JPS6137579B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for analyzing cations contained in a sample liquid by ion chromatography.

What is ion chromatography?H.Small in 1975
(Anaul.
Chem., 47, 1801 (1975)).

Ion chromatography has already been put into practical use and is being widely used for various trace analyzes such as analysis of environmental samples and biological samples, control analysis of various processes, and elemental analysis.

FIG. 1 is an explanatory diagram of the configuration of a flow path system of a conventional ion chromatograph for cation analysis.

In Fig. 1, the ion chromatograph consists of an eluent tank 1 that stores HCl as an eluent, a pump 2 that pumps the eluent in tank 1 to a sample injection valve 3, and a pump 2 that collects a predetermined amount of sample liquid and , a sample injection valve 3 that transports the collected sample liquid to the separation column 4 using an eluent, and a separation column 4 that is filled with a cation exchange resin and separates and elutes each ion species contained in the injected fluid. A background removal column 5 (hereinafter referred to as BSC), which is filled with a strongly basic anion exchange resin and captures ions in the eluent, and a fluid flowing out from the BSC 5 are introduced into the cell to improve the conductivity. It has a conductivity meter 6 for measuring.

The title of the ion chromatograph with the above configuration is in BSC.

One of them is that the BSC needs to be regenerated every 8 to 10 hours under normal analysis conditions. BSC
The BSC was designed to capture ions in the eluent, lower the background of the conductivity meter caused by the ions in the eluent, and improve the detection sensitivity of the measured ions, but the BSC loses its functionality over time. descend. This is because a reaction based on formula (1) takes place within the column, and the ion exchange resin shifts from the OH type to the Cl type.

HCl (eluent) + strong Resin-OH ⁺ (BSC) → Resin-Cl + H ₂ O (1) When all ion exchange resins become Cl type, the reaction based on formula (1) no longer proceeds, and the As the baseline rises, we lose the amplifying function for each cation. For this reason, conventional ion chromatographs are operated by flowing 1N to 3N NaOH through the BSC at predetermined time intervals to regenerate its function.
Of course, under analysis conditions that require high-concentration eluent to flow at a high flow rate, the regeneration operation interval described above is short, 1~
Sometimes it's every two hours.

Another problem is that when the fluid eluted from the separation column is passed through the BSC, the peak shape collapses. This means that BSC is 3~6mm (inner diameter) x 25~50cm
This is due to the structure in which the pipe line is filled with ion exchange resin.

The present invention has been made in view of the above points, and the present invention provides the following advantages:
The fluid eluted from the separation column is passed through an electrodialysis means having a channel formed of an anion exchange composition, without requiring a regeneration operation and without disturbing the shape of the separated peaks. , and are now being introduced into the measurement cells of conductivity meters.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 2 is an explanatory diagram of the configuration of an analyzer according to an embodiment of the present invention.

The analyzer of FIG. 2 uses an acidic eluent, e.g.
Eluent tank 1, which stores 0.002N HCl, and tank 1
A pump 2 that pumps the eluent of the sample to the sample introduction device 3, and a sample introduction that transports a predetermined amount of the sample liquid injected into the flow path by a microsyringe or the like to the separation column 4 by the eluent from the pump 2. An electrodialytic anion removal device (hereinafter referred to as an electrodialytic anion removal device) characterized by a device 4, a separation column 4 filled with a strongly acidic cation exchange resin having a low ion exchange capacity, and a cell 7 formed of an anion exchange composition described below. EBS), a conductivity meter 6 that introduces the fluid flowing out from the EBS into the cell and outputs a signal corresponding to the conductivity to a recorder, etc., and the analyzed fluid, EBS anolyte, and catholyte. Tanks 13a, 13b, 13 for storing etc.
It has c. The EBS includes a DC voltage generator 8 for applying voltage to the anode and cathode provided in the cell 7, and a storage tank 9 that stores an anolyte, for example, 0.002N NaOH, which fills the anolyte chamber.
and a pump 1 that pumps the anolyte in the tank 9 to the anolyte chamber.
0 and the catholyte filling the catholyte chamber, e.g.
It has a storage tank 11 that stores 0.002N NaOH, and a pump 11 that pumps the catholyte in the tank 11 to the catholyte chamber.

The EBS cell 7 has the configuration shown in FIG. Figure A in FIG. 3 is a cross-sectional view of the cell 7 in the axial direction, and Figure B is a cross-sectional view taken along line AA in Figure A.

The cell 7 includes a tube 71 made of an anion exchange composition that pressurizes the anode of a platinum wire 74, a tube 72 made of an anion exchange composition containing the tube 71, and a tube 73 made of stainless steel containing the tube 72. A triple tube is formed by providing an appropriate gap between each tube, and both ends of the triple tube are covered with lids 75 and 76 made of insulating material.
An eluent chamber 77 and an anolyte chamber 78 are closed and independent.
and holes 77a, 77b, 78a, 78 that form the catholyte chamber 79 and communicate each chamber with the outside.
b, 79a and 79b. In the eluent chamber 77, the fluid eluted from the separation column 4 flows in the direction of the hole 77a→chamber→77b, and in the anolyte chamber 78, the anolyte pumped by the pump 10 flows from the hole 78B→chamber→77b. In the catholyte chamber 79, the catholyte pumped by the pump 12 flows in the direction of hole 79b→chamber→79a.
The flow direction of this eluent and the flow directions of the anolyte and catholyte are opposite to each other.

On the other hand, between the tube 73 and the platinum wire 74,
A voltage E is provided by a DC voltage generator 8, with the tube 73 serving as a cathode and the platinum wire 74 serving as an anode.

Next, the operation of the analyzer having the above configuration will be explained.

By pump 2, the eluent of 0.002N HCl is
It flows at a flow rate of about 2.0 ml/min from the sample introduction device 3 to the separation column 4 to the eluent chamber 77 of the EBS cell 7 to the cell of the conductivity meter 6 to the tank 13a. Also, pump 10
The anolyte of 0.002N NaOH is approximately 1ml/mi
At a flow rate of n, the anolyte chamber 78 of the EBS cell 7 → tank 13b
flows to Similarly, by the pump 12,
0.002N NaOH catholyte at a flow rate of approximately 1ml/min.
It flows from the catholyte chamber 79 of the EBS cell 7 to the tank 13c.

Now, in sample introduction device 3, Na ⁺ 100mg/
(ppm) and K ⁺ 100 mg/(ppm) of each ion species are injected into the eluent stream and conveyed to the separation column 4. Each ion species is separated in the separation column 4. The chromatograph of the fluid at the outlet of the separation column 4 is as shown in FIG. That is, the conductivity of 0.002N HCl is approximately 420μ
S/cm is the baseline, and anions appear in this order (Cl ^- if the sample solution is made with Cl salt, NO ₃ ^- if it is made with NO ₃ salt), Na ⁺ , and K ⁺ . In reality, each cationic species associates with Cl ^- in the eluent, and Na ⁺ is eluted in the form of NaCl and K ⁺ is eluted in the form of KCl, so for example, the conductivity changes at the Na ⁺ peak. is approximately 20μS/cm.

Each ion species separated and eluted as above is
The following operations are performed in the EBS cell 7.

FIG. 4 is an explanatory diagram of the operation of EBS, and each symbol is used with the same meaning as in FIG. 3.

Due to the voltage E applied between the anode 74 and the cathode 73, cations move toward the cathode 73 and anions move toward the anode 74. However,
Due to the presence of anion exchange membranes 71 and 72,
Anions freely pass through these membranes to the anode 74.
can move through the membrane, but cations cannot pass through the membrane. Therefore, in the eluent
While HCl passes through the eluent chamber 77 as H ⁺ and Cl ^- , Cl ^- passes through the anion exchange membrane 72 and passes through the anode 7.
Move to 4. On the other hand, the catholyte NaOH flows from the catholyte chamber 79 through the anion exchange membrane 72.
OH ⁻ is supplied to the eluent chamber 77 . The eluent is (2)
As shown in the reaction equation, HCl is converted to H ₂ O, and its conductivity decreases significantly.

HCl−Cl ^- +OH ^- →H ₂ O (2) In addition, as mentioned above, each ion species separated and eluted in the separation column 4 enters the eluent chamber 77 in the form of NaCl and KCl, and (3 ) and (4).

NaCl−Cl ^- +OH ^- →NaOH (3) KCl−Cl ^- +OH ^- →KOH (4) In this way, HCl in the eluent changes to H ₂ O by the reaction in equation (2), so the eluent The conductivity of is significantly reduced and the baseline becomes very low and stable. Therefore, the chromatograph of the fluid that has passed through EBS is as shown in FIG. In other words, the anion peak shape disappears, and the Na ⁺ peak shape (conductivity difference) becomes approximately
20μS/cm → about 33μS/cm, the peak shape of K ⁺ (conductivity difference) changes from about 20μS/cm → about 31μS/cm, and the peak shapes of Na ⁺ and K ⁺ are amplified.
This means that Na ⁺ is converted from NaCl to NaOH by the reaction of equation (3).
The conductivity increases by approximately 1.7 times, and
This is because K ⁺ changes from KCl to KOH through the reaction of formula (4), and its conductivity increases by approximately 1.8 times (all comparisons are based on conductivity at 25°C).

Due to the amplifying effect of EBS, the detection sensitivity of the conductivity meter is significantly improved.

Note that if the anode 74 and cathode 73 of the cell 7 are ideal electrodes, if the voltage E applied to both electrodes is 1.23V or less, water electrolysis will not occur, and only equations (2) to (4) will be satisfied. proceed. Then, when the applied voltage E is made higher than the water electrolysis voltage, Cl ₂ is produced at the anode 74 and the cathode 7
Although H ₂ is generated in each of 3 and 3, the reaction efficiency of formulas (2) to (4) can be increased.

FIG. 5 is an explanatory diagram of the configuration of an EBS of an analyzer according to another embodiment of the present invention, in which figure A is a sectional view in the longitudinal direction, and figure B is a sectional view taken along line BB in figure A.

In FIG. 5, an EBS cell 7' has anion exchange membranes 71' and 72' interposed between two flat plates 73' made of stainless steel and spacers 17, 18 and 19 made of insulating material. are installed in two stages, and these are fixed using bolts 14, nuts 16, and spacers 15 made of insulating members to form three individually independent chambers, that is, eluent chambers 7.
7. It has an anolyte chamber 78 and a cathode chamber 79. And, like the cell 7 in FIG. 3, each chamber has holes 79'a, 79'b, and
78'a, 78'b, 77'a, and 77'b are used as inlets or outlets to form channels for eluent, anolyte, or catholyte. Further, the (+) pole of the output voltage E of the DC voltage generator 8 is connected to the flat plate 74', and the (-) pole is connected to the flat plate 73', so that the flat plate 74' is the anode and the flat plate 7
3' serves as a cathode.

The EBS having such a cell 7' operates in the same way as the EBS having the cell 7 shown in FIG. 3, and the chromatographs before and after passing through the cell 7' are as shown in FIG.
It will look like Figure 7.

In addition, although the above example shows a configuration using a separation column packed with a strongly acidic cation exchange resin, the present invention is not limited to this, and a separation column packed with a weakly acidic cation exchange resin can be used. It may be a device that has been installed. Alternatively, an alkaline eluent may be used. Further, the tube 73 or the flat plates 73' and 74' may be made of a plastic material to constitute a cell, and each electrode may be installed in the formed chamber. Furthermore, even if the anolyte chamber in each of the above embodiments is filled with catholyte and the catholyte chamber is filled with anolyte, and a (-) potential is applied to the anode and a (+) potential is applied to the cathode, the same effect as in the embodiments can be obtained. effect can be obtained. Furthermore, the pumps 10 and 12 in the above embodiment may be omitted, and the tanks 9 and 11 may be installed at a higher position than the cell 7, and the anolyte and catholyte may be made to flow using the head difference therebetween.

As explained above in detail, according to the analyzer of the present invention, since Cl ^- and OH ^- in the eluent are replaced by the anion exchange composition, the anolyte and catholyte do not need to be allowed to flow. For example, there is no need to interrupt the analysis and perform a regeneration operation, unlike in devices using BSC. Note that, since the driving force for dialyzing the cations in the eluent is based on the voltage between the electrodes, the anolyte and catholyte do not need to be fresh all the time, and can be used while being circulated.

Furthermore, by passing through EBS, the chromatograph has a low and stable baseline and a high cation peak, so the detection sensitivity of the conductivity meter is significantly improved.

Furthermore, since the eluent chamber of EBS does not need to be equipped with a packing, there is no risk of disturbing the chromatographic peak shape of the fluid passing through it.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of a flow path system of a conventional ion chromatograph for cation analysis, FIG. 2 is an explanatory diagram of the configuration of an analyzer according to an embodiment of the present invention, and FIG.
The figure is an explanatory diagram of the cell configuration of an anion removal device using an anion exchange composition, FIG. 4 is an explanatory diagram of the operation of the anion removal device, and FIG. 5 is an analysis according to another embodiment of the present invention. An explanatory diagram of the configuration of the anion removing device of the apparatus, FIG. 6 is a chromatogram at the outlet of the separation column, and FIG. 7 is a chromatogram at the outlet of the anion removing device. 1... Eluent tank, 2, 10 and 12... Pump, 3... Sample introduction device, 4... Separation column, 6... Conductivity meter, 7... Cell of anion removal device, 71 and 72... ...Tube made of anion exchange composition, 73...Tube made of stainless steel, 74...Platinum wire (anode), 75 and 76
... Lid, 77 ... Eluent chamber, 78 ... Anolyte chamber,
79...Catholyte chamber, 8...DC voltage generator, 9...
...Anolyte tank, 11...Catholyte tank.

Claims (1)

[Claims] 1. A predetermined amount of sample liquid is transported by an eluent and injected into a separation column packed with a cation exchange resin, and the eluate from the separation column is subjected to elution using an electrodialysis type anion removal device. The solution is introduced into a liquid chamber and brought into contact with the anolyte through the first anion exchange composition and the catholyte through the second anion exchange composition, and is subjected to electrodialysis using these compositions. A method in which anions in the eluate are exchanged with anions in the catholyte, and then the conductivity of the liquid eluted from the eluate is measured to analyze the cations contained in the sample liquid. 2. An eluent storage section that stores an eluent, a means for pumping the eluent to a sample introduction device, and a means for collecting a predetermined amount of the sample liquid and using the eluent to collect the sample liquid. A chamber having at least two walls formed of a sample introduction device for transporting a sample to a separation column, a separation column filled with a cation exchange resin, and first and second thin anion exchange compositions. , an eluent chamber forming a flow path for the fluid separated and eluted in the separation column, and a chamber sharing a wall with the first anion exchange composition, the chamber being filled with an anolyte. , an anolyte chamber having an anode in contact with the anolyte, and a chamber sharing a wall with the second anion exchange composition, the chamber being filled with a catholyte; An electrodialytic anion removal device comprising a catholyte chamber having a cathode in contact with the liquid and a DC voltage generator for generating a voltage applied between the electrodes; 1. An analyzer for analyzing cations contained in a sample liquid, comprising a conductivity meter for measuring conductivity. 3. The anion removal device includes a first tube made of an anion exchange composition containing a first electrode, a second tube made of an anion exchange composition containing the first tube, and the second tube made of an anion exchange composition containing the first tube. Using the second tube and the third tube containing the second electrode, a triple tube is formed with an appropriate gap between each tube, and both ends of the triple tube are closed with lids to form three independent tubes. 3. The analyzer according to claim 2, further comprising a cell which forms a chamber, and each chamber is provided with a hole for introducing a fluid from the outside and a hole for discharging a fluid from the outside. 4. The analyzer according to claim 3, wherein the third tube is made of a metal member and also serves as the second electrode, and the lids at both ends of the triple tube are made of an insulating member. 5 The chamber whose walls are the first tube is an anolyte chamber, the chamber whose walls are the first and second tubes are the eluent chamber, and the chamber whose walls are the second and third tubes are the cathode chamber. The analysis device according to claim 3, characterized in that it is a liquid chamber. 6 The chamber whose walls are the first tube is the catholyte chamber, the chamber whose walls are the first and second tubes are the eluent chamber, and the chamber whose walls are the second and third tubes are the anode chamber. The analysis device according to claim 3, characterized in that it is a liquid chamber. 7 The anion removal device has a box-shaped chamber partitioned by first and second anion exchange membranes to form a triple box having three independent chambers, and each chamber is injected with fluid from the outside. An inlet hole and an outlet hole are provided, and a first chamber is formed by the first anion exchange membrane and the wall of the box, and a second chamber is formed by the second anion exchange membrane and the wall of the box. 3. The analyzer according to claim 2, further comprising a cell having first and second electrodes in each chamber. 8 A part of the wall of the box forming the first and second chambers is made of a metal member, and the wall is a part of the wall of the box forming the first and second chambers, respectively.
8. The analysis device according to claim 7, which also serves as an electrode.