JP3442458B2 - Selection coefficient measurement method and ion concentration measurement device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention simplifies the selection coefficient for an interfering ion when the ion-selective electrode used for measuring the ion concentration in a solution is disturbed by an ion other than the ion to be measured. The present invention also relates to a selection coefficient measuring method for accurately obtaining the same and an ion concentration measuring apparatus using the method.

[0002]

2. Description of the Related Art Conventionally, it has been known that an ion selective electrode used in an ion concentration measuring device or the like is interfered with by ions other than the measurement target ion (hereinafter, simply referred to as interfering ion). The output potential of the ion-selective electrode when receiving this interference is generally expressed by the following Nicholski-Eisenman equation.

[0003]

[Equation 1] E = E ⁰ + αlog [a _M + ΣK _MN (a _N ) ^{m / n} ] (1) where E ⁰ is a reference potential, α is a potential gradient (sensitivity), and a _M
Is the activity (concentration) of the target ion M ^{m +} , K _MN is the selectivity coefficient for the interfering ion N ^{n +} , a _N is the activity (concentration) of the interfering ion N ^{n +} , and m and n are the target ion and the interfering ion, respectively. It is a valence, and Σ means the sum total of ions that interfere with the measurement target ion M ^{m +} . The Nikorski-Eisenman formula is basically valid for the activity of ions, but even if it is replaced by the concentration of ions, it is not a big problem in many cases.

As a method for experimentally obtaining the selection coefficient K _MN defined by the Nikorski-Eisenman equation, the conventional method is the mixed solution method as defined in Japanese Industrial Standards (JIS K 0122). Two major methods, the single solution method, were common.

The mixed solution method is a solution in which interfering ions coexist at a constant concentration, and the concentration of the ions to be measured is changed. At that time, the output potential of the ion-selective electrode is not affected by the interfering ions. Obtain the concentration of the ion to be measured that corresponds to the intersection of the tangent to the region that changes in proportion to the concentration and the region where the output does not change due to the influence of interfering ions, and calculate the selection coefficient from the relationship with the coexisting concentration of interfering ions. Is the way to do it. On the contrary, there is also a method of changing the interfering ion concentration with a solution in which the ions to be measured coexist at a constant concentration.

On the other hand, in the single solution method, the response characteristic of the output potential is separately obtained for the solution of the ion to be measured and the solution of the interfering ion, and the ion concentration at the same output potential is obtained or at the same concentration. This is a method of calculating the selection coefficient from the output potential of.

In these methods, the selection coefficient is theoretically obtained from three output potentials. However, whether or not these three output potentials are potentials at appropriate positions in the entire potential response curve must be judged from output potentials other than these. Therefore, in the actual selection coefficient measurement experiment, at least 5, 6 or more kinds of standard solutions were required.

For example, in the case of the mixed solution method, two measured potentials (G, I) are used in order to obtain the potential response line proportional to the concentration of the ion to be measured on the high concentration side as shown in FIG. It is necessary, and it is necessary to judge from these other measured potentials (H) that these two points are not affected by interfering ions.

On the other hand, in order to obtain a potential that has become constant due to the influence of interfering ions on the low concentration side, at least two output potentials (A, B) are necessary to determine whether the potential has saturated. That is, in order to accurately measure the selectivity by the mixed solution method, at least five kinds of liquids having different concentrations were required.

Further, when the selection coefficient cannot be predicted, it cannot be predicted in which density range each area appears. Therefore, it is necessary to set measurement points finely in a wide density range, and in reality, different density Solution was required for more than 5 of the above.

On the other hand, in the case of the single solution method, as shown in FIG. 8, in order to obtain the potential response curve in the solution of each ion, at least two kinds of solutions, that is, a total of four kinds of solutions are required. However, there is a problem that the response curve of the interfering ion in the solution does not show the same potential gradient as the response curve of the measured ion in the solution, or the proportional relationship with the ion concentration is lost on the low concentration side. There was a possibility that the selection coefficient could not be obtained.

Therefore, in order to carry out an accurate measurement, it is necessary to prepare at least three kinds of solutions of each ion, that is, six kinds of solutions in total, and in each linear region of the obtained potential response curve. , Potential comparison at the same concentration,
Alternatively, it was necessary to compare the concentrations at the same potential.

[0013]

As described above, in order to obtain the selectivity coefficient for the interfering ions of the ion selective electrode by the conventional mixed solution method or single solution method, at least five kinds of solutions are required. Further, when the selectivity coefficient cannot be predicted, more solution is required, so that the measurement operation becomes complicated and the calculation method is also complicated.

The present invention has been made in view of the above problems, and an object thereof is to provide a simple and accurate selection coefficient measuring method and an ion concentration measuring apparatus using the method.

[0015]

In order to achieve the above object, the present invention provides an ion selective electrode using a first standard solution, a second standard solution and a third standard solution having known concentrations. When measuring the selection coefficient from the output potential, the ratio of the concentration of the measurement target ion of the ion selective electrode to the concentration of the interfering ion having the same ion valence as the measurement target ion in the first standard solution; In the standard solution of No. 2, the ratio of the concentration of the ion to be measured of the ion selective electrode to the concentration of the interfering ion having the same ion valence as the ion to be measured is equalized, and The gist is that the ratio of the concentration of the measurement target ion of the ion selective electrode to the concentration of the interfering ion having the same ion valence as the measurement target ion is made different.

Specifically, referring to FIG. 1, M ^z (z is an ionic valence) which is an ion to be measured by the ion selective electrode.
And three interfering ions having the same ionic valence of known N ^z are prepared, and the respective concentrations of M ^z ion and N ^z ion are CM ₍₁₎ in the first standard solution. , C _{N (1)} ,
When C _{M (2)} and C _{N (2) are used} in the _second standard solution and C _{M ( 3)} and C _{N (3)} are used in the third standard solution, C _{M (1)} / C _{N (1)} = C _{M (2)} /
It is characterized in that the relationship of C _{N (2)} ≠ C _{M (3)} / C _{N (3)} holds, and the selectivity coefficient is measured from the output potential of the ion selective electrode in these three kinds of standard solutions. is there.

In other words, from the output potentials of the ion-selective electrodes in the above-mentioned three kinds of the first, second and third standard solutions, three constants of the Nicholski-Eisenman equation, a selection coefficient,
The potential gradient (sensitivity) and the reference potential are obtained, and M is calculated from the output potential in the sample liquid of which the concentration is unknown and the N ^z ion concentration measurement value of another ion-selective electrode in which the interfering ion N ^z is the measurement target ion. ^This is a method of obtaining the ^z ion concentration.

Preferably, the electrode potential formula (calibration curve) including the selection coefficient determined by the selection coefficient measuring method according to claim 1, the output potential in the sample solution of unknown concentration, and the interfering ion N ^z It is preferable to configure the ion concentration measuring device by including a means for obtaining the M ^z ion concentration from the measured value of the N ^z ion concentration of another ion selective electrode whose measurement target ion is.

In order to obtain a more accurate selection coefficient measurement,
It is preferable that the M ^z ion concentration C _{M (3)} and the N ^z ion concentration C _{N (3)} in the third standard solution have a relationship of C _{M (3)} <C _{N (3)} .

More preferably, using only the three types of standard solutions for measuring the selection coefficient according to claim 1, an ion-selective electrode having M ^z ions as measurement target ions and N ^z ions as interfering ions thereof are used. A method of simultaneously calibrating the ion-selective electrode as the measurement target ion may be used.

[0021]

The selection coefficient measuring method of the present invention comprises: a ratio of the concentration of the ion to be measured of the ion selective electrode in the first standard solution to the concentration of interfering ions having the same ion valence as the ion to be measured; The concentration of the ion to be measured of the ion selective electrode in the second standard solution and the concentration of the interfering ion having the same ion valence as the ion to be measured are made equal, and the ion selective electrode of the third standard solution The selection coefficient is measured from the output potential of the ion-selective electrode using these three types of standard solutions by making the ratio of the concentration of the measurement target ion and the concentration of the interfering ion having the same ion valence as the measurement target ion different. can do.

That is, according to the present invention, it is possible to simply and accurately measure the selectivity coefficient for interfering ions having the same ion valence with only three kinds of standard solutions. Further, even when the selection coefficient cannot be predicted, it is possible to accurately measure the selection coefficient with only one measurement operation. further,
It is very easy to automate because the selection coefficient can be obtained only by a simple calculation without requiring the graphical processing of the output characteristic graph as in the conventional mixed solution method.

Further, using the standard solution for measuring the selection coefficient according to claim 1, an ion-selective electrode having M ^z ion as an ion to be measured and another ion having an interfering ion, N ^z ion as an ion to be measured. It is possible to simultaneously calibrate the selective electrode with only three types of standard solutions.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment to which the present invention is applied will be described below with reference to the drawings. FIG. 2 is a block diagram showing the configuration of an ion concentration measuring apparatus to which the selection coefficient measuring method according to the present invention is applied.

Referring to FIG. 2, the ion concentration measuring apparatus according to the present embodiment has three types of standard solutions, that is, the first standard solution 1
A, the second standard solution 1B, the third standard solution 1C and the sample solution S, and three kinds of electrodes, that is, the M ^z ion selective electrode 3A, the N ^z ion selective electrode 3B, the reference electrode 5, and M ^z. A first potential difference measuring circuit 7A which is connected to the ion selective electrode 3A and the reference electrode 5 and measures the potential difference between them.
A second potential difference measuring circuit 7B connected to the N ^z ion selective electrode 3B and the reference electrode 5 and measuring the potential difference between them, and the first potential difference measuring circuit 7A and the second potential difference measuring circuit 7B. The calculation storage unit 9 is connected to the calculation storage unit 9 to which the potential difference measured by each of them is input, and the input unit 11 and the output unit 13 connected to the calculation storage unit 9.

Next, the operation of this embodiment will be described. First, the M ^z ion-selective electrode 3A and the N ^z ion-selective electrode 3B, which are disturbed by N ^z ions having the same valence, are immersed in each standard solution together with the reference electrode 5, and each reference electrode 5
The potential difference (output potential) from the first potential difference measuring circuit 7A,
The measurement is performed by the second potential difference measuring circuit 7B.

Then, the coefficient (constant) of the calibration curve of each ion-selective electrode 3 is calculated in the arithmetic storage unit 9 based on the known concentration of each standard solution input from the input unit 11. Next, the three electrodes are immersed in the sample solution S of unknown concentration, the potential difference is measured in the same manner, and each ion concentration is determined using the previously obtained calibration curve.

At this time, the M ^z ion concentration and the N ^z ion concentration in the three kinds of standard solutions are respectively C _{M (1)} , C _{M (2)} , C
_{If M (3)} , C _{N (1)} , C _{N (2)} , and C _{N (3)} , then C _{M (1)} / C
The relationship of _{N (1)} = _{CM (2)} / _{CN (2)} ≠ CM ₍₃₎ / _{CN (3)} is established (see FIG. 1).

When only the selection coefficient of the M ^z ion-selective electrode 3A which is disturbed by N ^z ions is measured,
When the interfering ions N ^z in the sample solution S have a negligibly low concentration, the N ^z ion-selective electrode 3B and its measuring circuit 7B can be omitted.

Next, the operation of this embodiment will be described with reference to FIGS. Among them, the flowchart shown in FIG. 3 is the calibration operation for obtaining the coefficient of the calibration curve of each ion-selective electrode, and the flowchart shown in FIG. 4 is the operation for measuring the ion concentration of the sample liquid.

First, the calibration operation will be described with reference to FIG. In step S1, the M ^z ion concentration and N ^z of each of the first standard solution 1A, the second standard solution 1B, and the third standard solution 1C.
The ion concentration is input from the input unit 11 and stored in the calculation storage unit 9. Next, in step S3, the M ^z ion selective electrode 3A, the N ^z ion selective electrode 3B and the reference electrode 5 are washed. Further, in step S5, the first standard solution 1
A, M ^z ion-selective electrode 3 washed in step S3
The A and N ^z ion-selective electrode 3B and the reference electrode 5 are immersed. In step S7, the potential difference between each of the ion selective electrodes 3A and 3B and the reference electrode 5 is measured, and the result is stored in the calculation storage unit 9.

Next, in step S9, the above step S
3 to M ^z ion selective electrode 3 used in step S7
The A and N ^z ion selective electrodes 3B and the reference electrode 5 are cleaned. In step S11, the M ^z ion-selective electrode 3A, the N ^z ion-selective electrode 3B, and the reference electrode 5 washed in step S9 are immersed in the second standard solution 1B. In step S13, the ion-selective electrodes 3A and 3B and the reference electrode 5 are
The potential difference between and is measured, and the result is stored in the arithmetic storage unit 9.

Next, in step S15, the M ^z ion-selective electrode 3A, N ^z ion-selective electrode 3B, and reference electrode 5 used in steps S9 to S13 are washed. In step S13, the third standard solution 1C is added to the M ^z ion-selective electrodes 3A and N washed in step S15.
^{The z-} ion selective electrode 3B and the reference electrode 5 are immersed. In step S19, the potential difference between each of the ion-selective electrodes 3A and 3B and the reference electrode 5 is measured, and the result is stored in the calculation storage unit 9.

Further, in step S21, the M ^z ion-selective electrode 3A, N ^z ion-selective electrode 3B and reference electrode 5 used in steps S15 to S19 are cleaned. Next, in step S23, the first standard solution 1A and the second standard solution 1B stored in the calculation storage unit 9 are stored.
The coefficient (potential gradient, reference potential, selection coefficient) of the calibration curve of each ion-selective electrode 3A, 3B is calculated and stored from the ion concentration of each third standard solution 1C and the measured potential difference.

Next, the operation of ion concentration measurement will be described with reference to FIG. In step S31, the sample liquid S
M ^z ion selective electrode 3A and N ^z ion selective electrode 3
B and the reference electrode 5 are immersed. Next, step S33.
Then, the potential difference between each of the ion selective electrodes 3A and 3B and the reference electrode 5 is measured, and the result is stored in the arithmetic storage unit 9.
In step S35, the M ^z ion concentration and N ^z ion of the sample solution S are calculated from the coefficient of the calibration curve of each ion-selective electrode 3A, 3B stored in the calculation storage section 9 and the potential difference measured in the sample solution S in step S35. Calculate the concentration. further,
The calculated M ^z ion concentration and N ^z ion concentration are output to the output unit 13 and displayed.

In addition, when it is desired to measure with high accuracy, FIG.
And the flowchart shown in FIG. 4 is repeated continuously and several times. If high accuracy is not required, after performing the calibration operation of the flowchart shown in FIG.
It is also possible to repeat the measurement operation of the flowchart shown in several times. The order of the standard solutions in the calibration operation shown in FIG. 3 is not limited to the procedure shown in FIGS. 3 and 4, and may be any order. Furthermore, the cleaning operation here does not only mean cleaning with another liquid such as pure water, but also includes the case of using a liquid for which the potential is measured next. Further, the cleaning operation shown in FIGS. 3 and 4 may be omitted, or may be appropriately performed at any place.

On the other hand, when the ion concentration of the sample liquid is not measured but only the selection coefficient of the M ^z ion-selective electrode 3A is measured, the operation for measuring the ion concentration of the sample liquid in the flowchart shown in FIG. 4 is performed. It can be omitted. In this case, the selection coefficient and the coefficient of the calibration curve obtained by the calibration of the potential gradient, the reference potential, etc. are displayed in step S31. The flow charts shown in FIGS. 3 and 4 show the operation of the immersion measuring device shown in FIG. 2, but the operation of immersion in steps S5, S11, S17, and S31 is performed by the switching valve. If replaced with the operation of switching the solution in the passage,
It can be applied to the measurement operation of the flow cell type flow measuring device shown in FIG.

The ion-selective electrode measuring system is not limited to the immersion type as shown in the embodiment of FIG. 2, but a flow cell type flow measuring system as shown in FIG. 5 is also possible. In the embodiment shown in FIG. 5, three kinds of standard solutions, that is, the first standard solution 1A, the second standard solution 1B, the third standard solution 1C and the sample solution S, are respectively changed by the switching valve 21 to the flow path P.
And is introduced into each ion-selective electrode. The solution is sucked by a pump 27 provided in the middle of the flow path and discharged into a drain tank 29. The ion-selective electrode in these examples is a general term for a potential detection type ion sensor, and is an ion-sensitive field effect transistor (IS).
FET) and the like.

The selection coefficient measurement method and the ion concentration measurement method including the calculation method will be described below. The output potentials (potential difference) of the first standard solution 1A, the second standard solution 1B, and the third standard solution 1C of the ^Mz ion-selective electrode 3A which are disturbed by N ^z ions are E _{M (1)} , E _{If M (2)} and E _{M (3)} , the potential gradient (sensitivity) α _{M of} the M ^z ion-selective electrode 3A, the selection coefficient K _{MN with} respect to N ^z , and the reference potential E _M ⁰ are respectively expressed by Equation (2) and Equation (3)
, Which is obtained from the equation (4).

[0040]

[Formula 2] α _M = (E _{M (1)} −E _{M (2)} ) / [log
(CM ₍₁₎ )-log (CM ₍₂₎ )] ... (2)

[Equation 3]

[Equation 4] E _M ⁰ = E _{M (1)} −α _M · log (C _{M (1)} + K _MN
C _{N (1)} ) (4) A calibration curve is created according to the equation of Nikolski Eisenman with α _M , K _MN and E _M ⁰ thus obtained.

Further, instead of the equation (3), the following equation (5), which is a modification of the equation (3), may be used.

[0042]

[Equation 5] On the other hand, the calibration curve of the N ^z ion-selective electrode 3B also shows the standard solution 1
It is created from the output potentials EN ₍₁₎ and EN ₍₂₎ at A and 1B according to the Nernst equation. The potential gradient (sensitivity) α _{N of} the N ^z ion-selective electrode 3B and the constant E _N ⁰ are expressed by the formula (6) and the formula, respectively.
It is calculated from (7).

[0043]

[Equation 6] α _N = (EN ₍₁₎ -EN ₍₂₎ ) / [log
(C _{N (1)} ) −log (C _{N (2)} )] (6)

[Equation 7] E _N ⁰ = E _{N (1)} −α _N · log (C _{N (1)} ) (7) Next, the output potentials of the two ion-selective electrodes in the sample solution S are expressed as E _{M ( S)} and E _{N (S)} , the N ^z ion concentration C _{N (S)} and the M ^z ion concentration C _{M (S)} of the sample solution S are expressed by the respective formulas.
(8), can be obtained by equation (9).

[0044]

[Equation 8]

[Equation 9] Here, the result of equation (8) is used as the value of C _{N (S)} included in equation (9). In such an ion concentration measuring device,
As the ion selective electrode 3A, an NH ₄ ⁺ ion selective electrode using nonactin as a sensitive substance was used. The NH ₄ ⁺ ion-selective electrode is disturbed by K ⁺ ions. Therefore,
As the first standard solution 1A (C _{NH4 (1)} = 5 mmol / l, C _{K (1)}
= 5 mmol / l), and as the second standard solution 1B (C _{NH4 (2)} =
0.5 mmol / l, C _{K (2)} = 0.5 mmol / l), as the third standard solution 1C (C _{NH4 (3)} = 0 mol / l, C _{K (3)} = 5 mmol / l)
Selectivity K for K ⁺ ion using 3 kinds of liquid
_The results of measuring _{NH4, K} are shown in Table 1. The results obtained by the conventional mixed solution method and the conventional single solution method are also shown.

[0045]

[Table 1] Selectivity coefficient K obtained from the measurement method according to the present invention
_{NH4, K} was in good agreement with the selectivity coefficient when 9 kinds or 10 kinds of solutions were used in the conventional mixed solution method or single solution method. On the other hand, the results of the mixed solution method and the single solution method performed with the minimum of 5 solutions and 6 solutions were values different from the measurement method according to the present invention and the case where a large number of solutions were used. As described above, it can be seen that the selection coefficient measuring method according to the present invention can accurately and rapidly determine the selection coefficient using only three kinds of standard solutions. Further, it is possible to obtain the selection coefficient from a simple numerical calculation without requiring the graphical processing of the potential curve graph as in the conventional method.

Further, the N of the third standard solution 1C according to the present invention is
Table 2 shows the measurement results of the selectivity coefficient when the H ₄ ⁺ ion concentration C _{NH4 (3)} and the K ⁺ ion concentration C _{K (3)} were changed. At this time, the respective ion concentrations of the first standard solution 1A and the second standard solution 1B are C _{NH4 (1)} = 5 mmol / l, CK ₍₁₎ = 5 mmol / l, C
_{NH4 (2)} = 0.5 mmol / l and C _{K (2)} = 0.5 mol / l.

[0047]

[Table 2] Thus, the ratio of NH ₄ ⁺ ion concentration C _{NH4 (3)} and K ⁺ ion concentration C _{K (3)} is the same as that of the other two standard solutions (1:
The selection coefficient obtained in the case of 1) was a value that was significantly deviated from other conditions. Further, the selectivity coefficient was obtained more accurately when C _{K (3)} had a higher concentration than C _{NH4 (3)} .

Thus, the selectivity coefficient K for K ⁺ ions is
_The NH ₄ ⁺ ion-selective electrode for which NH _{4 , K} was required was used together with the K ⁺ ion-selective electrode using valinomycin as a sensitizer to construct the ion concentration measuring device shown in FIG. 2. The NH ₄ ⁺ ion-selective electrode and the K ⁺ ion-selective electrode were calibrated using the above-mentioned three types of standard solutions, and the formula (8)
A calibration curve formula represented by (9) was created.

Then, the two electrodes were immersed in a sample solution of unknown concentration, the output potential was measured, and each ion concentration was determined from the calibration curve. 5 mmol / l KCl coexisted constantly.
FIG. 6 shows the NH ₄ ⁺ ion concentration measurement results when a 1 to 10 mmol / l NH ₄ Cl solution was used as the sample solution. In addition, the results of measurement using the Nernst equation that does not include the term of the selection coefficient are shown as the equation of the calibration curve of the NH ₄ ⁺ ion selective electrode.

As described above, the NH ₄ ⁺ ion concentration measured by using the selection coefficient obtained by the present invention was in good agreement with the NH ₄ ⁺ ion concentration of the sample liquid after the interference from K ⁺ ions was corrected. The measurement error at this time was within ± 9%.

In another embodiment, N-heptyl-N ',
N'-bis {8-[[3- (heptylmethylamino)-
1,3-Dioxopropyl] amino] octyl} -N-
Mg ²⁺ ion-selective electrode using methyl-propanediamide as a sensitizer and bis [di- (n-octylphenyl)]
Phosphato] An ion concentration measuring device was constructed using a Ca ²⁺ ion-selective electrode using calcium as a sensitive substance.
This Mg ²⁺ ion-selective electrode is disturbed by Ca ²⁺ ions.

Therefore, an Mg ²⁺ ion selective electrode is used as the ion selective electrode 23A in FIG.
A Ca ²⁺ ion-selective electrode was used as B. The first standard solution 1A was used for the three standard solutions (C _{Mg (1)} = 2 mmol / l,
C _{Ca (1)} = 4 mmol / l), as the second standard solution 1B (C
_{Mg (2)} = 0.2 mmol / l, C _{Ca (2)} = 0.4 mmol / l), and as the third standard solution 1C (C _{Mg (3)} = 0 mol / l, C _{Ca (3))}
= 4 mmol / l) were used.

As a result, Ca of the Mg ²⁺ ion-selective electrode
^The selectivity coefficient K _{Mg, Ca} for ²⁺ ions was 0.15. The values of the selection coefficients K _{Mg and Ca} were in good agreement with the results of the other mixed solution methods (using 9 solutions) and the single solution method (using 10 solutions). Also, the Mg ²⁺ ion concentration C of the third standard solution 1C
_As a setting condition of _{Mg (3)} and C ²⁺ ion concentration C _{Ca (3)} , the ratio of C _{Mg (3)} and C _{Ca (3) was} the same ratio as the other two standard solutions (1: 2). In this case, the selectivity coefficient was a value far different from the results under other conditions. Further, in order to obtain a more accurate selection coefficient, it was desirable that C _{Ca (3)} had a higher concentration than C _{Mg (3)} , as in the result of the NH ₄ ⁺ ion selective electrode.

As a result of measuring Mg ²⁺ from the calibration curve formula according to the Nicholski-Eisenman formula using this selectivity coefficient and the Ca ²⁺ concentration obtained from the Ca ²⁺ ion-selective electrode, it was found that 0. 1 to 4 mmol / l MgCl ₂ solution (4 mmol / l C
The measurement error in the aCl ₂ coexistence condition was within ± 8%.

As yet another embodiment, NO ₃ containing trioctylmethylammonium nitrate as a sensitive substance.
^- an ion-selective electrode, Cl to silver chloride and sensitive material ^-
An ion concentration measuring device was constructed using an ion selective electrode. This NO ₃ ⁻ ion selective electrode is subject to the interference of Cl ⁻ ions to a considerable extent. As the first standard solution 1A (C
_{NO3 (1)} = 5 mmol / l, C _{Cl (1)} = 10 mmol / l), and as the second standard solution 1B (C _{NO3 ( 2)} = 0.5 mmol / l, C _{Cl (2)} =
1 mmol / l), and as the third standard solution 1C (C _{NO3 (3)} = 0.
1 mmol / l, C _{Cl (3)} = 10 mmol / l) was used to measure the selectivity coefficient K _{NO3, Cl} for Cl ⁻ ions of the NO ₃ ⁻ ion selective electrode, and the result was 0.07. Met. Moreover, using this selection coefficient value, 0.3 to 8 mmol / l
NO _{3 in} KNO ₃ solution (10 mmol / l KCl constant coexistence)
^- the measurement error of the ion concentration was within 6% ±.

As described above, according to the selection coefficient measuring method of the present embodiment and the ion concentration measuring apparatus to which this selection coefficient measuring method is applied, the selection coefficient for the interfering ions having the same ion valence with only three kinds of standard solutions is used. Can be measured easily and accurately. In addition, it is possible to accurately measure the selection coefficient with only one measurement operation.

In addition, since the selection coefficient can be obtained only by a simple calculation without requiring the graphic processing of the output potential characteristic graph as in the conventional method, the automation of the apparatus is very easy. In addition, this ion concentration measuring device can simultaneously calibrate another ion-selective electrode that uses the interfering ion as the ion to be measured by using the standard solution for measuring the selection coefficient described above. By correcting the effect of ions, the concentration of target ions can be accurately measured.

[0058]

As described above, according to the present invention, the selection coefficient can be measured easily and accurately.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the concept of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of an embodiment to which a selection coefficient measuring method according to the present invention is applied.

FIG. 3 is a flowchart showing a measurement operation of the embodiment shown in FIG.

FIG. 4 is a flowchart showing a measurement operation of the embodiment shown in FIG.

FIG. 5 is a diagram showing another solution measurement system in one example of the present invention.

FIG. 6 is a diagram showing the relationship between the ammonium ion concentration measured in one example of the present invention, the ammonium ion concentration measured without correcting the influence of interfering ions, and the ammonium ion concentration in the sample liquid.

FIG. 7 is an explanatory diagram of selection coefficient measurement by a conventional mixed solution method.

FIG. 8 is an explanatory diagram of the selection coefficient measurement by the conventional single solution method.

[Explanation of symbols]

1 Standard Solution 1A First Standard Solution 1B Second Standard Solution 1C Third Standard Solution 3A ^Mz Ion Selective Electrode 3B ^Nz Ion Selective Electrode 5 Reference Electrode 7A First Potential Difference Measuring Circuit 7B Second Potential Difference Measurement circuit 9 Calculation storage unit 11 Input unit 13 Output unit 21 Switching valve 23 Ion-selective electrode 27 Pump 29 Drain tank P Solution channel S Sample solution

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01N 27/26-27/49

Claims (4)

(57) [Claims] 1. A first standard solution in which the concentration of the ions to be measured and the concentration of interfering ions having the same ion valence as the concentration of the ions to be measured are known is added to an ion selective electrode and a reference electrode.
Immerse the electrode in the ion-selective electrode and the reference electrode.
Measuring a first output potential difference; and a second standard in which the ratio of the concentration of the measurement target ion to the concentration of the interfering ion is equal to and different from the first standard solution, and the concentration is known. Liquid, the ion selectivity
Immersing an electrode and the reference electrode, the ion-selective electrode
And a step for measuring a second output potential difference between the reference electrode and the reference electrode.
And flop, the ratio of the concentration of the measurement target ion concentration of the interfering ion in the third standard solution the first standard solution and the second standard solution and different and the concentration is known, the ion Election
Immersing the selective electrode and the reference electrode, the ion selectivity
Measuring the output potential difference between an electrode and the reference electrode
From the output potential difference of the first to third standard solutions,
Steps that determine the selectivity coefficient of the Schi-Eisenman formula
Flop, selectivity coefficient measuring method characterized by including the capital. 2. The measuring object in the third standard solution
The concentration of ions can be adjusted to the interference index in the third standard solution.
The concentration is smaller than the ON concentration.
Method for measuring the selection coefficient described. 3. A first to a third standard solution and a sample solution
A first ion-selective electrode to be immersed, A second ion-selective electrode immersed in the liquid; A reference electrode immersed in the liquid, Output voltages of the first ion-selective electrode and the reference electrode
A first measuring circuit for measuring the difference, Output power of the second ion-selective electrode and the reference electrode
A second measuring circuit for measuring the difference, The output power output from the first and second measurement circuits.
Selection of Nikorski Eisenman's formula based on disparity
The coefficient is determined, and the Nicholski Eisenman From the formula
An arithmetic storage unit for calculating the ion concentration of the sample liquid; The calculation storage unit stores the ion concentrations of the first to third standard solutions.
An input section for entering the degree, Io of the sample liquid calculated by the arithmetic storage unit
And an output unit that outputs the concentration of In the first standard solution, the concentration of the ion to be measured and the measurement
Concentration of interfering ions with the same valence as the target ion concentration
Degree is known, and in the second standard solution,
The ratio of the concentration of ON to the concentration of the interfering ion is the first standard.
Equal to the semi-liquid and the concentration is different and the concentration is known
In the third standard solution, the concentration of the ion to be measured is high.
The ratio of the concentration of the interfering ions to the concentration of the first standard solution
Different from the second standard solution and the concentration is known
An ion concentration measuring device characterized by the above. 4. The first ion-selective electrode is magnesi
The second ion selectivity, which is an ion-selective electrode
The electrode is a calcium ion selective electrode
The ion concentration measuring device according to claim 3.