JP6361980B2 - Method for analysis of oxalic acid in organic solution - Google Patents

Description

  The present invention relates to a method for analyzing oxalic acid in an organic solution. More specifically, the present invention relates to a method for analyzing oxalic acid in an organic solution used in a process of recovering a noble metal or a compound in an organic solution using oxalic acid.

Oxalic acid is a highly polar substance having two carboxyl groups in the molecule, and is very easy to dissolve in water, but hardly dissolves in an organic solvent. And oxalic acid is a substance generally present in nature, and is contained in many vegetables such as spinach, ginger and peppers. However, if a person consumes these plants in excess, oxalic acid in the plant is said to cause kidney stones and kidney damage.
For this reason, conventionally, various methods for analyzing oxalic acid have been proposed for those containing water such as plants and environmental water (for example, Patent Document 1).

  On the other hand, oxalic acid is a substance having strong reducibility, and is therefore used as an important reducing agent. For example, in addition to general oxidation-reduction titration, in recent years, it has been used for reaction processes in various fields such as industrial chemistry, electrochemistry, and biochemistry. For example, in the field of industrial chemistry, in a gold recovery process by wet refining, a desired metal is recovered from an organic solution by bringing oxalic acid into contact with the organic solution (for example, Patent Document 2).

Japanese Patent No. 2890320 Japanese Patent Laid-Open No. 11-140549

As described above, since oxalic acid is used as an important reducing substance together with an organic solution, it is important to grasp oxalic acid in the organic solution.
However, like the method for analyzing oxalic acid in vegetables of Patent Document 1, there is a method for analyzing oxalic acid from an aqueous solution, but there is currently no method for analyzing oxalic acid from an organic solution.

  An object of this invention is to provide the analysis method of the oxalic acid in the organic solution which can grasp | ascertain the oxalic acid in an organic solution in view of the said situation.

The method for analyzing oxalic acid in an organic solution according to the first invention is a method for analyzing oxalic acid, which is obtained by a pretreatment step of bringing water into contact with an organic solution insoluble in water, and the pretreatment step. sequentially row have the organic solution and analysis step, the analyzing the aqueous solution to be, characterized in that a bis (2-butoxyethyl) ether.
The method for analyzing oxalic acid in an organic solution of the second invention is characterized in that, in the first invention , the aqueous solution obtained in the pretreatment step is analyzed using liquid chromatography and / or ion chromatography.

According to the first invention, since oxalic acid can be detected from bis (2-butoxyethyl) ether which is an organic solution , it is grasped whether oxalic acid is present in bis (2-butoxyethyl) ether. can do. Moreover, an analytical sample can be prepared simply by bringing water into contact with bis (2-butoxyethyl) ether , which is a hydrophobic organic solution. For this reason, an analysis process can be made very simple, and an analysis result can be obtained quickly. Moreover, an unexpected reduction reaction that occurs when gold is extracted into bis (2-butoxyethyl) ether can be suppressed.
According to the second invention, it is possible to accurately grasp the amount of oxalic acid in bis (2-butoxyethyl) ether that is an organic solution.

It is a flowchart of the analysis method of oxalic acid of this embodiment. It is the figure which showed the result of the Example (mass spectrum). It is the figure which showed the result of the Example ( ^13C nucleus NMR spectrum), (A) is the ^13C nucleus NMR spectrum of a sample, (B) is the ^13C nucleus NMR spectrum of a standard sample. It is the figure which showed the result of the Example (HPLC chromatogram). It is the figure which showed the result of the Example (IC chromatogram).

  The method for analyzing oxalic acid in an organic solution of the present invention is characterized in that oxalic acid can be detected from an organic solution.

  The organic solution used in the method for analyzing oxalic acid in the organic solution of the present invention is a mixture of a plurality of organic solvents having such properties in addition to the case where an organic solvent insoluble in water is used alone. A mixed solution or a solution containing an extraction solvent or an extraction solvent used when extracting a desired substance from an aqueous solution. These organic solvents are not particularly limited as long as they are insoluble in water as described above. For example, if it is a nonpolar organic solvent, it will be easy to isolate | separate after making it contact with water.

Examples of these organic solutions include ether organic solvents, ester organic solvents, ketone organic solvents, amine organic solvents, alcohol organic solvents, and the like.
Examples of the ether organic solvent include bis (2-butoxyethyl) ether (so-called dibutyl carbitol, hereinafter simply referred to as DBC), ethylene glycol monoethyl ether, and the like.
Examples of the ester organic solvent include ethyl acetate, isobutyl acetate, isopropyl acetate and the like. Examples of the ketone organic solvent include diisobutyl ketone and methyl isobutyl ketone. Examples of the amine-based organic solvent include trioctylamine and aniline.

In addition, when water is brought into contact with the organic solution in the method for analyzing oxalic acid in the organic solution of the present invention, the two are mechanically stirred, the liquid is mixed by bubbling, It is a concept including contact by countercurrent.
Hereinafter, as a method for bringing the organic solution into contact with water, a case where both solutions are mixed will be described as a representative.

  As shown in FIG. 1, the method for analyzing oxalic acid in an organic solution of the present invention (hereinafter simply referred to as the present analytical method) comprises a pretreatment step of preparing an analytical sample by bringing water into contact with the organic solution. And an analysis step of analyzing the analysis sample prepared in the pretreatment step.

(About pretreatment process)
In the pretreatment step of this analysis method, first, water is brought into contact with the organic solution. Since such an organic solution is insoluble in water, it can be easily separated after contacting both. If the aqueous solution corresponding to the aqueous phase is separated from the two separated solutions, it can be used as an analysis sample to be used in the next step.

  Since oxalic acid is a substance having a polarity in the molecule, it is very easy to dissolve in water, but its solubility in a hydrophobic organic solvent is very low. For this reason, by utilizing such a difference in solubility, oxalic acid can be selectively extracted from such an organic solvent if oxalic acid is present in the organic solution.

The water used in the pretreatment step of the present analysis method is not particularly limited as long as it can be selectively extracted using the solubility of the organic solution of oxalic acid and water described above.
For example, water used in the pretreatment of a general analytical method can be used.
In particular, when an organic solution having a very low oxalic acid concentration in the organic solution is mixed with water, water containing as little organic matter as possible is preferable in order to suppress a decrease in the extraction rate of oxalic acid.
In addition, when using a liquid chromatograph mass spectrometer, a high performance liquid chromatograph, etc. as an analytical instrument, organic substances contained in water may become a disturbing component. It is preferable to use water.
As water mentioned above, the water for analysis like A1-A4 of JISK0557 etc. can be mentioned, for example.

  Needless to say, this analytical sample may be appropriately subjected to treatment such as dilution according to the analytical instrument used in the next step. For example, when the infusion method is used, a sample diluted about 10 to 1000 times according to the concentration of the detection component can be used as the analysis sample. In addition, when using an analytical instrument having high resolution, it is preferable to use a sample diluted about 10 to 1000 times according to the concentration of the detection component as described above.

(About analysis process)
The analysis step of this analysis method is a step of measuring the analysis sample prepared in the pretreatment step described above using a predetermined analytical instrument.

  The analytical instrument is preferably an instrument capable of measuring oxalic acid by simply or diluting the analytical sample. In addition, when the analysis sample cannot be measured as it is or after dilution, an instrument that can measure by making oxalic acid into methyl ester or the like may be used.

  Examples of analytical instruments that can be used in the analysis step of the present analytical method include chromatography, nuclear magnetic resonance (NMR), and infrared spectroscopy.

  Among these analytical instruments, a liquid chromatograph used for chromatography is preferable, and a high performance liquid chromatograph and an ion chromatograph are preferable for obtaining quantitativeness.

In addition, if a liquid chromatograph mass spectrometer or a high performance liquid chromatograph mass spectrometer using a mass spectrometer as a detector is used, the obtained value can be compared with the theoretical value of the mass of oxalic acid. Detection accuracy can be improved.
If a time-of-flight (TOF) mass spectrometer or a double-focusing mass spectrometer is used as the mass spectrometer, an accurate mass value can be obtained. Then, since it can compare with the theoretical value with the exact mass of oxalic acid, detection accuracy can be improved more.

On the other hand, when using a gas chromatograph or gas chromatograph mass spectrometer used in gas chromatography, oxalic acid can be measured using this analytical instrument if oxalic acid is methylesterified with diazomethane or BF ₃ / methanol. be able to.

As described above, since this analysis method is a simple process of measuring an analytical sample prepared by adding an organic solution and water, mixing and separating, oxalic acid is present or remains in the organic solution. It is possible to quickly analyze whether or not.
In addition, if you want to know the desired analysis result, for example, the presence or absence of oxalic acid in an organic solution, or if you want to know the concentration of oxalic acid in an organic solution, simply select an analytical instrument as needed. Results can be provided. Therefore, it is possible to feed back appropriate analysis information to the site where the organic solution is sampled.

(Method for analyzing oxalic acid in DBC)
Below, the case where the oxalic acid which exists or remains in DBC is analyzed using the analysis method of the oxalic acid in the organic solution of this invention is demonstrated as a representative.

  First, a part of DBC (corresponding to an organic solution in FIG. 1) is collected. Water is added to the collected DBC and stirred, and then allowed to stand for a predetermined time. Then, a part of the aqueous phase (corresponding to the aqueous phase in FIG. 1) after being allowed to stand for a predetermined time is fractionated and used as an analytical sample for use in instrumental analysis.

  Since the analysis sample is an aqueous solution, it can be analyzed using a liquid chromatograph mass spectrometer as it is. Then, a peak of oxalic acid is searched from a chromatogram obtained by a liquid chromatograph mass spectrometer, and the concentration of oxalic acid present or remaining in DBC is calculated based on the peak area.

  For example, when DBC is used to extract gold present in an acidic aqueous solution in a refining process, about 1.0 g / l of oxalic acid is present in DBC after a series of gold recovery is completed. Even if you do, you can grasp its existence.

  When such DBC is repeatedly used in a gold recovery process, gold extraction efficiency by DBC may be reduced by oxalic acid present in DBC. This phenomenon is presumed to be an unexpected reduction reaction caused by oxalic acid in DBC, which occurs when gold is extracted into DBC from an acidic aqueous solution containing gold. For this reason, if the oxalic acid concentration in DBC is grasped using this analysis method, even if DBC is repeatedly used in the gold recovery process, it is possible to suppress a decrease in gold extraction by DBC. There is.

The effectiveness of the method for analyzing oxalic acid in an organic solution of the present invention was confirmed.
In the experiment, DBC is used as a representative organic solution to confirm whether (I) oxalic acid present or remaining in DBC can be detected, and (II) oxalic acid present or remaining in DBC can be quantified. Confirmed whether or not.

(I) Using the method for analyzing oxalic acid in an organic solution of the present invention, it was confirmed whether oxalic acid present or remaining in DBC could be detected.

(Preparation of analysis sample)
In the experiment, DBC repeatedly used as an extractant in the gold recovery process in the refining process was used as an analysis target solution.

  In the gold recovery process, DBC is brought into contact with the acidic chlorine leaching solution of anode slime to extract gold into the DBC from the chlorine leaching solution (extraction step). By mixing the DBC containing gold obtained in the extraction step with an oxalic acid aqueous solution, the gold in the DBC is reduced with oxalic acid to recover gold powder (reduction step). And DBC after a reduction process is used for an extraction process again (extractant circulation process). That is, since DBC circulates in the system of the above-described circulation process, DBC after the reduction step in the circulation process was used as a solution to be analyzed in this experiment.

  30 ml of a 100 ml capacity separatory funnel was taken from DBC, which is the solution to be analyzed. 30 ml of ultrapure water was put into this separatory funnel and shaken for 1 minute. After shaking, the sample was allowed to stand for 10 minutes, and then the aqueous phase located in the lower phase was separated to prepare an analytical sample.

  The analysis sample was analyzed using a liquid chromatograph mass spectrometer (LC / MS) and a nuclear magnetic resonance apparatus (NMR).

  In the LC / MS analysis, an infusion method was adopted as an injection method. When analyzing using such an injection method, 1 ml of the analysis sample for dilution was dispensed from the analysis sample into a volumetric flask for a volume of 100 ml. Thereafter, ultra pure water was put in the volumetric flask and the volume was adjusted to obtain an analysis sample for infusion.

  The equipment and analysis conditions used in the experiment are as follows.

(LC / MS)
LC / MS: QSTAR XL (AB Sciex)
Injection method: Infusion method Injection volume: 1 ml
Ionization method: Electrospray ionization method (ESI)
Measurement mode: negative

(NMR)
NMR: AVANCE400 (Buruker Biospin)
Observation nuclei: ¹³ C nuclear accumulation: 5000 times

(result)
In FIG. 2, the experimental result analyzed using LC / MS is shown.
In FIG. 3, the experimental result analyzed using NMR is shown.
FIG. 3B shows NMR results analyzed using a standard sample of oxalic acid (manufactured by Wako Pure Chemical Industries, Ltd .; oxalic acid dihydrate (reagent special grade)).

As shown in FIG. 2, a strong peak was detected at m / z = 88.9876 in the mass spectrum.
This measurement mode is a negative mode. For this reason, oxalic acid is detected as a peak from which one proton (hydrogen) is removed.
When one proton is removed from oxalic acid (molecular formula C ₂ H ₂ O ₄ ), that is, the theoretical accurate mass of C ₂ HO ₄ is 88.9880. This value was in good agreement with the actually measured value (88.9876) shown in FIG.
Therefore, the peak of m / z = 88.9876 shown in FIG. 2 was estimated to be a peak derived from oxalic acid.

Moreover, when the NMR analysis result ( ¹³ C nuclear NMR spectrum of FIG. 3 (A)) of the original solution is compared with the NMR analysis result ( ¹³ C nuclear NMR spectrum of FIG. 3 (B)) of the standard sample of oxalic acid, In FIG. 3 (A), a peak corresponding to a peak around 165 ppm (peak indicated by the arrow in FIG. 3) derived from the oxalic acid standard sample of FIG. 3 (B) was detected.

In addition, the peak around 80 ppm detected in FIGS. 3A and 3B is a peak derived from chloroform, which is a reference substance used for NMR measurement.
In addition, the plurality of peaks other than those derived from chloroform of 100 ppm or less detected in FIG. 3A were peaks derived from DBC.
Therefore, the peak detected in the vicinity of 165 ppm shown in FIG. 3A was estimated to be a peak derived from oxalic acid.

From the above results, it was confirmed that oxalic acid can be detected from DBC by using the method for analyzing oxalic acid in an organic solution of the present invention. That is, it was confirmed that oxalic acid in DBC can be identified by using the method for analyzing oxalic acid in an organic solution of the present invention.
Therefore, it has been confirmed that the use of the method for analyzing oxalic acid in an organic solution of the present invention makes it possible to determine whether oxalic acid is present in the organic solution.

(II) Using the method for analyzing oxalic acid in an organic solution of the present invention, it was confirmed whether oxalic acid present or remaining in DBC could be quantified.

  In the experiment, the analysis sample prepared in (I) was analyzed using a high performance liquid chromatograph (HPLC) and an ion chromatograph (IC).

  The equipment and analysis conditions used in the experiment are as follows.

HPLC: Agilent 1100 (Agilent Technology)
Detector: UV detector (manufactured by Agilent Technologies; 1100 series diode array detector)
Detection wavelength: 210nm
Column: Supelcogel C-610H (manufactured by Supelco)
Mobile phase: 0.1% phosphoric acid aqueous solution

IC: ICS-1000 (Thermo Fisher Scientific)
Detector: Electrical conductivity detector (manufactured by Thermo Fisher Scientific; ICS-1000 type)
Column: Dionex IonPac AS22 (manufactured by Thermo Fisher Scientific)
Mobile phase: 4.5 mmol / LNa ₂ CO ₃ +1.4 mmol / LNaHCO ₃

(result)
FIG. 4 shows the experimental results analyzed using HPLC.
FIG. 5 shows the experimental results analyzed using IC.

From the chromatogram obtained by using the HPLC of FIG. 4, a peak (peak indicated by the arrow in FIG. 4) was detected around 9.5 minutes. This peak was assumed to be derived from oxalic acid.
On the other hand, after adding a standard solution of oxalic acid to the analytical sample prepared in (I), analysis was performed using HPLC under the same conditions. As a result, the peak intensity at the same location as the peak detected at around 9.5 minutes shown in FIG. 4 was improved. From this result, it was confirmed that this peak was oxalic acid.

  Based on the peak detected at around 9.5 minutes, the concentration of oxalic acid in the solution to be analyzed in (I) was calculated. As a result, the concentration of oxalic acid in the solution to be analyzed in (I) was 1.1 mmol / l (0.1 g / l).

The concentration of oxalic acid was calculated by the following method.
The peak of oxalic acid was searched from the chromatogram obtained from HPLC, and the peak area of this peak was calculated. Then, the calculated peak area is substituted into a relational expression calculated from a calibration curve (a calibration curve based on the relationship between the peak area and the absolute amount when oxalic acid having a known concentration is measured by HPLC), and 30 ml of the solution to be analyzed The absolute amount of oxalic acid in it was calculated. Then, the calculated value was divided by the solution amount (30 ml) of the analysis target solution to calculate the concentration of oxalic acid present in the analysis target solution of (I).

  From the chromatogram obtained using the IC of FIG. 5, it was confirmed that the peak detected at around 15.7 minutes (the peak indicated by the arrow in FIG. 5) was derived from oxalic acid.

Based on the peak detected at around 15.7 minutes, the concentration of oxalic acid in the solution to be analyzed in (I) was calculated. As a result, the concentration of oxalic acid in the solution to be analyzed in (I) was 1.1 mmol / l (0.1 g / l).
In addition, the density | concentration of the oxalic acid was computed by the method similar to the case where HPLC mentioned above is used.

  From the above results, it was confirmed that the concentration of oxalic acid in DBC can be calculated appropriately. That is, it was confirmed that oxalic acid in DBC can be quantified by using the method for analyzing oxalic acid in an organic solution of the present invention.

  As described above, by using the method for analyzing oxalic acid in an organic solution of the present invention, (I) the presence or absence of oxalic acid in DBC can be grasped, and (II) the concentration of such oxalic acid is appropriately set. It was confirmed that it can be calculated.

  The method for analyzing oxalic acid in an organic solution according to the present invention is used in a method of recovering a metal by bringing an organic solution into contact with an aqueous solution containing metal ions in wet refining and then bringing the oxalic acid into contact with the organic solution. Suitable for analyzing oxalic acid in organic solutions.

Claims (2)

A method for analyzing oxalic acid,
A pretreatment step of bringing water into contact with an organic solution insoluble in water;
Order row physician and analysis step of analyzing the solution obtained in the pretreatment step, the
The organic solution is
A method for analyzing oxalic acid in an organic solution, which is bis (2-butoxyethyl) ether . The aqueous solution obtained by the pretreatment step analysis method liquid chromatography and / or oxalic acid in the organic solution of claim 1, wherein the analyzed using ion chromatography.