solution is calculated from the pH measured by the pH electrode.

However, since the method disclosed in Non-Patent Document 1 uses a pH electrode, there is a problem that maintenance is troublesome. For example, in order to use a pH electrode, the pH electrode must first be conditioned by immersing it in a pH standard solution. In addition, pH electrode drift and sensitivity reduction may affect the total alkalinity _AT of the solution. Therefore, it is possible to accurately measure the value of carbonic acid measurement items (for example, total carbonic acid concentration, total alkalinity, hydrogen ion concentration index, carbon dioxide partial pressure, etc.) of a solution (for example, seawater) with a simpler method. A method and apparatus that can be used has been desired.

  The present invention has been made in view of the above circumstances, and the object of the present invention is to measure the carbonic acid content of a solution accurately (total carbonic acid concentration, total alkalinity, hydrogen ion concentration index, An object of the present invention is to provide a measuring method and a measuring apparatus using the measuring method, which can measure a value of at least one of carbon dioxide partial pressures.

  In order to achieve the above object, the present invention employs the following configuration. That is, the first invention is a method for measuring a solution component using an absorbance method. The solution component measurement method using the above-described absorbance method is a method in which an acid is dropped into a sample water containing at least one colorimetric indicator in a sample solution, and the absorbance of the sample water at a predetermined wavelength is measured. And setting at least one of the values necessary for calculating the value of the carbonic acid measurement item of the sample solution by the colorimetric method as a parameter, and using the absorbance, the value of the parameter A second step of calculating an optimal solution of the parameter by performing a predetermined numerical calculation, and a step of calculating the value of the measurement item by substituting the optimal solution of the parameter value into a predetermined mathematical formula 3 steps.

  According to a second invention, in the first invention, the value of a carbonic acid measurement item is measured by an open cell method (open titration).

  According to a third invention, in the first invention, the value of a carbonic acid measurement item is measured by a closed cell method (sealed titration).

  According to a fourth aspect of the present invention, in the first aspect, the first step is to measure the absorbance of the test water at at least three different wavelengths, and to obtain a waveform of an absorption spectrum unique to the pH indicator added to the sample solution. Approximate and measure the absorbance value of the test water at the predetermined wavelength based on the waveform.

  In a fifth aspect based on the first aspect, at least one of the dissociation constants of the pH indicator added to the sample solution is set as a parameter.

  According to a sixth invention, in the first invention, the ratio of molar extinction coefficients of the sample solutions at different wavelengths is less than three times the number of types of pH indicator added to the sample solution. Set the above parameters.

  In a seventh aspect based on the first aspect, the concentration of the acid dropped into the test water is set as the parameter.

  In an eighth aspect based on the first aspect, the weight or volume of the sample solution is set as the parameter.

  In a ninth aspect based on the first aspect, the temperature of the sample solution is set as a parameter.

  In a tenth aspect based on the first aspect, the salt concentration of the sample solution is set as the parameter.

  The eleventh invention is the ratio of the weight of the sample solution and the weight of the acid dropped onto the test water in the first invention, or the volume of the sample solution and the acid dropped onto the test water. The ratio to the volume of is set as the above parameter.

The twelfth invention is a solution component measuring apparatus using an absorbance method. That is, the measuring device uses the solution component measuring method using the absorbance method according to the first invention. The apparatus includes a first container containing test water containing at least one pH indicator in a sample solution, a second container containing acid dropped into the test water, and the first container. Dropping means for dropping the acid contained in the second container into the test water contained in the container; and measuring means for measuring the absorbance of the test water each time the acid is dropped by the dropping means; In addition, at least one of the values required for calculating the value of the carbonic acid measurement item of the sample solution by the colorimetric method is set as a parameter, and an optimal solution for the parameter value is determined in advance using the absorbance. a first calculation means for calculating by performing numerical computation that is, by substituting the predetermined et a formula an optimal solution of the value of the parameter, calculating means for calculating the value of the measurement item of carbonated Second calculating means.

A thirteenth aspect of the invention is a solution component measuring apparatus using an absorbance method. That is, the measuring device uses the solution component measuring method using the absorbance method according to the first invention. The apparatus includes a container containing an acid containing at least one pH indicator, a first liquid feeding means for feeding a sample solution at a predetermined flow rate, and an acid containing the pH indicator. a second liquid supply means for feeding at a predetermined et flow rate, and mixing means for mixing the acid was contained pH indicator which is placed in the container with the sample solution and mixed by the mixing means A measurement means for measuring the absorbance of the mixed solution by a continuous flow analysis method, and at least one of the values necessary for calculating the value of the carbonic acid measurement item of the sample solution by a colorimetric method is set as a parameter. , substituting the first calculating means and, predetermined et a formula an optimal solution of the value of the parameter is calculated by performing a predetermined mathematical operation to the optimal solution of the value of the parameter using the absorbance By carbonic acid And a second calculating means for calculating means for calculating the value of the measurement item.

  In a fourteenth aspect based on the thirteenth aspect, the first calculation means sets, as a parameter, a ratio between the flow rate of the sample solution and the flow rate of the acid containing the pH indicator.

A fifteenth invention is a solution component measuring apparatus using an absorbance method. That is, the measuring device uses the solution component measuring method using the absorbance method according to the first invention. The apparatus includes a first container containing an acid, a second container containing the pH indicator, a first fluid feeding means for feeding at a predetermined et flow rate of the sample solution, the first feeding the acid was placed in the container and the second fluid feeding means for feeding at a predetermined et flow rate, in the at least one predetermined et flow rate a pH indicator which is placed in the second container A third liquid feeding means for liquid; a mixing means for mixing the sample solution, the acid and the pH indicator; a measuring means for measuring the absorbance of the mixed solution mixed by the mixing means by a continuous flow analysis method; In addition, at least one of the values required for calculating the value of the carbonic acid measurement item of the sample solution by the colorimetric method is set as a parameter, and an optimal solution for the parameter value is determined in advance using the absorbance. First calculated by performing the calculated numerical value Comprising a calculation unit, by substituting the predetermined et a formula an optimal solution of the value of the parameter, and a second calculation means calculating means for calculating the value of the measurement item of carbonated.

According to the measurement method and apparatus of the present embodiment, the troublesome maintenance of the pH electrode can be eliminated, and the drift and sensitivity of the pH electrode, which was the main error factor of the measurement value of the carbonic acid measurement item The value of the carbonic acid measurement item (at least one of total carbonic acid concentration, total alkalinity, hydrogen ion concentration index, and carbon dioxide partial pressure) can be obtained with a simpler method and with high accuracy. it can be measured.

Schematic diagram of an apparatus using the measuring method according to the present invention Flow chart showing the flow of measurement using the open cell method The figure which shows the change of the light absorbency when the acid solution 10 is dripped at the sample solution 11 containing bromophenol blue. The figure which shows an example of the measurement result (time series) of the measurement by the open cell method The figure which shows the acid titration by the open cell system, the value of R of the sample solution 11 in each titration point, and the relationship of pH. Figure showing the standard deviation and the average value of total alkalinity _AT Figure showing the relationship between acid titration and total alkalinity _AT when pK _(BPB) is changed Flow chart showing the flow of measurement using the closed cell method The figure which shows an example of the measurement result (time series) of the measurement by a closed cell system The figure which shows the acid titration by a closed cell system, the value of R of the sample solution 11 in each titration point, and the relationship of pH. Diagram showing examples of plots for calculating total alkalinity _AT and total carbonic acid concentration C _T A figure showing the value of r ² when K _(BPB) , K _(BTB) , and ψ are set and changed with parameters of provisional values (when ψ = 0.11) A diagram showing the value of r ² when K _(BPB) , K _(BTB) , and ψ are set and changed with provisional value parameters (when ψ = 0.13) A diagram showing the value of r ² when K _(BPB) , K _(BTB) , and ψ are set and changed with provisional value parameters (when ψ = 0.15) The figure which shows an example of a structure of the apparatus which concerns on 3rd Embodiment. The figure which shows an example of an apparatus structure containing the light absorbency measurement means which concerns on a 1st modification. The figure which expanded the part enclosed with the broken line a of FIG. 16, and shows the inside of the optical fiber cell 37 The figure which shows an example of an apparatus structure containing the light absorbency measurement means which concerns on a 2nd modification. The figure which shows an example of a structure of the apparatus which concerns on 4th Embodiment. The figure which shows an example of a structure of the apparatus which concerns on 5th Embodiment. The figure which shows an example of the internal structure of the light source 25

  In the present invention, the hydrogen ion concentration of a solution is measured by a colorimetric analysis method, and based on the obtained results, measurement items of carbonic acid (total carbonic acid concentration, total alkalinity, hydrogen ion concentration index, carbon dioxide partial pressure At least one). That is, the present invention is a method for measuring a solution component using light absorption by measuring the intensity of light absorption of the solution by irradiating the solution with light.

  First, an outline of a method for measuring a solution component using the absorbance method according to the present invention (hereinafter sometimes simply referred to as a measuring method) will be described. Note that the measurement method according to the present invention is realized by, for example, an apparatus configuration as shown in FIG.

  FIG. 1 is a schematic diagram of a measuring apparatus (hereinafter, simply referred to as an apparatus) using the measuring method according to the present invention. As shown in FIG. 1, as an example, the apparatus, first, the processing means 13 instructs the dropping means (arrow 19 in FIG. 1) to drop the sample solution 11 containing the acid solution 10 containing an acid-base indicator. (Arrows 15 and 16 in FIG. 1). On the other hand, the absorbance measuring means 12 emits light from the light source provided in the absorbance measuring means 12 (arrow 17 in FIG. 1), and measures the absorbance of the sample solution 11. Then, the processing means 13 measures the hydrogen ion concentration of the sample solution 11 based on the signal (arrow 18 in FIG. 1) output from the absorbance measurement means 12. That is, the absorbance measuring means 12 and the processing means 13 calculate the hydrogen ion concentration of the sample solution 11 with respect to the sample solution 11 by indicator titration, that is, colorimetric analysis. In the following description, an acid-base indicator may be simply referred to as an indicator.

  Thereafter, based on the signal output from the absorbance measuring means 12 (arrow 18 in FIG. 1), the processing means 13 performs measurement items (total carbonic acid concentration, total alkalinity, hydrogen ion concentration index, dioxide dioxide) in the sample solution 11. A value of at least one of the carbon partial pressures).

  First, the colorimetric analysis method used in the measurement method according to the present invention will be described with reference to the schematic diagram of the apparatus configuration shown in FIG.

  For example, when one kind of acid-base indicator (referred to as indicator A) is contained in the sample solution 11, the acid-base indicator A is dissociated in the sample solution 11 represented by the following formula (1). Holds.

  Examples of acid-base indicators include bromophenol blue, bromothymol blue, metacresol purple, methyl red, phenol red, thymol blue, and the like.

Further, when the dissociation constant of the indicator A at this time is K _(A) , the K _(A) can be expressed by the following formula (2). Further, the pH (hydrogen ion concentration index) of the sample solution 11 can be expressed by the following formula (3) from the following formula (2). [HA] is the concentration of non-dissociated form (acid form) in indicator A, [A ⁻ ] is the concentration of dissociated form (alkali form) in indicator A, and [H ⁺ ] is the hydrogen ion concentration. is there.

_{K (A) = ([H} +] · [A -]) / [HA] ... (2)
_{pH = pK (A) + log} ([A -] / [HA]) ... (3)

However, pH = −log ([H ⁺ ]) and pK _(A) = − log (K _(A) ).

Here, the molar extinction coefficients of the non-dissociated form (HA) and dissociated form (A ⁻ ) at a certain wavelength λ ₁ and wavelength λ ₂ are ₁ ε _HA , ₁ ε _A- , ₂ ε _HA , and ₂ ε _A- , respectively. . If the optical path length (specifically, the length of the container containing the sample solution 11) is L, the absorbance Abs ₁ and Abs ₂ of the sample solution 11 at a certain wavelength λ ₁ and wavelength λ ₂ are as follows. It can represent with Formula (4) and Formula (5).

_{Abs 1 = 1 ε A- · L} · [A -] + 1 ε HA · L · [HA] ... (4)
_{Abs 2 = 2 ε A- · L} · [A -] + 2 ε HA · L · [HA] ... (5)

Here, in the above formulas (4) and (5), the ratio of absorbance Abs ₁ and Abs _{2 at} a certain wavelength λ ₁ and wavelength λ ₂ is R = Abs ₁ / Abs ₂ , and the molar extinction coefficient ratio is , E _{1 (A)} = ₁ ε _HA / ₂ ε _HA , e _{2 (A)} = ₁ ε _A- / ₂ ε _HA , e _{3 (A)} = ₂ ε _A- / ₂ ε _HA 4) and Formula (5) can be shown by the following Formula (6). That is, the ratio between [HA] and [A ⁻ ] can be calculated from the absorbance and molar extinction coefficient of two wavelengths (here, a wavelength λ ₁ and a wavelength λ ₂ ).

^{([A -] / [HA} ]) = (Re 1 (A)) / (e 2 (A) -R · e 3 (A)) ... (6)

  Therefore, the following formula (7) can be derived from the above formula (3) and the above formula (6).

pH = pK _(A) + log [(Re _{1 (A)} ) / (e _{2 (A)} -R · e _{3 (A)} )] (7)

Further, as described above, the R value is obtained by the processing means 13 when the absorbance measuring means 12 irradiates the sample solution 11 with light and measures the intensity of light absorption of the sample solution 11. Although details will be described later, the hydrogen ion concentration of the sample solution 11, that is, [H ⁺ ], is as follows using e _{1 (A)} , e _{2 (A)} , e _{3 (A)} , and K _(A) as parameters. It can be shown by equation (8).

[H ⁺ ] = F [R, K _(A) , e1 _(A) , e2 _(A) , e3 _(A) ] (8)

Note that λε _A− and λε _HA can be obtained experimentally if pK _{(A) is} made sufficiently high alkaline or sufficiently low acidity.

λε _A− = λAbs ₁ (A ⁻ ) / [A ⁻ ] · L (9)
λε _HA = λAbs ₁ (HA) / [HA] · L (10)

  Next, for example, when two kinds of acid-base indicators (for example, indicator A and indicator B) are contained in the sample solution 11, the dissociation equilibrium represented by the following formulas (11) and (12) Holds.

Further, as described above, when the dissociation constant of indicator A is K _{(A) in} the same way as when one kind of acid-base indicator, that is, indicator A is contained in the sample solution 11, the dissociation constant K _(A) is the following equation (13), and when the dissociation constant of indicator B is K _(B) , the dissociation constant K _(B) can be represented by the following equation (14). From the following formulas (13) and (14), the pH (hydrogen ion concentration index) of the sample solution 11 can be expressed by the following formulas (15) and (16).

[HA] and [HB] are the concentrations of the non-dissociated forms (acid forms) of indicator A and indicator B, respectively, and [A ⁻ ] and [B ⁻ ] are the dissociation of indicator A and indicator B, respectively. It is the concentration of the form (alkali foam), and [H ⁺ ] is the hydrogen ion concentration.

_{K (A) = ([H} +] · [A -]) / [HA] ... (13)
_{K (B) = ([H} +] · [B -]) / [HB] ... (14)
_{pH = pK (A) + log} ([A -] / [HA]) ... (15)
_{pH = pK (B) + log} ([A -] / [HB]) ... (16)

Here, the molar extinction coefficients of the non-dissociated form (HA) and dissociated form (A ⁻ ) at a certain wavelength λ ₁ and wavelength λ ₂ are ₁ ε _HA , ₁ ε _A- , ₂ ε _HA , and ₂ ε _A- , respectively. . Similarly, the molar extinction coefficients of the non-dissociated form (HB) and dissociated form (B ⁻ ) at a certain wavelength λ ₁ and wavelength λ ₂ are ₁ ε _HB , ₁ ε _B- , ₂ ε _HB , and ₂ ε _B- , respectively. . If the optical path length (specifically, the length of the container containing the sample solution 11) is L, the absorbance Abs ₁ and Abs ₂ of the sample solution 11 at a certain wavelength λ ₁ and wavelength λ ₂ are as follows. It can represent with Formula (17) and Formula (18).

_{Abs 1 = 1 ε A- · L} · [A -] + 1 ε HA · L · [HA] + 1 ε B- · L · [B -] + 1 ε HB · L · [HB] ... (17)
_{Abs 2 = 2 ε A- · L} · [A -] + 2 ε HA · L · [HA] + 2 ε B- · L · [B -] + 2 ε HB · L · [HB] ... (18)

Here, in the above formula (17) and the above formula (18), the ratio of absorbance Abs ₁ and Abs _{2 at} a certain wavelength λ ₁ and wavelength λ ₂ is R = Abs ₁ / Abs ₂ , and the molar extinction coefficient ratio is , E _{1 (A)} = ₁ ε _HA / ₂ ε _HA , e _{2 (A)} = ₁ ε _A- / ₂ ε _HA , e _{3 (A)} = ₂ ε _A- / ₂ ε _HA , e _{1 (B)} = ₁ ε _HB / ₂ ε _HB , e _{2 (B)} = ₁ ε _B− / ₂ ε _HB , e _{3 (B)} = ₂ ε _B− / ₂ ε _HB , the above formula (17) and the above formula ( 18) can be expressed by the following equation (19).

β _(A) = [e _{3 (A)}・ (Re _{2 (A)} )] + α _(A) (Re _{1 (A)} )
= -ψ [β _(B) · [e _{3 (B)} · (Re _{2 (B)} )] + [α _(B) (Re _{1 (B)} )]] (19)

In the above equation (19), α _(A) , α _(B) , β _(A) , β _(B) are represented by the following equations (20) to (23), respectively.

Ψ is the ratio of the absorbance of the non-dissociated form at a certain wavelength λ ₂ when the indicator A and the indicator B are each non-dissociated. That is, ψ can be expressed by the following equation (24).

_{ψ = ABS 2 (HA) /} ABS 2 (HB) = {[([HA] + [A -]) · 2 ε HA] / [([HB] + [B -]) · 2 ε HB]} ... (24)

Here it is possible to calculate the [H ^+] with a, b, the equation solutions in c for [H ^+]. In addition, a, b, and c can be shown by the following formulas (25) to (28).

a ・ [H ⁺ ] ² + b [H ⁺ ] + c = 0 (25)
a = (Re _{1 (A)} ) + ψ · (Re _{1 (B)} ) (26)
b = K _(A)・ e _{3 (A)}・ [(Re _{2 (A)} ) / e _{3 (A)} ] + K _(B)・ (Re _{1 (A)} ) + ψ ・ K _(B)・ e _{3 (B)} [(Re _{2 (B)} ) / e _{3 (B)} ]
+ ψ · K _(A) (Re _{1 (A)} ) (27)
c = K _(A)・ K _(B)・ e _{3 (A)} [(Re _{2 (A)} ) / e _{3 (A)} ] + ψ ・ K _(A)・ K _(B)・ e _{3 (B)} [(Re _{2 (B)} ) / e _{3 (B)} ] (28)

Further, as described above, the R value is obtained by the processing means 13 when the absorbance measuring means 12 irradiates the sample solution 11 with light and measures the intensity of light absorption of the sample solution 11. As will be described in detail later, the hydrogen ion concentration of the sample solution 11, that is, [H ⁺ ], for example, takes the value of R as a measurement value, and ψ, K _(A) , K _(B) , e _{1 (A)} , e It can be represented by the following formula (29) using _{2 (A)} , e _{3 (A)} , e _{1 (B)} , e _{2 (B)} , and e _{3 (B)} as parameters, respectively.

[H ⁺ ] = G [R, ψ, K _(A) , K _(B) , e _{1 (A)} , e _{2 (A)} , e _{3 (A)} , e _{1 (B)} , e _{2 (B)} , E _{3 (B)} ] (29)

Next, measurement items of carbonate system in the sample solution 11, specifically, the total carbonate concentration C _T of the solution, the method of measuring the total alkalinity A _T will be described. For example, in the schematic diagram of the apparatus shown in FIG. 1, based on the signal output from the absorbance measuring means 12 to the processing means 13, that is, the signal indicating the absorbance (arrow 18 in FIG. 1), the processing means 13 11. Calculate 11 total carbonic acid concentration C _T and total alkalinity _AT .

  The sample solution 11 shown in FIG. 1 is not particularly limited as long as it is a solution having alkalinity. However, as an example, the sample solution 11 will be described below assuming that it is seawater.

  First, here, seawater that exists generally will be described.

  Generally, the seawater that exists is 95% or more of the total alkalinity, which is derived from carbonate-derived salts such as carbonates and bicarbonates.

Regarding the total alkalinity A _{T of} seawater, total carbonic acid concentration C _T , and carbonic acid system equilibrium, DOE (1994) Handbook of methods for the analysis of the various parameters of the carbon dioxide system in sea water. From AGDickson & C. Goyet, eds.ORNL / CDIAC-74:

When carbon dioxide dissolves in water, bicarbonate ion HCO ₃ ^- (aq), carbonate ion CO ₃ ^2-(aq) is generated, the following equation (30) to (33) the equilibrium reaction as shown in the establishment To do.

The above formula (30) - In (33), since the H ₂ CO ₃ (aq) and CO ₂ (aq) and it is difficult to discuss distinguished, H ₂ CO ₃ (aq) and CO ₂ (aq) Is expressed as CO ₂ ^* (aq), the following equations (34) to (35) are obtained.

  The balance of the above formulas (34) and (35) can be expressed by the following formulas (36) to (38) by using the equilibrium constant.

K ₁ = [H ⁺ ] [HCO ⁻ ] / [CO ₂ ^* ] (37)
K ₂ = [H ⁺ ] [CO ₂ ⁻ ] / [HCO ⁻ ] (38)

  here,

  Is the fugacity of carbon dioxide, and the relationship with the carbon dioxide partial pressure can be expressed by the following equation (39).

As shown in the above equation (39), if the partial pressure of carbon dioxide (x (CO ₂ ) · p) is measured, the fugacity of carbon dioxide can be calculated from the total pressure of gas and the salinity of water (for example, seawater). .

As described above, pH = −log ([H ⁺ ]), but there are a plurality of definitions for pH. For example, an NBS (National Bureau Standard) scale often used in fresh water or the like can be represented by the following formula (40).

In the above formula (40), a _{[H +]} is the hydrogen ion activity.

  Moreover, in seawater, it can show as follows.

pH _F = [H ⁺ ] _F
pH _F : Free scale
[H ⁺ ] _F : Free hydrogen ion concentration
_{^{[H +] T = [H}} +] F + [HSO 4 -]
pH _T = -log [H ⁺ ] _T
pH _T : Total scale
_{^{[H +] sws = [H}} +] F + [HSO 4 -] + [HF]
pH _sws = _-log [H ⁺ ] _sws
pH _sws : SWS scale

Then, the total carbonate concentration C _T of seawater is defined by the following equation (41).

C _T = [CO ₂ ^* ] + [HCO ₃ ⁻ ] + [CO ₃ ²⁻ ] (41)

The total alkalinity _AT of seawater is defined by the difference between a proton donor and a proton acceptor, as shown in the following formula (42). In addition, what is omitted in the following formula (42) is so small that it can be ignored.

^{_{A T = [HCO 3 -]}} +2 [CO 3 2-] + [B (OH) 4 -] + [OH -] + [HPO 4 2-] +2 [PO 4 3-] + [SiO (OH ) ₃ ^-]
_{+ [NH 3] + [HS} -] + ··· - [H +] F - [HSO 4 -] - [HF] - [H 3 PO 4] - ... (42)

Furthermore, the alkali carbonate A _C can be expressed by the following formula (43).

A _C = [HCO ₃ ⁻ ] +2 [CO ₃ ²⁻ ] (43)

Here, the relationship between the total alkalinity A _T and the carbonate alkalinity A _C can be expressed by the following equation (44). In addition, what is omitted in the following formula (44) is so small that it can be ignored.

_{A c = A T - ([} B (OH) 4 -] + [OH -] + [HPO 4 2-] +2 [PO 4 3-] + [SiO (OH) 3 -]
_{+ [NH 3] + [HS} -] + ··· - [H +] F - [HSO 4 -] - [HF] - [H 3 PO 4] -) ... (44)

Normally, in the open sea surface seawater, and a salinity and temperature and pH, boric acid, phosphoric acid, hydrofluoric acid, sulfuric acid or the like is calculated, to calculate the carbonate alkalinity A _C from total alkalinity A _T.

Further, the total alkalinity _AT shown in the above formula (42) is developed into the following formula (45) in order to define the proton state corresponding to the equivalence point. Note that, in the following formula (45), those omitted in the formula (42) are not considered.

_{^{[H +] F + [HSO}} 4 -] + [HF] + [H 3 PO 4] = [HCO 3 -] +2 [CO 3 2-] + [B (OH) 4 -] + [OH -]
^{_{+ [HPO 4 2-] +2 [}} PO 4 3-] + [SiO (OH) 3 -]
_{+ [NH 3] + [HS} -] ... (45)

Here, in fresh water and seawater, items measurable with carbon dioxide-related substances are pH, carbon dioxide partial pressure, total carbonic acid, and total alkalinity. Among them, by measuring the two or more items, the equilibrium equation of Equation (36), (37), can be computed for all of the items from (38), also, HCO ₃ ^- (aq) and CO ₃ ^2- (aq) can also be calculated.

This concludes the description of the total alkalinity A _T and the total carbonate concentration C _T of seawater.

Next, the alkalinity titration with an acid will be described for measuring the total alkalinity _AT .

In the apparatus using the measuring method according to the present invention, the dropping means 14 drops the acid solution 10 onto the sample solution 11 as described above. In this case, the acidity C _H during the titration of the sample solution 11 (that is, seawater) at each titration point can be expressed by the following formula (46).

^{_{C H = [H +] F}} + [HSO 4 -] + [HF] + [H 3 PO 4] - [HCO 3 -] -2 [CO 3 2-] - [B (OH) 4 -] - [ OH ^{-]
_{- [HPO 4 2-] -2 [}} PO 4 3-] - [SiO (OH) 3 -] - [NH 3] - [HS -] ... (46)
Incidentally, at the equivalent point of the total alkalinity _AT , the acidity C _H = 0, and C _H = −A _T at the start of titration.

The acid used for titration, that is, the acid solution 10 dropped by the dropping unit 14 in FIG. 1 onto the sample solution 11 has a predetermined concentration (hereinafter, the concentration of acid used for titration may be referred to as C). Since an acid is used, the acidity C _H during titration can be expressed by the following formula (47). That is, the acidity C _H of the sample solution 11 can be represented by the weight m ₀ of the sample solution 11 before the start of measurement and the acid titration m so far.

C _H = (mC−m ₀ A _T ) / (m ₀ + m) (47)

  Therefore, the following formula (48) can be derived from the above formula (46) and formula (47).

(MC-m ₀ A _T ) / (m ₀ + m) = [H ⁺ ] _F + [HSO ₄ ⁻ ] + [HF] + [H ₃ PO ₄ ] − [HCO ₃ ⁻ ]
-2 [CO ₃ ² -]-[B (OH) ₄ ^- ]-[OH ^- ]-[HPO ₄ ^2- ] -2 [PO ₄ ^3- ]
^{_{- [SiO (OH) 3 -}} ] - [NH 3] - [HS -] ... (48)

  Each parameter is shown as follows.

_{B T = [B (OH)} 3] + [B (OH) 4 -]
^{_{S T = [HSO 4 -]}} + [SO 4 2-]
_{F T = [HF] + [} F -]
_{P T = [H 3 PO 4} ] + [H 2 PO 4 -] + [HPO 4 2-] + [PO 4 3-]
_{Si T = [Si (OH)} 4] + [SiO (OH) 3 -]
NH _3T = [NH ₄ ⁺ ] + [NH ₃ ]
_{H 2 S T = [H 2} S] + [HS -]
^{_{K 1 = [H +] [}} HCO 3 -] / [CO 2 *]
^{_{K 2 = [H +] [}} CO 3 2-] / [HCO 3 -]
^{_{K B = [H +] [}} B (OH) 4 -] / [B (OH) 3]
^{_{K Si = [H +] [}} SiO (OH) 3 -] / [Si (OH) 4]
K _NH3 = [H ⁺ ] [NH ₃ ] / [NH ₄ ⁺ ]
^{_{K H2S = [H +] [}} HS -] / [H 2 S]
^{_{K S = [H +] F}} [SO 4 2-] / [HSO 4 -]
^{_{K F = [H +] [}} F -] / [HF]
^{_{K 1P = [H +] [}} H 2 PO 4 -] / [H 3 PO 4]
^{_{K 2P = [H +] [}} HPO 4 2-] / [H 2 PO 4 -]
K _3P = [H ⁺ ] [PO ₄ ^3- ] / [HPO ₄ ^2- ]
[H ⁺ ] _F = [H ⁺ ] / Z
Z = 1 + S _T / K _S

Here, as a method for determining the [H ^+], if pH electrode, after calibrating the electrode in advance by pH calibration solution, a method of obtaining the [H ^+] from the measured potential, if colorimetric method, K _(A) , E _{1 (A)} , e _{2 (A)} , e _{3 (A)} may be obtained in advance and determined. If a pH electrode is used, there is a problem that maintenance is troublesome, and if it is a colorimetric method, K _(A) , e _{1 (A)} , e _{2 (A)} , e _{3 (A)} are highly accurate. It is necessary to decide.

Now, in the above equation (8), for example, temporary values are set for K _(A) , e _{1 (A)} , e _{2 (A)} , and e _{3 (A)} , respectively. On the other hand, in the above formula (8), the value of R at each titration point is the absorbance measurement, specifically, the absorbance measurement means 12 irradiates the sample solution 11 with light, and the intensity of light absorption of the sample solution 11. Is obtained by the processing means 13. Then, the temporary values of K _(A) , e _{1 (A)} , e _{2 (A)} , e _{3 (A)} and the R value at each titration point are substituted into the above equation (8). Further, the hydrogen ion concentration of the sample solution 11 at each titration point is set as a temporary hydrogen ion concentration [H ′].

Similarly, in the above formula (29), for example, ψ, K _(A) , K _(B) , e _{1 (A)} , e _{2 (A)} , e _{3 (A)} , e _{1 (B)} , e ₂ Temporary values are set in _(B) and e3 _(B) , respectively. On the other hand, in the above formula (29), the value of R at each titration point is the absorbance measurement, specifically, the absorbance measurement means 12 irradiates the sample solution 11 with light, and the intensity of light absorption of the sample solution 11. Is obtained by the processing means 13. And ψ, K _(A) , K _(B) , e _{1 (A)} , e _{2 (A)} , e _{3 (A)} , e _{1 (B)} , e _{2 (B)} , e _{3 (B)} respectively The hydrogen ion concentration of the sample solution 11 at each titration point obtained by substituting the provisional value of R and the value of R at each titration point into the above equation (29) is defined as [H ′]. .

[H ⁺ ] is replaced with [H ′], and the following equation (49) is calculated from the above equation (8). The same applies to equation (28). Further, although details will be described later, [H ⁺ ] is obtained as an optimal solution of each expression by a nonlinear least square method or the like.

f = [H ⁺ ] / [H '] (49)

Depending on the salinity S and liquid temperature T of the sample solution 11 (ie seawater), K ₁ , K ₂ , K _B , K _Si , K _NH3 , K _H2S , K _S , K _F , K _1P , K _2P , K _3P term is determined by the molecular weight and salinity _{S, B T, S T,} F T, P T, Si T, NH 3T, H 2 S T is obtained. Therefore, the above equation (48) can be transformed into the following equation (50). In this way, it is possible to show the relationship between the total alkalinity A _T and the total carbonate concentration C _T at each titration point.

A _T -C _T・ [(K ₁ f [H '] + 2K ₁ K ₂ ) / ((f [H']) ² + K ₁ f [H '] + K ₁ K ₂ )]
-B _T [1 / (1+ (f [H ']) / K _B )]
-P _T [(K _1P K _2P (f [H ']) + 2K _1P K _2P K _3P- (f [H'] ³ )
/ ((f [H ']) ³ + K _1P (f [H']) ² + K _1P K _2P (f [H ']) + K _1P K _2P K _3P )]
-Si _T [1 / (1+ (f [H ']) / K _Si )]
-NH _3T [1 / (1+ (f [H ']) / K _NH3 )]
-H ₂ S _T [1 / (1+ (f [H ']) / K _H2S )]
+ S _T [1 / (1 + K _S Z / (f [H ']))]
+ F _T [1 / (1 + K _F / (f [H ']))]
+ [(m ₀ + m) / m ₀ ] [f [H '] / ZK _W / f [H']]-m / m ₀ * C = 0 (50)

In the above formula (50), K ₁ , K ₂ , K _B , K _Si , K _NH3 , K _H2S , K _S , K _F , and the like are determined according to the salinity S and the liquid temperature T of the sample solution 11 (that is, seawater). K _1P, K _2P, terms of K _3-Way is determined by the molecular weight and salinity _{S, B T, S T,} F T, P T, Si T, NH 3T, H 2 S T is obtained.

  Furthermore, in the above formula (50), if the following formula (51) and formula (52) are used, the above formula (50) can be expressed by the following formula (53).

X ([H ']) = [(K ₁ f [H'] + 2K ₁ K ₂ ) / ((f [H ']) ² -K ₁ f [H'] + K ₁ K ₂ )]… ( 51)

Y ([H ']) = B _T [1 / (1+ (f [H']) / K _B )]
+ P _T ((K _1P K _2P (f [H ']) + 2K _1P K _2P K _3P + (f [H']) ³ )
/ ((f [H ']) ³ + K _1P (f [H']) ² + K _1P K _2P (f [H ']) + K _1P K _2P K _3P )]
+ Si _T [1 / (1+ (f [H ']) / K _Si )]
+ NH _3T [1 / (1+ (f [H ']) / K _NH3 )]
+ H ₂ S _T [1 / (1+ (f [H ']) / K _H2S )]
-S _T [1 / (1 + K _S Z / (f [H ']))]
-F _T [1 / (1 + K _F / (f [H ']))]
-[(m ₀ + m) / m ₀ ] [f [H '] / ZK _W / f [H']] + m / m ₀ * C (52)

Y ([H ′]) = − C _T · X ([H ′]) + A _T (53)

  Next, each embodiment of the measuring method of the value of the measurement item of carbonic acid type concerning the present invention is described.

(First embodiment)
First, as a measuring method according to the first embodiment, a method for measuring a value of a carbonic acid measurement item by an open cell method (open titration) will be described. Also in the description of the present embodiment, a method for measuring the value of a carbonic acid measurement item in the sample solution 11 will be described below with reference to the schematic diagram of the apparatus shown in FIG. Further, in the present embodiment, the sample solution 11 is not particularly limited as long as it is a solution having alkalinity. However, as an example, the sample solution 11 will be described below assuming that the sample solution 11 is seawater.

  FIG. 2 is a flowchart showing a flow of measurement by the open cell method. In general, in the measurement by the open cell method, since the value of the measurement item of carbonic acid is measured in a relatively narrow range of pH, usually one kind of acid-base indicator (provisionally referred to as indicator A) is included in the sample solution 11. ) Is often contained, but two types can be used. Here, a case where one kind of acid-base indicator is used will be described.

  As shown in step S11 of FIG. 2, in the measurement of the value of the carbonic acid measurement item of the sample solution 11 by the open cell method, first, before the start of measurement, that is, before the start of titration, an acid ( For example, hydrochloric acid) is added dropwise. Then, the processing means 13 proceeds to the next step S12.

  In step S12, the processing means 13 determines whether the pH value of the sample solution 11 is in the range of 3.5 to 4 using, for example, temporary [H ′]. And the process means 13 advances a process to following step S13, when the judgment of the said step S12 is affirmed (YES). On the other hand, the processing means 13 returns processing to step S11 when the determination of the said step S12 is denied (NO), and an acid is dripped at the sample solution 11. FIG.

In step S13, the processing means 13 performs deaeration. More specifically, the processing means 13 slowly rotates a stirrer (not shown) in the sample solution 11 to drive carbon dioxide in the sample solution 11 into the gas phase, that is, the sample solution. 11 so that the total carbonic acid concentration _CT is sufficiently small. Thus, in the above formula (53), total carbon concentration C _T becomes substantially zero. Note that carbon dioxide-free gas may be blown into the sample solution 11 to drive carbon dioxide in the sample solution 11 into the gas phase.

  Next, proceeding to step S14, the processing means 13 starts titration and measures the value of R while dropping the acid into the sample solution 11. Specifically, for example, the dropping unit 14 shown in FIG. 1 drops the acid solution 10 onto the sample solution 11 at a predetermined amount and a predetermined interval in accordance with an instruction from the processing unit 13. At the same time, the value of R is obtained by the processing means 13 when the absorbance measuring means 12 irradiates the sample solution 11 with light and measures the intensity of light absorption of the sample solution 11.

  Here, as an example, for example, when the sample solution 11 contains bromophenol blue (hereinafter sometimes referred to as BPB) as the indicator A and the acid solution 10 is dropped onto the sample solution 11, the change in absorbance is shown in FIG. Shown in As shown in FIG. 3, every time the acid solution 10 is dropped onto the sample solution 11, an absorption spectrum of the bromophenol blue depending on the hydrogen ions of bromophenol blue can be obtained.

  In FIG. 3, the peak observed near the wavelength of 450 nm is derived from the non-dissociated form of bromophenol blue (acid form), and the peak observed near the wavelength of 600 nm is derived from the dissociated form of bromophenol blue (alkali form). .

Since R = Abs ₁ / Abs ₂ as described above, for example, in FIG. 3, the absorbance at a wavelength of 450 nm is Abs _1, and the absorbance at a wavelength of 592 nm is Abs ₂ . That is, the absorbance Abs ₁ and Abs ₂ are obtained by measuring the intensity of light absorption of the sample solution 11 at a wavelength of 450 nm and a wavelength of 592 nm by the absorbance measuring means 12 irradiating the sample solution 11 with light. The processing means 13 calculates. Each time the acid solution 10 is dropped into the sample solution 11, the processing means 13 calculates the value of R based on the absorbance Abs ₁ and the absorbance Abs ₂ , and temporarily stores it in the processing means 13, for example. deep.

The processing means 13 calculates the value of R based on the absorbance Abs ₁ and the absorbance Abs ₂ every time the acid solution 10 is dropped on the sample solution 11, but the R value may be calculated by another method. it can.

In general, the waveform of the absorption spectrum of an indicator varies from one indicator to another, but even the same indicator is affected not only by pH but also by coexisting substances, salinity, and temperature. The absorption spectrum of bromophenol blue has a waveform as shown in FIG. If any three wavelengths are assumed to be wavelengths λ ₃ , λ ₄ , and λ ₅ , the absorbance measuring means 12 irradiates the sample solution 11 with light, and the sample solution 11 at the wavelengths λ ₃ , λ ₄ , and λ ₅ is irradiated. The intensity of light absorption is measured each time the acid solution 10 is dropped onto the sample solution 11. Then, the processing unit 13 obtains the absorbance Abs ₃ at the wavelength lambda _3, the absorbance Abs ₄ at a wavelength lambda _4, the absorbance Abs ₅ at a wavelength lambda _5, respectively.

Further, the processing unit 13, the absorbance Abs ₃ at the wavelength lambda _3, the absorbance Abs ₄ at a wavelength lambda _4, based on the absorbance Abs ₅ at a wavelength lambda _5, that is, the resultant three points, approximate the indicator specific waveform of the absorption spectrum To do. More specifically, the processing unit 13, the absorbance Abs ₃ at the wavelength lambda _3, the absorbance Abs ₄ at a wavelength lambda _4, based on the absorbance Abs ₅ at a wavelength lambda _5, the absorption spectra of bromophenol blue as long as the present embodiment Approximate the waveform. As an approximation method, there is an approximation method by the Gauss method. Even in this way, the processing means 13 can calculate the value of R. Thereby, the error when the absorbance measurement means 12 irradiates the sample solution 11 with light and measures the intensity of light absorption of the sample solution 11 can be reduced.

  Returning to the description of FIG. 2, in step S <b> 15, the processing means 13 obtains a temporary [H ′] using the initial value of the parameter, calculates the temporary pH, and the pH of the sample solution 11 is 3. Judge whether it was below. And the process means 13 advances a process to following step S16, when the judgment of the said step S15 is affirmed (YES). On the other hand, if the determination in step S15 is negative (NO), the processing unit 13 returns the process to step S14 and continues titration.

In step S16, the processing means 13 performs additional titration. That is, the processing means 13 performs the end determination using the temporary [H ′], but the temporary [H ′] is slightly different from the optimized [H ⁺ ], and therefore additional titration is performed. Then, make a little extra measurement, and make the necessary measurement even when optimized.

  Here, as an example, FIG. 4 shows an example of measurement results (time series) of measurement by the open cell method. The measurement conditions are as shown in Table 1 below.

In Table 1 above, the concentration of acid (hydrochloric acid) is 0.1M. In Table 1, e _{1 (BPB)} , e _{2 (BPB)} , e _{3 (BPB)} are ratios of molar extinction coefficients, respectively, and e _{1 (BPB)} = ₅₉₂ ε _HA / ₄₅₀ ε _HA , e _{2 (BPB)} = ₅₉₂ ε _A− / ₄₅₀ ε _HA , e _{3 (BPB)} = ₄₅₀ ε _A− / ₄₅₀ ε _HA , respectively.

  FIG. 4 is a graph showing the relationship between measurement time, acid titer and absorbance. Specifically, in FIG. 4, the horizontal axis represents time, and the vertical axis represents acid (hydrochloric acid) titration (upper FIG. 4) and absorbance (lower FIG. 4). As shown in FIG. 4, first, a certain amount of acid (hydrochloric acid) is added to the sample solution 11 to drive carbon dioxide in the sample solution 11 into the gas phase, that is, degassing is performed (degassing shown in step S13 of FIG. 2). Equivalent to care).

  Thereafter (after degassing), acid (hydrochloric acid) is dropped into the sample solution 11 at predetermined intervals, whereby the absorbance at a wavelength of 450 nm increases and the absorbance at a wavelength of 592 nm decreases (step S14 in FIG. 2). Equivalent to the titration shown in the above).

  Then, after dropping a certain amount of acid (hydrochloric acid), the titration is finished.

  Returning to the description of FIG. 2, in step S <b> 17, the processing means 13 performs an operation, and the processing of the flowchart of FIG.

As described above, the value of R at each titration point is calculated in step S14. Therefore, the processing means 13 calculates the pH of the sample solution 11 at each titration point. Specifically, the processing means 13 uses the value of R obtained at each titration point, and obtains the hydrogen ion concentration of the sample solution 11 at each titration point based on Expression (8). In the formula (8), e _{1 (BPB)} , e _{2 (BPB)} , e _{3 (BPB)} are obtained in advance from the experimental conditions shown in Table 1 above, and the value of R is determined for each titration. Is earned in points. Then, a temporary value parameter is set for K _(BPB) , and the temporary hydrogen ion concentration of the sample solution 11 at each titration point [H ′] is calculated using the equation (8).

As described above, in the measurement of the value of the carbonic acid measurement item by the open cell method, first, before starting the titration, an acid is dropped onto the sample solution 11 to drive the carbonic acid in the sample solution 11 into the gas phase. . Thus, the total alkalinity _AT at each titration point can be obtained from the above equation (52). That is, in the above formula (51), K ₁ , K ₂ , K _B , K _Si , K _{NH 3} , K _{H 2 S} , K _S , K _F , K _{1 P} , K _{2 P} , K _{3 P} , B _T , S _T , F _{T , P T, Si T, NH} 3T, H 2 S T is previously a sought constant, and the concentration C, titrated weight m ₀ and the acid of the sample solution before measurement start acids (hydrochloric acid) is used to titrate The quantity m is known. Therefore, the equation (53) can be expressed by the following equation (54), can be determined total alkalinity A _T of the sample solution 11 in each titration point.
Y ([H ']) = A _T (54)

Specifically, for example, the processing means 13 uses the value of R obtained at each titration point, and obtains the hydrogen ion concentration of the sample solution 11 at each titration point based on the above formula (8). For example, in the above formula (8), e _{1 (BPB)} , e _{2 (BPB)} , e _{3 (BPB)} are obtained in advance from the experimental conditions in Table 1 above, and the value of R is the titration point. Is obtained. Then, in the above equation (8), for example, a parameter of a temporary value is set for K _(BPB) , and the temporary hydrogen ion concentration of the sample solution 11 at each titration point is calculated using the equation (8). Find [H ']. Further, the processing means 13 obtains the temporary total alkalinity _AT of the sample solution 11 at each titration point using the above formula (52) based on the temporary hydrogen ion concentration [H ′].

The R value shown in FIG. 5 is based on the absorbance value at a wavelength of 850 nm, that is, R = (Abs _{450 (BPB)} -Abs _{850 (BPB)} ) / (Abs _{592 (BPB)} -Abs _{850 ( BPB)} ). FIG. 5 shows the titration of acid (hydrochloric acid) on the horizontal axis and the R value (“×” in FIG. 5) and pH (“◯” and “●” in FIG. 5) on the vertical axis. It is shown.

In FIG. 5, the optimum solutions ₍ described later ₎ of e _{1 (BPB)} , e _{2 (BPB)} , e _{3 (BPB)} , and K _(BPB) obtained in advance from the experimental conditions in Table 1 are used, respectively, and the equation (8 The pH at each titration point determined based on In FIG. 5, “◯” is a value of R when pH> 3.5 or pH <3, and is a point not used for calculating the total alkalinity _AT . On the other hand, “●” is the value of R when 3 <pH <3.5, and is the point used for calculating the total alkalinity _AT .

The total alkalinity of A _T of the sample solution 11 (sea water) in the pH = 3.0-3.5 is known to be constant. Here, the processing means 13 calculates | requires temporary total alkalinity _AT of several points (for example, 10-20 points) among titration points by the method mentioned above, for example. Then, the processing means 13 uses a standard deviation (hereinafter referred to as “SD”) of the temporary total alkalinity _AT of the titration point, that is, a variation in the total alkalinity _AT of the titration point. For example, K _(BPB) is obtained by a nonlinear least square method.

  Note that as a nonlinear least square algorithm as a method for obtaining an optimal parameter solution, there are Newton's method, Gauss-Newton method, Powell's least square method, and the like. Some spreadsheet software has this function when finding the optimal parameter solution. For example, the Microsoft spreadsheet "Excel" uses the solver function to calculate the target in a formula that includes multiple variables. The value of the optimal variable for obtaining the value

  The solver can determine the interrelation between variables while changing the values of a plurality of variables, and calculate an optimum value. You can place specific constraints on a variable, or change the value of another variable to obtain the maximum or minimum value for a specific variable. If a solver is used, the solution of simultaneous equations and the complicated calculation of a carbonic acid system using the colorimetric method as described above can be performed.

This will be described more specifically with reference to FIG. FIG. 6 is a diagram showing a standard deviation of the total alkalinity _AT from the titration result of the open cell method and showing an average value of the standard deviation and the total alkalinity _AT . In FIG. 6, K _(BPB) is expressed in logarithmic representation (pK _(BPB) ). Specifically, pK _(BPB) represents -log (K _(BPB) ). For example, as shown in FIG. 6, the standard deviation of the provisional total alkalinity _AT is obtained by changing pK _(BPB) . In the example of FIG. 6, it can be seen that the standard deviation is minimized when pK _(BPB) is around 3.5.

Furthermore, as shown in FIG. 7, if pK _(BPB) is changed and pK _(BPB) when the standard deviation of the temporary total alkalinity _AT is minimized is used, the sample solution 11 at each titration point is used. The total alkalinity _AT is constant. In other words, pK of total alkalinity A _T becomes constant _(BPB) is the optimal solution, total alkalinity A _T at this time is the true total alkalinity A _T of the sample solution 11.

Further, as described above, e _{1 (BPB)} , e _{2 (BPB)} , and e _{3 (BPB)} are obtained in advance from the experimental conditions in Table 1 above, and the value of R is obtained at each titration point. Therefore, if the optimum solution of pK _(BPB) is obtained, the hydrogen ion concentration of the optimum solution can be obtained from the above equation (8). As a result, the hydrogen ion concentration of the optimum solution of the sample solution 11 at each titration point can also be obtained.

Note that the optimal solution of pK _(BPB) converges to a certain value by performing the process in step S17 about three times. For example, “●” in FIG. 6 is the optimal solution and pK _(BPB) = 3. 545, A _T = 2391.2.

Hereinafter, the calculation result in step S17 is shown. Specifically, the calculation results are shown in Table 2 below. In Table 2, the initial value of pK _(BPB) is a temporary value for the pK _(BPB).

In step S17, the total alkalinity _AT was determined so that the standard deviation was the smallest in the range of pH 3.0 to pH 3.5. In the case of seawater, the sample solution 11 exceeded pH 3.5. (specifically seawater) is present H ⁺ dissociation of carbonate remaining in the (H ₂ CO _3), and (in particular sea water) sample solution 11 falls below the pH3.0 with H ⁺ in This is because SO ₄ ²⁻ aggregates and affects the desired total alkalinity _AT .

In addition, hereinafter, the total alkalinity _AT measurement of the sample solution 11 was performed by the open cell method which is a measurement method according to the present embodiment, and the reproducibility thereof was verified. The results are shown in Table 3 below.

  As shown in Table 3, it is a very good result, and it can be seen that the measurement method according to the present invention is a measurement method with excellent reproducibility.

Thus, according to the measuring method according to the present embodiment, the total alkalinity _AT can be measured without using a pH electrode. That is, the troublesome maintenance of the pH electrode can be eliminated. In addition, there is no possibility of pH electrode drift or sensitivity reduction, which is a major error factor in the measurement values of carbonic acid measurement items. Therefore, the total alkalinity _AT of the sample solution can be accurately measured by a simpler method.

On the other hand, according to the measurement method according to the present embodiment, even if K _(BPB) is unknown, an optimal solution of K _(BPB) can be obtained. Furthermore, if the optimum solution of K _(BPB) can be obtained, the pH of the sample solution 11 before addition of the acid can be calculated. Thereby, the total carbonic acid concentration and the carbon dioxide partial pressure can also be calculated by carbonic acid calculation.

In general, it is known that the dissociation constant of an indicator greatly changes depending on the temperature and salt concentration of a sample solution containing the indicator. In other words, the dissociation constant of the indicator also changes as the temperature and salt concentration of the sample solution containing the indicator change. That is, in order to obtain the measurement value of the carbonic acid measurement item of the sample solution with high accuracy, it is necessary to obtain an accurate indicator dissociation constant in advance. However, if the measurement method according to the present invention is used, it is not necessary to previously determine the dissociation constant of the indicator, and the total alkalinity _AT of the sample solution can be measured with high accuracy.

In the above-described example, a temporary parameter is set for K _(BPB) . However, the present invention is not limited to this. For example, if K _(BPB) is known, a temporary value is set as a parameter for e _{1 (BPB)} , e _{2 (BPB)} , e _{3 (BPB)} , and more specific. The ratio of the molar extinction coefficient that is three times or less the number of added indicators (in this embodiment, since there is one indicator added, there are three molar extinction coefficients, ie, e _{1 (BPB)} , e _{2 (BPB)} , e _{3 (BPB)} ) can be set as parameters, and an optimal solution can be obtained by the above-described numerical calculation. In other words, the optimum solution of the parameters related to the colorimetric calculation, that is, the parameters related to the hydrogen ion concentration calculation of the sample solution 11 can be obtained by the numerical calculation described above.

In the above description, for example, K _(BPB) , e _{1 (BPB)} , e _{2 (BPB)} , e _{3 (BPB)} are fixed values, and [H ′] is obtained, and is taken in the above equation (54). One or more of water temperature, titration temperature, acid temperature, sample weight, acid weight (titrated amount), acid concentration, sample salinity concentration are set as unknown values and moved as parameters. The optimum value can be obtained so that the standard deviation of the total alkalinity _AT is minimized.

As described above, the equilibrium constant of carbonic acid, the equilibrium constant of other substances (K ₁ , K ₂ , K _B , K _Si , K _NH3 , K _H2S , K _S , K _F , K _1P , K _2P , K _3P , , B _T , S _T , F _T , P _T , Si _T , NH _3T , and H ₂ S _T ), the relational expressions are respectively determined and determined depending on the salinity concentration and temperature. For example, the weight of the sample (weight m ₀ of the sample solution before the start of measurement) can be moved as a parameter, and the optimum value is calculated so that the standard deviation of the total alkalinity _AT at that time is minimized. I can do it. In this way, since it is not necessary to weigh or measure up the weight of the sample in advance, it is possible to save labor and simplify the measurement.

(Second Embodiment)
Next, as a measuring method according to the second embodiment, a method for measuring a value of a carbonic acid measurement item by a closed cell method (closed titration) will be described. In the description of the present embodiment, the method for measuring the value of the carbonic acid measurement item in the sample solution 11 will be described below with reference to the schematic diagram of the apparatus configuration shown in FIG. Also in this embodiment, the sample solution 11 is not particularly limited as long as it is a solution having alkalinity. However, as an example, the sample solution 11 will be described below assuming that it is seawater.

In the measurement by closed-cell method, unlike the measurement by open cell method described above, the total alkalinity A _T and the total carbonate concentration C _T of the sample solution 11 can be calculated respectively by titration.

  FIG. 8 is a flowchart showing a flow of measurement by the closed cell method. In general, in the measurement by the closed cell method, in order to measure the value of the measurement item of carbonic acid in a relatively wide range of pH, two acid-base indicators (provisional indicator A and indicator B) are included in the sample solution 11. In some cases, a single indicator may be contained.

  The two types of indicators contained in the sample solution 11 are not particularly limited, but as an example, bromophenol blue (hereinafter sometimes referred to as BPB) as the indicator A and bromothymol blue (which may be referred to as BPB) Hereinafter, a case of containing BTB) may be described. A combination of several indicators such as bromocresol and phenol red is also conceivable.

  As shown in step S <b> 21 of FIG. 8, the processing means 13 starts titration and measures the value of R while dropping the acid into the sample solution 11. Specifically, for example, the dropping unit 14 shown in FIG. 1 drops the acid solution 10 onto the sample solution 11 at a predetermined amount and a predetermined interval in accordance with an instruction from the processing unit 13. At the same time, the value of R is obtained by the processing means 13 when the absorbance measuring means 12 irradiates the sample solution 11 with light and measures the intensity of light absorption of the sample solution 11.

As described above, since R = Abs ₁ / Abs ₂ , for example, the absorbance at a wavelength of 450 nm is Abs ₁ and the absorbance at a wavelength of 592 nm is Abs ₂ (see FIG. 3). Then, each time the acid solution 10 is dropped onto the sample solution 11, the processing means 14 measures the value of R, and the R value obtained each time the acid solution 10 is dropped is temporarily stored in the processing means 14, for example. Remember me.

  In step S22 of FIG. 2, the processing means 13 obtains a temporary [H ′] using the initial value of the parameter, calculates the temporary pH, and determines whether the pH of the sample solution 11 is lower than 3. to decide. And the process means 13 advances a process to following step S23, when the judgment of the said step S22 is affirmed (YES). On the other hand, when the determination of step S22 is negative (NO), the processing unit 13 returns the processing to step S21 and continues titration.

  In step S23, the processing means 13 performs additional titration. The processing performed in step S23 has been described in step S17 in FIG.

  Here, as an example, FIG. 9 shows an example of the measurement result by the measurement by the closed cell method. The measurement conditions are as shown in Table 4 below.

In Table 4 above, the concentration of acid (hydrochloric acid) is 0.1M. In Table 4 above, e _{1 (BPB)} , e _{2 (BPB)} , e _{3 (BPB)} , e _{1 (BTB)} , e _{2 (BTB)} , e _{3 (BTB)} are the molar extinction coefficient ratios, respectively. E _{1 (BPB)} = ₅₉₂ ε _HA / ₄₅₀ ε _HA , e _{2 (BPB)} = ₅₉₂ ε _A- / ₄₅₀ ε _HA , e _{3 (BPB)} = ₄₅₀ ε _A- / ₄₅₀ ε _HA , e _{1 ( BTB)} = ₅₉₂ ε _HB / ₄₅₀ ε _HB , e _{2 (BTB)} = ₅₉₂ ε _B− / ₄₅₀ ε _HB , e _{3 (BTB)} = ₄₅₀ ε _B− / ₄₅₀ ε _HB , respectively.

  FIG. 9 is a graph showing the relationship between measurement time, acid titer and absorbance. Specifically, in FIG. 9, the horizontal axis indicates the measurement time, and the vertical axis indicates the acid (hydrochloric acid) titration (upper FIG. 9) and absorbance (lower FIG. 9). As shown in FIG. 9, when acid (hydrochloric acid) is dropped into the sample solution 11 at a predetermined interval, the absorbance at a wavelength of 450 nm increases and the absorbance at a wavelength of 592 nm decreases.

  Returning to the description of FIG. 8, in step S <b> 24, the processing means 13 of FIG. 1 performs an operation and ends the processing of the flowchart of FIG. 8.

As described above, the value of R at each titration point is calculated in step S21. Therefore, the processing means 13 calculates the pH of the sample solution 11 at each titration point. Specifically, the processing means 13 uses the value of R obtained at each titration point, and obtains the hydrogen ion concentration of the sample solution 11 at each titration point based on the equation (29). In the formula (29), e _{1 (BPB)} , e _{2 (BPB)} , e _{3 (BPB)} , e _{1 (BTB)} , e _{2 (BTB)} , e _{3 (BTB)} are represented by, for example, Table 4 above. The value of R is obtained at each titration point. Then, temporary parameter values are set for K _(BPB) , K _(BTB) , and ψ, and the temporary hydrogen ion concentration of the sample solution 11 at each titration point is calculated using the equation (29) [H '] Is calculated.

  In addition, when there is only one kind of indicator, the above formula (8) may be used in the same manner as described in the first embodiment (the description in the open cell system).

Specifically, for example, the processing means 13 uses the value of R obtained at each titration point, and obtains the pH of the sample solution 11 at each titration point based on the above formula (29). For example, in the above formula (29), e _{1 (BPB)} , e _{2 (BPB)} , e _{3 (BPB)} , e _{1 (BTB)} , e _{2 (BTB)} , e _{3 (BTB)} It is obtained in advance from the experimental conditions, and the value of R is obtained at each titration point. In the above formula (29), for example, for K _(BPB) , K _(BTB) and ψ, parameters of temporary values are set, and the sample solution at each titration point is set using the formula (29). 11 [H ′] is obtained for the temporary hydrogen ion concentration.

  FIG. 10 shows the relationship between the titration amount of acid (hydrochloric acid), the R value of the sample solution 11 at each titration point, and the pH.

In FIG. 10, “●” is the R value obtained at each titration point at pH> 3, and “◯” is the R value not used in the optimization calculation at pH <3. “X” is the pH at each titration point determined based on the equation (28), and e _{1 (BPB)} , e _{2 (BPB)} , e ₃ determined in advance from the experimental conditions in Table 4 above. _(BPB) , e _{1 (BTB)} , e _{2 (BTB)} , e _{3 (BTB)} , and optimal solutions for K _(BPB) , K _(BTB) , and ψ described later are used.

Then, using the calculated temporary hydrogen ion concentration [H ′], the calculated value in the above equation (51) is plotted on the x axis and the calculated value in the above equation (52) is plotted on the y axis for each titration point. Then, a graph as shown in FIG. 11 is obtained. In FIG. 11, the initial value is a relationship between x [H '] and y [H'] for each titration point by setting temporary values for K _(BPB) , K _(BTB) , and ψ. Are plotted.

Using this plot, for example, find the optimal solution for the parameter of the temporary value by the nonlinear least square method (Neton method, Gauss-Newton method, Powell's least square method, etc.), for example, so that the straightness is the highest . Specifically, in order to evaluate linearity, the correlation coefficient r may be obtained, and in the following equation (55), the optimum solution for each parameter that maximizes r ² may be obtained.

As an example, FIGS. 12 to 14 show the values of r ² when temporary parameter values are set and varied for K _(BPB) , K _(BTB) , and ψ, respectively. In the following description, pK _(BPB) = − log (K _(BPB) ) and pK _(BTB) = − log (K _(BTB) ).

FIGS. 12 to 14 show values of r ² when, for example, pK _(BPB) , pK _(BTB) , and ψ are set as parameters and the parameters are changed. In addition, there are Newton's method, Gauss-Newton's method, Powell's least square method, etc. as nonlinear least square algorithm as a method for obtaining the optimal solution of parameters, but the solver function is in Microsoft spreadsheet software "Excel". Thus, the optimum solution was found to be pK _(BPB) = 3.553, pK _(BTB) = 6.5504, φ = 0.1303, and r ² = 1.000, respectively.

Here, from the above equation (53), in FIG. 11, the total carbonic acid concentration _CT is obtained from the amount of change with respect to a certain amount of acid dripping (that is, the slope of the linear approximation equation). On the other hand, the total alkalinity _AT is obtained from the intercept of the linear approximation formula.

Hereinafter, Table 5 shows the calculation result in step S24. In Table 5, the initial values of pK _(BPB) , pK _(BTB) , and ψ are provisional values.

As shown in Table _{5, pK (BPB), pK} (BTB), if optimal solution ψ is determined, obtained is the total alkalinity A _T and the total carbonate concentration C _T of the sample solution 11. As described above, e _{1 (BPB)} , e _{2 (BPB)} , e _{3 (BPB)} , e _{1 (BTB)} , e _{2 (BTB)} , e _{3 (BTB)} are the experimental conditions shown in Table 4 above. Since the value of R is obtained at each titration point, the optimum solution of pK _(BPB) , pK _(BTB) , and ψ can be obtained from the above equation (28). The hydrogen ion concentration can be determined. As a result, the pH of the sample solution 11 at each titration point can be obtained, and the pH of the sample solution 11 can be obtained.

In the following, the closed-cell method is a measurement method according to the present embodiment performs the measurement of total alkalinity A _T and the total carbonate concentration C _T of the sample solution 11, and verify the reproducibility. The results are shown in Table 6 below.

  As shown in Table 6, it is a very good result, and it can be seen that the measurement method according to the present invention is a measurement method with excellent reproducibility. In this way, the total alkalinity and total carbonic acid are obtained by the closed method, and the pH of the sample (sample solution 11) is obtained from the optimal solution of the parameters. If (39) is used, the carbon dioxide partial pressure can also be calculated. (For example, see "DOE (1994) Handbook of methods for the analysis of the various parameter of the carbon dioxide system in sea water. Version 2, A.G.Dickson & C. Goyet, eds.ORNL / CDIAC-74")

  Thus, according to the measurement method according to the present embodiment, the same effects as those of the measurement method according to the first embodiment described above can be obtained.

On the other hand, according to the measurement method according to the present embodiment, even if K _(BPB) , K _(BTB) , and ψ are unknown, the optimum of each of K _(BPB) , K _(BTB) , and ψ You can also find a solution.

In the above-described example, temporary value parameters are set for K _(BPB) , K _(BTB) , and ψ. However, it is not limited to this, for example, K _(BPB) , K _(BTB) , ψ, e _{1 (BPB)} , e _{2 (BPB)} , e _{3 (BPB)} , e _{1 (BTB)} , e _{2 (BTB)} , E _{3 (BTB)} , the optimal solution can be obtained by setting parameters of temporary values for any three of them.

For example, K _(BPB) , K _(BTB) , e1 _(BPB) , e2 _(BPB) , _{e3 (BPB)} , e1 _(BTB) , e2 _(BTB) , _{e3 (BTB)} are fixed values As parameters, the sample weight, hydrochloric acid weight (titer), acid concentration, salinity concentration, and temperature can be used as parameters. In the case of the closed method, the same measurement is performed, and K _(BPB) is determined as a fixed value. For example, the weight of the sample (the weight m ₀ of the sample solution before the start of measurement) is set as an unknown parameter. Similarly, the weight of the sample may be obtained so as to minimize the standard deviation of the temporary total alkalinity _AT of the titration point by the nonlinear least square method so as to satisfy the equation (53). Hereinafter, with respect to other parameters, parameters other than the unknown parameters are fixed, and the parameters are moved so as to minimize the standard deviation of the total alkalinity _AT so as to satisfy the equation (54). What is necessary is just to obtain | require with a multiplication.

That is, in the closed cell method, the measurement is performed in the same manner, and K _(BPB) , K _(BTB) , and ψ are determined to be fixed values, and each of the expressions (29) and (53) is set with the weight of the sample as a parameter. plotted for each titration point, a non-linear least squares method, so that r ² is maximized, it may be obtained the weight of the sample. Other parameters may be obtained by a non-linear least square method by fixing parameters other than the unknown parameters and moving the parameters so that r ² is maximized.

Furthermore, in the above-described example, two kinds of acid-base indicators (specifically, bromophenol blue as the indicator A and bromothymolphenol as the indicator B) are included in the sample solution 11, but the acid-base indicator is 2 Not limited to species. That is, three or more acid-base indicators may be included in the sample solution 11. For example, when indicator C is included in sample solution 11 in addition to indicator A and indicator B, the molar extinction coefficient of non-dissociated form (HC) and dissociated form (A ⁻ ) at a certain wavelength λ ₁ and wavelength λ ₂ Are ₁ ε _HC , ₁ ε _C- , ₂ ε _HC , ₂ ε _C- respectively, and the molar extinction coefficient ratio is e _{1 (C)} = ₁ ε _HC / ₂ ε _HC , e _{2 (C)} = ₁ ε _C− / ₂ ε _HC , e _{3 (C)} = ₂ ε _A− / ₂ ε _HA

  Next, embodiments of an apparatus using a measurement method according to the present invention (hereinafter sometimes simply referred to as an apparatus) will be described with reference to the drawings.

(Third embodiment)
FIG. 15 is a diagram illustrating an example of the configuration of the apparatus according to the present embodiment. The apparatus according to the present embodiment measures the absorbance of the sample solution while dropping acid directly into the sample solution. As shown in FIG. 15, the apparatus according to this embodiment includes a sample bottle 22, a syringe pump 24, an acid storage tank 23, a stirrer 33, a processing unit 29, a thermometer 34, and the like.

  Specifically, as shown in FIG. 15, first, the acid (for example, hydrochloric acid) from the acid storage tank 23 should be measured by the syringe pump 24 passing through the acid nozzle 35 and entering the sample bottle 22. It is dropped into the sample solution 21 (for example, seawater) (arrow 26 in FIG. 15). Next, the light emitted from the light source 25 passes through the sample bottle 22 and is detected by the detector 28. The detector 28 converts the light incident on the detector 28 into an electrical signal and outputs the electrical signal to the processing unit 29 (specifically, the preamplifier 30). Thereafter, the electrical signal is output to a CPU (Central Processing Unit) 32 via the interface 31, and the CPU 32 performs numerical calculations (calculation of optimum solutions of pH and parameters, measurement of carbonated measurement items, etc.). .

  The syringe pump 24 is a dropping unit that sucks the acid stored in the acid storage tank 23 and drops the acid to the sample solution 21 in the sample bottle 22. In addition, since the measurement of the value of carbonic acid measurement items requires high-precision titration, a microsyringe pump or an auto burette that is excellent in suctioning and discharging minute amounts and capable of controlling liquid feeding with high accuracy is used. It is preferable.

  The acid storage tank 23 stores acid for titration. Any tank may be used as long as it has hermeticity so that the concentration of stored acid does not change and is resistant to acid corrosion.

  The stirrer 33 is a magnetic stirrer or the like, and rotates the rotor 36 put together with the sample solution 21 into the sample bottle 22 at a predetermined rotation speed. Then, the sample solution 21 is stirred by the rotation of the rotor 36 by the stirrer 33, and the neutralized reaction in the dropped acid and the sample solution 21 can be promoted.

  The processing unit 29 includes a preamplifier 30, an interface 31, a CPU 32, and the like, and performs titration control of the syringe pump 24, rotation control of the stirrer 33, output control of the light source 25, and the like. Specifically, electrical signals (output signals) from the thermometer 34 and the detector 28 are amplified and adjusted by the preamplifier 30 and input to the CPU 32 via the interface 31. Then, the CPU 32 adjusts the dropping amount of the syringe pump 24 and the rotation speed of the stirrer 4 based on these electric signals.

  The light source 25 is a light emission source such as a light emitting diode (hereinafter simply referred to as LED), a tungsten lamp, or a xenon lamp. Note that light emitted from an LED, a tungsten lamp, a xenon lamp, or the like is dispersed by a not-shown spectrometer (spectrometer) provided in the light source 25, and light having a desired wavelength is emitted. ing. The detector 28 is configured by, for example, a photodiode, and converts the light transmitted through the sample bottle 22 into an electrical signal. The sample bottle 22 may be made of transparent glass, quartz or the like so that light from the light source 25 can be transmitted.

  As described above, the light source 25 and the detector 28 correspond to an example of the absorbance measurement unit 12 in the schematic diagram of the apparatus using the measurement method according to the present invention (see FIG. 1). Here, first and second modified examples of the absorbance measuring means 12 will be described.

  First, a first modification of the absorbance measurement unit 12 will be described. FIG. 16 is a diagram illustrating an example of an apparatus configuration including the absorbance measurement unit 12 according to the first modification. Hereinafter, an example of an apparatus configuration including the absorbance measurement unit 12 according to the first modification will be described with reference to FIG. In the description of FIG. 16, the same components as those shown in FIG. 15 are denoted by the same reference numerals, and the description thereof is omitted.

  As shown in FIG. 16, the first modification of the absorbance measurement unit 12 includes a light source 25, a detector 28, and an optical fiber cell 37. That is, the absorbance of the sample solution 21 is measured by using the light source 25, the detector 28, and the optical fiber cell 37. As will be apparent from the description below, a light projecting optical fiber 38 is connected to the light source 25 so that the light emitted from the light source 25 can be projected into the optical fiber cell 37. On the other hand, a light receiving fiber 39 is also connected to the detector 28 so that the light emitted from the light source 25 can be received in the optical fiber cell 37. Here, an enlarged view of the optical fiber cell is shown.

  FIG. 17 is an enlarged view of the portion surrounded by the broken line a in FIG. 16 and shows the inside of the optical fiber cell 37. As shown in FIG. 17, the optical fiber cell 37 includes a light projecting optical fiber 38 connected to the light source 25 and a light receiving optical fiber 39 connected to the detector 28. In the optical fiber cell 37, the tip of the light projecting optical fiber 38 and the light receiving optical fiber 39 is provided with a mirror 40. Therefore, the light emitted from the light projecting optical fiber 38 is reflected by the mirror 40, and the light receiving optical fiber is reflected. Light is received at 39. Even in this way, the absorbance of the sample solution 21 can also be measured.

  Next, a second modification of the absorbance measurement unit 12 will be described. FIG. 18 is a diagram illustrating an example of a device configuration including the absorbance measurement unit 12 according to the second modification. Hereinafter, an example of an apparatus configuration including the absorbance measurement unit 12 according to the second modification will be described with reference to FIG. In the description of FIG. 18, the same components as those illustrated in FIG. 15 are denoted by the same reference numerals, and the description thereof is omitted.

  As shown in FIG. 18, the second modification of the absorbance measurement unit 12 includes a light source 25, a detector 28, an absorbance measurement cell 41, and an A pump 42. That is, the absorbance of the sample solution 21 is measured by using the light source 25, the detector 28, the absorbance measurement cell 41, and the A pump 42.

  As shown in FIG. 18, the absorbance measurement cell 41 includes a pipe line 43 made of, for example, transparent glass or quartz. The sample solution 21 is allowed to flow through the pipe line 43, and the light emitted from the light source 25 is transmitted through the flowing sample solution 21. And the light absorbency is measured by detecting the light which permeate | transmitted the pipe line 43 with the detector 28. FIG. Even in this way, the absorbance of the sample solution 21 can also be measured.

  The sample solution 21 is fed to the pipe line 43 by, for example, an A pump 42 using an A1 nozzle 44 having one end immersed in the sample solution 21 and the other end connected to the pipe line 43. The measured sample solution 21 is drained into the sample bottle 22 by an A2 nozzle 45 having one end immersed in the sample solution 21 and the other end connected to a pipe 43.

(Fourth embodiment)
Next, another embodiment of an apparatus using the measurement method according to the present invention (hereinafter sometimes simply referred to as an apparatus) will be described with reference to the drawings. FIG. 19 is a diagram illustrating an example of the configuration of the apparatus according to the present embodiment. In the following description, the same components as those shown in FIG. 15 are denoted by the same reference numerals, and the description thereof is omitted.

The apparatus according to the present embodiment mixes a sample solution and an acid / indicator mixed solution, and measures the absorbance of the mixed solution by a flow analysis method. As shown in FIG. 19, the apparatus according to this embodiment includes a sample solution supply source 46, a B pump 47, an acid / indicator mixed solution supply source 48, a C pump 49, a mixing coil 50, an absorbance measurement cell 41, a light source 25, And a detector 28. Although not shown, the light source 25 and the detector 28 are connected to the processing unit 29.

  Specifically, as shown in FIG. 19, the sample solution 46 is fed by a B pump 47 at a predetermined flow rate (RaB). Note that the sample solution 46 may be stored in a container, or the seawater may be collected in the field by the B pump 47 and sent without using the container.

  On the other hand, the acid / indicator mixed solution in the acid / indicator mixed solution supply source 48 is sent from the acid / indicator mixed solution supply source 48 by the C pump 49 at a predetermined flow rate (RaC).

  Then, the sample solution 46 is sent to the mixing coil 50 through a B pipe 51 between the B pump 47 and the mixing coil 50. Similarly, the acid / indicator mixed solution in the acid / indicator mixed solution supply source 48 is sent to the mixing coil 50 through a C pipe line 52 between the C pump 49 and the mixing coil 50. Thereafter, the sample solution and the acid / indicator mixed solution are thoroughly mixed by passing through the mixing coil 50. Further, the absorbances of the sample solution and the acid / indicator mixed solution that have passed through the mixing coil 50 are measured by the light source 25, the detector 28, and the absorbance measurement cell 41.

  For example, the B pump 47 and the C pump 49 are controlled by the processing unit 29 (not shown) to change the mixing ratio between the sample solution supply source 46 and the acid / indicator mixed solution in the acid / indicator mixed solution supply source 48. You may let them. That is, the processing unit 29 (not shown) may change the ratio Ra {= (RaB) / (RaC)} between the amount of the sample solution fed and the amount of the acid / indicator mixed solution sent.

For example, the ratio Ra, that is, the ratio between the weight m _{0 of the} sample and the titration amount m of hydrochloric acid can be used as a parameter. For example, the ratio Ra may be obtained by setting the ratio Ra as an unknown and using the nonlinear least square method to minimize the standard deviation of the temporary total alkalinity _AT of the titration point in Equation (54) as a parameter. . Further, using the ratio Ra as a parameter, Expression (29) and Expression (53) are used, and the ratio Ra may be obtained so that r ² is maximized by the nonlinear least square method in Expression (55).

(Fifth embodiment)
Next, another embodiment of a device using the measurement method according to the present invention (hereinafter sometimes simply referred to as a device) will be further described with reference to the drawings. FIG. 20 is a diagram illustrating an example of the configuration of the apparatus according to the present embodiment. In the following description, the same components as those shown in FIGS. 15 and 19 are denoted by the same reference numerals, and the description thereof is omitted.

  The apparatus according to the present embodiment mixes a sample solution, an acid solution, and an indicator, and measures the absorbance of the mixed solution by a flow analysis method. As shown in FIG. 20, the apparatus according to this embodiment includes a sample solution 46, a B pump 47, an acid supply source 53, a D pump 55, an indicator supply source 54, an E pump 56, a mixing coil 50, an absorbance measurement cell 41, A light source 25 and a detector 28 are included. Although not shown, the light source 25 and the detector 28 are connected to the processing unit 29.

  Specifically, as shown in FIG. 19, the sample solution 46 is fed by a B pump 47 at a predetermined flow rate (RaB). The acid in the acid supply source 53 is sent from the acid supply source 53 by the D pump 55 at a predetermined flow rate (RaD). Further, the indicator in the indicator supply source 54 is sent by the E pump 56 from the indicator supply source 54 at a predetermined flow rate (RaE).

  Then, the sample solution 46 is sent to the mixing coil 50 through a B pipe 51 between the B pump 47 and the mixing coil 50. Further, the acid in the acid supply source 53 is sent to the mixing coil 50 through the D pipe 57 between the D pump 55 and the mixing coil 50. Further, the indicator in the indicator supply source 54 is sent to the mixing coil 50 through the E pipe 58 between the E pump 56 and the mixing coil 50. The sample solution, acid, and indicator are sufficiently mixed by flowing through the mixing coil 50 to become a mixed solution. Thereafter, the absorbance of the mixed solution passed through the mixing coil 50 is measured by the light source 25, the detector 28, and the absorbance measurement cell 41.

For example, the B pump 47, the D pump 55, and the E pump 56 may be controlled by the processing unit 29 (not shown) to change the mixing ratio of the sample solution, the acid, and the indicator in the mixing coil 50. That is, for example, the ratio Ra can be used as a parameter. For example, the ratio Ra may be obtained by setting the ratio Ra as an unknown and using the nonlinear least square method to minimize the standard deviation of the temporary total alkalinity _AT of the titration point in Equation (54) as a parameter. . Further, using the above formula Ra (29) and (53) as a parameter, the above formula (55) is plotted for each titration point, and the above is set so that r ² is maximized by the non-linear least square method. What is necessary is just to obtain | require ratio Ra.

  As described above, according to the apparatuses according to the third to fifth embodiments described above, the measurement method according to the present invention can be used. Moreover, the apparatus which concerns on the above-mentioned 3rd-5th embodiment measures the light absorbency of the said sample solution, dripping an acid directly to a sample solution. That is, since the apparatus according to the third to fifth embodiments described above can be performed in one container from titration to measurement, for example, each time the acid is dropped on the sample solution, the sample solution is subjected to another spectrophotometry. The time required for measurement can be shortened compared with the case of measuring with a meter.

  Furthermore, according to the apparatuses according to the fourth and fifth embodiments described above, each solution (for example, sample solution, acid, indicator) required for measurement can be made in a small amount.

  The light source 25 described above can use an LED or the like in addition to a general tungsten lamp, xenon lamp, or the like as a light emission source.

  FIG. 21 is a diagram showing an example in which an LED is used as the light emission source of the light source 25 described above. For example, as shown in FIG. 21, a case is assumed in which a first light emitter 59 and a second light emitter 60 are provided as light emission sources of the light source 25. For example, the wavelength of the light emitted from the first light emitter 59 is a wavelength at which a peak derived from the non-dissociated form (acid form) of the indicator is obtained, and the wavelength of the light emitted from the second light emitter 60. Is a wavelength at which a peak derived from the dissociated form (alkaline form) of the indicator is obtained. By doing in this way, since the light source 25 does not need to be provided with a spectrometer (spectrometer), the light source 25 needs a simple structure. In terms of appearance, LEDs in which two or more light emitters are housed in one package are also commercially available.

  That is, by providing at least two or more light emitters that can emit light of a desired wavelength in the light source 25, lighting the light emitters separately, and measuring the light intensity with the detector 28. The absorbance of the sample solution 21 can be measured.

  Note that the light source 25 including at least two light emitters that can emit light having a desired wavelength is not limited to being used as a light source of an apparatus using the measurement method according to the present invention. That is, for example, not only seawater but also various solutions can be obtained by the light source 25 including at least two light emitters each capable of emitting light having a desired wavelength and the detector capable of measuring the light intensity. Can be measured.

  Although the present invention has been described in detail above, the above description is merely an example of the present invention in all respects and is not intended to limit the scope thereof. It goes without saying that various improvements and modifications can be made without departing from the scope of the present invention.

  INDUSTRIAL APPLICABILITY The present invention is useful for a measurement method capable of measuring the value of a measurement item of carbonic acid in seawater with a simple method with high accuracy, a measurement apparatus using the measurement method, and the like.

DESCRIPTION OF SYMBOLS 10 ... Acid solution 11 ... Sample solution 12 ... Absorbance measuring means 13 ... Processing means 14 ... Dropping means

Claims (15)

A method for measuring solution components using an absorbance method, wherein an acid is dropped into a sample water containing at least one colorimetric indicator in a sample solution, and the absorbance of the sample water at a predetermined wavelength is measured. A first step of:
At least one of the values required for calculating the value of the carbonic acid measurement item of the sample solution by the colorimetric method is set as a parameter, and the optimal solution for the parameter value is determined in advance using the absorbance. A second step of calculating by performing a numerical operation;
A solution component measurement method using an absorbance method, comprising: a third step of calculating a value of the measurement item by substituting an optimal solution of the parameter value into a predetermined mathematical formula.   The method for measuring a solution component using the absorbance method according to claim 1, wherein the value of a carbonic acid measurement item is measured by an open cell method (open titration).   The method for measuring a solution component using the absorbance method according to claim 1, wherein the value of a carbonic acid measurement item is measured by a closed cell method (sealed titration).   In the first step, the absorbance of the test water is measured at at least three different wavelengths and approximated to a waveform of an absorption spectrum unique to a pH indicator added to the sample solution, and is determined based on the waveform. The method for measuring a solution component using the absorbance method according to claim 1, wherein the absorbance value of the test water at a wavelength is measured.   The method for measuring a solution component using the absorbance method according to claim 1, wherein at least one dissociation constant is set as a parameter among dissociation constants of each pH indicator added to the sample solution.   2. The absorbance according to claim 1, wherein the parameter is set with a value of a ratio of molar extinction coefficients of the sample solutions at different wavelengths, which is three or less times the number of types of pH indicator added to the sample solution. Method of measuring solution components using the method.   The method for measuring a solution component using the absorbance method according to claim 1, wherein the concentration of the acid dropped into the test water is set as the parameter.   The method for measuring a solution component using the absorbance method according to claim 1, wherein the weight or volume of the sample solution is set as the parameter.   The method for measuring a solution component using the absorbance method according to claim 1, wherein the temperature of the sample solution is set as a parameter.   The method for measuring a solution component using the absorbance method according to claim 1, wherein the salt concentration of the sample solution is set as the parameter.   The ratio between the weight of the sample solution and the weight of the acid dropped onto the test water, or the ratio between the volume of the sample solution and the volume of the acid dropped onto the test water is set as the parameter. Item 4. A method for measuring a solution component using the absorbance method according to Item 1. An apparatus for measuring solution components using an absorbance method,
A first container containing test water containing at least one pH indicator in a sample solution;
A second container containing an acid dropped into the test water;
Dropping means for dropping the acid contained in the second container into the test water placed in the first container;
Measuring means for measuring the absorbance of the test water each time the acid is dropped by the dropping means;
At least one of the values required for calculating the value of the carbonic acid measurement item of the sample solution by the colorimetric method is set as a parameter, and the optimal solution for the parameter value is determined in advance using the absorbance. First calculating means for calculating by performing a numerical operation;
By substituting the predetermined et a formula an optimal solution value of the parameter, and a second calculation means calculating means for calculating the value of the measurement item of carbonated, the solution components using spectrophotometry measuring device. An apparatus for measuring solution components using an absorbance method,
A container containing an acid containing at least one pH indicator;
A first liquid feeding means for feeding a sample solution at a predetermined flow rate;
A second liquid supply means for feeding at a predetermined et flow rate of acid moistened the pH indicator,
A mixing means for mixing the sample solution with an acid containing a pH indicator contained in the container;
Measuring means for measuring the absorbance of the mixed solution mixed by the mixing means by a continuous flow analysis method;
At least one of the values required for calculating the value of the carbonic acid measurement item of the sample solution by the colorimetric method is set as a parameter, and the optimal solution for the parameter value is determined in advance using the absorbance. First calculating means for calculating by performing a numerical operation;
By substituting the predetermined et a formula an optimal solution value of the parameter, and a second calculation means calculating means for calculating the value of the measurement item of carbonated, the solution components using spectrophotometry measuring device.   14. The apparatus for measuring a solution component using the absorbance method according to claim 13, wherein the first calculation means sets a ratio of a flow rate of the sample solution and a flow rate of the acid containing the pH indicator as a parameter. An apparatus for measuring solution components using an absorbance method,
A first container containing an acid;
a second container containing a pH indicator;
A first fluid feeding means for feeding at a predetermined et flow rate of the sample solution,
A second liquid supply means for feeding in said first predetermined et flow rate of acid in a container,
A third fluid feeding means for feeding said at least one predetermined et flow rate a pH indicator which is placed in a second container,
A mixing means for mixing the sample solution, the acid and the pH indicator;
Measuring means for measuring the absorbance of the mixed solution mixed by the mixing means by a continuous flow analysis method;
At least one of the values required for calculating the value of the carbonic acid measurement item of the sample solution by the colorimetric method is set as a parameter, and the optimal solution for the parameter value is determined in advance using the absorbance. First calculating means for calculating by performing a numerical operation;
By substituting the predetermined et a formula an optimal solution value of the parameter, and a second calculation means calculating means for calculating the value of the measurement item of carbonated, the solution components using spectrophotometry measuring device.

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