JPS6236178B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a background removal device for an ion chromatograph.

(Prior art) Ion chromatography is the name of high-performance liquid chromatography, which is a method for mainly analyzing inorganic ions, announced by H. Small et al. in 1975 (Anal. Chem. 47, 1801 (1975)). It has already been put into practical use and is widely used for analysis of environmental samples and biological samples, management analysis of various processes, etc. FIG. 1 is an explanatory diagram showing the basic configuration of an ion chromatograph that is a device for such ion chromatography. In this figure, the ion chromatograph includes an eluent tank 1 that stores NaOH as an eluent, a pump 2 that pumps the eluent in the tank 1 to a sample injection valve 3, and a predetermined amount of sample liquid. A sample injection valve 3 that transports the collected sample liquid to the separation column 4 using an eluent, and a resin that is adjusted to be anionic as a whole by electrostatically bonding an anion exchange resin to a cation exchange resin. a separation column 4, which is filled with ions and separates and elutes each ion species contained in the injected fluid; and a background removal column 5, which is filled with a strongly acidic cation exchange resin and captures ions in the eluent. (hereinafter referred to as BSC) and a conductivity meter 6 that measures the conductivity by introducing the fluid flowing out from the BSC 5 into the cell.
and has.

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
BSC was designed to capture ions in the eluent, lower the background of the conductivity meter due to ions in the eluent, and improve the detection sensitivity of the measured ions, but the BSC's function has deteriorated over time. descend. This is because a reaction based on formula (1) takes place in the column, and the ion exchange resin shifts from H type to Na type.

NaOH (eluent) + strong Resin-H ⁺ (BSC) → Resin-Na + H ₂ O (1) When all the ion exchange resin becomes Na type, the reaction based on equation (1) no longer progresses, and the As the baseline increases, the amplification function for each anion will be lost. For this reason,
Conventional ion chromatographs operate by flowing 1N to 3N HCl 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 is short, and may be every 1 to 2 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 10~50cm
This is due to the structure in which ion-exchange resin is filled in the ion exchange resin.

Recently, a background removal device developed to solve the above problems was announced (Anal.
Chem.1981, 53, 1488-1492). according to it,
The main parts of the background removal device are two cheese unions 51 and 52, as shown in FIG.
, a center tube 53, eight polyethylene ion exchange membrane tubes 54 (length approximately 1.8 m, inner diameter 300 μm, outer diameter 380 μm), an eluent inlet tube 55, an eluent outlet tube 56, and a regenerating tube. Liquid inlet tube 57 and regeneration liquid outlet tube 5
8, and the eluent containing the target component separated by the separation column (0.003M NaHCO ₃ /0.0024M
Na ₂ CO ₃ ) is flowed at a rate of about 64 ml/h in the direction of eluent inlet tube 55 → hollow part of ion exchange membrane tube 54 → eluent outlet tube 56, and regenerant (0.02NH ₂ SO ₄ ) , regeneration inlet tube 57
The flow rate is approximately 64 ml/h in the direction of →outside of the ion exchange membrane tube 54 →regeneration liquid outlet tube 58.

FIG. 3 is a chromatogram obtained by ion chromatography using the background removing apparatus described above. As a sample, 3.3ppmF ^- ,
^4ppmCl- , _20ppmNO2- ^, _54ppmPO43- ^,
A standard solution consisting of 10 ppm Br ^- , 34 ppm NO ₃ ^- and 54 ppm SO ₄ ^2- is used.

As mentioned above, the new background removal device can remove the background of the chromatogram by flowing the regenerating liquid outside the ion exchange membrane tube 54, so it requires less maintenance man-hours than the conventional device using BSC. is reduced.

However, the background removal device described above is
As shown in the figure, the peak width was considerably broadened, and it took 20 minutes to separate the seven component ions.
In addition, as shown in FIGS. 4 and 5, the above device has a lower peak height at the same concentration than the conventional device using BSC, resulting in poor sensitivity. That is, Fig. 4 is a Cl ^- concentration/peak height characteristic diagram, and Fig. 5 is a Br ^- concentration/peak height characteristic diagram. b and c are conventional 9φ
Characteristics of ×110mmBSC and 2.8φ×300mmBSC are shown.

In this way, the background removal device described above
It is believed that the characteristics are inferior to BSC due to the structure of the ion exchange membrane tube 54 and the regeneration liquid.
In other words, the broadening of the peak width is due to the fact that the flow rate of the eluent in each ion exchange membrane tube is not uniform, and the instability of the baseline is due to the fact that the H ₂ SO ₄ in the regeneration solution is affected only by the ion exchange action. H ₂ SO ₄
This seems to be due to the fact that its own leakage (diffuse transmission) is quite large.

(Problems to be Solved by the Invention) The present invention has been made in view of the above situation, and its purpose is to provide a chromatogram with a stable baseline and a stable peak shape without requiring maintenance work. An object of the present invention is to provide a background removal device.

(Specific Means for Solving the Problems) A feature of the present invention that solves the above-mentioned problems is that in the background removal device, the first tube made of one cation exchange membrane tube and the first tube are connected to each other. The cation exchange membrane is formed with an appropriate distance between the tube and the second tube, which is a liquid-tight structure tube that does not contain an ion exchange composition, so that the central axes of the cation exchange membrane coincide with each other, and share the wall of the cation exchange membrane. A double tube configured with an inner chamber and an outer chamber and provided with respective inlets and outlets communicating these chambers with the outside, means for controlling the temperature of the double tube to a predetermined temperature, and the separation column. means for flowing an eluent containing the components separated and eluted in the inner chamber at a predetermined flow rate, and a scavenge liquid of a strong acid with a high degree of dissociation and a large counter anion to the H ⁺ ion into the other chamber of the double tube. The reason is that a means for causing the flow to flow at a predetermined flow rate is provided.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIGS. 6A and 6B (A--A sectional view in A) are explanatory diagrams of the configuration of a background removing device according to an embodiment of the present invention.

For example, the device 7 has an inner diameter of 0.4 mm, an outer diameter of about 0.55 mm,
A cation exchange membrane tube 71 with a length of about 5 m, for example, a Nafion tube (trade name, Du.Pont), and a flexible tube 72 with an inner diameter of about 1.0 mm containing the tube 71, for example, a Teflon tube (trade name). , Du Pont Co.), a double tube is formed with appropriate spacing between each tube, and both ends of the double tube are closed with lids 73 and 74 to create an independent eluent chamber 75 and a scavenge chamber. Holes 75a, 75b, which form a hole 76 and communicate each chamber with the outside.
76a and 76b are provided.

Such a background removal device 7 is usually installed in a constant temperature bath together with a separation column 4 and a conductivity meter 6 as shown in FIG. , hole 75
The scavenge liquid is made to flow in the direction of a→chamber 75→hole 75b, and the scavenge liquid flows in the direction of hole 76b→chamber 76→hole 76a.

Next, the operation of the background removing device will be explained.

Now, the 0.004M Na ₂ CO ₃ /0.004M NaCO ₃ eluent is introduced at a flow rate of approximately 2.0ml/min into the sample introduction device 3 → separation column 4 → eluent chamber 75 of the background removal device 7 → conductivity meter 6. At the same time, the scavenge liquid of dodecylbenzenesulfonic acid (hereinafter referred to as DBS) is passed from the cell to the discharge system at a rate of approximately 2.0
It flows at a flow rate of ml/min in the direction from the scavenger liquid chamber 76 of the background removal device 7 to the discharge system.

In the above state, Cl ^- 100mg/(ppm),
NO ₃ ^- 100mg/(ppm) and SO ₄ ^2- 100mg/
(ppm) of sample solution containing each ion species 100μ
into the eluent.

FIG. 7 is a chromatogram of the sample at the outlet of separation column 4. That is,
Approximate conductivity of 0.004M Na ₂ CO ₃ /0.004M NaHCO ₃
1550 μs/cm is the baseline, and cations (Na ⁺ if the measured anion is Na, K ⁺ if the measured anion is K)
), Cl ^- , NO ₃ ^- , SO ₄ ^2- appear in this order. In reality, each anionic species associates with Na ⁺ in the eluent, Cl ^- with NaCl, NO ₃ ^- with NaNO ₃ , SO ₄ ^2- with
Each salt of Na ₂ SO ₄ is 0.004M
Since it is eluted in the form contained in Na ₂ CO ₃ /0.004M NaHCO ₃ , for example, the conductivity change at the Cl ⁻ peak is about 25 μ/cm.

Each of the ion species separated and eluted in this manner undergoes the following operations in the background removal device 7 to obtain the chromatogram shown in FIG.

The scavenge liquid DBS becomes H ⁺ and DBS ^- as shown in FIG.
During passage through tube 7, the cation exchange composition
The operation of substituting the cation exchange groups with H ⁺ on the wall of the tube 71 continues, and the tube 71 becomes a so-called H-type cation exchange composition. The eluate containing each ion species separated and eluted in the separation column 4 comes into contact with the wall of this tube 71, and the reaction of equation (2) takes place, and the Na ⁺ in the eluate is removed from the tube 71.
It replaces H ⁺ and the eluent becomes H ₂ CO ₃ .

Due to this reaction, the electrical conductivity of the eluent is approximately 1550 μ
s/cm to 10 to 15 μs/cm, and the background of the chromatogram becomes extremely small.

On the other hand, the Na ⁺ that entered the wall of the tube 71 is because the Na ⁺ concentration in the skip gear fluid is almost zero.
It moves by diffusion through the wall towards the scavenging liquid and reaches the contact surface with the scavenging liquid. Since the scavenge liquid is a DBS solution with a relatively high concentration, the reaction of equation (3) takes place, and the Na ⁺ in the wall of the tube 71 is replaced with H ⁺ in the scavenge liquid (this reaction is caused by the ion exchange resin This reaction is the same as that seen when regenerating ion exchange resin in a water purification system using

Resin−Na ⁺ +DBS→Resin−H ⁺ +DBS−Na (3) Similarly, cations other than ⁺ in the above eluent also
It moves through the wall of the tube 71 by diffusion and reaches the surface in contact with the scavenge liquid. The transferred cations 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 cation exchange composition will always be regenerated by the scavenge fluid (in H type).

In addition, the anion species separated and eluted in the separation column 4 enter the eluent chamber 75 in the form of NaCl, NaNO ₃ and Na ₂ SO ₄ as described above, and enter the eluent chamber 75 in the form of equations (4) and (5). as well as
Perform the reaction of equation (6).

NaCl+Resin−H ⁺ →HCl+Resin−Na ⁺ (4) NaNO ₃ +Resin−H ⁺ →HNO ₃ +Resin−Na ⁺ (5) NaSO ₄ +Resin−2H ⁺ →H ₂ SO ₄ +Resin−2Na ⁺ (6) In this way, The eluent is caused by the reaction of equation (2).
At the same time as it changes to H ₂ CO ₃ , each ionic species also undergoes the reactions of formulas (4) to (6) and changes from the Na salt form to the acid form.
As shown in Figure 8, the chromatogram of the fluid that has passed through the background removal device 7 has a very low and stable baseline, the peak shape of cations has disappeared, and the peak shape of anion species has a large shape. (Generally, the conductivity of the solution is higher in the acid type than in the salt type). That is, in the background removing device, the conductivity of the anion species is amplified. Therefore, the background removing device described above has a characteristic superior in sensitivity than the BSC or the known background removing device shown in FIG.

By the way, the above operation reduces the set temperature of the thermostat to approximately
The temperature is set at 40℃, but the rationale for setting the temperature at 40℃ is as follows.

In the aforementioned background removing device 7 shown in FIG. 6, when the temperature of the device increases, the amount of acid leaking from the scavenge liquid chamber 76 to the eluent chamber 75 through the tube 71 increases, resulting in a high background. Therefore, the S/N ratio of the detection signal deteriorates. For example, the background at 50℃ is 40
It is about 1.5 times that at ℃. Also, as the temperature rises, CO ₂ is more likely to be generated from Na ₂ CO ₃ and NaHCO ₃ , and the generated CO ₂ (bubbles) can be measured with a conductivity meter 6.
destabilizes the measurement.

On the other hand, when the temperature of the device 7 becomes low, the tube 7
The reaction efficiency (ion permeation efficiency) of No. 1 decreases, a sufficient peak height in the chromatogram cannot be obtained, and the S/N ratio deteriorates. For example, the temperature is 20
When the temperature is below ℃, the reaction efficiency becomes extremely poor.

Further, since the ambient temperature of an ion chromatograph (temperature in a laboratory, laboratory, etc.) is usually within a range of 5 to 35°C, it is easy to control the constant temperature bath to 40°C.

Furthermore, 40° C. is a preferable temperature for the separation column 4 and conductivity meter 6 in terms of operation.

In view of the above, the temperature setting of the constant temperature bath is 40°C.

Next, the length of the flow path (hereinafter simply referred to as flow path length) of 5 m in the background removal device 7 will be explained.

The present inventors have found through experiments that, like the above-mentioned temperature, the flow path length also greatly affects the effectiveness of the background removal device.

The experiment regarding the flow path length was carried out in the apparatus shown in FIG. 1 without the separation column 4, in which the BSC 5 was equipped with the background removing apparatus according to the present invention.

Figure 9 is a background removal characteristic diagram, with constant temperature bath temperature 40℃ and scavenge liquid (0.05M DBS).
It was determined using the eluent flow rate as a parameter at a flow rate of 2 ml/min. graphs a, b and c
are 1ml/min, 2ml/min, and 3ml/min, respectively.
This was obtained by running min eluent. From FIG. 9, it can be seen that when the channel length is 4 m to 6 m, the background is sufficiently removed and the baseline is stable regardless of the eluent flow rate.

10 and 11 show that from the sample injection valve 3,
They are a peak area-channel length characteristic diagram and a peak height-channel length characteristic diagram in a chromatogram when 100 μ of 10 ppm Cl ⁻ ions were injected. Each figure shows a constant temperature bath at 40℃, an eluent (0.004M Na ₂ CO ₃ / 0.004M
Flow rate of each of NaHCO ₃ ) and scavenge liquid: 2 ml/
min, the concentration of the scavenger liquid was used as a parameter. The scavenger fluids in graphs d and e are 0.05M DBS and
It is 0.2M DBS. As is clear from each graph, both the peak area-channel length characteristic and the peak height-channel length characteristic are saturated at a channel length of 4 m to 6 m.

From the above results, in the background removal device with the above configuration, the temperature is 40°C and the eluent flow rate is 1 to 1.
3ml/min, scavenge liquid flow rate approx. 2ml/min
It can be seen that the most stable characteristics can be obtained when the flow path length is 4 m to 6 m when used in

In addition, as a scavenge liquid, it has properties similar to DBS, that is, it is a strong acid with a high degree of dissociation (can act as an acid as an H ⁺ ion donor), and has a large counter anion to H ⁺ ions (there is a concentration gradient). Even if a solution containing alkylbenzenesulfonic acid (as an alkyl group, such as a dodecyl group), higher alcohol sulfuric acid, or N-methyltauric acid is used, the same result as described above can be used. It is thought that this will give good results.

Furthermore, in ion chromatography, the eluent is selected depending on the type of separation column, but the background removal device does not have the above-mentioned eluent even when NaOH, potassium hydrogen phthalate, phthalic acid, etc. are used as the eluent. It is thought that the same conclusion can be obtained as if the

As explained in detail above, the background removal device according to the present invention allows cations to pass through the cation exchange membrane tube, replaces Na ⁺ in the eluent with H + in the scavenge liquid, and converts ^{H + into} Since the supply and removal of Na ⁺ are performed simultaneously, there is no need to interrupt the analysis and perform a regeneration operation as with BSC, as long as the scavenger fluid is flowing.

Also, the length of the flow path of the background removal device is
With a length of 4 m to 6 m, background can be sufficiently removed and the peak area and peak height in the chromatogram can be detected in a stable state.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the basic configuration of a conventional ion chromatograph, FIG. 2 is an explanatory diagram of the configuration of the main parts of a known background removing device, and FIG. 3 is an illustrative diagram of the basic configuration of a conventional ion chromatograph. Chromatograms in graphs, Figures 4 and 5
The figure is a peak height/concentration characteristic diagram in a known background removing device, FIG. 6 is an explanatory diagram of the configuration of the main parts of a background removing device according to an embodiment of the present invention, and FIGS. 7 to 9 are , an explanatory diagram of the removal effect by the background removal device according to the present invention,
10 and 11 are a peak area/channel length characteristic diagram and a peak height/channel length characteristic diagram of a chromatogram in the background removal apparatus according to the present invention. 7... Background removal device, 71... Cation exchange membrane tube, 72... Teflon tube, 75
...Eluent chamber, 76...Scavenger chamber.

Claims (1)

[Scope of Claims] 1. In a background removal device that is connected to and installed at the latter stage of a separation column in an ion chromatograph, a first tube consisting of a single cation exchange membrane tube and the tube are arranged so that their central axes are aligned with each other. The inner chamber is made to share the wall of the cation exchange membrane by providing an appropriate space between the second tube, which is a liquid-tight structure tube that does not contain the ion exchange composition contained therein. A double pipe with a length of 4 m to 6 m, which has an outer chamber and is provided with an outlet and an outlet that communicates each of these chambers with the outside,
means for controlling the temperature of the double tube to a predetermined temperature; means for flowing an eluent containing the components separated and eluted in the separation column into the inner chamber at a predetermined flow rate ^; 1. A background removal device comprising means for flowing a strong acid scavenge liquid containing large anions into the other chamber of the double pipe at a predetermined flow rate. 2. The background removing device according to claim 1, wherein the set temperature of the temperature control means is 40°C. 3 The eluent was 0.004M sodium carbonate and
It is a mixture of 0.004M sodium bicarbonate,
2. The background removing device according to claim 1, wherein the scavenge liquid is 0.05M dodecylbenzenesulfonic acid. 4. The background removing device according to claim 3, wherein the flow rates of the eluent and the scavenge liquid are 2 ml/min.