JP6399003B2 - Sample solution preparation method - Google Patents

Description

  The present invention relates to a method for preparing a sample solution.

  Conventionally, inductively coupled plasma (ICP) emission spectroscopy (hereinafter referred to as “ICP”) has been used as an elemental analysis method for elements contained in solution samples.

  ICP can be generated using various gases, and in particular, ICP using Ar gas (ICP-AES) is widely used.

  FIG. 3 shows a plasma torch for generating plasma in a general ICP analyzer. As shown in FIG. 3, plasma is generated by flowing Ar gas 20 in advance in the plasma torch 10 and flowing high-frequency current through the high-frequency dielectric coil 40. Then, the atomized solution sample 30 is introduced into the plasma torch 10, excited in the plasma flame, and a spectrum emitted when returning to the ground state is detected by a spectroscope (not shown).

  Here, if the solution sample 30 contains a highly volatile organic solvent as a part or all of the solvent, the organic solvent is vaporized before the solution sample 30 reaches the plasma torch, and the plasma torch. The gas flow rate in 10 becomes unstable, leading to plasma instability and misfire, which in turn causes measurement accuracy to deteriorate.

  Therefore, in a liquid chromatograph equipped with an ICP device as an analysis means, a solvent that stably maintains plasma immediately before being introduced into the ICP device with respect to the sample solution discharged from the column outlet and introduced into the ICP device. A method for diluting a sample solution by mixing the sample solution with a sample solution has been reported (for example, see Patent Document 1).

JP-A-60-209171

  By the way, when analyzing a trace amount of metal elements contained in the solution to be analyzed, the content of the metal elements contained in the sample solution for ICP measurement is increased as much as possible, and the content of the organic solvent is reduced. It is desirable to prepare a sample solution suitable for ICP analysis.

  Therefore, the present invention provides a method for preparing a sample solution that can improve measurement accuracy by suppressing misfire and instability of plasma when elemental analysis is performed by ICP on a solution containing a large amount of an organic solvent.

  In order to achieve the above object, in the present invention, a solution to be analyzed is diluted with water as a diluent solvent to prepare a diluted solution, and the organic solvent content is reduced by vaporizing the organic solvent in the diluted solution. Reduced until ICP analysis is possible.

That is, the method disclosed herein is a method for preparing a sample solution for detecting the content of a metal element contained in a solution containing an organic solvent using a high-frequency inductively coupled plasma emission spectroscopy, A step of diluting a part of the solution with water to obtain a diluted solution, and a step of evaporating the organic solvent in the diluted solution to obtain the sample solution, wherein the concentration of the organic solvent in the diluted solution with respect to the water is less than 0.13 mol / L ultra 0.57 mol / L, the concentration for the aqueous organic solvent of the sample solution is 0.18 mol / L than der is, evaporate the organic solvent in the diluent The period of time is 1 day or more and 14 days or less .

  In order to detect a trace amount of metal elements contained in a solution using high-frequency inductively coupled plasma optical emission spectrometry, it is desirable to increase the content of the solution in the sample solution as much as possible. However, if the amount of the organic solvent in the sample solution is increased by increasing the content of the solution, plasma misfire or instability is caused, leading to a decrease in measurement accuracy.

According to the present invention, a part of the solution is diluted with water to obtain a diluted solution, and the organic solvent content in the diluted solution is vaporized, whereby the content of the organic solvent in the diluted solution is determined by high frequency inductively coupled plasma emission. The sample solution can be obtained by reducing the amount to a level capable of performing blank measurement by spectroscopic analysis. As a result, while maintaining the dispersed state of the metal element to be analyzed contained in the sample solution, the content thereof is increased, and the amount of organic solvent is reduced to a concentration at which metal components can be detected in high frequency inductively coupled plasma emission spectrometry. Measurement accuracy can be improved by suppressing plasma misfire and instability. Moreover, the time for vaporizing the organic solvent in the diluent is 1 day or more and 14 days or less. As a result, the content of the metal element to be analyzed contained in the sample liquid can be increased and the highly dispersed state can be maintained, and the amount of the organic solvent can be reduced while suppressing an excessive decrease in the amount of water.

  In this specification, “blank measurement” is possible when the sample liquid is introduced into the ICP apparatus, and the emission intensity value of the component of the sample liquid can be obtained without causing plasma misfire or instability. When blank measurement is possible, it is determined that ICP measurement is possible.

In a preferred embodiment, in the step of obtaining the sample solution, the organic solvent in the diluent is vaporized under the condition that water contained in the diluent is vaporized while maintaining a predetermined vaporization rate.

In a preferred embodiment, in the step of obtaining the sample solution, the organic solvent in the diluted solution is vaporized under the condition that the vaporization rate of water from the diluted solution is 5.0 mg / day to 10.0 mg / day. . As a result, the content of the metal element to be analyzed contained in the sample liquid can be increased and the highly dispersed state can be maintained, and the amount of the organic solvent can be reduced while suppressing an excessive decrease in the amount of water.

  Specific examples of the solution include an electrolytic solution for a Li ion secondary battery and an electrolytic solution for an electric double layer capacitor, and preferably an electrolytic solution for a Li ion secondary battery. Thereby, content of trace metal components, such as Mn, Ni, Co, contained in electrolyte solution, can be measured accurately.

  At this time, as the organic solvent, for example, a general organic solvent for Li ion secondary batteries such as carbonate ester can be used. Specifically, it is at least one selected from, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), and ethylene carbonate (EC), and particularly preferably DMC or DEC. It is a mixed organic solvent of EC and EC.

  As described above, according to the present invention, while maintaining the dispersion state of the metal element to be analyzed contained in the sample solution, the content thereof can be increased, and the metal component can be detected in the high frequency inductively coupled plasma emission spectrometry. The amount of organic solvent can be reduced to the concentration, and plasma misfire and instability can be suppressed to improve measurement accuracy.

FIG. 1 is a flowchart for explaining a sample solution preparation method according to an embodiment of the present invention. FIG. 2 is a graph showing the vaporization rate of water. FIG. 3 is a diagram schematically showing a plasma torch of the ICP analyzer.

  Hereinafter, embodiments of the present invention will be specifically described. The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or its application.

<About the solution>
As the ICP analysis target solution, a solution containing a metal element or the like to be analyzed and using an organic solvent as a part or all of the solvent can be used. Specific examples include electrolytes for Li ion secondary batteries, electrolytes for electric double layer capacitors, electrolytes for lithium ion capacitors, electrolytes for lithium polymer batteries, and the like.

  As the organic solvent contained in the solution, an organic solvent generally used for an electrolyte solution for a Li ion secondary battery or the like can be used. Specifically, for example, carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), ethylene carbonate (EC), acetonitrile, benzonitrile, methylene chloride, tetrahydrofuran , Dimethylformamide, dimethyl sulfoxide and the like. These may be one kind or a mixed solvent of two or more kinds.

  The metal element to be analyzed may be a general metal element contained in the electrolytic solution or the like. Specifically, for example, Li, Mn, Ni, Co, Al, etc. included in the lithium ion secondary battery as an electrolyte or positive electrode material, and other Na, Mg, Ca, Zn, Cu, Fe, Zr, Ti, etc. . Thereby, for example, the deterioration state of the Li ion secondary battery can be examined with high accuracy.

<Preparation method of sample solution for ICP analysis>
Hereinafter, the method for preparing the sample solution according to the present embodiment will be described by taking as an example the case of measuring the content of the metal element in the electrolyte solution for Li ion secondary battery by ICP analysis.

(Dilution process)
When measuring the content of the metal element contained in the electrolyte solution 2 (solution) of the Li ion secondary battery containing the organic solvent 1, a sample solution for ICP analysis is prepared by the following steps.

  First, a predetermined amount of water 3 is previously placed in a container as a diluent solvent. Next, the electrolytic solution 2 used in the Li ion secondary battery is taken out, and as shown in FIG. 1, a certain amount of the electrolytic solution 2 is weighed with an electronic balance, a microsyringe, or the like (S1). Then, a certain amount of the weighed electrolytic solution 2 is added to a container containing the predetermined amount of water 3 to prepare a diluent 4 (S2).

  Here, the concentration of the electrolyte of the electrolytic solution 2 is a concentration used for a general Li ion secondary battery, preferably 0.1 mol / L or more and 2.0 mol / L or less, more preferably 0.3 mol / L. It is 1.7 mol / L or less, particularly preferably 0.5 mol / L or more and 1.5 mol / L or less.

  And the addition amount of the water 3 is the volume of the amount of the organic solvent contained in a part of the electrolytic solution 2 from the viewpoint of maintaining the dispersed state of the metal element in the electrolytic solution 2 to be analyzed and increasing the content thereof. The ratio is more than 20 times and less than 100 times, preferably 25 times or more and 90 times or less, particularly preferably 30 times or more and 80 times or less.

  In other words, the concentration of the organic solvent in the diluent with respect to the water is preferably more than 0.13 mol / L and less than 0.57 mol / L, preferably 0.14 mol / L or more and 0.50 mol / L or less, particularly Preferably they are 0.15 mol / L or more and 0.45 mol / L or less.

(Vaporization process)
Next, the diluent 4 is placed under conditions that allow the water 3 contained in the diluent 4 to vaporize while maintaining a predetermined vaporization rate (S3). Specifically, any means can be used as long as the vaporization rate of the water 3 can be maintained. For example, a container having a lid or a stopper is used as a container in which the electrolytic solution 2 is weighed and the lid or the stopper is attached. Then, it is left in the atmosphere or under an inert gas such as Ar or N ₂ .

  The temperature is preferably 10 ° C. to from the viewpoint of effectively suppressing the content of the organic solvent 1 while suppressing the excessive decrease in the water content while maintaining the dispersion state of the metal element in the electrolytic solution 2 to be analyzed. 40 degreeC, More preferably, it is 15 to 35 degreeC, Most preferably, it is 20 to 30 degreeC.

  In addition, the number of days to be left (vaporization time) suppresses an excessive decrease in the amount of moisture while effectively reducing the content of the organic solvent 1 while maintaining the dispersion state of the metal element in the electrolytic solution 2 to be analyzed. From the viewpoint, it is preferably 1 day to 14 days, more preferably 1 day to 12 days, and particularly preferably 2 days to 10 days.

  The evaporation rate of water from the diluent 4 suppresses an excessive decrease in the amount of water and effectively reduces the content of the organic solvent 1 while maintaining the dispersion state of the metal element in the electrolytic solution 2 to be analyzed. From the viewpoint, it is preferably 5.0 mg / day to 10.0 mg / day, more preferably 6.0 mg / day to 9.0 mg / day, and particularly preferably 7.0 mg / day to 8.0 mg / day. .

  As described above, in the mixed solution containing the organic solvent 1 and the water 3, the vaporization of the organic solvent 1 proceeds and the content of the organic solvent 1 is reduced because water is an incombustible liquid, but organic Since the solvent is a volatile flammable liquid, it is thought to vaporize faster than water. Table 1 shows the types, boiling points, and flash points of organic solvents used in Examples described later.

  As shown in Table 1, the boiling point of the organic solvent is the same as or higher than the boiling point of water, but the flash point is lower than the boiling point of water or higher than the boiling point of water. The temperature is significantly lower than the boiling point. Thereby, even if the diluent 4 is allowed to stand at the temperature as described above, the vaporization of the organic solvent proceeds and the content thereof is considered to be reduced.

  The concentration of the organic solvent 1 in the sample solution 5 with respect to the water 3 is desirably reduced as much as possible. Specifically, it is preferably less than 0.18 mol / L, more preferably 0.001 mol / L or more and 0.18 mol. / L, particularly preferably 0.01 mol / L or more and 0.17 mol / L or less. As a result, the content of the metal element to be analyzed contained in the sample liquid 5 can be increased, and the content of the organic solvent 1 can be reduced to suppress plasma misfire and instability, thereby improving measurement accuracy. .

<About ICP analysis>
A commercially available measuring instrument can be used for ICP analysis. Using the calibration curve method, the content of the metal element to be analyzed is measured.

  According to the method for preparing a sample solution according to the present embodiment, the content of the metal element to be analyzed contained in the sample solution 5 is increased while maintaining the dispersion state, and the metal element is used in the high frequency inductively coupled plasma emission spectrometry. Thus, the content of the organic solvent 1 can be reduced to a concentration at which it can be detected, and plasma misfire and instability can be suppressed to improve measurement accuracy.

  The organic solvents used in Examples, Comparative Examples and Reference Examples are shown in Table 1 above.

<Reference examples>
In Reference Examples 1 to 7, samples corresponding to the diluted solution and the sample solution were prepared for the organic solvent DMC without adding an electrolyte, and the possibility of ICP measurement was examined. The conditions and results are shown in Table 2.

[Reference Example 1]
First, a polyethylene container with a lid was prepared, and 20 mL of ion-exchanged water was added. And as shown in Table 2, 0.050 mL of DMC was measured using the micro syringe, and it put into the container and produced the dilution liquid. And about this dilution liquid, the possibility of the ICP measurement mentioned later was examined.

[Reference Example 2]
Sample preparation and examination were performed in the same manner as in Reference Example 1 except that the amount of DMC was changed to 0.10 mL.

[Reference Example 3]
Sample preparation and examination were performed in the same manner as in Reference Example 1 except that the amount of DMC was 0.20 mL.

[Reference Example 4]
First, a polyethylene container with a lid was prepared, and 20 mL of ion-exchanged water was added. And as shown in Table 2, DMC0.30mL was measured using the micro syringe, and it put into the container and produced the dilution liquid. And about this dilution liquid, the possibility of ICP measurement was examined.

  And the lid | cover of the container which put the dilution liquid was closed, and it was left to stand in air | atmosphere, and it was examined whether ICP measurement was possible every day from the start of leaving to 14th day.

[Reference Example 5]
Sample preparation and examination were performed in the same manner as in Reference Example 4 except that the amount of DMC was 0.40 mL.

[Reference Example 6]
Sample preparation and examination were performed in the same manner as in Reference Example 4 except that the amount of DMC was 0.50 mL.

[Reference Example 7]
Sample preparation and examination were performed in the same manner as in Reference Example 4 except that the amount of DMC was 1.0 mL.

<Examples and Comparative Examples>
Next, conditions and results are shown in Table 3 for Examples 1 to 9 and Comparative Examples 1 to 3.

[Example 1]
As a measurement sample, lithium hexafluorophosphate (LiPF ₆ ) was dissolved in an organic solvent in which diethyl carbonate (DEC) and ethylene carbonate (EC) were mixed at 3: 7 so as to have a concentration of 1 mol / L. The electrolytic solution A was used. Further, in order to confirm whether or not a trace metal element can be detected, nickel nitrate hexahydrate (Ni (NO ₃ ) ₂ .6H ₂ O) is added as a trace metal element to ion-exchanged water. Aqueous solution B was prepared so as to have a concentration of 0.001 mol / L. In addition, the nickel nitrate hexahydrate (Ni (NO ₃ ) ₂ · 6H ₂ O) was prepared in the form of an aqueous solution in consideration of solubility.

  A polyethylene container with a lid was prepared, and 19.7 mL of ion-exchanged water was added. And as shown in Table 3, each electrolyte solution A0.30mL and aqueous solution B0.30mL were measured using the micro syringe, and it added to the container, and produced the dilution liquid. And about this dilution liquid, the possibility of ICP measurement was examined.

  Next, the lid of the container containing the diluted solution was closed and left in the atmosphere, and whether or not ICP measurement was possible was examined on the 8th day.

  When ICP measurement was possible, Li and Ni concentrations (ppm) were measured.

[Example 2]
Preparation and examination were performed in the same manner as in Example 1 except that the amount of electrolytic solution A was 0.40 mL, the amount of aqueous solution B was 0.40 mL, and the amount of ion-exchanged water was 19.6 mL.

[Example 3]
Preparation and examination were performed in the same manner as in Example 1 except that the amount of electrolytic solution A was 0.50 mL, the amount of aqueous solution B was 0.50 mL, and the amount of ion-exchanged water was 19.5 mL.

[Example 4]
Preparation and examination were performed in the same manner as in Example 1 except that the amount of the electrolytic solution A was 0.75 mL, the amount of the aqueous solution B was 0.75 mL, and the amount of ion-exchanged water was 29.25 mL. After starting to stand in the atmosphere, whether or not ICP measurement was possible was examined on the 12th day in addition to the 8th day.

[Example 5]
Preparation and examination were performed in the same manner as in Example 1 except that the amount of electrolytic solution A was 1.00 mL, the amount of aqueous solution B was 1.00 mL, and the amount of ion-exchanged water was 29.0 mL. After starting to stand in the atmosphere, whether or not ICP measurement was possible was examined on the 12th day in addition to the 8th day.

[Comparative Example 1]
A polyethylene container with a lid was prepared, and 19.95 mL of ion-exchanged water was added. And as shown in Table 3, 0.050 mL of electrolyte solution A and 0.050 mL of aqueous solution B were each measured using the micro syringe, and it added to the container, and produced the dilution liquid. And about this dilution liquid, the possibility of ICP measurement was examined. Since ICP measurement was possible as a result, Li and Ni concentrations (ppm) were measured.

[Comparative Example 2]
Preparation and examination were performed in the same manner as in Comparative Example 1 except that the amount of electrolytic solution A was 0.10 mL, the amount of aqueous solution B was 0.10 mL, and the amount of ion-exchanged water was 19.9 mL.

[Comparative Example 3]
Preparation and examination were performed in the same manner as in Comparative Example 1 except that the amount of electrolytic solution A was 0.20 mL, the amount of aqueous solution B was 0.20 mL, and the amount of ion-exchanged water was 19.8 mL.

[Example 6]
As a measurement sample, lithium hexafluorophosphate (LiPF ₆ ) was dissolved in an organic solvent in which dimethyl carbonate (DMC) and ethylene carbonate (EC) were mixed at 3: 7 so as to have a concentration of 1 mol / L. The electrolytic solution A was used. In addition, an aqueous solution in which nickel nitrate hexahydrate (Ni (NO ₃ ) ₂ .6H ₂ O) is dissolved in ion exchange water as a trace amount of metal element so that the concentration of Ni ions is 0.001 mol / L. B was prepared.

  A polyethylene container with a lid was prepared, and 19.5 mL of ion-exchanged water was added. And as shown in Table 3, 0.50 mL of electrolyte solution and 0.50 mL of aqueous solution B were each measured using the micro syringe, and it added to the container, and produced the dilution liquid. And about this dilution liquid, the possibility of ICP measurement was examined.

  Next, the lid of the container containing the diluted solution was closed and left in the atmosphere, and whether or not ICP measurement was possible was examined on the 8th day.

  When ICP measurement was possible, Li and Ni concentrations (ppm) were measured.

[Example 7]
Preparation and examination were performed in the same manner as in Example 6 except that the amount of electrolytic solution A was 1.25 mL, the amount of aqueous solution B was 1.25 mL, and the amount of ion-exchanged water was 48.75 mL.

[Example 8]
Preparation and examination were performed in the same manner as in Example 6 except that the amount of electrolytic solution A was 0.30 mL, the amount of aqueous solution B was 0.30 mL, and the amount of ion-exchanged water was 19.7 mL.

[Example 9]
Preparation and examination were performed in the same manner as in Example 6 except that the amount of electrolytic solution A was 0.45 mL, the amount of aqueous solution B was 0.45 mL, and the amount of ion-exchanged water was 29.55 mL.

<About ICP measurement>
ICP measurement was performed using an ICP emission spectroscopic analyzer (ICP-S8100, manufactured by Shimadzu Corporation). The measurement conditions and the calibration curve solution preparation method are as follows.

  That is, the measurement conditions were: high frequency output: 1.6 kW, observation height: 15 cm, integration time: 15 seconds × 3, argon gas amount: 16 L / min for cooling, auxiliary 1.5 L / min, carrier 0.7 L / min Quantitative method: calibration curve method, analysis wavelength: 610.365 nm (Li), 222.295 nm (Ni).

  A calibration curve solution was prepared by the following procedure. First, for both Li and Ni, a commercially available standard solution for ICP analysis (10000 μg / mL) was used, and a predetermined amount was measured so that the concentration would be stepwise in the range of 0 to 10 ppm. Prepared by measuring up to 100 mL.

  When the relationship between the Li concentration and Ni concentration (unit: ppm) obtained based on the measurement result of the calibration curve solution by the ICP emission spectroscopic analyzer and the emission intensity by ICP measurement is plotted, the obtained calibration curve is obtained. The correlation coefficient R of each was 0.999, and a result having good linearity was obtained.

  In Reference Examples 1 to 7, since no electrolyte was added, it was confirmed whether or not ICP measurement can be performed, that is, whether or not blank measurement is possible without causing plasma misfire or instability. .

  In Examples 1 to 9 and Comparative Examples 1 to 3, it was confirmed whether ICP measurement could be performed without causing plasma misfire or instability, and the Li and Ni concentrations (ppm) of the sample solution were measured.

<About the vaporization speed of water>
Regarding the lidded polyethylene containers used in the above Reference Examples, Examples, and Comparative Examples, the amount of water vaporized per day when the containers were covered and left in the atmosphere was examined.

  Specifically, 20 g of water was put in a container, covered with a lid, left in the atmosphere, the total weight was weighed every day, and the weight difference (mg) from the total weight on the 0th day was calculated. . The results are shown in FIG.

  From FIG. 2, the water vaporization rate (mg / day) was 7.4 mg / day.

<Discussion>
As shown in Table 2, in Reference Examples 1 to 3, the ICP measurement was possible on the 0th day (the same day) when the ICP measurement of the diluted solution was examined.

  On the other hand, in Reference Example 4, ICP measurement can be performed after the second day, in Reference Example 5 from the fifth day, and in Reference Example 6, from the seventh day. In Reference Example 7, ICP measurement was impossible within 14 days.

  From the above, it was found that the DMC concentration in water shown in Reference Examples 1 to 3 can be measured without affecting the plasma of ICP. Moreover, it turned out that it becomes measurable by vaporizing DMC in the DMC density | concentration with respect to water shown to the reference examples 4-6.

  Next, as shown in Table 3, in Comparative Examples 1 to 3, when ICP measurement of the diluted solution was examined, ICP measurement was possible on the 0th day (same day).

  On the other hand, ICP measurement was possible on the 8th day in Examples 1 to 4 and on the 12th day in Example 5. In Examples 6 to 9, ICP measurement was possible on the 8th day.

  In Comparative Examples 1 to 3, although the Li concentration was measurable, no Ni-derived peak could be confirmed for the Ni concentration.

  On the other hand, in Examples 1-9, the peak derived from Ni was confirmed and Ni concentration was measurable with Li concentration.

  The present invention increases the content of a metal element to be analyzed contained in a sample solution while maintaining the dispersion state, and reduces the amount of organic solvent to a concentration at which a metal component can be detected in high frequency inductively coupled plasma emission spectrometry. The measurement accuracy can be improved by reducing the plasma misfire and instability, which is extremely useful.

1 Organic solvent 2 Electrolytic solution (solution)
3 Water 4 Diluent 5 Sample solution

Claims (5)

A method for preparing a sample solution for detecting the content of a metal element contained in a solution containing an organic solvent using a high-frequency inductively coupled plasma emission spectroscopy method,
Diluting a part of the solution with water to obtain a diluted solution;
Evaporating the organic solvent in the diluted solution to obtain the sample solution,
The concentration of the organic solvent in the diluent with respect to the water is more than 0.13 mol / L and less than 0.57 mol / L,
Concentration for the aqueous organic solvent of the sample solution is state, and are less than 0.18 mol / L,
The method for preparing a sample solution, wherein the time for vaporizing the organic solvent in the diluted solution is 1 day or more and 14 days or less . In claim 1,
In the step of obtaining the sample solution, the organic solvent in the diluent is vaporized under the condition that water contained in the diluent is vaporized while maintaining a predetermined vaporization rate.
A method for preparing a sample solution. In claim 2 ,
In the step of obtaining the sample solution, the organic solvent in the diluent is vaporized under a condition where the vaporization rate of water from the diluent is 5.0 mg / day to 10.0 mg / day. To prepare a sample solution. In any one of Claim 1 thru | or 3,
The said solution is electrolyte solution for Li ion secondary batteries, The preparation method of the sample solution characterized by the above-mentioned. In claim 4,
The method for preparing a sample solution, wherein the organic solvent is a carbonate ester.

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