JP2001066283A - Electrochemical detector and liquid chromatography - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve reliable measurement with a simple configuration and at the same time eliminate the need for maintaining a reference electrode by using an ion-selective electrode that selectively responds to ion species existing in reaction liquid by a fixed amount as the reference electrode. SOLUTION: An electrochemical detector 1 used, for example, for liquid chromatography is provided with, for example, a reference pH electrode 32. The electrode 32 is composed by forming a pH-sensitive film that is made of iridium oxide where the ratio of oxygen to iridium is within a specific range on a sensitive film support being fixed, for example, on the end face of a holder 31. While a liquid-contacting part with the reaction liquid of the pH-sensitive film is left, the sensitive film support is covered with an insulation film, and a porous insulation film preferably with a specific hole diameter is deposited on the liquid-contacting part of the pH-sensitive film. As the reference electrode, a sodium ion electrode, a lithium ion electrode, a potassium ion electrode, a nitrogen ion electrode, a nitric acid ion electrode, or the like can be used and is composed by each specific sensitive film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to an electrochemical detector having a working electrode, a counter electrode and a reference electrode and used as a flow cell for measuring the electrolytic current of an analyte and such an electrochemical detector. The present invention relates to liquid chromatography using a vessel.

[0002]

2. Description of the Related Art In recent years, in general, substances which are soluble in water are used as objects of analysis, and liquids are used for measurement of inorganic anions, alkali metal ions, alkaline earth metal ions, transition metal ions, organic acid ions, amines, etc. Chromatography is used. FIG. 7 shows a schematic configuration of the liquid chromatography.

According to this embodiment, the eluent contained in the eluent container 101 is supplied to the dissolved gas removing device 102 with oxygen,
After removing carbon dioxide and the like, it is fed to the separation column 106 by the pump 103. On the other hand, the sample is injected from the injector 104 or the auto-injector 105 into the eluent and mixed, and the mixed solution is separated from the separation column 10.
Sent to 6. The analyte in the sample is separated by the separation column 106 and measured by the detector 1 installed downstream.

As the detector 1, there are an absorbance detector, an electric conductivity detector, an electrochemical detector, and the like. The present invention relates to an electrochemical detector, and therefore, the electrochemical detector will be described. . An example of a conventional electrochemical detector is shown in FIGS.

The electrochemical detector 1A of this embodiment is of a flow cell type and has a flow cell body 2 having a substantially cylindrical shape.
Having. The working electrode 3 is arranged at one end of the flow cell main body 2, and the reference electrode device 40 is arranged at the other end.
A counter electrode 4 is disposed above the flow cell body 2.

The sample supplied from the separation column 106 is supplied from the inlet 11 of the flow cell body 2 to the working electrode 3 via the flow path 14, and then the flow cell body 2
Through the flow path 16 and the liquid reservoir 17 formed inside the
It flows to the outlet 18 formed in the counter electrode 4 and is discharged from the flow cell body 2.

[0007] The reference electrode device 40 is provided with a liquid container 42 containing a reference electrolyte solution such as KCl, that is, an internal liquid 41, and a reference electrode 43 is disposed in the liquid container 42. The reference electrode 43 is a bar-shaped silver 43a as shown in the figure.
, And a silver / silver chloride electrode composed of granular silver chloride 43b. At the lower end side of the liquid container 42, the flow cell body 2
A cylindrical tube 44 protruding inward and extending is attached to the flow cell main body 2 by a fixture 45. A liquid junction 46 is provided at the distal end of the cylindrical tube 44 and communicates with the liquid reservoir 17 formed in the flow cell body 2.

[0008]

The electrochemical detector 1A having the above structure can measure various analytes with high accuracy. However, the replenishment and replacement of the internal liquid 41 requires a liquid container 42A. Need to be frequently removed from the flow cell body 2 or clogging of the liquid junction 46 usually made of ceramics or the like occurs, so that the liquid junction 46 must be cleaned, and maintenance of the reference electrode device 40 is performed. Is complicated. Further, the liquid container 42 is connected to the flow cell main body 2.
At the time of attachment, bubbles accumulate near the liquid junction 46, and in some cases, KCl of the internal liquid 41 crystallizes,
In some cases, the flow of the internal liquid 41 is deteriorated, or the potential fluctuates, which causes noise.

In particular, the electrochemical detector 1A is used as a detector 1 in liquid chromatography as shown in FIG.
When used as a sample, since the sample flowing in the flow cell body 2 is maintained in a pressurized state, the sample flows back into the liquid reservoir through the liquid junction 46 and the internal liquid 4
There is also a risk of reducing the number 1 and deteriorating the reproducibility of data, which is a problem in reliability. To solve this, the liquid container 4
Although it is conceivable to pressurize the inside of the reference electrode device 40,
Complicate, increase costs, and are not realistic. At present, the problem is dealt with by frequently replacing the internal liquid 41, and there is also a problem that the maintenance management is complicated.

Therefore, an object of the present invention is to provide a simple configuration,
An object of the present invention is to provide an electrochemical detector capable of performing highly reliable measurement and requiring no maintenance, and a liquid chromatography using the same.

[0011]

The above object is achieved by an electrochemical detector according to the present invention and a liquid chromatography using the same. In summary, according to a first aspect of the present invention, in an electrochemical detector having a working electrode, a counter electrode and a reference electrode, the reference electrode selectively responds to an ion species present in a certain amount in a reaction solution. An electrochemical detector is provided that employs an ion-selective electrode.

According to one embodiment of the present invention, the ion-selective electrode is a pH electrode, a sodium ion electrode, a lithium ion electrode, a potassium ion electrode, a chloride ion electrode or a nitrate ion electrode.

According to another embodiment of the present invention, the pH
The electrode is made of a pH of iridium oxide having an oxygen to iridium ratio of 2.5 to 3.5 on a sensitive membrane support.
Preferably, a porous insulating film having a pore size of 3 ° or more and 15 ° or less is applied to at least the entire surface of the pH-sensitive film in contact with the reaction solution.

According to a second aspect of the present invention, there is provided a liquid chromatography using the above-mentioned electrochemical detector.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an electrochemical detector according to the present invention will be described in more detail with reference to the drawings. In this embodiment, the case where the electrochemical detector of the present invention is used as a detector in the liquid chromatography described with reference to FIG. 7 will be described.
In addition, it can be used for various applications such as measurement of dissolved oxygen, measurement of chlorine dioxide, and measurement of glucose using glucose oxidase.

FIG. 1 and FIG. 2 show an embodiment of the electrochemical detector of the present invention. In the present embodiment, the electrochemical detector 1
It is of a flow cell type and has an integral flow cell body 2 of a generally cylindrical shape, usually made of synthetic resin, as in the prior art. As shown in FIG. 3, a spacer 5 is arranged at one end of the flow cell main body 2, that is, at the right end in FIG. The spacer 5 is made of, for example, a synthetic resin and has a diameter (D) of 10 to 30 mm and a thickness (t1) of 5 to 1 for example.
The disk is a 00 μm disk, and a long hole 6 is formed in the center thereof. The long hole 6 has a length (L) of 8 to 20 m, for example.
m and a width (W) of 1.5 to 3 mm. Further, the disk-shaped working electrode 3 is arranged outside the spacer 6.
The working electrode 3 has a diameter of, for example, 10 to 25 mm,
The thickness (t2) is 0.5 to 3 mm, and the connection terminal 7 is fixed to the outer surface. The connection terminal 7 is electrically connected to an external cable 8 (FIG. 2). The spacer 5 and the working electrode 3 connect the working electrode fixture 10 to the flow cell body 2.
For example, by being screwed together, they are brought into close contact with each other and are electrically connected. As the working electrode 3, in addition to glassy carbon, a Pt or Au electrode, and further, a Ni—Ti alloy or the like may be used depending on the application.

A sample inlet 11 is formed in the flow cell body 2 at the other end opposite to the working electrode 3, that is, below the left end in FIG. At 12, an inlet tube 13 is attached. The inflow port 11 communicates with the elongated hole 6 of the spacer 5 through the flow path 14.

At the center of the left end of the flow cell body 2 in FIG. 1, a reference electrode mounting hole 15 is formed adjacent to the sample inlet 11, and a reference electrode plug 30 is detachably provided. Fixedly mounted. In this embodiment, a flow path 16 is formed by communicating the tip of the reference electrode mounting hole 15, that is, the right end in FIG. 1 with the elongated hole 6 of the spacer 5, and the reference electrode plug 30 is attached to the mounting hole 15. A liquid reservoir 17 that forms a part of the flow path is formed between the reference electrode plug 30 and the flow path 16 when the liquid storage part 15 is mounted. The reference electrode plug 30 will be described later in more detail.

A counter electrode 4 having a sample outlet 18 is mounted above the flow cell body 2. Outlet 1
An outlet tube 20 is connected to an outer end of the tube 8, and an inner end of the tube 8 is communicated with the liquid reservoir 17 through a flow path 21 formed in the flow cell body 2. The counter electrode 4 is connected to the sample outlet 18
SUS-31 having an outer diameter of 13 mm and an inner diameter of 7 mm is usually used in order to maintain electrical contact with the sample flowing through
6 and connected to an external cable 21 (FIG. 2) via a lead 19. The counter electrode 4 can be manufactured using glassy carbon or the like.

According to the present invention, the reference electrode plug 30
A holder 31 formed of an insulator such as a synthetic resin, and a reference electrode 32 integrally formed at the center of the tip of the holder 31
And A lead wire 33 is electrically connected to the reference electrode 32 and is drawn out of the holder 31 to the outside.

The reference electrode 32 is an ion-selective electrode that selectively responds to a certain amount of ion species present in a sample as a reaction solution. That is, as the reference electrode 32, any electrode can be used as long as it shows a constant potential to the reaction solution. For example, if the pH of the reaction solution is always constant, a pH electrode can be used as the reference electrode, and if the reaction solution has a constant concentration of sodium ions, a sodium ion electrode can be used as the reference electrode. in this case,
The ions to which the ion electrode selectively responds must be present in the reaction solution at a certain concentration.

Considering the composition of the reaction solution used in the electrochemical detector 1, particularly the indicator electrolyte, the reference electrode 32 has a lithium ion electrode, a potassium ion electrode, a chlorine ion electrode in addition to the pH electrode and the sodium ion electrode. An electrode, a nitrate ion electrode, or the like can be used.

In the present embodiment, a pH electrode was used as the ion-selective electrode serving as the reference electrode 32. An example is shown in FIG. In this embodiment, the pH electrode 32 is
A pH-sensitive film 35 made of iridium oxide having an oxygen to iridium ratio of 2.5 to 3.5 is formed on a sensitive film support 34 fixed to the end face of the substrate. pH
The photosensitive film support 34 is covered with the insulating film 36 except for the part of the sensitive film 35 that comes into contact with the reaction solution. Preferably, an insulating film 37 of a porous film having a pore diameter of 3 ° or more and 15 ° or less is applied to at least the entire surface of the pH-sensitive film 35 in contact with the reaction solution.

More specifically, the pH electrode 32 of the present embodiment is formed by forming a thin insulating film 36 on the surface of a conductive support 34 in advance by a conventional thin film manufacturing technique such as natural oxidation, anodic oxidation, or evaporation. Formed by the pH of iridium oxide
When forming the sensitive film 35, a part of the insulating film 36 is removed in advance, and a pH photosensitive film 35 of iridium oxide is formed on the removed portion of the insulating film 36, and simultaneously with the formation of the pH sensitive film 35, 35 can be manufactured so as to be electrically connected to the lower conductive support 34.

A lead wire 33 is connected to the other surface of the conductive support 34 and taken out of the holder 31.
An external cable (not shown) is connected.

As the conductive support 34, any metal having conductivity such as aluminum, tantalum, platinum, titanium, and iridium may be used. The insulating film 36 to be deposited on the surface of the conductive support 34 is made of an insulating oxide such as alumina (Al ₂ O ₃ ), tantalum pentoxide (Ta ₂ O ₅ ), or silicon dioxide (SiO ₂ ). Thing or
An insulating nitride such as silicon nitride (Si ₃ N ₄ ), or
Plastic materials such as fluororesin can be used. Of course, in addition to iridium oxide, Ir, Pd, Pt, Sn, Rh, Ta, Os, R
An oxide of a metal selected from u, W, and Ti can be used. Further, the porous film 37 that can be provided on the pH-sensitive film 35 includes an insulating oxide such as alumina (Al ₂ O ₃ ), tantalum pentoxide (Ta ₂ O ₅ ), or silicon dioxide (SiO ₂ ). An object, a plastic material such as a fluororesin can be used, and a film is formed by a vacuum thin film manufacturing technique such as sputtering or CVD, or a dip coating method using a metal alkoxide as a raw material.

As the reference electrode 32, a pH responsive glass pH electrode utilizing a phenomenon that a potential corresponding to the pH of the solution is generated on the glass film can be used instead of the metal oxide pH electrode. As the reference electrode 32, in addition to these pH electrodes, as described above, a sodium ion electrode, a lithium ion electrode, a potassium ion electrode, a chloride ion electrode, a nitrate ion electrode, and the like can be used.
In this case, a sensitive film corresponding to each of these electrodes is used instead of the pH sensitive film 35. Further, a glass electrode that responds to sodium ions can also be used.
An ion clathrate such as valinomycin or a sparingly soluble salt of the ion to be measured is attached to the tip of a plastic support tube as an ion-sensitive substance, and an ion electrode for measuring a potential generated according to the concentration of the ion to be measured is also a reference electrode 32. Applicable as

An electrochemical detector 1 according to the present invention having the above-structured metal oxide pH electrode as a reference electrode 32 is:
It was used as a liquid chromatography detector as shown in FIG. 7, and saccharide analysis was performed using a saccharide mixed solution as a sample. An anion exchange column was used as the separation column 106, and a 1/10 M sodium hydroxide solution was used as an eluent. The working electrode 3 used a Ni-Ti alloy, and the counter electrode 4 used SUS-316.

That is, the sample fed from the separation column 106 is supplied from the inlet 11 of the flow cell body 2 to the working electrode 3 through the flow path 14 formed inside the flow cell body 2, The liquid flowed to the outlet 18 of the counter electrode 4 via the liquid reservoir 17 in which the electrode 32 was provided, and was discharged from the flow cell body 2. Figure 5 shows the measurement results.
(A) and (B) show. FIG. 5A shows the measurement result at the start of the measurement, and FIG. 5B shows the measurement result after three days. The measurement results were the same, and it was confirmed that the measurement data had reproducibility.

FIGS. 6A and 6B show a conventional reference electrode 43 shown in FIG. 8 in which a reference electrode 43 is installed in a container 42 containing KCl as an internal liquid 41 and has a liquid junction 46. The measurement result when the chemical detector 1A is used is shown. FIG.
(A) shows the measurement result at the start of the measurement, and FIG. 6 (B)
Is the measurement result after 3 days, but the measurement result was different, and there was a problem in reproducibility of the measurement data. It was found that this was because the sample flowed back through the liquid junction 46 and the internal liquid 41 was thinned.

As will be understood from the above, unlike the conventional detector 1A, the electrochemical detector 1 of the present invention requires frequent removal of the liquid container from the flow cell body for replenishment and replacement of the internal liquid. In addition, there is no danger of clogging of the liquid junction, and furthermore, air bubbles accumulate in the liquid junction when the liquid reservoir is attached to the flow cell main body, which is generated in the conventional detector, and KCl of the internal liquid is generated. Does not crystallize and does not deteriorate the flow of the internal liquid at all.

Further, even when the sample flowing in the flow cell body is used as a detector in liquid chromatography in which the sample is maintained in a pressurized state, the sample passes through a liquid junction and is collected in a liquid reservoir as in a conventional detector. There is no danger of backflow into the container to dilute the internal liquid and to impair the reproducibility of the data.

[0033]

As described above, according to the present invention, an electrochemical detector having a working electrode, a counter electrode and a reference electrode selectively responds to a certain amount of ion species present in a reaction solution as a reference electrode. Since the configuration uses an ion-selective electrode, highly reliable measurement is possible with a simple configuration, and further, maintenance is not required, and the device can be suitably used as a liquid chromatography detector. And the like.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an electrochemical detector according to the present invention.

FIG. 2 is a perspective view of an electrochemical detector according to the present invention.

FIG. 3 is a front view of a spacer.

FIG. 4 is a detailed partial cross-sectional view of a reference electrode plug.

FIG. 5 is a graph showing the results of analysis of sugar in a saccharide mixture solution using the electrochemical detector according to the present invention, and FIG. 5 (A) is a measurement result at the start of measurement. 5
(B) is the measurement result after 3 days.

FIG. 6 is a graph showing the results of analysis of sugar in a saccharide mixture solution using a conventional electrochemical detector, and FIG. 6 (A) shows the measurement results at the start of measurement, and FIG. B)
Is the measurement result after 3 days.

FIG. 7 is a schematic diagram showing the overall configuration of liquid chromatography.

FIG. 8 is a sectional view of a conventional electrochemical detector.

FIG. 9 is a sectional view of a conventional electrochemical detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrochemical detector 2 Flow cell main body 3 Working electrode 4 Counter electrode 30 Reference electrode plug 31 Holder 32 Reference electrode 33 Lead wire 34 Conductive support 35 pH sensitive film 36 Insulating film 37 Porous film

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G01N 27/46 351J

Claims (5)

[Claims] 1. An electrochemical detector having a working electrode, a counter electrode, and a reference electrode, wherein an ion-selective electrode selectively responding to a certain amount of ion species present in a reaction solution is used as the reference electrode. Characteristic electrochemical detector. 2. The electrochemical detector according to claim 1, wherein the ion-selective electrode is a pH electrode, a sodium ion electrode, a lithium ion electrode, a potassium ion electrode, a chloride ion electrode, or a nitrate ion electrode. 3. The pH electrode according to claim 1, wherein a pH-sensitive membrane made of iridium oxide having an oxygen to iridium ratio of 2.5 to 3.5 is formed on a sensitive membrane support. The electrochemical detector according to claim 2, wherein 4. The pH electrode is characterized in that an insulating film of a porous film having a pore diameter of 3 ° or more and 15 ° or less is applied on at least the entire surface of the pH-sensitive film in contact with the reaction solution. The electrochemical detector according to claim 3, wherein 5. A liquid chromatography comprising the electrochemical detector according to claim 1.