JPH0233986B2 - SUIYOEKICHUNOZENTANSANNOTEIRYOHO - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for easily quantifying total carbonic acid in an aqueous solution. Conventionally, methods for quantitatively analyzing total carbonic acid such as carbonate ions and bicarbonate ions in an aqueous solution include decomposing carbonate ions, etc. to carbon dioxide and analyzing the generated carbon dioxide using gas chromatography, the Orsat method, or infrared absorption. There are methods for quantifying it, such as by methods. However, since carbonate ions, bicarbonate ions, etc. in aqueous solutions generally coexist with metal ions such as sodium and potassium, high temperatures of over 1000°C are required to thermally decompose the carbonate ions, etc. to carbon dioxide. shall be. Therefore, such carbonate ions,
In order to decompose bicarbonate ions and the like into carbon dioxide, a method using acids such as sulfuric acid and phosphoric acid is generally adopted. However, the method of decomposition using acid as described above not only requires special accessory equipment such as a sulfuric acid decomposition device, but also tends to cause corrosion, especially when using an analytical method using an instrument, which requires maintenance and management of the equipment. It becomes a problem. On the other hand, methods for quantitatively analyzing carbonate ions, bicarbonate ions, etc. in aqueous solutions include neutralization titration using barium chloride and strontium chloride and liquid chromatography. However, the neutralization titration method described above has the disadvantage that accurate analytical values cannot be obtained when there are many coexisting substances in the aqueous solution, and the method using liquid chromatography not only requires expensive equipment but also requires continuous As an analyzer, it has the disadvantage of not being generally applicable due to problems such as the lifespan of the filler. The present inventors have conducted extensive research to solve the drawbacks of such conventional methods, and as a result, have discovered a simple and rapid quantitative method suitable for quantifying total carbonic acid in an aqueous solution. That is, in the present invention, when quantifying the total carbonic acid in an aqueous solution, the aqueous solution is prepared in the presence of ammonium ions in an amount equal to or greater than the sum of twice the number of moles of carbonate ions and the number of moles of bicarbonate ions in the aqueous solution. To,
This is a method for quantifying total carbon dioxide in an aqueous solution, which is characterized by quantifying carbon dioxide generated by heating. According to the quantitative method of the present invention, all carbonic acid in an aqueous solution can be quantitatively decomposed into carbon dioxide at a temperature of about 100°C or higher, which is significantly lower than the conventional thermal decomposition temperature of 1000°C or higher. Furthermore, unlike conventional acid decomposition methods, the present invention does not use acid, so equipment is not corroded by acid, which not only simplifies maintenance and management of the equipment, but also allows for application to continuous automatic analysis. It's easy. Furthermore, compared to conventional methods, the present invention has the characteristics that the measurement time is much shorter, the measurement operation is simpler, and accurate analytical values can be obtained. Therefore, the quantitative method of the present invention can also be applied to process control of products at manufacturing sites by taking advantage of the above-mentioned characteristics, paving the way to achieving extensive rationalization of process control. . The total carbonic acid in the aqueous solution as used in the present invention means carbonate ions and bicarbonate ions that are dissociated in the aqueous solution. Such an aqueous solution containing carbonic acid is generally produced by dissolving in water a water-soluble salt having carbonate ions and bicarbonate ions as anions and metal ions as cations. Common metal ions include sodium ions and potassium ions. In addition, in the present invention, water-soluble coexisting ions such as calcium ion, magnesium ion,
The presence of sulfate and chloride ions does not affect the determination of total carbonic acid. In the present invention, it is extremely important to have ammonium ions present in the aqueous solution containing carbonate ions and bicarbonate ions. That is, due to the presence of ammonium ions, carbonate and bicarbonate ions, which had previously coexisted with sodium and potassium ions, were decomposed at surprisingly low temperatures of about 100°C or higher. This is probably because ammonium ions react with carbonate ions and bicarbonate ions in the aqueous solution at room temperature or under heating, and are converted into ammonium carbonate or ammonium bicarbonate. The ammonium ion used in the present invention is not particularly limited as long as it is a water-soluble ammonium salt, and ammonium nitrate, ammonium sulfate, ammonium hydrochloride, (ammonium acetate), etc. are used.
Among them, ammonium nitrate, which has high solubility in water, is preferably employed. It is sufficient that the amount of ammonium ions present is at least twice the molar ratio of carbonate ions and at least the same amount as bicarbonate ions.
However, if the aqueous solution already contains ammonium ions, the amount can be reduced by that amount. That is, it is necessary to maintain the amount of ammonium ions present in the aqueous solution at least twice the number of moles of carbonate ions plus the number of moles of bicarbonate ions. In this way, if the amount of ammonium ions in an aqueous solution is maintained at more than twice the number of moles of carbonate ions plus the number of moles of bicarbonate ions, when this solution is thermally decomposed at a temperature of about 100°C or higher, ,
Can be 100% decomposed. If the amount of ammonium ions in the aqueous solution is less than the above value, carbonate ions and bicarbonate ions will not decompose 100%,
Only carbon dioxide corresponding to the amount of ammonium ions is generated. Using this principle, it is also possible to indirectly quantify the amount of ammonium ions in a solution. In the method of the present invention, after ammonium ions are present in an aqueous solution, carbonate ions and bicarbonate ions in the aqueous solution are converted into carbon dioxide by heating. The heating device is not particularly limited;
Any conventionally known device can be used without any restriction as long as it is capable of heating to temperatures above 0.degree. C. and recovering the generated carbon dioxide. Furthermore, the method (device) for quantifying the generated carbon dioxide is not particularly limited, and gas chromatography, Orsatz method, infrared absorption method, etc. are employed. In particular, gas chromatography, which is equipped with a heating device and a device for analyzing generated gas, is preferably employed. When using gas chromatography in the method of the present invention, carbonate ions and bicarbonate ions are quantitatively decomposed into carbon dioxide by raising the temperature of the sample vaporization chamber to 300°C or higher, and the resulting gas chromatogram It also gave a sharp carbon dioxide peak. Separation columns can be used without any restriction as long as they have a packing material that separates carbon dioxide from other components such as air and water, but Polapack R is especially convenient because water elution can be completed in a short time. (Product name)
is preferably used. For other gas chromatography measurement conditions, normal analysis conditions are applied as they are. The present invention will be further explained in detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. Example 1 Sodium carbonate standard solution (2.53g/100ml) 25
ml was collected in a 100 ml volumetric flask, 2 g of ammonium nitrate (ammonium ion/carbonate ion molar ratio 4.2) was added and dissolved, and the volume was made up to 100 ml with water.
2μ of this solution was taken into a microsyringe and injected into a gas chromatograph set under the following conditions to determine the peak area of carbon dioxide generated by thermal decomposition. Gas chromatography conditions Separation column: Polapak R, inner diameter 3 mm, length 1.5 m Column temperature: 100°C Inlet temperature: 300°C Detector temperature: 200°C Carrier gas: Hydrogen 50ml/min Detector: Thermal conductivity type (TCD) 120 mA From the peak area, the total amount of carbonic acid in the solution was calculated using a calibration curve previously determined using sodium carbonate and ammonium nitrate. The results are shown in Table 1.
For comparison, Table 1 also shows quantitative values determined by the Orsat method using sulfuric acid decomposition for the same sample.

[Table] Example 2 Sodium carbonate standard solution (100μg/ml) 30ml
0.3 g of ammonium nitrate (ammonium ion/carbonate ion molar ratio of about 60) was added and dissolved therein. 5μ of this solution was taken into a microsyringe and injected into a gas chromatograph set under the following conditions to determine the peak area of carbon dioxide generated by thermal decomposition. Gas chromatography conditions Separation column: Polapak R, inner diameter 3 mm, length 1.5 m Column temperature: 70°C → 150°C (temperature increase at 20°C/min) Inlet temperature: 300°C Detector temperature: 150°C Carrier gas: Hydrogen 50ml /min Detector: Thermal conductivity type (TCD) 150 mA From the peak area, the total amount of carbonic acid in the solution was calculated using a calibration curve previously determined using sodium carbonate and ammonium nitrate. The results are shown in Table 2.
For comparison, Table 2 also shows quantitative values determined by neutralization titration after decomposing the same sample with sulfuric acid and absorbing it in a barium hydroxide solution.

[Table] Comparative Example 1 The same procedure as in Example 1 was conducted except that ammonium nitrate was not used in Example 1, and no carbon dioxide was generated at all. That is, in the absence of ammonium ions, under the conditions of Example 1, sodium carbonate would not be thermally decomposed at all. Example 3 In Example 1, instead of the sodium carbonate standard solution 2.53 g/100 ml, ammonium carbonate 8-10 g/100 ml and sodium carbonate 1-2
Example 1 was carried out in exactly the same manner as in Example 1, except that a mixed solution of g/100 ml was used, and the results are shown in Table 3. Third
For comparison, the table also shows quantitative values determined by the Orsat method using sulfuric acid decomposition for the same sample.

[Table] Example 4 The results obtained in Example 4 were carried out in exactly the same manner as in Example 2, except that the samples listed in Table 4 were used instead of the 100 μg/ml sodium carbonate standard solution as the sample. Shown in the table. For comparison, Table 4 also shows quantitative values determined by neutralization titration after decomposing the same sample with sulfuric acid and absorbing it in a barium hydroxide solution.

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Claims (1)

[Scope of Claims] 1. When quantifying the total carbonic acid in an aqueous solution, the aqueous solution is treated with the presence of ammonium ions in an amount equal to or greater than the sum of twice the number of moles of carbonate ions and the number of moles of bicarbonate ions in the aqueous solution. A method for quantifying total carbon dioxide in an aqueous solution, which is characterized by quantifying carbon dioxide generated by heating the solution. 2. The quantitative method according to claim 1, in which the generated carbon dioxide is determined by gas chromatography. 3. The quantitative method according to claim 1, wherein the heating temperature is 100°C or higher.