JPS608744B2 - How to measure persulfate ion concentration - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring persulfate ion concentration in an alkaline aqueous solution containing persulfate ions.

In general, chemically colored solutions for metals such as copper and copper alloys using persulfates as oxidizing agents are often made into strong alkaline solutions and overflowed in order to enhance the oxidizing effect. However, the persulfate in this coloring solution is susceptible to thermal decomposition,
If metal ions or the like are present in the solution, the catalytic action becomes even more intense. Therefore, when coloring metals with a coloring solution using persulfate as an oxidizing agent, it is essential to maintain the persulfate ion concentration in the coloring solution at a constant level in order to maintain a constant quality of the colored product. Both were necessary. Conventionally, methods for quantifying persulfate ions include reduction titration, iodine titration, and neutralization titration, but the former two require acidic solutions to accurately detect persulfate ion concentration. The latter involves hydrolysis, which makes measurement difficult if the alkaline concentration is too high, and both methods require a considerable amount of time to obtain final results as the reaction proceeds slowly. Moreover, the measurement operation was also complicated.

Therefore, there is no suitable measurement method that can be used in a short time to control the persulfate ion concentration in the coloring solution during metal coloring work. It was difficult to obtain colored products. In view of the above-mentioned points, an object of the present invention is to provide a method for measuring the persulfate ion concentration in an alkaline aqueous solution in a short time, accurately and easily.

That is, the gist of the present invention is to immerse a metal steel electrode, an electrode insoluble in the aqueous solution, and a reference electrode or standard electrode in an alkaline aqueous solution of an alkali metal salt of persulfuric acid; Persulfuric acid, characterized in that a current is applied to measure the potential difference between the metal steel electrode and the reference or standard electrode, and the time from when the current is applied until this potential difference shows an inflection point is measured. It consists in the method of measuring ion concentration. In the present invention, the solution whose persulfate ion concentration is to be measured is an alkaline aqueous solution of an alkali metal salt of persulfate.

Examples of the alkali metal salts of persulfate include lithium persulfate, sodium persulfate, potassium persulfate, and the like. The alkaline aqueous solution may be any alkaline aqueous solution, but aqueous solutions of alkali metal hydroxides or carbonates, such as sodium hydroxide, potassium hydroxide, and sodium carbonate, are preferred.

The insoluble electrode used in the present invention is an electrode that hardly dissolves in the above-mentioned alkaline aqueous solution, and includes, for example, an electrode made of platinum, gold, or the like.

The reference electrode and standard electrode used in the present invention are electrodes that generate a constant electrode potential when the concentration and temperature of the electrolyte solution are constant and do not change over time. Standard electrodes include, for example, a sweet electrode, a silver/silver chloride electrode, a hydrogen electrode, etc., which are almost insoluble in alkaline aqueous solutions.

To measure persulfate ion concentration using the measurement method of the present invention,
First of all, use a metal electrode to measure the alkaline aqueous solution!
The metal steel electrode is set to be positive and the solid electrode is set to be negative, so that current flows between the two electrodes. As the above-mentioned current increases, the measurement time becomes shorter and the error increases; conversely, as the current decreases, the measurement time becomes longer, so the current is preferably 0.5 to 10 A/c, more preferably 1 to 5 mA. / is. At the same time, a reference electrode or a standard electrode is immersed in the alkaline aqueous solution, and the electrode is set so that the potential difference between it and the metal steel electrode can be measured.

To measure the potential difference, a high impedance e.g.
Beauty.

Incorporating a potentiometer with almost no current flowing above ○,
Moreover, it is preferable to use a potentiometer or the like that can record at a constant speed over time. Next, when a current is passed between the metal steel electrode and the insoluble electrode and the potential difference between the metal steel electrode and the reference electrode or standard electrode is measured,
Initially, the potential difference is in a constant ground state, but after a certain period of time, it rapidly increases and shifts to the next equilibrium state.

The change in potential difference at this time is about 0.6 volts, and this change in potential difference hardly changes even if the concentration of persulfate ions changes. However, the time from when a current is applied to the inflection point at which this potential difference changes shows regularity in the change in the concentration of persulfate ions, and metal ions that are intestinal ions for persulfate ions, such as sodium and potassium, show regularity. There is no difference in the concentration of persulfate ions, which is an anion. According to the present invention, persulfate is dissolved in an aqueous solution having the same alkaline concentration to prepare several standard solutions having different persulfate ion concentrations, and the standard solutions are connected to a metal steel electrode and a reference electrode or a reference electrode at a constant temperature. When measuring the change over time in the potential difference between a standard electrode and the persulfate ion concentration, a relationship expressed by the following equation is usually established between the persulfate ion concentration and the time from when current is applied until the potential difference reaches an inflection point. . [C]=A+Brl/2 However, [C]: persulfate ion concentration, t: time from when current is applied until the potential difference shows an inflection point, A, B: constants.

The constants of A and B are factors that change depending on the alkali concentration, solution temperature, etc., so if you determine them from the above standard solution or create a test line, you can use the measurement solution with unknown persulfate ion concentration as described above. By measuring the time t until the potential difference reaches the inflection point, the persulfate ion concentration [C] can be determined from the above equation or the calibration curve.

The time required to measure the concentration can be reduced by using a method that clarifies the inflection point by passing the change in potential difference through a differentiating circuit, or a method that directly displays the concentration by passing the signal from the potentiometer through an arithmetic circuit using the above-mentioned relational expression. This is preferable because it can be further shortened and carried out with high precision. The range of persulfate ion concentration that can be suitably measured by the method of the present invention is 0.01 mol/
It is preferably 0.1 mol/range.

This is because as the concentration of persulfate ions decreases, the elapsed time until the potential difference changes becomes longer, whereas when the concentration is high, the elapsed time becomes extremely short and errors are likely to occur.

The alkali IJ concentration after being measured is preferably in the range of 0.1 mol/l to 2.5 mol/l because the higher the alkali concentration, the longer the elapsed time until the potential difference changes. As described above, the method for measuring persulfate ion concentration of the present invention involves immersing a metal steel electrode, an insoluble electrode, and a reference or standard electrode in a measurement solution, and applying an electric current between the metal steel electrode and the impregnable electrode. The measurement is simple, as all you have to do is measure the time it takes for the potential difference between the metal steel electrode and the reference or standard electrode to reach an inflection point while flowing
It is highly accurate and can be done in a short amount of time.

Therefore, according to the measuring method of the present invention, the concentration of the metal colored solution can be measured easily and in a short time, so that the concentration of the metal colored solution can be easily controlled by adding a reduced amount of persulfate, replacing the solution, etc.

Next, the method of the present invention will be explained based on examples.

Example 12, Comparative Example 150/A predetermined amount of potassium persulfate was dissolved in an aqueous sodium hydroxide solution having the same concentration to obtain a sample solution having a persulfate ion concentration shown in Table 1.

A metal steel electrode and a platinum electrode (non-melting electrode) were obtained by leaving one closed part on one side of a 20 x 50 x 0.3 (willow) copper plate and sealing the other part with epoxy resin. A silver monochloride electrode (standard electrode) was immersed in the sample solution, and the platinum electrode was placed at a distance from the opening of the metal steel electrode on one side.

Next, set the metal steel electrode to be the positive pole and the platinum electrode to be the negative pole, and apply the specified amount of current shown in Table 1 to observe the change in the dew level difference between the metal steel electrode and the silver-iron chloride electrode. Measurement was carried out using a potentiometer, and the time required for the potential difference to reach an inflection point was measured, and the results are shown in Table 1.

For comparison, the time required for the potential difference to reach the inflection point was measured in the same manner without passing any current between the metal steel electrode and the platinum electrode, and the results are shown in Table 1.

Furthermore, the relationship between the persulfate ion concentration and the time required to reach an inflection point is shown in FIG. In the figure, 1 is Comparative Example 1 (current 0), 2 is Example 1 (current 3 A), and 3 is Example 2 (current 5 A).
The results are shown below. Table 1 Time to reach the inflection point (unit: seconds)

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between persulfate ion concentration and time until the potential difference reaches an inflection point.

Claims (1)

[Claims] 1. A metallic copper electrode, an electrode insoluble in the aqueous solution, and a reference or standard electrode are immersed in an alkaline aqueous solution of an alkali metal salt of persulfuric acid, and a metal copper electrode and a reference or standard electrode are immersed in an alkaline aqueous solution of an alkali metal salt of persulfuric acid. The method is characterized in that a constant current is applied to measure the potential difference between the metal copper electrode and the reference or standard electrode, and the time from when the current is applied until the potential difference reaches an inflection point is measured. Method for measuring sulfate ion concentration. 2 Persulfate ion concentration [C] is expressed by the formula [C] = A + Bt^-
The measuring method according to claim 1, which is determined by ^1/^2 (where t is the time from when the current is applied until the potential difference shows an inflection point, and A and B are constants).