JP5324492B2 - Analysis method of boron - Google Patents

Description

  The present invention relates to a technique for quantitatively analyzing boric acid in water by an electrochemical technique using a complex of boric acid.

  Currently, seawater desalination technology using reverse osmosis membranes is used in areas where drinking water sources are scarce. This desalination technology is a technique that removes many ions contained in seawater by allowing seawater to permeate through the reverse osmosis membrane at a pressure equal to or higher than the osmotic pressure. It is difficult to get rid of.

  Boron exists in an equilibrium state of boric acid-borate ions, but pKa of boric acid is 9.02, and most of it is not ionized in seawater (pH 8.2). Small boric acid permeates the reverse osmosis membrane.

Sea water contains about 4.5 mg / dm ³ of boron. Boron is an essential element of living organisms, but if it is consumed in excess, it causes reproductive toxicity. In addition, as acute toxicity to humans, it is also known to cause disorders such as nausea, vomiting, abdominal pain, and diarrhea. For this reason, the boron concentration of drinking water is defined as 0.5 mg / dm ³ in the WHO guidelines, and 1.0 mg / dm ³ or less in Japanese tap water quality standards.

  From the above background, in a seawater desalination system using a reverse osmosis membrane method (hereinafter referred to as RO method), it is necessary to monitor boron in treated water.

  Conventionally, inductively coupled plasma-atomic emission (ICP-AES) or inductively coupled plasma-mass spectrometry (ICP-MS) has been used to monitor the water quality of trace inorganic components in tap water. It was not a general-purpose analyzer that can be used on site in terms of handling methods.

  As a technique that can analyze boron more simply, Patent Document 1 introduces a technique in which a boric acid-tyrone complex is generated from boron and quantified by an electrochemical technique.

  This technique combines electrically inert boron with polyhydroxyl compounds (polyols) by dehydration condensation to form an electrochemically active boric acid-tyrone complex, and the concentration of boron is indirectly determined by voltammetry. It is to be quantified.

This technique is an excellent analytical method for the boric acid to 5.0 mg / dm ³ can be quantified with high sensitivity 0.1 mg / dm ^3, in response to Tyrone itself applied voltage added for complexation, It was found to affect the response of boric acid complex.

Practically, a sample containing an unknown amount of boric acid is added with 5-10 mmol / dm ³ of tyrone to form a complex, and the boric acid concentration is determined from the response of boric acid-tyrone complex near 900 mV. Since unreacted Tyrone also shows a response in the vicinity of 500 mV, the measurement accuracy is particularly affected for a sample having a low boric acid concentration.

  Furthermore, the above-described method uses a sensor composed of a working electrode, a counter electrode, and a reference electrode, and quantifies boric acid by cyclic voltammetry or differential pulse voltammetry. At this time, it was found that the Tyrone and boric acid-tyrone complex near the electrode were oxidized and adhered to the electrode surface, resulting in a decrease in sensor response.

  The Tyrone is a general name and refers to a compound called sodium 1,2-dihydroxy-3,5-benzenedisulfonate, which is a reagent used for colorimetric analysis of boron and other metals.

For this reason, in practical use, there has been a problem that complicated maintenance is required to polish the sensor surface and remove the influence of adhering matter at every measurement.
JP 2009-150836 A

  The present invention provides an inexpensive measuring instrument that can be widely applied to the analysis and management of fresh water and factory wastewater generated by the RO method, using a measuring method that can easily determine boron in water.

  In the present invention, azomethine H and a predetermined amount of 1-amino-8-naphthol-3,6-disulfonic acid (hereinafter referred to as H acid) or salicylaldehyde and H are added to electrochemically inert boric acid. This is a method for analyzing boron, characterized in that an acid is added to a specimen to produce an electrochemically active boric acid-azomethine H complex, and the concentration of this complex is measured using voltammetry.

  In addition, in the voltammetry of boric acid-azomethine H complex, a highly sensitive response having concentration dependence on boric acid can be obtained at a reduction potential of about -1,050 mV.

  In the boron analysis method of the present invention, it is possible to remove the influence of the additive on the response of the complex by optimizing the combination of salicylaldehyde and H acid added as a complex-forming reagent, and high sensitivity to boron. Quantitative analysis becomes possible.

  Furthermore, the peak observed by voltammetry of the above complex is due to the reduction reaction of the boric acid-azomethine H complex, which eliminates electrode fouling caused by the oxidation reaction in the vicinity of the electrode like the boric acid-tyrone complex mentioned above. can do.

  Therefore, by using the boron analysis method according to the present invention, it is possible to provide an inexpensive measuring instrument that can realize simple and highly sensitive quantification and does not require complicated maintenance.

In the boron analysis method of the present invention, as a pretreatment of a sample containing an unknown amount of boric acid, a pH adjuster, for example, 1 mol / dm ³ acetic acid (CH ₃ COOH) and 0.5 mol / dm ³ ammonium acetate are used. In addition, the pH is adjusted to around 4.5. The pH adjusting agent is not limited to the above-described reagent, and a reagent that can maintain a predetermined pH and does not contain boron, such as phthalate and phosphate, may be used.

  After pH adjustment, azomethine H and H acid or salicylaldehyde and H acid are added to the specimen to form an electrochemically active boric acid-azomethine H complex. This reaction is shown in the following formulas (1) and (2).

Azomethine H is a reagent used for the formation of boric acid-azomethine H complex when quantitative analysis of boron is performed by absorptiometry, and is generated by reacting salicylaldehyde and H acid 1: 1. Is. This reaction is shown in the following formula (3).

  In practice, in order to prevent oxidation of the added reagent such as salicylaldehyde, it is desirable to add an appropriate amount of an antioxidant such as ascorbic acid in addition to the reagent.

  The electrochemically active boric acid-azomethine H complex produced by the above operation is quantitatively analyzed by voltammetry, for example, by applying a reduction potential of −100 to −1,400 mV. The sensor unit used for voltammetry is a glassy carbon electrode, platinum electrode, gold electrode or the like as a working electrode, a platinum electrode or other metal electrode as a counter electrode, a silver-silver chloride electrode, a carmelo electrode, a hydrogen electrode, or the like. Any one of them is used as a reference electrode.

  FIG. 2 shows voltammetric measurement results when azomethine H is added to a sample containing a known amount of boric acid.

  A peak of boric acid-azomethine H complex appears around -1,050 mV, and a correlation can be confirmed between the boric acid concentration and the peak height. In addition, peaks other than the complex can be confirmed before and after the peak of the boric acid-azomethine H complex (-950 mV and -1,300 mV).

Furthermore, the measurement result performed in order to confirm each responsiveness of azomethine H, a salicyl aldehyde, H acid, and boric acid-azomethine H complex in FIG. 3 is shown.
Each sample was prepared and used so that azomethine H, salicylaldehyde, H acid was 5 mmol / dm ³ , and boric acid was 1 mg / dm ³ as a boron concentration.

  From the results of FIG. 3, it was found that the peak near -950 mV was due to azomethine H, and the peak near -1,300 mV was due to salicylaldehyde.

  When quantifying boron from the voltammetric measurement results, the peak height of the complex around -1,050 mV is read, and the boron concentration in the sample is derived using a calibration curve prepared in advance using a known amount of sample. .

  In order to ensure analysis accuracy, a baseline correction operation is required when determining the peak height, and the baseline is determined from the response around -1,050 mV.

  For this reason, it is necessary to suppress the influence of the peaks of azomethine H and salicylaldehyde, which show responses before and after the complex peak, on the baseline correction.

  As a technique for suppressing the above influence, in the boron analysis method of the present invention, the amount of salicylaldehyde added is suppressed to suppress the residual salicylaldehyde in the sample, and the concentration of azomethine H remaining in the sample after complex formation Reduce.

  In addition, it is desirable to add an excessive amount of H acid to be added at the same time in order not to respond to voltammetry and to promote formation of boric acid-azomethine H complex.

  Based on the above conditions, the reagent to be practically added with respect to complex formation has a molar ratio in the specimen after the addition of azomethine H or a ratio of H acid to salicylaldehyde of 1: 1 to 1:50. It is added so that the ratio is within a range, preferably about 1:10.

More specifically, in order to realize a measurement device to analyze the boron up to 10 mg / dm ^3, when using the azomethine H and H acid, 1～10Mmol azomethine H / dm ^3, preferably 2 mmol / dm ³ around , H acid is added to the specimen so as to be about 1 to 100 mmol / dm ³ , desirably about 20 mmol / dm ³ .
Also, when using salicylaldehyde and H acid, salicylaldehyde 1~10mmol / dm ^3, preferably 2 mmol / dm ³ around the H acid 1 to 100 mmol / dm ^3, such that preferably is about 20 mmol / dm ³ To the sample.

FIG. 1 shows voltammetry when reagents are added to various samples having a boron concentration of 0 to 10 mg / dm ^{3 so} that salicylaldehyde is 2 mmol / dm ³ and H acid is 24 mmol / dm ³ . In addition, to the specimen, ascorbic acid was added as an antioxidant to 11 mmol / dm ³ together with the reagent.

  By reducing the concentration of salicylaldehyde, voltammetry was obtained in which the influence of the salicylaldehyde and azomethine H peaks was greatly suppressed, enabling highly accurate quantitative analysis of boron.

FIG. 4 shows the response characteristics of the sensor in a practical range using the boron analysis method of the present invention. Sensor output current (absolute value) is highly correlated to the boron concentration, measurement can be boron concentration of 0.5 to 10 mg / dm ^3, to suppress the measurement error below ± 0.1 mg / dm ³ it can.

Further, FIG. 5 shows voltammetry when a sample having a boron concentration of 5 mg / dm ³ is measured three times.
When the boron analysis method of the present invention is used, the sensitivity of the sensor is not lowered by repeated measurement, and the maintenance work of the sensor, which is a problem in voltammetry using the boric acid-tyrone complex of the prior art, becomes unnecessary.

According to the present invention, it is possible to realize a measuring device that can easily analyze boron in water without requiring troublesome maintenance, and of course, a batch type measuring device used for laboratories, seawater desalination requiring continuous measurement It can also be widely used for monitoring and control in wastewater treatment systems such as plants and glass factories.
When applied to a wastewater treatment system or the like in which the boron concentration exceeds 10 mg / dm ³ , the measurement may be performed after a dilution operation with purified water as a pretreatment of the specimen.

Boron concentration is a diagram showing a voltammetric case of adding 0-10 mg / dm ³ of analyte salicylaldehyde (2mmol / dm ³⁾ and H acid (24mmol / dm ^3). It is a figure which shows the voltammetry at the time of adding azomethine H (5 mmol / dm < ³ >) to the test substance whose boron concentration is 0-10 mg / dm < ³ >. It is a figure which shows the responsiveness of the voltammetry which each of azomethine H, a salicyl aldehyde, H acid, and a boric acid-azomethine H complex shows. It is a figure which shows the response characteristic of the voltammetry with respect to the test substance whose boron concentration is 0-10 mg / dm < ³ >. It is a figure which shows the voltammetry at the time of measuring repeatedly the test substance whose boron concentration is 5 mg / dm3 ³ times.

Claims (5)

  Add azomethine H and 1-amino-8-naphthol-3,6-disulfonic acid (hereinafter referred to as H acid) or salicylaldehyde and H acid to boric acid in an electrochemically inert liquid. A method for analyzing boron, comprising producing an electrochemically active boric acid-azomethine H complex, and measuring the concentration of the complex using voltammetry.   The method for analyzing boron according to claim 1, wherein the molar concentration in the specimen is such that the ratio of H acid to azomethine H or salicylaldehyde is 1: 1 to 1:50. The method for analyzing boron according to claim 1, wherein azomethine H is added to the specimen so as to be within a concentration range of 1 to 10 mmol / dm ³ and H acid within a range of 1 to 100 mmol / dm ³ . The method for analyzing boron according to claim 1, wherein salicylaldehyde is added to the specimen so that the concentration is 1 to 10 mmol / dm ³ and the H acid is in the concentration range of 1 to 100 mmol / dm ³ .   The method for analyzing boron according to claim 1, wherein voltammetry applying a reduction potential of −100 to −1,500 mV is used.