JPH0219425B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method and apparatus for analyzing cations contained in a sample liquid by ion chromatography, which is a type of high-performance liquid chromatography.

<Prior art> Ion chromatography was developed in 1975 by H.
This is the name of high-performance liquid chromatography for inorganic ions, as announced by Small et al. (Anal.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 Figure 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 that collects a predetermined amount of sample liquid and , a sample injection valve 3 that transports the collected sample liquid to a separation column 4 using an eluent, and a separation column 4 that is filled with a cation exchange resin and that separates and elutes each cation species contained in the injected sample liquid. Background Stripping Column 5 is filled with a strongly basic anion exchange resin and captures anions contained in the eluate and sample solution.
It has a conductivity meter 6 into which the fluid flowing out from the BSC 5 is introduced and measures the conductivity.

<Problems to be Solved by the Invention> The problem with the ion chromatograph having the above configuration lies in the BSC.

One of them is that the BSC needs to be regenerated every 8 to 10 hours under normal analysis conditions.
BSC is designed to capture anions in the eluent, lower the background of conductivity caused by anions in the eluent, and improve the detection sensitivity of measured ions. As time goes on, its functionality declines. It is expressed by the following formula (1) in the column.
This is because a reaction based on ions takes place, 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, it is no longer possible to
The reaction based on equation (1) stops progressing, the baseline in the conductivity meter rises, and the amplification function for each cation is lost. For this reason, in conventional ion chromatographs, 1N to 3N NaOH is flowed through the BSC at predetermined time intervals to regenerate its function. Of course, under analysis conditions that require the flow of a highly concentrated eluent at a high flow rate, the interval between the regeneration operations may be even shorter, such as every 1 to 2 hours.

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

The present invention was made in view of the above situation, and its purpose is to achieve a high concentration of cations without requiring regeneration operations that interrupt the analysis, and without changing the peak shape of the cations separated by the separation column. An object of the present invention is to provide a method and apparatus for analyzing cations in a sample liquid with high sensitivity.

<Means for Solving the Problems> The present invention provides a method and apparatus for analyzing cations contained in a sample liquid, in which a predetermined amount of the sample liquid is transported with an eluent and filled with a strongly acidic cation exchange resin. After separating the cations in the sample liquid, the eluate from the separation column is introduced into the eluent chamber of a diffusion-type anion removal device using an anion exchange composition and allowed to flow. A scavenge liquid is caused to flow in a direction opposite to the flow direction of the eluent in the eluent chamber into the scavenge liquid chamber of the diffusion type anion removal device to remove the eluate and the anions contained in the eluate, and then the eluate is removed. This problem was solved by measuring the electrical conductivity of the liquid.

<Operation> The present invention operates as follows. That is, the fluid eluted from the separation column is passed through a diffusion type anion removal device having a flow path formed of an anion exchange composition and introduced into a measurement cell of the conductivity meter. By doing so, anions in the eluent contained in the fluid eluted from the separation column can be removed without requiring a regeneration operation. Moreover, the peak shape of the cations separated by the separation column is not disrupted. Therefore, the cations in the sample liquid can be dispersed accurately and with high sensitivity.

<Example> The present invention will be described in detail below 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.
An eluent tank 1 that stores 0.002N HCl, a pump 2 that pumps the eluent in the tank 1 to a sample introduction device 3, and a predetermined amount of sample liquid injected into a flow path using a microsyringe or the like. A sample introduction device 3 that transports the sample to the separation column 4 using the eluent from the pump 2, a separation column 4 filled with a strongly acidic cation exchange resin having a low ion exchange capacity, and a wall formed of an anion exchange composition. A diffusion-type anion removal device 7 consisting of an eluent chamber and a scavenging liquid chamber that share a scavenger liquid (e.g.
A scavenger liquid tank 8 that stores 0.1N NaOH or KOH), a pump 9 that pumps the scavenge liquid in the tank 8 to the scavenge liquid chamber of the anion removal device 7, and an eluent liquid chamber of the anion removal device 7. A conductivity meter 6 that introduces the fluid flowing out into the cell and outputs a signal corresponding to the conductivity to a recorder, etc., a tank 10 that stores the liquid measured by the conductivity meter 6, and an anion removal device. It has a tank 11 for storing the scavenge liquid flowing out from the tank 7.

Next, the configuration of the anion removal device 7 will be explained in detail with reference to FIG. 3. FIG. 3 is an explanatory diagram of the configuration of the anion removal device, where A is a cross-sectional view of the device in the axial direction, and B is a cross-sectional view taken along line A-A in FIG. The device 7 uses a tube 71 made of an anion exchange composition (for example, a perfluorocarbon sulfonic acid type anion exchange composition) and a tube 72 made of stainless steel containing the tube 71,
A double tube is formed by providing an appropriate interval between each tube. Here, the double pipes are usually arranged so that their central axes coincide with each other. Further, both ends of this double tube are closed with lids 73 and 74 to form an independent eluent chamber 75 and a scavenge chamber 76, and holes 75a, 75b, 76a, and 76a, which communicate each chamber with the outside, are formed.
and 76b. and,
In the eluent chamber 75, the fluid eluted from the separation column 4 flows in the direction of hole 75a → eluent chamber 75 → hole 75b, and in the scavenging liquid chamber 76, a pump 9 flows.
Scavenging liquid (e.g. 0.1N
An alkaline solution having a high degree of dissociation such as NaOH or KOH and having a large counter ion of H ⁺ ions is used) flows in the direction of the hole 76b → the scavenge liquid chamber 76 → the hole 76a. Further, the flow direction of this eluent and the flow direction of the scavenge liquid are opposite to each other.

Next, the operation of the analyzer having the above configuration will be explained. In FIG. 2, by pump 2,
0.002N HCl eluent flows at a flow rate of approximately 2.0ml/min from sample introduction device 3 → separation column 4 → eluent chamber 75 of anion removal device 7 → cell of conductivity meter 6 → tank 10. There is. In addition, a scavenge liquid consisting of 0.1N NaOH is pumped by the pump 9.
At a flow rate of approximately 1.0ml/min, the anion removal device 7
The liquid flows into the tank 11 through the skiavenge liquid chamber (the skivengeer liquid chamber 76 in FIG. 3).

Now, Na ⁺ 100mg/
(ppm) and K ⁺ 100 mg/(ppm) of each ion species are injected into the eluent flow of 100 μ and transported to the separation column 4 . Each ion species is separated in the separation column 4. The chromatogram of the fluid at the outlet of separation column 4 is as shown in FIG. That is, the conductivity of HCl of 0.002N is approx.
420 μS/cm is the baseline, and anions (Cl ^- if the counter ion of the measured cation is Cl, Br ^- if Br, etc.), Na ⁺ , and K ⁺ appear in this order. In reality, each cationic species associates with Cl ^- in the eluent and
Na ⁺ is in the form of NaCl and K ⁺ is in the form of KCl, and these are contained in 0.002N HCl and are eluted, so for example, the conductivity change at the peak of Na ⁺ is about 25 μS/ cm.

The third section describes the actions performed by each ion species separated and eluted as described above in the anion removal device 7.
This will be explained with reference to the figures.

NaOH, which is a scavenge liquid, is a mixture of Na ⁺ and NaOH.
While passing through the scavenge liquid chamber 76 as OH ^- ,
On the wall of the tube 71, which is an anion exchange composition, the operation of substituting the anion exchange group with OH ^- is continuously performed, and the tube 71 has a so-called OH
type anion exchange composition. The eluent HCl containing each ion species separated and eluted in the separation column 4 in ^FIG . 3
In place of OH ^- in tube 71 in the figure, the eluent becomes water.

HCl＋Resin－OH ^- → H ₂ O＋Resin－Cl ^- ...(2) Due to this reaction, the electrical conductivity of the eluent is approximately
10~ from 420μS/cm (conductivity of 0.002N HCl)
The conductivity of water is 15μS/cm (conductivity close to that of pure water), and the background of the chromatogram is extremely small.

On the other hand, since the Cl ^- concentration in the scavenging liquid is almost zero, the Cl ^- that has entered the wall of the tube 71 moves toward the scavenging liquid by diffusion through the wall of the tube 71 and reaches the contact surface with the scavenging liquid. reach. Since the scavenge liquid is a NaOH solution with a relatively high concentration, the reaction of equation (3) below takes place, and Cl ^- in the wall of the tube 71 is replaced with OH ^- in the scavenger liquid (this reaction is
This is the same reaction that occurs when regenerating ion exchange resin in a pure water production device using ion exchange resin).

Resin−Cl ^- +NaOH→ Resin−OH ^- +NaCl ...(3) Similarly, anions other than Cl ^- in the above eluent,
It moves through the wall of the tube 71 by diffusion and reaches the surface in contact with the scavenge liquid. The anions that have migrated are carried away by the continuous flow of scavenge fluid and discharged outside, so they do not accumulate inside the room. For this reason,
The diffusion rate on the walls of tube 71 is not reduced. That is, the tube 71 consisting of the anion exchange composition will always be regenerated by the scavenge liquid (in the OH type).

Further, as described above, the cationic species separated and eluted in the separation column 4 enters the eluent chamber 75 in the form of NaCl and KCl, and undergoes the reactions of equations (4) and (5).

NaCl＋Resin−OH ⁻ → NaOH＋Resin−Cl ⁻ ……(4) KCl＋Resin−OH ⁻ → KOH＋Resin−Cl ⁻ ……(5) In this way, the eluent HCl is
In addition to changing to H ₂ O, each ion species also has the following equations (4) and (5):
Because the salt type changes into the hydroxide type through the reaction of the formula, the chromatogram of the fluid that has passed through the anion removal device 7 has a very low baseline and a stable chromatogram, as shown in Figure 5. The peak shape of the anion disappears, and the peak shape of the cation species becomes larger (generally, the conductivity of the solution is higher in the hydroxide type than in the salt type). That is, in the anion removal device, the conductivity of the cation species is amplified.

Next, Be ²⁺ , Zn ²⁺ , Cu ²⁺ , Cd ²⁺ were added to the sample solution.
We will explain the case where this is included. In the conventional method using BSC, it was not possible to measure the concentration of each of these ion species. on the other hand,
Even in the apparatus shown in FIG. 2, if an attempt is made to convert all HCl into H ₂ O, the above-mentioned ion species may precipitate as hydroxides with low solubility, making measurement impossible. In such a case, the above problem can be solved by appropriately determining the concentration of the scavenging liquid or the flow path length (length of tube 71) of the eluent chamber of the anion removal device.
Therefore, the device shown in Figure 2 contains Be ²⁺ , Zn ²⁺ , Cu ²⁺ ,
Each ion species such as Cd ²⁺ can be measured.

Although the above embodiments show 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 is used. It may be an apparatus using a column. Further, the present invention does not need to limit the configuration of the anion removal device to that of the embodiment. In short, it is sufficient to have two chambers that share a wall for the anion exchange composition, that is, an eluent chamber and a scavenge chamber. For example, a box-shaped container can be divided into two by an anion exchange membrane to form two chambers. However, one may be used as an eluent chamber and the other as a scavenging liquid chamber. Furthermore, there is no need to pump the scavenge liquid. The scavenger liquid tank may be installed at a higher position than the anion removal device, and the liquid may be flushed using the head difference between the two.

<Effects of the Invention> As explained in detail above, according to the analyzer of the present invention, anion is passed through the anion exchange composition, and Cl ^- in the eluent and OH ^- in the scavenge liquid are introduced. Instead, it supplies OH ^- and removes Cl ^- , so as long as the scavenge liquid is flowing, the conventional example (apparatus using BSC)
There is no need to interrupt analysis and perform playback operations as in .

Furthermore, by passing through the anion removal device, the chromatogram has a low baseline and a high peak of cations, so the detection sensitivity of the conductivity meter is significantly improved.

Furthermore, since the anion removal device does not need to be provided with a packing in its eluent chamber, there is no risk of disrupting the peak shape of the chromatogram of the fluid passing through it.

Furthermore, more ion species can be measured by appropriately setting the flow path length of the eluent chamber of the anion removal device or by adjusting the concentration of the scavenge liquid.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the flow path system configuration 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. FIG. 4 is a chromatogram at the outlet of the separation column, and FIG. 5 is a chromatogram at the outlet of the diffusion-type anion removal device. 1... Eluent tank, 2 and 9... Pump, 3...
Sample introduction device, 4... Separation column, 6... Conductivity meter, 7... Diffusion type anion removal device, 71...
...tube consisting of an anion exchange composition, 72...
...Tube made of stainless steel, 75...Eluent chamber, 76...Scavenger liquid chamber, 8...Scavenge liquid storage tank, 10 and 11...tanks.

Claims (1)

[Scope of Claims] 1. A predetermined amount of sample liquid is transported using an eluent and injected into a separation column packed with a strongly acidic cation exchange resin, and after separating cations in the sample liquid, the separation column The eluate is introduced into the eluent chamber of a diffusion-type anion removal device using an anion exchange composition, and the flow direction of the eluent in the eluent chamber is By flowing a scavenge liquid in the opposite direction to remove the eluate and anions contained in the eluate, and then measuring the electrical conductivity of the eluate,
A method for chromatographically analyzing cations in the sample liquid. 2. The cation analysis method according to claim 1, wherein the scavenge liquid is a 0.1N sodium hydroxide solution. 3. An eluent storage section that stores an eluent, a sample introduction device that collects a predetermined amount of a sample solution, a means for pumping the eluent to the sample introduction device, and a strong acid cation exchanger with a low ion exchange capacity. a separation column filled with resin and which chromatographically separates cations in the sample liquid when the sample liquid is carried in by the eluent; and a separation column in which the eluate from the separation column is carried in by the eluent. a diffusion-type anion removal device that removes the eluate and anions contained in the eluate; a skiavenge liquid storage tank that stores a skiavenge liquid; and a conductivity meter for measuring the electrical conductivity of the eluate into which the eluate from the diffusion type anion removal device is carried by the eluent, In a cation analyzer for analyzing ions, a certain distance is provided between a first tube made of an anion exchange composition and a second tube made of stainless steel contained therein so that their central axes coincide with each other. to form a substantially concentric double tube, and both ends of the double tube are closed with lids to form independent inner and outer chambers, and each conductor is provided to communicate these chambers with the outside. A cation analyzer comprising the diffusion type anion removal device provided with an entrance and exit.