JP2012107986A - Ph measuring method and measuring device using the method - Google Patents

Abstract

A pH measuring method and a measuring device using the method are provided that can easily and accurately calculate the pH of a solution of a measuring solution, particularly seawater.
An electrode in which a potential difference between a pair of electrodes consisting of a glass electrode and a reference electrode is set to 0 mV in a solution having a pH in the range of 7.2 to 8.2, and seawater is used as a measurement solution. This is a measurement method for measuring the pH of the measurement solution based on a voltage (potential difference) generated therebetween. Further, the measuring device comprises at least one means selected from the group consisting of a pair of electrodes (electrode pair), a voltmeter, a salinity measuring means, a carbonic acid measuring means, a titration measuring means, and an absorbance measuring means; And processing means.
[Selection] Figure 1

Description

  The present invention relates to a pH measurement method and a measurement apparatus using the method.

In recent years, the concentration of carbon dioxide in the atmosphere has increased, which is known to be related to global warming. On the other hand, when the concentration of carbon dioxide in the atmosphere increases, it is also known that a part thereof is dissolved in seawater. In general, carbon dioxide dissolved in seawater produces ions such as bicarbonate ions (HCO ₃ ⁻ ) and carbonate ions (CO ₃ ²⁻ ). Therefore, even if carbon dioxide dissolves in seawater, the pH is around neutral (approximately pH 7.) due to the action of hydrogen carbonate ions (HCO ₃ ⁻ ) and carbonate ions (CO ₃ ²⁻ ) that neutralize the acid (H ⁺ ). 4 ~ 8.2).

However, in recent years, the mass of fossil fuels has increased the concentration of carbon dioxide dissolved in seawater as a gas, and the ocean is becoming acidic. Therefore, measuring the pH of seawater with high accuracy is an important issue in discussing the global warming problem. In addition, measuring the pH of seawater with high accuracy generally means measuring with high accuracy up to the order of 10 ^{−3 in} the field of marine research.

Conventionally, the hydrogen ion index of a solution (pH: pH = -log [H ⁺ ]; [H ⁺ ] is the hydrogen ion concentration in the solution) is expressed as a logarithmic value of the hydrogen ion concentration and is measured electrochemically. Is known to have a hydrogen ion activity (pH = -log [hydrogen ion activity]). However, when there is a high concentration of salinity such as seawater, it is difficult to measure the activity, there is an interaction of ions in the solution, and there are also problems of ion selectivity and dissolution of gas components. Careful discussion is required to determine the pH of the standard solution.

  For example, the International Weights and Measures Committee (CIPM) defines a Harned cell composed of a hydrogen gas electrode and a silver-silver chloride electrode as the primary standard method and the pH values of a plurality of buffer solutions as the primary standard. In the US National Bureau of Standards (NBS), the primary pH buffer solution was first assigned a value and applied mutatis mutandis in the American Society of Testing and Materials (ATSM) and Japanese Industrial Standards (JIS) standards. . In addition, equimolar mixed phosphate buffer solution and potassium hydrogen phthalate buffer solution determined by NBS are referred to as NBS buffer system.

Usually, the hydrogen ion index (pH) of a solution is expressed as a logarithmic value of the hydrogen ion concentration. However, the pH in the case of seawater is different from the pH in the case of the normal solution described above, such as total scale pH (may be described as pH _T ) and seawater scale pH (may be described as pHsws). Is defined (for example, Non-Patent Document 1).

The above total scale pH is pH _T = -log ([H ⁺ ] + [HSO ₄ ⁻ ]), [H ⁺ ] is the hydrogen ion concentration in the solution, and [HSO ₄ ⁻ ] is in the solution. The sulfate ion concentration.

On the other hand, the seawater scale pH is pHsws = -log ([H ⁺ ] + [HSO ₄ ⁻ ] + [F ⁻ ]), where [H ⁺ ] is the hydrogen ion concentration in the solution and [HSO ₄ ⁻ ] is The sulfate ion concentration in the solution, [F ⁻ ], is the fluorine ion concentration in the solution.

For example, when measuring the total scale pH of seawater (that is, pH _T ) and seawater scale pH (that is, pHsws) using a pH electrode, a calibration solution (Tris-HCl buffer solution) that is usually assumed to measure seawater AMP buffer, etc.) is used as a standard solution by dissolving the buffer in a solvent close to the composition of seawater, and the pH electrode is calibrated. In the following description, calibration solutions (Tris-HCl buffer, AMP buffer, etc.) that are supposed to measure seawater may be referred to as seawater buffers.

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

  However, the seawater buffer described above has a problem that it is very difficult to handle. Specifically, a case is considered where the pH of seawater is to be measured accurately using a pH electrode. At this time, when calibration of the pH electrode is performed with the seawater buffer, the seawater buffer needs to have the same composition as the seawater to be measured. For this reason, there is a problem that it takes much time to adjust the seawater buffer.

  Further, it is known that the pH of the above-mentioned seawater buffer solution, particularly Tris-HCl buffer solution, varies depending on the temperature. That is, in order to measure accurate pH, it is required that the water temperature of the measurement solution to be measured is constant. For this reason, there is a problem that the pH electrode calibrated with the seawater buffer solution is not suitable for measuring the pH of seawater whose water temperature changes such as 0 ° C to 35 ° C.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to use a pH measurement method and method capable of easily and accurately calculating the pH of a measurement solution, particularly seawater. It is to provide a measuring device.

  In order to achieve the above object, the present invention has the following features. That is, the first invention uses an electrode in which the potential difference between a pair of electrodes consisting of a glass electrode and a reference electrode is set to 0 mV in a solution having a pH in the range of 7.2 to 8.2, and seawater is used as a measurement solution. As a measurement method for measuring the pH of the measurement solution based on the voltage (potential difference) generated between the electrodes.

  2nd invention is a measuring method which measures pH based on the difference in the liquid junction of a glass sensitive film | membrane and the said comparative electrode in the said 1st invention being the difference between a glass electrode and a comparative electrode. The internal electrode of the glass electrode and the internal electrode of the comparison electrode may have the same structure.

  3rd invention is a measuring method which measures the pH of the said measurement solution which uses seawater as a measurement solution based on the voltage (potential difference) produced between the said electrodes using a pair of electrode which consists of a glass electrode and a comparison electrode. The above method uses a plurality of predetermined calibration solutions to calibrate the glass electrode at least twice with different calibration solutions, and substitutes the voltage value output in each calibration step into a predetermined mathematical formula. The correction number calculation step for calculating the correction number indicating the characteristics of the glass electrode by the calculation, the first measurement step for measuring the pH of the measurement solution using the pair of electrodes as the first pH scale, and the correction number calculation step A scale conversion step of converting to a second pH scale different from the first pH scale measured in the first measurement step using a correction number and a predetermined mathematical formula.

  4th invention is a measuring method which measures pH of the said measurement solution which uses seawater as a measurement solution based on the voltage (potential difference) which produced between the said electrodes using a pair of electrode which consists of a glass electrode and a comparison electrode. The above method includes a calibration step of calibrating the glass electrode using a predetermined calibration solution, a salinity measurement step of measuring the salinity and temperature of the measurement solution, and the pH of the measurement solution using a pair of electrodes as a first pH scale. And a scale conversion step of converting to a second pH scale different from the first pH scale measured in the first measurement step based on a predetermined mathematical formula using the salinity and temperature measured in the salinity measurement step. With.

  5th invention is a measuring method which measures pH of the said measurement solution which uses seawater as a measurement solution based on the voltage (potential difference) which produced between the said electrodes using a pair of electrode which consists of a glass electrode and a comparison electrode. The method includes a calibration step of calibrating a glass electrode using a predetermined calibration solution, a first measurement step of measuring the pH of a measurement solution as a first pH scale using a pair of electrodes, and a predetermined mathematical formula. A first pH scale based on a carbonic acid measurement step for measuring at least two or more carbonic acid measurement items of seawater in the measurement solution used, a value of the measurement item measured in the carbonic acid measurement step, and a predetermined mathematical formula; A calculation step for calculating the second pH scale of different measurement solutions, and a correction for calculating a correction function indicating the relationship between the value of the first pH scale measured in the first measurement step and the value of the second pH scale calculated in the calculation step A function calculation step, and a scale conversion step of converting to a second pH scale different from the first pH scale using the correction function calculated in the correction function calculation step.

  6th invention is a measuring method which measures pH of the said measurement solution which uses seawater as a measurement solution based on the voltage (potential difference) produced between the said electrodes using a pair of electrode which consists of a glass electrode and a comparison electrode. The method described above is based on the alkalinity titration in at least one of the alkalinity titration in the closed cell method (sealed alkalinity titration) and the alkalinity titration in the semi-closed method (alkalinity titration in a state close to sealing). A titration step for measuring at least two or more measurement items of carbonic acid in seawater in advance, a calibration step for calibrating a glass electrode using a predetermined calibration solution, and a pH of the measurement solution using a pair of electrodes as a first pH A first measurement step for measuring as a scale, a calculation step for calculating a second pH scale of a measurement solution different from the first pH scale based on a value of a measurement item measured in the titration step and a predetermined mathematical formula, and a first measurement Calculate a correction function indicating the relationship between the value of the first pH scale measured in the process and the value of the second pH scale calculated in the calculation process That comprises a correction function calculating step, and a scale conversion step of converting said first 1pH scale using a correction function calculated in the correction function calculating step different from the 2pH scale.

  In a seventh aspect based on the sixth aspect, the measurement item of the carbonic acid system of the seawater of the measurement solution measured by the titration step includes total carbonic acid concentration, total alkalinity, hydrogen ion concentration index, and carbon dioxide partial pressure. It is characterized by being at least two or more selected from the group.

  The eighth invention is a measurement method for measuring the pH of a measurement solution using seawater as a measurement solution based on a voltage (potential difference) generated between the electrodes using a pair of electrodes consisting of a glass electrode and a reference electrode. In the above method, acid is dropped into the measurement solution containing at least one colorimetric indicator in the measurement solution, the absorbance of the measurement solution at a predetermined wavelength is measured, and the measurement solution is measured based on a predetermined mathematical formula. An absorbance measurement step of measuring the hydrogen ion concentration of seawater in advance, a calibration step of calibrating the glass electrode using a predetermined calibration solution, and a first measuring the pH of the measurement solution as a first pH scale using a pair of electrodes Measured in the measurement step, the calculation step for calculating the second pH scale of the measurement solution different from the first pH scale based on the value of the hydrogen ion concentration measured in the absorbance measurement step and a predetermined mathematical formula, and the first measurement step A correction function calculating step for calculating a correction function indicating a relationship between the value of the first pH scale and the value of the second pH scale calculated in the calculating step, and the correction function calculating step. And a scale conversion step of converting a different second 2pH scale the first 1pH scale using the correction functions.

  9th invention is a measuring apparatus which uses seawater as a measurement solution and measures the pH of the measurement solution. The apparatus includes a pair of electrodes (electrode pair) composed of a glass electrode and a reference electrode, a voltmeter for measuring a voltage (potential difference) generated between the pair of electrodes, and a salinity measuring means for measuring the salinity and temperature of the measurement solution. , A carbonic acid measurement means for measuring a carbonic acid measurement item of the measurement solution, a titration measurement means for measuring the carbonic acid measurement item of the measurement solution by an alkalinity titration method, and at least one colorimetric indicator is contained in the measurement solution Selected from the group consisting of absorbance measurement means for dropping acid into the measurement solution, measuring the absorbance of the measurement solution at a predetermined wavelength, and measuring the hydrogen ion concentration of seawater in the measurement solution based on a predetermined mathematical formula Calculating the pH scale of the measurement solution as needed based on at least one of the measurement means to be measured, the voltage measured by the voltmeter and the value measured by the measurement means And a physical means. In addition, the equipotential pH of the electrode pair is in the range of 7.2-8.2.

  According to the present invention, it is possible to provide a measurement method that can easily and accurately calculate the solution of a measurement solution, in particular, the pH of seawater, and a measurement device using the method.

Schematic of a measuring apparatus using the measuring method according to the present invention Battery diagram when measuring pH using the pH glass electrode 2 and the comparative electrode 3 in the apparatus according to the present invention. Diagram when equipotential pH is 7 Diagram when equipotential pH is 8 Diagram when equipotential pH is 4 Flowchart showing the flow of pH measurement by the apparatus shown in FIG. 2 (first embodiment) Shows the f _NBS calculated by f _T and NBS buffer calculated in seawater buffer Figure showing pH (IN _T ) calculated with seawater buffer and pH (IN _NBS ) calculated with NBS buffer Flowchart showing the flow of pH measurement by the apparatus shown in FIG. 2 (second embodiment) The flowchart which showed the procedure of the method which concerns on 3rd Embodiment Diagram showing the relationship between pH _T and pH _NBS

  Before describing the pH measurement method and the measurement apparatus using the method according to the present invention, first, a general definition of pH will be briefly described.

  In the text of this specification, for the sake of convenience, constants, correction terms, and the like may be written in ordinary typefaces instead of the usual italic type.

The following formulas (1) and (2) are battery diagrams when pH is measured using a glass electrode (glass [H ⁺ ] electrode). First, to measure the electromotive force E _x of the battery.

Next, to measure the electromotive force E _S of the battery.

  Now, all the batteries are maintained at the same temperature, and the same reference electrode and salt bridge are used. At this time, the pH of the solution X (referred to as pH (X)) and the pH of the solution S (referred to as pH (S)) are defined by the equation (3).

  In the above formula (3), R is a gas constant, T is a temperature (K), and F is a Faraday constant.

  The above is the explanation about the general definition of pH.

  Next, the pH in the case of seawater will be briefly described below.

Numerous salts are dissolved in seawater. Unlike the general definition of pH described above, total scale pH (sometimes described as pH _T ), SWS scale pH (sometimes described as pHsws), etc. Various scales of pH have been defined.

  In seawater, it can be shown as follows.

pH _F = [H ⁺ ] _F
pH _F : Free scale
[H ⁺ ] _F : Free hydrogen ion concentration
_{^{[H +] T = [H}} +] F (1 + S T / Ks) ≒ [H +] F + [HSO 4 -] ... (4)

pH _T : Total scale
_{^{[H +] sws = [H}} +] F + [HSO 4 -] + [HF]
pH _sws = _-log [H ⁺ ] _sws
pH _sws : SWS scale
^{_{S T = [HSO 4 -]}} + [SO 4 2-]
^{_{K S = [H +] F}} [SO 4 2-] / [HSO 4 -] ... (6)

That is, the total scale pH (pH _T ) is a value defined by the above formulas (4) and (5), and the pH in the case of seawater is different from the general definition of pH described above. It is often indicated by the total scale pH (pH _T ). Specifically, when measuring the total scale pH (pH _T ), the calibration of the pH electrode assumes that seawater is measured, and a buffer solution is dissolved in a solvent close to the composition of seawater to obtain a standard solution. The pH electrode is calibrated using the calibration solution (Tris-HCl buffer, AMP buffer, etc.). In the following description, calibration solutions (Tris-HCl buffer, AMP buffer, etc.) that are supposed to measure seawater may be referred to as seawater buffers.

  The above is description about pH in the case of seawater.

The pH measurement method according to the present invention is based on a conversion method based on the above-described formulas, and a JIS buffer system (a calibration method defined by the Japanese Industrial Standard (JIS) standard) or an NBS buffer system (National Bureau of Standards ( NBS) is a calibration method defined in (NBS), and a pH measurement method that can calculate the total scale pH (pH _T ) with high accuracy even with measurement using a pH electrode calibrated. is there.

  Next, a method for measuring pH according to the present invention (hereinafter sometimes simply referred to as a measuring method) will be described. Note that the measuring 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 includes a voltmeter 1 (sometimes referred to as a potentiometer) connected to a pH glass electrode 2 and a reference electrode 3 (reference electrode). The apparatus shown in FIG. 1 is said to be a so-called glass electrode method. The pH glass electrode 2 and the comparative electrode 3 are immersed in a measurement solution (sample), and the voltage (potential difference) generated between these electrodes is measured. Thus, the processing means described later calculates the pH of the measurement solution. The measurement solution shown in FIG. 1 will be described below assuming that it is seawater as an example unless otherwise specified.

  The pH glass electrode 2 has a thin film of pH sensitive glass 5 (pH sensitive glass) that reacts sensitively to pH at the tip of the support tube 4 and is immersed in the saturated KCl solution 6 as an internal solution in the support tube 4. An Ag / AgCl electrode is provided.

  Further, the reference electrode 3 is formed with a liquid junction (also called a salt bridge, which is made of a minute hole, a porous ceramic, a glass slide, a glass or a material not sensitive to pH) at the tip of the support tube 4. The support tube 4 is provided with an Ag / AgCl electrode immersed in a saturated KCl solution 6 as an internal liquid.

  That is, in the apparatus shown in FIG. 1, the pH glass electrode 2 and the comparison electrode 3 are symmetrical except for the pH sensitive glass 5 and the liquid junction 7.

  The voltmeter 1 is connected to a processing means 8 and measures the voltage (potential difference) generated between the pH glass electrode 2 and the comparison electrode 3 immersed in the measurement solution, thereby adjusting the pH of the measurement solution. calculate. Further, the processing means 8 is provided with a storage means (not shown). As will be apparent from the description below, the storage means stores a conversion formula used when the processing means 8 calculates the pH of the measurement solution in advance, or a calibration result when the pH glass electrode 2 is calibrated. Etc. are memorized.

  Next, each embodiment of the measuring method according to the present invention will be described. The method according to each of the following embodiments uses the apparatus shown in FIG.

(First embodiment)
First, as a first embodiment, the processing means 8 calculates and stores a correction number indicating the characteristics of the pH glass electrode 2 when the pH glass electrode 2 is calibrated with two or more different arbitrary buffer solutions. . The processing means 8 measures the pH of the measurement solution, and converts the pH into a total scale pH (pH _T ) using the correction number.

  Here, FIG. 2 shows a battery diagram when the pH is measured using the pH glass electrode 2 and the comparative electrode 3 in the above apparatus. The Nernst equation is established in the battery diagram shown in FIG. 2, and the potential in the battery diagram can be expressed by the following equation (7) from the above equation (3). In the following formula (7), pH (X) is the pH of the measurement solution (sample), pH (IN) is the pH inside the pH glass electrode 2, R is the gas constant, and T is the temperature ( K) and F are Faraday constants.

From FIG. 2 and the above formula (7), pH (IN) is the pH inside the pH glass electrode 2. For example, not only seawater but also a solution having the same composition and the same pH as the internal liquid is measured. When measured as a solution, a solution having the same composition is measured with the pH sensitive glass 5 as a boundary. Therefore, E _IN = E _{X and no} potential is generated. From the above formula (7), pH (X) = pH (IN), and the pH (IN) of the internal solution is 0 mV of the electrode pair shown in FIG. The equipotential pH shown is obtained. Furthermore, not only the electrode pair shown in FIG. 2, but the electrode pair when measuring pH is generally based on the equipotential pH.

を水素イオンの活量として、以下の式（８）に従うことが知られている。

Is known to follow the following formula (8), where

  That is, in the battery diagram of FIG. 2, by changing the pH of the solution “sat.KCl + pH (IN) buffer” (saturated KCl solution + buffer whose pH is pH (IN)) on the pH glass electrode 2 side, etc. The potential pH can be changed. Here, if there is no difference in potential between the Ag / AgCl electrodes on the comparison electrode 3 side and the glass electrode 2 side and the potential of the liquid junction is small enough to be ignored, the equipotential pH is “sat.KCl + pH (IN) buffer”. ”(Saturated KCl solution + buffer where pH is pH (IN)). Therefore, if the internal solution, that is, “sat.KCl + pH (IN) buffer” (saturated KCl solution + buffer whose pH is pH (IN)) is pH 6.86 or pH 7.00, the equipotential pH is Takes pH 6.86 or pH 7.00.

  Here, assuming that the internal solution, that is, “sat.KCl + pH (IN) buffer” (saturated KCl solution + buffer whose pH is pH (IN)) is a buffer solution that does not change much with temperature, equipotential pH However, FIG. 3 to FIG. 5 show the electrode potentials when the pH electrode at pH 7.0, pH 8.0, and pH 4.0 was measured at various temperatures for solutions near pH 8.

  As described above, the pH glass electrode 2 has a Nernst response based on the equipotential pH. Therefore, as shown in FIGS. 3 to 5, when measuring a measurement solution near pH 8, the equipotential pH is set to pH = If it is set to 8, it can be seen that the electrode pair of the battery diagram shown in FIG.

  As an example, the method according to the present invention and the measurement apparatus using the method are supposed to measure the pH of seawater. The pH of seawater is pH 7.4-8.2. Therefore, in order to accurately measure the pH of seawater, the equipotential pH should be close to pH 8 in the electrode pair of the battery diagram shown in FIG.

  Next, calibration of the pH glass electrode 2 shown in FIG. 1 will be described. The calibration is to determine the relationship between the output from the measuring instrument and the value to be measured. The calibration referred to in this description is the so-called pH electrode calibration in the electrochemical field. Point to.

  Here, when calibrating using two kinds of calibration liquid 1 (X1) and calibration liquid 2 (X2), when the temperature of these two kinds of calibration liquids is constant, the pH glass shown in FIG. 1 and FIG. If the electrode for measuring pH is not limited to the electrode 2 and ideally has a Nernst response, the above equation (8) is followed. However, in reality, there is a case where Nernst response does not occur ideally. Therefore, if the correction term for the potential width is Ks, the following expressions (8) and (9) are established from the above expression (7).

Now, the pH of calibration fluid 1 is pH (X1), the output potential at that time (for example, the value of the voltmeter in the case of the apparatus of FIG. 1) is E _x1 , the pH of calibration fluid 2 is pH (X2), If the output potential at that time (for example, the value of the voltmeter in the case of the apparatus of FIG. 1) is E _x2 and E _IN = 0, the pH (IN) is corrected from the above equations (9) and (10) The term ks can be obtained. Based on the determined pH (IN) and the correction term ks, the correction number indicating the characteristics of the pH glass electrode 2 can be calculated.

  Hereinafter, the measurement procedure of the method according to the first embodiment will be specifically described. Note that the method according to the first embodiment can use, for example, the apparatus shown in FIG. 1, and therefore the case where the apparatus shown in FIG. 1 is used will be described as an example.

FIG. 6 is a flowchart showing a flow of pH measurement by the apparatus shown in FIG. In addition, the measurement solution of FIG. 1 is demonstrated below as seawater. First, in the method according to the first embodiment, it is necessary to obtain the correction number in advance before actually measuring the total scale pH (pH _T ) of the measurement solution (steps 11 to 16 in FIG. 6).

Specifically, in step 11 of FIG. 6, the pH glass electrode 2 is calibrated with a seawater buffer solution (1). Specifically, the seawater buffer is the Tris-HCl buffer, the pH of the Tris-HCl buffer is pH (X _Tris ), and the output potential at that time (for example, the voltmeter in the apparatus of FIG. 1). _Is E _Tris .

Next, in step 12 of FIG. 6, the pH glass electrode 2 is calibrated with a seawater buffer solution (2). Specifically, the seawater buffer is an AMP buffer, the pH of the AMP buffer is pH (X _AMP ), and the output potential at that time (for example, the value of a voltmeter in the case of the apparatus of FIG. 1) E _AMP .

Then, the processing means 8 sets pH (X1) to pH (X _Tris ), pH (X2) to pH (X _AMP ), and E _IN = 0, from the above formula (9) and formula (10), The pH (IN) and the correction term ks can be obtained (step 13 in FIG. 6). Note that the total scale pH (pH _T ) of seawater is usually calibrated for the pH glass electrode 2 using a buffer solution that assumes seawater such as a Tris-HCl buffer solution and an AMP buffer solution. 9) and pH (IN) obtained from equation (10) are set to pH (IN _T ), and the correction term ks is set to ks _T.

Next, in step 14 of FIG. 6, the pH glass electrode 2 is calibrated with a buffer solution (for example, phosphate buffer solution, phthalate buffer solution, etc.) in the NBS buffer system. Specifically, two different buffer solutions in the NBS buffer system are used as a calibration solution (NBS1) and a calibration solution (NBS2), respectively. Then, pH (X _NBSl) the pH of the calibration solution (NBSl) to the output potential of the E _NBSl the output potential when, and pH The pH of the calibration solution (NBS1) (X _NBS2) at that time and E _NBSl.

Thereafter, the processing unit 8 the pH (X1) and pH (X _NBSl), pH and (X2) and pH (X _NBS2), if E _IN = 0, the above equation (9) and (10), The pH (IN) and the correction term ks can be obtained. Note that the pH (IN) obtained by the above equations (9) and (10) is set to pH (IN _NBS ), and the correction term ks is set to ks _NBS (step 15 in FIG. 6).

  In the following description, a buffer solution in the NBS buffer system may be referred to as an NBS buffer solution.

  In step 16 of FIG. 6, the processing means 8 calculates correction numbers α and β, respectively. Α and β are correction numbers for differences in the characteristics of the pH glass electrode 2. In general, the pH electrode is not limited to the pH glass electrode 2 shown in FIGS. 1 and 2, and the pH electrode has characteristics inherent to the pH electrode (for example, due to differences in manufacturer or model number), and α and β are pH values. This is the correction number for correcting the difference in the characteristics of the electrodes.

In addition, since the scale is originally different between NBS and Total on the pH scale, the pH (IN _T ) calculated with Tris-HCl buffer and AMP buffer and the pH (IN _NBS ) calculated with NBS buffer are never coincide, not necessarily coincide with ks _NBS calculated in the ks _T and NBS buffer calculated in seawater buffer. Therefore, when converting to another scale, it is necessary to correct the characteristics by the correction numbers α and β. The correction by α and β can be expressed by the following equations (11) and (12).

ks _T = ks _NBS + α (11)
pH (IN _T ) = pH (IN _NBS ) + β (12)

Here, the results of actually calculating pH (X _T ) and ks _T , and pH (X _NBS ) and ks _NBS are shown in FIGS. 7 and 8, respectively. Moreover, as shown in FIG.7 and FIG.8, the said process 11-13 and the process 14-15 were each performed 5 times. In the flowchart of FIG. 6, steps 14 to 15 may be performed first, and then steps 11 to 13 may be performed.

First, as shown in FIG. 7, since ks _NBS ≈ks _T , α≈0 can be set.

Further, from FIG. 8, since pH (IN _T ) −pH (IN _NBS ) = − 0.102, β = −0.102 is calculated.

  Thus, the processing means 8 calculates α and β. The calculated values of α and β are stored in the storage unit of the processing unit 8. That is, the calculated values of α and β are correction numbers for correcting the difference in the characteristics of the pH glass electrode 2 between the calibration with the seawater buffer and the calibration with the NBS buffer.

The above is the method for obtaining the number of corrections performed before actually measuring the total scale pH (pH _T ) of the measurement solution. From the following steps, the total scale pH (pH _T ) of the measurement solution is actually measured.

Thereafter, in the subsequent step 17, for example, just before actually measuring the total scale pH (pH _T ) of the measurement solution, several calibrations of the pH glass electrode 2 are performed with the NBS buffer system to measure the pH of the measurement solution ( Step 17). In addition, since the value measured at this time was calibrated by the NBS buffer system, it is output from, for example, the processing means 8 as pH _NBS (step 18).

Since the processing means 8 stores the values of the correction numbers α and β in the step 16, the pH _NBS measured in the step 18 is converted into the total scale pH (pH _T ) using the above formula (12). To do.

As described above, according to the measurement method according to the first embodiment, the total scale pH (pH _T ) of the measurement solution can be calculated easily and accurately. That is, the pH in the case of seawater is often indicated by the total scale pH (pH _T ), unlike the pH in the case of a normal solution. The total scale pH is pH _T = -log ([H ⁺ ] + [HSO ₄ ⁻ ]), [H ⁺ ] is the hydrogen ion concentration in the solution, and [HSO ₄ ⁻ ] is the sulfuric acid in the solution. Ion concentration.

In general, when measuring the total scale pH (pH _T ) of seawater using a pH electrode, calibration of the pH electrode is usually performed using a calibration solution for seawater (Tris-HCl buffer, AMP buffer, etc.). However, the seawater calibration solution is very cumbersome to handle. That is, a case is assumed where the pH of seawater is to be measured accurately using a pH electrode. At this time, when calibration of the pH electrode is performed with the seawater buffer solution, it is necessary to make the seawater buffer solution the same as the composition of the seawater to be measured. In addition, the pH of the Tris-HCl buffer varies depending on the temperature.

Therefore, as described above, the characteristics of the pH electrode are investigated with the calibration solution for seawater and the NBS buffer that is relatively easy to handle, and the characteristics are stored, and the NBS that is relatively easy to handle in actual measurement. After calibrating with the buffer solution, the pH of the measurement solution, that is, pH _NBS is measured. Here, since the characteristics of the pH electrode are known in advance, pH _NBS can be easily converted to the total scale pH (pH _T ). That is, when measuring the total scale pH (pH _T ) of a measurement solution using a pH electrode, it is not necessary to calibrate the pH electrode each time with a calibration solution for seawater, which is cumbersome to handle. The total scale pH (pH _T ) can be calculated.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. As a second embodiment, the measuring the pH _NBS measurement solution of Figure 2, based on the salt of the measurement solution measured (or estimated) as a result, a method for converting the pH _NBS to pH _T.

  Hereinafter, the measurement procedure of the method according to the second embodiment will be specifically described. As in the case of the first embodiment described above, the method shown in FIG. 1 can be used in the method according to the second embodiment, for example, so that the apparatus shown in FIG. 1 is used. Will be described as an example.

  FIG. 9 is a flowchart showing a flow of pH measurement by the apparatus shown in FIG. In addition, the measurement solution of FIG. 1 is demonstrated below as seawater.

In step 21 of FIG. 9, the pH glass electrode 2 is calibrated with a buffer solution (for example, a phosphate buffer solution, a phthalate buffer solution, etc.) in an NBS buffer system, for example, immediately before the measurement solution is measured. Then, the pH of the measurement solution, that is, pH _NBS is measured, and the processing unit 8 stores the result in the storage unit (step 22 in FIG. 9).

  In step 23 of FIG. 9, the processing means 8 reads the salinity and temperature of the measurement solution measured in advance with, for example, a salinity meter.

Here, in the above formula (4), S _T is the concentration of sulfuric acid seawater, since it is not the composition would normally seawater varies greatly as a function of salinity, can be shown by the following equation (13).

S _T = (0.14 / 96.062) * (Salinity / 1.80665) (13)

Also,
Z = [1+ (0.14 / 96.062) * (Salinity / 1.80665)] / K _s (14)
In other words, from the above equation (14), the above equation (4) can be arranged as the following equation (15).

[H ⁺ ] _T = [H ⁺ ] _F / Z (15)

  Here, for example, assuming that the salinity (S) and temperature T (K) of the measurement solution measured in advance with a salinometer or the like are S (Salinity) = 35 and T (K) = 20, Z is 1.29. Calculated.

  In addition, since the value of S does not fluctuate greatly if it is an open-sea water, it can also be estimated.

In step 24 of FIG. 9, the processing means 8 calculates the total scale pH (pH _T ) based on the values measured and calculated in the previous steps.

  Specifically, in the step 24, the following equation (16) is used.

Note that a _{[H +]} is the hydrogen ion activity (the above formula (8)), f _free is an activity coefficient for free hydrogen ions, f _free = 0.9 to 1.0, and there is a method of estimating from salt content.

The value of S as described above is sought, can be obtained the value of S _T from the above equation (13). Similarly, the value of Z is obtained as described above, and the value of K _s can be obtained from the above equation (14).

Therefore, by substituting each value into the above equation (4), [H ⁺ ] _T can be obtained, and as a result, the total scale pH (pH _T ) can be calculated.

Thus, if the salinity and temperature of the measurement solution are measured and estimated in advance, the measurement solution is calibrated with the NBS buffer solution, which is relatively easy to handle, and then the pH of the measurement solution, that is, the pH _NBS is measured. The total scale pH (pH _T ) can be measured. That is, it is not necessary to calibrate the pH electrode each time with a calibration solution for seawater that is complicated to handle, and the total scale pH (pH _T ) of the measurement solution can be calculated easily and accurately.

  In the second embodiment, the processing means 8 may calculate the correction numbers α and β for the pH glass electrode 2 in advance, as in the first embodiment.

(Third embodiment)
Next, a third embodiment of the present invention will be described. As a third embodiment, the seawater is imitated with a buffer solution having a known pH _T and containing ions mimicking seawater (for example, the above-mentioned buffer solution for seawater such as Tris-HCl buffer solution and AMP buffer solution may be used). Determine the pH _T of the buffer containing ions. And the buffer solution containing the ion which imitated the said seawater is measured with the pH electrode calibrated by the NBS buffer system, and pH, ie, pH _NBS , is calculated _| required. Thereafter, by examining the relationship between pH _T and pH _NBS , a conversion formula for converting the pH _NBS obtained by actually measuring the measurement solution into pH _T is obtained.

Moreover, pH _T is calculated _| required by arbitrary methods (for example, the method which concerns on 1st or 2nd embodiment) from actual seawater. And the said seawater is measured with the pH electrode calibrated by the NBS buffer system, and pH, ie, pH _NBS , is calculated _| required. Thereafter, by examining the relationship between pH _T and pH _NBS , a conversion formula for converting the pH _NBS obtained by actually measuring the measurement solution into pH _T is obtained.

  Hereinafter, the measurement procedure of the method according to the third embodiment will be specifically described with reference to FIG. Note that the method according to the third embodiment can use the apparatus shown in FIG. 1, for example, and therefore, the case where the apparatus shown in FIG. 1 is used will be described as an example. FIG. 10 is a flowchart showing the procedure of the method according to the third embodiment.

  First, in step 31 of FIG. 10, for example, the pH glass electrode 2 is calibrated with an NBS buffer system immediately before starting the measurement.

Next, in step 32 of FIG. 10, first, a buffer solution containing ions simulating seawater having a known pH _T using the pH glass electrode 2 (for example, the above-described Tris-HCl buffer solution, AMP buffer solution, etc. for seawater). PH _NBS of a solution obtained by determining pH _T by using the method according to the first or second embodiment, for example, from actual sea water may be measured. For example, the pH _NBS is stored in the storage unit of the processing unit 8.

In step 33, pH _T is measured or calculated. As described above, the pH _T is known using the pH glass electrode 2, and the seawater standard pH buffer solution containing ions imitating seawater or the pH _{T of} actual seawater is obtained and the pH _T is known. Measure the pH _NBS . It especially when obtaining the pH _T actual seawater, for example, a method according to the first or second embodiment, by the following method (1) to (5), also to determine the pH _T actual seawater .

The method (1): total alkalinity A _T and total alkalinity A _T method seawater seeking pH _T from the total carbonate concentration C _T of seawater, the total carbonate concentration C _T, and the equilibrium carbon dioxide system, DOE (1994) Handbook of methods for the analysis of the various parameters of the carbon dioxide system in sea water. Detailed in Version 2, 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 (20) to (23) the equilibrium reaction as shown in the establishment To do.

The above formula (17) to (20), 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 (21) to (22) are obtained.

  The balance of the above formulas (21) and (22) can be expressed by the following formulas (23) to (25) by using the equilibrium constant.

K ₁ = [H ⁺ ] [HCO ⁻ ] / [CO ₂ ^* ] (24)
K ₂ = [H ⁺ ] [CO ₂ ⁻ ] / [HCO ⁻ ] (25)

    here,

  Is the fugacity of carbon dioxide, and the relationship with the partial pressure of carbon dioxide can be expressed by the following equation (26).

As shown in the above equation (26), by measuring the carbon dioxide partial pressure (x (CO ₂ ) · p), the fugacity of carbon dioxide can be calculated from the total pressure of gas and the salinity of seawater.

The total carbonate concentration C _T of seawater is defined by the following equation (27).

C _T = [CO ₂ ^* ] + [HCO ₃ ⁻ ] + [CO ₃ ²⁻ ] (27)

Furthermore, 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 (28). In addition, what is omitted in the following formula (28) 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] - ... (28)

Also, carbonate alkalinity A _C can be represented by the following equation (29).

A _C = [HCO ₃ ⁻ ] +2 [CO ₃ ²⁻ ] (29)

Here, the relationship between the total alkalinity A _T and the carbonate alkalinity A _C can be expressed by the following equation (30). In addition, what is omitted in the following formula (30) 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] -) ... (30)

Note that the total alkalinity _AT shown in the above formula (28) is developed into the following formula (31) in order to define a proton state corresponding to the equivalence point. Note that, in the following formula (31), those omitted in the above formula (28) 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} -] ... (31)

Here, in seawater, items that can be measured with carbon dioxide-related substances are pH, carbon dioxide partial pressure (x (CO ₂ ) · p), total carbonic acid concentration (C _T ), and total alkalinity (A _T ). . Among these, if two or more items are measured, all items can be calculated from the equations (23), (24), and (25) of the equilibrium formula.

That, pH from total alkalinity A _T and the total carbonate concentration C _T of seawater, that is, it is possible to determine the total scale pH (pH _T).

In addition, the solution whose pH _T is known includes, for example, CRM (Certified Reference Material) available from the University of California, Scripps Marine Research Institute, and RM (Reference Material) available from Environmental Technology Co., Ltd. In these, CT and AT are measured, and pH _T can be calculated.

Method (2): Method for obtaining pH _T from total alkalinity _{AT of} seawater and partial pressure of carbon dioxide As described above, in seawater, items that can be measured with carbon dioxide-related substances are pH, partial pressure of carbon dioxide (x (CO ₂ ) · p), total carbonic acid concentration (C _T ), and total alkalinity (A _T ). Of these, if two or more items are measured, all items can be calculated from the equations (23), (24), and (25) of the equilibrium formula, so the same idea as the above method (1). The total scale pH (pH _T ) can be determined from the total alkalinity _{AT of} seawater and the partial pressure of carbon dioxide.

Method (3): Method for obtaining pH _T from total carbonic acid concentration C _T and carbon dioxide partial pressure in seawater As described above, in seawater, items that can be measured with carbon dioxide-related substances are pH, carbon dioxide partial pressure (x (CO ₂ ) · p), total carbonic acid concentration (C _T ), and total alkalinity (A _T ). Of these, if two or more items are measured, all items can be calculated from the equations (23), (24), and (25) of the equilibrium formula, so the same idea as the above method (1). The total scale pH (pH _T ) can be determined from the total carbonic acid concentration C _{T of} seawater and the partial pressure of carbon dioxide.

Method (4): Method for determining pH _T from electrode E ₀ and seawater measured potential during alkalinity titration in closed cell method (closed titration)

  First, the alkalinity titration in the closed cell method (sealed titration) will be briefly described.

Seawater generally has a pH of around 8, and carbon dioxide (CO ₂ ) in seawater exists as carbonate ions [CO ₃ ²⁻ ] and bicarbonate ions [HCO ₃ ⁻ ]. When acid is dropped into the seawater, carbonates (herein, carbonate ions and bicarbonate ions) are degassed as carbon dioxide (CO ₂ ). The alkalinity titration of closed cell type (closed type titration), was added dropwise an acid to seawater, by monitoring the degassing of the carbonate, and requests and total alkalinity A _T and the total carbonate concentration C _T .

Specifically, when performing alkalinity titration using actual seawater, the acidity C _H of the seawater at each titration point can be expressed by the following equation (32).

^{_{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 -}} ] ... (32)
At the equivalent point of total alkalinity _AT , acidity C _H = 0 during titration, and C _H = −A _T at the start of titration.

The acidity C _H during titration can be expressed by the following equation (33) from the total amount m of acid having a concentration of seawater weight (m ₀ ) C used for alkalinity titration.

C _H = (mC−m ₀ A _T ) / (m ₀ + m) (33)

  Therefore, the following formula (34) can be derived from the above formula (31) and formula (33).

_{(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 -] ... (34)

Each parameter is 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, the hydrogen ion concentration [H ⁺ ] is expressed by the following equation (35) according to the Nernst equation.
E = E ^0- (RT / F) ln [H ⁺ ] (35)

[H ⁺ ] is obtained from the E ⁰ of the electrode during the alkali titration and the measured potential of the seawater.

The terms of K ₁ , K ₂ , K _B , K _Si , K _NH3 , K _H2S , K _S , K _F , K _1P , K _2P , K _3P are obtained from the salinity S and liquid temperature T of the seawater. is, 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 total scale pH (pH _T ) of seawater can be obtained from the above equation (8).

In addition, although the method (4) described above has described the method for obtaining pH _T from the E ₀ of the electrode and the measured potential of seawater during alkalinity titration in the closed cell method (sealed titration), the semi-closed cell method, In a state close to sealing, pH _T may be obtained from the E ₀ of the electrode at the time of alkalinity titration and the measured potential of seawater.

Method (5): In Method method described above obtains the relative pH _T with alkalinity titration by color process (4), there a way to determine the pH _T from the measured potential of E ₀ and seawater alkalinity titration of electrodes However, the method (5) described below is a method for determining pH _T using alkalinity titration by a colorimetric method.

  First, the alkalinity titration by the colorimetric method will be briefly described here.

  When one kind of acid-base indicator (referred to as indicator A) is contained in seawater, the acid-base indicator A has a dissociation equilibrium represented by the following formula (36) in seawater.

  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 indicator A at this time is K _(A) , the K _(A) can be expressed by the following equation (37). From the following equation (37), the pH (hydrogen ion concentration index) of seawater can be expressed by the following equation (38). [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] ... (37)
_{pH = pK (A) + log} ([A -] / [HA]) ... (38)

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 seawater) is L, the absorbances Abs ₁ and Abs ₂ of the measurement solution 11 at a certain wavelength λ ₁ and wavelength λ ₂ are expressed by the following formulas ( 39) and formula (40).

_{Abs 1 = 1 ε A- · L} · [A -] + 1 ε HA · L · [HA] ... (39)
_{Abs 2 = 2 ε A- · L} · [A -] + · 2 ε HA · L · [HA] ... (40)

Here, in the above formula (39) and the above formula (40), 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 respectively , 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 39) and equation (40) can be represented by the following equation (41). 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)) ... (41)

  Therefore, the following formula (42) can be derived from the above formula (38) and the above formula (41).

pH = pK _(A) + log [(Re _{1 (A)} ) / (e _{2 (A)} -R · e _{3 (A)} )] (42)

The value of R may be obtained by, for example, irradiating seawater with a known absorbance measuring means and measuring the intensity of light absorption in the seawater. In other words, [H ⁺ ] can be expressed by the following formula (43) using e _{1 (A)} , e _{2 (A)} , e _{3 (A)} , and K _(A) as parameters.

[H ⁺ ] = F [R, K _(A) , e1 _(A) , e2 _(A) , e3 _(A) ] (43)

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) (44)
λε _HA = λAbs ₁ (HA) / ([HA] · L) (45)

If e _{1 (A)} , e _{2 (A)} , e _{3 (A)} , and K _(A) are obtained in advance, the hydrogen ion concentration [H ⁺ ] of seawater can be obtained. If pK _(A) is obtained from the total scale pH (pH _T ) of seawater, it can be calculated as described above. In fact, there are literature values for metacresol purple, phenol red, and thymol blue.

Thus, for example, the pH _{T of} actual seawater is obtained by the methods (1) to (5) above, and the pH _{NBS of} actual seawater from which the pH _T is obtained is calibrated with an NBS buffer system. Measurement is performed using the glass electrode 2.

  The above is description of the process 33 of FIG.

Here, the pH _T obtained in the above step 33 (especially above (4)), the solution used in the step 33 is measured (i.e. step 31-32), asked to pH _NBS, and the pH _T and pH _NBS The relationship is shown.

FIG. 11 is a diagram showing the relationship between the pH _T and the pH _NBS . In FIG. 11, the vertical axis represents the pH _NBS value when the solution used in step 33 was measured (that is, steps 31 to 32), and the horizontal axis was obtained in step 33 (particularly (4) above). Indicates the value of pH _T. And it plotted 4 points | pieces.

The regression line in FIG. 11 was y = 1.0055x + 0.0394, and the correlation coefficient was r ² = 0.9999. Note that x = pH _T and y = pH _NBS . Note that this regression line is considered to be a relational expression specific to the electrode, and is considered to vary depending on the manufacturer and model number of the pH electrode.

That is, if a relational expression peculiar to the electrode is calculated in step 34 in FIG. 10, the pH of the measurement solution, that is, pH _NBS is measured after calibrating with a relatively easy NBS buffer, and the relational expression is calculated. It can be used to measure the total scale pH (pH _T ) of the measurement solution.

  In addition, by using the method according to the third embodiment described above and the method according to the second embodiment described above, a relational expression different from the relational expression calculated in the step 34 can be derived. .

[H ⁺ ] _T = [H ⁺ ] _NBS * (1 + S _T / K _S + f ₁ (Salinity, T)) (46)
[H ⁺ ] _T = [H ⁺ ] _NBS * (1 + S _T / K _S * f ₂ (Salinity, T)) (47)

In the above formulas (46) and (47), f ₁ and f ₂ are functions of salinity (S) and temperature (T).

In the above equations (46) and (47), the value of [H ⁺ ] _T and [H ⁺ ] _NBS are obtained by the method according to the third embodiment described above, and S _T and K _S are calculated according to the second method described above. If the method according to the embodiment is used, the functions f ₁ and f ₂ can be obtained.

  Further, if the potential interferes with salinity, the following formula (48) can be expressed.

In the above formula (48), E ^# is a function of salinity (S) and temperature (T) as shown in the following formula (49), and can be expressed by the following formula (50).

E ^# = f ₃ (Salinity, T)… (49)

E ^# = f ₃ (Salinity, T) = a (f3) * [log (Salinity / 35) -log (1/10)] * (RTln10 / F)… (50)

  Note that a (f3) is considered to be a constant that varies depending on the electrode.

Then, a [H ^+] _F, then, obtains the [H ^+] _T by _{^{[H +] T = [H}} +] F (1 + S T / K S).

Specifically, the pH, that is, pH _NBS, is measured with a CRM (Certified Reference Material) available from the University of California, Scripps Marine Research Institute, using an electrode that has been calibrated for pH glass electrode 2 using an NBS buffer system. Using the above equations (4), (48), and (50), a (f3) in the equation (50) was obtained, and a (f3) = − 0.005 was actually calculated.

If a (f3) is a (f3) = − 0.005, there is not much difference from the method according to the second embodiment described above. However, depending on the pH glass electrode 2 to be used (electrode characteristics, that is, manufacturing) Some values were calculated such as (manufacturer and model number), a (f3) = 0.110, and a (f3) = 0.131. If a (f3) <0.01, then pH _NBS ≒ [H ⁺ ] _F holds, but for example, if a (f3) = 0.1, considering pH _NBS ≒ [H ⁺ ] _F , the pH is about 0.1. An error occurs.

Table 1 shows an example of the results measured by the methods according to the first to third embodiments described above.

The Table 1, embodiments of the pH _T and first obtained by calibration with seawater buffer, the method according to the second embodiment is in very good agreement was found that these methods are appropriate.

  The pH measurement method and the measurement apparatus using the same according to the present invention are useful for a method that can easily and accurately measure the pH of seawater, and the device according to the present invention is simple and accurate. It can be used as a pH measuring device or the like that can measure.

DESCRIPTION OF SYMBOLS 1 ... Voltmeter 2 ... pH glass electrode 3 ... Comparative electrode 4 ... Support tube 5 ... pH reaction glass 6 ... Saturated KCl solution 7 ... Liquid junction 8 ... Processing means

Claims (9)

  An electrode in which the potential difference between a pair of electrodes consisting of a glass electrode and a reference electrode was set to 0 mV in a solution having a pH in the range of 7.2 to 8.2 was generated between the electrodes using seawater as a measurement solution. A measurement method for measuring the pH of the measurement solution based on voltage (potential difference). The measurement method according to claim 1,
The difference between the glass electrode and the comparison electrode is a glass sensitive film and an electrode pair that is a liquid junction of the comparison electrode. A measurement method for measuring the pH of the measurement solution using seawater as a measurement solution based on a voltage (potential difference) generated between the electrodes using a pair of electrodes consisting of a glass electrode and a reference electrode,
A calibration step of performing calibration of the glass electrode at least twice with different calibration solutions using a plurality of predetermined calibration solutions;
A correction number calculating step of calculating a correction number indicating the characteristics of the glass electrode by substituting the value of the voltage output in the calibration step into a predetermined mathematical formula;
A first measurement step of measuring the pH of the measurement solution as a first pH scale using the pair of electrodes;
A scale conversion step of converting to a second pH scale different from the first pH scale measured in the first measurement step using the correction number calculated in the correction number calculation step and a predetermined mathematical formula; Measuring method. A measurement method for measuring the pH of the measurement solution using seawater as a measurement solution based on a voltage (potential difference) generated between the electrodes using a pair of electrodes consisting of a glass electrode and a reference electrode,
A calibration step of calibrating the glass electrode using a predetermined calibration solution;
A salinity measurement step of measuring the salinity and temperature of the measurement solution;
A first measurement step of measuring the pH of the measurement solution as a first pH scale using the pair of electrodes;
A scale conversion step of converting to a second pH scale different from the first pH scale measured in the first measurement step based on a predetermined mathematical formula using the salinity measured in the salinity measurement step and the temperature; Method for measuring pH. A measurement method for measuring the pH of the measurement solution using seawater as a measurement solution based on a voltage (potential difference) generated between the electrodes using a pair of electrodes consisting of a glass electrode and a reference electrode,
A calibration step of calibrating the glass electrode using a predetermined calibration solution;
A first measurement step of measuring the pH of the measurement solution as a first pH scale using the pair of electrodes;
A carbonic acid measurement step for measuring at least two carbonic acid measurement items of seawater in the measurement solution using a predetermined mathematical formula;
A calculation step of calculating a second pH scale of the measurement solution different from the first pH scale based on a value of the measurement item measured in the carbonic acid measurement step and a predetermined mathematical formula;
A correction function calculating step for calculating a correction function indicating a relationship between the value of the first pH scale measured in the first measuring step and the value of the second pH scale calculated in the calculating step;
A pH measurement method comprising: a scale conversion step of converting to a second pH scale different from the first pH scale using the correction function calculated in the correction function calculation step. A measurement method for measuring the pH of the measurement solution using seawater as a measurement solution based on a voltage (potential difference) generated between the electrodes using a pair of electrodes consisting of a glass electrode and a reference electrode,
Carbonation of seawater in the measurement solution by at least one of alkalinity titration in the closed cell method (sealed alkalinity titration) and alkalinity titration in the semi-closed method (alkalinity titration in a state close to sealing) A titration step of measuring at least two or more measurement items of the system in advance;
A calibration step of calibrating the glass electrode using a predetermined calibration solution;
A first measurement step of measuring the pH of the measurement solution as a first pH scale using the pair of electrodes;
A calculation step of calculating a second pH scale of the measurement solution different from the first pH scale based on a value of the measurement item measured in the titration step and a predetermined mathematical formula;
A correction function calculating step of calculating a correction function indicating a relationship between the value of the first pH scale measured in the first measuring step and the value of the second pH scale calculated in the calculating step;
A pH measurement method comprising: a scale conversion step of converting to a second pH scale different from the first pH scale using the correction function calculated in the correction function calculation step.   The seawater carbonic acid measurement item of the measurement solution measured by the titration step is at least two or more selected from the group consisting of total carbonic acid concentration, total alkalinity, hydrogen ion concentration index, and carbon dioxide partial pressure. The measurement method according to claim 6, wherein: A measurement method for measuring the pH of the measurement solution using seawater as a measurement solution based on a voltage (potential difference) generated between the electrodes using a pair of electrodes consisting of a glass electrode and a reference electrode,
An acid is dropped into the measurement solution containing at least one colorimetric indicator in the measurement solution, the absorbance of the measurement solution at a predetermined wavelength is measured, and the seawater of the measurement solution is based on a predetermined mathematical formula. An absorbance measurement step for measuring the hydrogen ion concentration in advance;
A calibration step of calibrating the glass electrode using a predetermined calibration solution;
A first measurement step of measuring the pH of the measurement solution as a first pH scale using the pair of electrodes;
A calculation step of calculating a second pH scale of the measurement solution different from the first pH scale based on a value of the hydrogen ion concentration measured in the absorbance measurement step and a predetermined mathematical formula;
A correction function calculating step for calculating a correction function indicating a relationship between the value of the first pH scale measured in the first measuring step and the value of the second pH scale calculated in the calculating step;
A pH measurement method comprising: a scale conversion step of converting to a second pH scale different from the first pH scale using the correction function calculated in the correction function calculation step. A measurement device for measuring the pH of the measurement solution using seawater as the measurement solution,
A pair of electrodes consisting of a glass electrode and a reference electrode (electrode pair);
A voltmeter for measuring a voltage (potential difference) generated between the pair of electrodes;
Salinity measurement means for measuring the salinity and temperature of the measurement solution, carbonic acid measurement means for measuring the carbonic acid measurement item of the measurement solution, titration measurement for measuring the carbonic acid measurement item of the measurement solution by the alkalinity titration method Means, an acid is dropped into the measurement solution containing at least one colorimetric indicator in the measurement solution, the absorbance of the measurement solution at a predetermined wavelength is measured, and the measurement solution is based on a predetermined mathematical formula At least one means selected from the group consisting of absorbance measuring means for measuring the hydrogen ion concentration of seawater
Processing means for calculating the pH scale of the measurement solution as needed based on the voltage measured by the voltmeter and the value measured by the measurement means;
The measuring apparatus characterized in that the equipotential pH of the electrode pair is in the range of 7.2-8.2.

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