JPS58144739A - Electrochemical detector - Google Patents

Abstract

PURPOSE:To enable manufacture of an electrode device which has a high-sensitivity and a small capacity, by a method wherein a porous flat plate and a measuring electrode are positioned facing and opposite to each other, and a contrast electrode and an auxiliary electrode are located to the back of the flat plate. CONSTITUTION:A measuring electrode 1 has a flat responsing surface which is located so that it forms one wall surface of a flow path of liquid to be measured. A porous flat plate 3 is positioned in parallel and close and facing and opposite to the responsing surface of the electrode 1 at a distance being sufficiently shorter than a width in all the directions of the responsing surface of the electrode 1. The flat plate 3 forms the other wall surface of the flow path, and has denseness, a water-containing property, and a property which prevents liquid to be measured from flowing therethrough but allows ion to permeate therethrough. An electrolyte gathering part 4 and a reference electrode 2 are placed to the pack of the flat plate 3. The liquid to be measured flows between the electrode 1 and a porous liquid path 3, and an electrolytic current produced by an oxidizing reduction method flows in the direction of the reference electrode 2 from the electrode 1 through the liquid path 3, and thereby the current is amplified to record it.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is installed in the path of a flowing liquid such as a developing liquid of a high-performance liquid chromatograph, and the concentration of redox substances in the flowing liquid is reduced to 1! This invention relates to a device for vapor chemical monitoring.

High performance liquid chromatography is one of the most widely used methods for separating and analyzing inorganic substances, organic substances, biochemical substances, etc. in solutions. It consists of two methods: a quantitative detection method for separated substances in a liquid. For the latter detection method, optical detection methods such as ultraviolet absorption method, color method, fluorescence method, and differential refraction method have been mainly used. Complete chemical detection methods were also introduced. A typical example is Kissinger et al.
ANA-LYTICAL L[! :TT RE3.6
+51. P, 495-477 (+978)) is a buttonometric electrode device for detecting adrenergic hormones, which has already been commercialized by several companies, and the detection device of the present invention is similar to this. Although it is a device that applies the same electrochemical reaction.

It has a completely different configuration from existing ones, and has significantly improved measurement sensitivity. -This detection device can be used not only for high-performance liquid chromatographs, but also for detecting substances in the flowing liquid that have been separated by other methods, such as substances injected from the outside into the flowing liquid, or substances generated by enzyme reactions, etc. It can be widely applied to existing substances.

In the currently used Kissinger-type devices for high-performance liquid chromatography, a carbon electrode is used as the measurement electrode, and a potential around 10.8 volts (C vs. Ag/AgC) is applied to detect physiologically active amines. There is. Taking adrenaline as an example, this detection reaction is expressed by the following formula.

For this reason, a current flows from the measuring electrode to the reference electrode (auxiliary electrode), and by measuring the strength of this current, the concentration of the substance flowing within the device is continuously detected.

Now, two characteristics are required of a detection device for a substance separated in a diluted liquid such as a high performance liquid chromatograph effluent. One is that the detection chamber is accurate and sensitive, and the other is that the volume of the detection section is small. The former is a necessary element for all instruments, but the latter is especially required for flow-through systems, such as in high-performance liquid chromatographs, where extremely sharp separation bands can be obtained, so that they do not dull them. A significantly smaller volume to measure in (
(20μ) or less). In the above-mentioned Kirasinger type detection device, all electrodes such as the measurement electrode, reference electrode, and auxiliary electrode are arranged along the flow path of the liquid to be measured, as will be explained in detail later. Make it bigger! It is possible to reduce the volume by making the flow path thinner while increasing the sensitivity.

It was impossible. In order to solve this problem, the present invention places a flat plate made of porous material and a measurement electrode facing each other, and contrasts the back side of the former. By adopting a configuration in which poles and auxiliary electrodes are placed,
Manufacture of a high-sensitivity, yet small-volume 1[electrode] device by forming a thin-layer detection portion over a large area.As shown in Figure 1, this device consists of a measuring electrode part a, a nuvesa part b, and a %electrode. Rinal from the third part of liquid reservoir C. a is a plastic plate equipped with the measurement electrode (1), 0 is a plastic plate with a porous plate electrolyte reservoir, reference electrode, auxiliary Km, etc. stored inside it, b
(That is, (5)) is a spacer inserted between a and C above, and is an extremely thin plastic film with a hollowed out center. When in use, the 11 constant electrode, part of the spacer, and solution reservoir part C are assembled in close contact with each other using six screws, but in this figure, a, b, and c are separated for ease of understanding. This is shown in the form below.

(1) in Figure 1 is a measurement of a flat plate! 10-20 depending on the type of substance to be detected, concentration, sensitivity of separation scissors, etc.
It has an area of 00-. Its materials include carbon plates such as Guoshi Carbon, precious metal plates such as platinum and gold or platinum black electrodeposited on them, nickel plates, lead plates, plastic plates mixed with precious metal powder, vapor-deposited precious metals or A wide variety of materials are used, including electrified Gafmis numbers or ceramic boards. These three extremes are all phenolic compounds such as adrenaline, amines such as histamine,
It is used to detect an extremely wide variety of redox substances such as various amino acids, sugars, oxygen, hydrogen peroxide, ascorbic acid, and metal ions. It is desirable to select the electrode material depending on the properties of the electrode. A constant potential is applied to the measurement electrode with reference to the reference electrode to cause it to react with the substance to be detected, but sometimes the potential is raised to detect it through an oxidation reaction.
It is necessary to lower the potential to perform a reduction reaction and select a positive value. For example, when detecting catecholamines (adrenaline, μ-adrenaline, dopamine, etc.), which are medically important hormones, when carbon electrodes are used, PH
10, 8 Bo/I/) around 2, +0 around PH5.
A rising pressure of around 6 volts (vs. Ag/AσC1) is appropriate; if it is higher than this, the residual current will increase rapidly, and if it is lower, the detection reaction will generally decrease, and in both cases the detection accuracy will deteriorate.

Figure 1 (2) is the control electrode, which is usually a high volume Ag/AgCl electrode saturated or immersed in 1 M kCl. (3) is a hydrophilic porous material, which is extremely dense (that is, the passage pores are extremely thin) and has virtually no flowability, but it contains a large amount of electrolyte solution and allows easy movement of ions. , it is necessary to have sufficient conductivity. There are a wide variety of such materials, but the best one is a bore glass with a pore diameter of about 10 nm and a porosity of 60%, which has a porosity of about 0.5 m at a size of about 5 m1B. I
MNaC! Although it has an electrical conductivity of more than 100 times the value required for electrolytic analysis in No. 1, almost no liquid can pass through it even under pressures of 1 atmosphere or more. In addition, extremely dense porous ceramics, extremely fine semi-molten glass powder (Sintert Gala 7), dense hard sponge-like hydrophilic plastics, etc. can be used. In addition, if the material is not dense enough so that liquid can flow through it, it is effective to impregnate it with agar, acrylamide, etc. and then gel it. The surface of this porous material facing the working electrode is a precisely polished flat surface along with the Buwosnack supporter (6), and the spacer (
5), it faces the measurement electrode (1) across a very short distance, and the liquid to be measured passes through this gap at a constant speed. For the spacer (5), a plastic film of 10 to 1002 μm made of Teflon, polypropylene, polycarbonate, or the like is used. Note that the back surface of the porous plate (3) is in contact with the electrolytic solution (4). A similar porous material is also used for electrical continuity between the reference electrode (2) and the electrolyte (4), but this material is better than the porous material facing the measurement electrode of @ period. It is also desirable to have good conductivity. The electrolytic solution (4) may be any dilute salt solution, but usually a solution with the same salt composition as the circulating fluid to be measured is stored and sealed, or the circulating fluid that has been measured is injected. Pass through using pipe (9) and outflow pipe αq.

(6) in FIG. 1 is a plastic material that holds the measurement electrode part (part a) and the electrolyte reservoir part (part 0), and acrylic resin, polycarbonate resin, Diflon, etc. are used. In part a, a measuring electrode (1) is fixed at the center, and a liquid to be measured inflow pipe (7) and a liquid to be measured outflow pipe (8) are inserted near the upper and lower ends, respectively. These tubes are usually Teflon tubes with an inner diameter of 0.2 mm and an outer diameter of 1.51 mm, the outer surface of which is etched and then fixed with epoxy resin. The same plastic material as the X5 part is used for the 0 part,
Epoxy resin is used to fix the porous material (3), electrolyte inflow pipe (9) and electrolyte outflow pipe QO (described later) to the plastic support plate (6), and epoxy resin is used to fix the reference electrode (2). Silicone resin is used. Note that the portions a and 0 that face each other are precisely machined so that the entire surface is flat. Now, in FIG. 1, as described above, the electrodes are tightly fixed by screws.

These screw holes are shown in part a of Figure 1, but these holes do not exist in the cross section of this figure, and there are six in total, two on the opposite side and two on the front side, so their positions cannot be determined. is shown by the dotted line.

When measuring with a two-electrode circuit (described later) using the device assembled as described above, it is sufficient to apply a necessary potential between the measurement electrode (1) and the reference voltage fMT2), but a three-electrode circuit ( (described later), an auxiliary pole is required in addition to this. For this purpose, the outflow pipe Ql shown in Figure 1 can be made of stable metal such as all-platinum or stainless steel and used as an auxiliary pole, or a separate platinum wire or the like can be inserted into the electrolyte reservoir. It may also be used as The method of connection with the electrical system at this time is shown in FIG. 2 IB+, which will be explained below.

FIG. 2 (IAI and IB) is an overview of the electrical system used in the electrode device of the present invention. In this figure, reference for the measuring electrode '#L
The potential with respect to the electrode is set to +0.7 volts, but this is a value for detecting catecholamines at a pH of around 8.5, and this potential depends on the type of substance to be detected and the P[( In the bipolar system shown in Figure 2 IA), the sample liquid to be measured fills the gap between the measurement electrode and the porous liquid junction (corresponding to (3) in Figure 1). The electrolytic current generated by the redox reaction (oxidation for catecholamines) flows from the measurement electrode (1) through the porous liquid junction (3) to the reference electrode (2), so this current is amplified. and record it. The three-electrode type in 21st ans) is similar to the two-electrode type in that the potential of the measuring electrode (1) can be maintained at a constant value with respect to the reference electrode (2), but this potential maintenance is done by the operational amplifiers A' and A1. carried out through
Electrolytic current due to oxidation-reduction of the sample does not flow to the reference electrode (2) but instead flows to the auxiliary electrode QQ. Therefore, there is an advantage that the reference electrode (2) is not consumed at all, but there is a disadvantage that the noise of the operational amplifiers A' and A# affects the a-electrode potential and becomes amplified noise. Particularly in a system that uses a large-area measurement electrode (action chamber FM) as in the present invention, the noise originating from this operational amplifier is significantly amplified due to the addition of the two-pole capacitance factor, and measurement accuracy tends to be extremely poor. It is. It is possible that this can be improved to a considerable level by selecting circuit components and other factors, but at this stage, in order to perform extremely rapid detection, it is recommended to measure using a bipolar method using a large-capacity reference electrode. shows good results. However, when the concentration of the sample is high and the accuracy may be lowered somewhat, it is advantageous to use a triode system because the reference electrode is not consumed.

FIG. 8 IA) and IB+ are cross-sectional views showing the basic configuration of conventional electrode devices, respectively.
placed on the flow path. When adopting this configuration, if the gap between the measuring electrode (1) and the wall (plastic) facing it is made extremely thin in order to reduce the flow rate on the electrode surface, the electrical resistance of the liquid increases and the measured liquid S A large potential gradient occurs within the As a result, a normal electrode reaction occurs only at the periphery of the measurement electrode (1) on the reference electrode (2) side, and most of the measurement electrode surface does not react or does not react under the specified conditions. will carry out reaction iii at different potentials.

FIG. 8+B) is a sectional view showing the basic configuration of the present invention, in which the measuring electrode (1) is a uniform porous liquid junction (3).
) and facing each other across a thin layer of the liquid to be measured 8, and the control electrode (2) and auxiliary electrode QG are arranged in the electrolytic solution (4) on the back side of the porous liquid junction (3). Since the conductivity within this electrolyte (4) is sufficiently greater than that within the porous liquid junction (3),
From the measurement electrode (1) to the reference electrode (2) or the auxiliary chamber m (
The conductivity to the IG is uniform over the entire surface of the measurement electrode Oυ. For this reason, no matter how large the measuring bipolar surface is, or even if the layer of the flowing liquid to be measured is made extremely thin, the electrode reaction will be uniform over the entire surface, which will increase the polarization reaction value. However, reducing the valley deposit on the measurement surface (that is, performing sensitive monitoring) improves pJ performance. As a result, the device of the present invention has a Flt structure that can electrolyze all or most of the substance to be measured in the flowing liquid even at the flow rate (111 t s +//min) used in Azusa for local velocity liquid chromatographs. Therefore, a large output can be obtained even from a trace amount of substance, and the accuracy of 41+ is significantly increased. In contrast, conventional electrochemical detection devices electrolyze only a small portion of the sample, resulting in a small measurement end and low accuracy. As mentioned above, the analysis method in which all or most of the substance to be measured is electrolyzed is a method that has been used for a long time and is called coulometric analysis for samples in a certain container. There has been no example of analysis of a sample in an fk@ liquid as in the invention.

Figure 4 1-. ■, IC) uses the electrochemical detection device of the present invention and an optical detection device, which is currently commonly used, at the same time to improve the accuracy of the high-performance liquid chromatography effluent of catecholamine hormones. This is a comparison. In this experiment, a silica-based sulfone-type cation exchanger column (IEliX 510, a product of Toyo Soda Co., Ltd.) with an IK diameter and length of 800 m was charged with a mixture of four types of catecholamines, and a PH4J column containing 0.2 M Na1l was charged. 0.1 M formic acid buffer was flowed at a flow rate of 1 d/- for development, and the effluent was first analyzed with an optical detection device (280 nm
Absorption method) and then the method of the present invention! The results were monitored through a fi chemical detector and recorded with a two-pen recorder.

FIG. 4 IA) shows the results of monitoring the effluent with an optical detection device, and FIG. 4 IB) shows the same solution monitored with the electrochemical detection device of the present invention. The vertical axis of the graph in Figure 4 IAJ is the absorbance at 280 nm (unit: A b s A
-ancθ:A), the scale of which is shown near the right shoulder of the figure. The horizontal axis is time, and the flow rate of the liquid (i*/
Since si*) is constant, it also indicates the volume of effluent, the scale width of which corresponds to 1 minute or 1- is shown in the lower right corner of FIG. 4 IBJ. In this experiment, the four catecholamines 'epinephrine (adrenaline), norepinephrine (noradrenaline), dopa, and dopamine'
A sample was used in which 100 pmol (IO-'°7) of Q was mixed. 14 in the graph indicates the position time when this catecholamine mixture was charged, ■ indicates the void volume position of the column (position where substances that pass through without being adsorbed appear), and 14 D, F, , N, and p are the dopa , showing the efflux peaks of epinephrine, norepinephrine, and dopamine. 41:, 41A), in the above amount (IQO picomole) of catecholamine,
The separation curve obtained by optical θ11 constant is accompanied by quite large noise.

No. 4111B) is the result of monitoring the above-mentioned chromatographic effluent using the electrical detection device of the present invention, in which the vertical axis shows the amount of electrolytic current, and the width per IQOnA is shown on the right shoulder of the figure. There is. I, V, D, J on the horizontal axis or graph
N, P, etc. are the same as in the case of IAI in FIG. 4. As is clear from this figure, the curve recorded by the detection device of the present invention contains no noise at all, and the detection pattern is monitored extremely accurately.

Figure 4+C) is a sample of the catecholamine mixture of t/loO amount in the case of Figure 4 IA) and IB) described above, that is, a sample containing 1 bicomo)v (1011 mol) of each component. The results of monitoring with the electrochemical detection device of the present invention are shown. It can be seen that even a very small amount is detected accurately without any noise. In addition,
In this case as well, an optical detection device was placed in front of the electrochemical detection device of the present invention for simultaneous monitoring, but only noise was recorded and no peaks derived from the sample were observed. Omitted. Also, further in this case.

10 minutes OO, t bicomo lv (10-'moA/)
Even when different catecholamine mixed samples were charged, monitoring with sufficient accuracy was possible with only slight noise observed when using the detection device of the present invention.

From the above experimental results and many other experimental results, the electrochemical detection device according to the present invention has the following characteristics:
It has been revealed that the accuracy is more than 100 times higher than that of conventional electrochemical devices, making it extremely effective for monitoring the amount of redox substances in flowing liquids such as high-performance liquid chromatography effluents. It was confirmed that

[Brief explanation of the drawing]

Figure 1 of the drain shows the device of the present invention, while Figure 2 shows the device of the present invention.
IAI and IBI are schematic diagrams showing the conventional device and the device of the present invention, respectively (a diagram showing the differences between the two), and FIG.
[Figure 4 shows the results of monitoring IAId 11 constant solution with a conventional device, Figure 4 IBI is Figure 4 + AlO field 1
FIG. 3 is a diagram showing the results of monitoring a 710 Q mO catecholamine mixed sample using the apparatus of the present invention. (1)...411j constant electrode, (2)...control electrode,
(3)...Hiraya made of porous material, (5)...Spacer, (6)...Plastic support plate, (7)...Given Ij constant liquid inlet pipe, (8)... ...m measurement liquid outflow pipe, (9
)... Bolyte solution inflow pipe, OQ... Electrolyte solution outflow pipe (also serves as auxiliary electrode). Agent Patent Attorney Takaharu Higashishima Figure 1 Figure 2 (A) Figure 2 (B)

Claims (6)

[Claims] (1) A flow path for a liquid to be measured, a working electrode having a planar reaction surface provided so as to constitute one wall of the flow path;
A dense, water-containing, and water-containing layer is provided parallel to and close to the reaction surface of the working electrode at a distance sufficiently shorter than the width of the reaction surface in either direction, and constitutes another wall surface of the flow path. a flat plate made of a porous material that does not allow the measurement liquid to flow through it but has ion conductivity, and the action tFM of the flat plate made of the porous material;
an electrolytic solution reservoir provided in contact with the surface opposite to the surface facing the electrolytic solution reservoir, that is, the back surface, and having the back surface as one wall surface; and a pair l! provided so as to be in contact with the electrolytic solution in the electrolytic solution reservoir. An electrochemical detection device for detecting oxidizing and reducing substances in a flowing liquid, characterized by comprising an @electrode. (2) The electrochemical production device according to claim (1), wherein the flow path is a flow path connected to a column outlet of a high performance liquid chromatograph. (3) The distance between the reaction surfaces of the opposing working electrodes and the flat plate made of porous material is 0. The electrochemical detection device according to claim 1 or 2, wherein the reaction surface is O1 to 0.2 (+111) and has an area of 10 to 2000 (-). (4) a flow path for a liquid to be measured, a working electrode having a planar reaction surface provided to constitute one wall of the flow path;
Measurement is performed on a dense and water-containing layer that is provided parallel to the reaction surface of the working electrode, close to and opposite to the reaction surface at a distance sufficiently shorter than the width of the reaction surface in either direction, and that constitutes another wall surface of the flow channel. A flat plate made of a porous material that does not allow liquid to flow through it but has ion conductivity, and is provided in contact with the surface of the flat plate of the porous material opposite to the surface facing the working electrode, that is, the back surface, and the back surface is one wall surface. 1. An electrochemical detection device for detecting oxidation/elementary substances in a flowing liquid, comprising: an electrolyte reservoir; and an auxiliary electrode provided in the electrolyte reservoir. (5) An electrochemical detection device according to claim 1, wherein the flow path is a flow path connected to a column outlet of a high-performance liquid chromatograph. (6) The distance between the reaction surface of the working electrode and the flat plate of the porous material facing it is 0. 1 to 0.2 (gl), and the area of the reaction surface is 10 to gooo(-), the electrochemical detection device according to claim 4 or claim 5.