JPH03223665A - Coulometric electrochemical detector - Google Patents

Abstract

PURPOSE:To perform the measurement corresponding to the reversibility or non- reversibility of the electrolytic reaction of an objective substance by constituting one set of a detector of an acting electrode cell and a reference electrode/opposed electrode cell to arrange two or more sets of detectors in series and continuously passing a solution through the detectors to detect the reducing current thereof. CONSTITUTION:Fixed blocks 1, 2 have liquid passing pipe connection ports 1a, 2a and the respective ports have liquid passing ports 1b, 2b having outer diameters opened to the internal end surfaces thereof. Channel holes 6 each having the same caliber as each of the liquid passing ports 1b, 2b are formed to respective acting electrodes 3a, 3d on the respective axes of center holes 5 and opposed electrode main body cells 4a, 4d. By this constitution, a liquid passage composed of the repeating arrangement of the center holes 5 and the channel holes is formed between the liquid passing ports 1b, 2b. An opposed electrode main body 4 has the reference electrode 8 communicating with the channel holes and a reference electrode 14 is inserted therein. An opposed electrode terminal 5 is inserted in a terminal hole 16. The inlet 1 of this detector is connected to a liquid chromatograph to allow a solution to pass through the detector to detect a reducing current.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a flow-through coulometric electrochemical detector.

Conventional technology electrochemical detectors are high performance liquid chromatographs (HPLC)
It is widely used as a detector suitable for flow injection analysis (FIA).

In general, electrochemical detectors are more selective in target substances than detectors using optical or physical mechanisms, and can detect these target substances with relatively high sensitivity. Further, it has advantages such as imparting specificity to the substance to be measured by chemically modifying the electrode surface, and having a relatively simple structure.

On the other hand, it should be noted that electrochemical detectors are also destructive detectors that change the molecular structure because they electrochemically oxidize or reduce the substance to be measured.

Problems to be Solved by the Invention Since the structure of conventional electrochemical detectors is mostly of the thin-layer cell type and the surface area of the working electrode is small, only amperometric electrochemical detectors with low electrolysis efficiency can be constructed. There wasn't.

The object of the present invention is to increase the surface area of the working electrode in an electrochemical detector, to use a coulometry type that electrolyzes almost the entire amount of the target substance, and to use a multichannel system in which a plurality of detection units are connected in series to detect the target substance. An object of the present invention is to provide an electrochemical detector that can perform measurements depending on the reversibility and irreversibility of an electrolytic reaction.

Means for Solving the Problems In order to achieve the above object, the present invention includes loading a porous electrode material into the center hole of a flat insulator, and providing an inlet and an outlet to the center hole on both sides of the insulator, respectively. a working electrode cell comprising: a through flow path along its central axis having end face openings corresponding to the working electrode cell inlet and outlet; and a reference electrode support hole directly communicating with the flow path; Each of the working electrodes is provided with a plurality of reference electrodes and counter electrode cells, each of which has a terminal attachment hole for connecting the part to the outside as a counter electrode, at least a part of which is in contact with the through-flow channel is made of a conductive material, and the part is made of a conductive material. A cell, a reference electrode, and a counter electrode cell are alternately stacked so that the entrance and exit of the center hole and the end face opening of the through-flow channel are communicated to form one detection channel, and the function is located on the upstream side. A series multi-channel flow-slow type coulometric electrochemical detector is constructed in which an electrode cell and a reference electrode and a counter electrode cell adjacent to the downstream side are connected to a measurement circuit as a set of detectors. It is something.

The general principle of a working electrochemical detector is that a predetermined voltage is applied to the working electrode based on the reference electrode potential, and constant potential electrolysis of the sample liquid is performed between the working electrode and the counter electrode (auxiliary electrode). A so-called three-electrode constant potential electrolysis method is applied to measure the concentration of an electrochemically active substance contained in a solution.

In the above configuration, the present invention arranges in series a plurality of sets in which one working electrode cell and one reference electrode cell and one counter electrode cell are arranged very close to each other to form one measurement channel, and the solution is passed through these channels. It is designed to pass through continuously. An arbitrarily set applied voltage is applied to each channel from each independent potentiostat, and the oxidation or reduction current in the solution passing through these is detected and measured. Therefore, selective measurement of oxidized or reduced components by varying the applied voltage for each channel, discrimination between reversible components and irreversible components related to oxidation and reduction reactions, etc. can be effectively performed.

Example In FIG. 1 showing the appearance of the electrochemical detector in the example, (1) is a liquid inlet fixed block, (2) is a liquid outlet fixed block that also serves as the counter electrode body of the final channel, and (3) is a liquid inlet fixed block.
) and (4) collectively indicate the working electrode cells and counter electrode bodies (one reference electrode and one counter electrode cell) that are alternately stacked between the liquid inlet fixed block (1) and the liquid outlet fixed block (2). It is.

As best shown in FIG.
2) are liquid pipe connection ports (1) each opened on the outer end surface.
a) and (2a), and each connection port has small diameter liquid passage ports (1b) and (2b) that open on the inner end surface. Each of the working electrodes (3a) to (3d) has a center hole (5), and each of the counter electrode main cells (4a) to (4d) has a liquid passage hole (5) in the center axis thereof.
A channel hole (6) having the same diameter as that of 1b) and (2b) is formed, so that a channel hole (6) consisting of a repeating arrangement of a central hole (5) and a channel hole (6) is formed between the liquid passage ports (1b) and (2b). A liquid path is formed. The diameters of the liquid passage ports (lb), (2b) and channel hole (6) are set to 0.5 mm in this case. Note that (21) and (22) are liquid passing vibrators on the inlet side and the outlet side, respectively. Next, details of each part will be explained.

Liquid inlet fixing block (1) is liquid outlet fixing block (2)
for tightening all cells and counter electrode bodies together with
One block is made of a resin material with excellent mechanical strength and electrical insulation properties, such as trifluorochloroethylene resin, and is a rectangular parallelepiped with a substantially square cross section, preferably with four corners chamfered in an arc shape. There is. Further, holes (7) for bolts inserted from the outer end surface are formed at positions close to the four corners.

In this case, the liquid outlet fixing block (2) also serves as the counter electrode body cell (4d) of the final stage channel, and is made of stainless steel, which is electrically conductive and has excellent mechanical strength and corrosion resistance. In this block (2), a reference electrode mounting hole (8) for supporting a reference electrode is opened from the upper side of the inner side portion which becomes the counter electrode main body (4d).

The bottom of this opening (8) communicates with the liquid passage port (2b) through a small hole.

Also, near the four corners, there are bolt holes (
A bolt hole (9) corresponding to 7) is provided. The outer end surface of the liquid outlet fixing block (2) is as shown in FIG.

The working electrode cell (3), as shown in FIGS. 4 and 5, is a relatively flat, e.g. It is made of a plate made of ethylene chloride resin, and its central through hole is filled with porous gladi-carbon (11) supported by a heat-shrinkable tube (10) forming the central hole (5). , this gran-carbon (11) is used as the working electrode. In this case, the heat-shrinkable tube (10) is thermally processed so that both edges protruding from both end faces of the grady-carbon working electrode (11) are heat-shrinked, and the cell (3) is slightly thermally expanded. ) is inserted into the through hole of the cell (3) and fixed by shrinkage after cooling of the cell (3). Further, the tube (1) is aligned with the end face of the cell (3).
A suitable adhesive is filled and fixed in the gap between the edge of cell (3) and the through hole of cell (3). In order to enhance the adhesion of this adhesive, the through holes of the cells (3) can preferably be suitably pretreated. The tip of a signal lead line (12) protruding from the upper side of the cell (3) is in contact with the working electrode (11). Due to this configuration of the cell (3), the electrode (11)
The circumferential sides of the Grazi-Carbon material are completely sealed, providing a leak-free working electrode with a very large surface area.

Incidentally, it is desirable that the signal lead line (12) is also formed of the same material as the electrode (11), that is, grady carbon. Both end faces of the working electrode cell thus formed are connected to each block (1), (2) or the corresponding counter electrode body (4) via a resin backing (13) having appropriate flexibility and liquid tightness. ) adjacent to the end face of the

As shown in Figures 1 to 3 and Figure 6, the counter electrode body (4) is opened from the upper side through the channel hole (6) (fixed block)
The dual-purpose portion 2) serves as a liquid passage port (2b). ), into which a reference electrode (14) is inserted. Since the counter electrode body (4) acts as a counter electrode, it is made of the same material (stainless steel) as the liquid outlet fixing block (2), and a counter electrode terminal (15) made of a conductive screw material is connected from the lower side. A terminal hole (16) for insertion is provided. Reference electrode (14
), a non-leak type silver-silver chloride electrode is used in this case. Like the working electrode cell (3), the counter electrode body cell (4) also has bolt insertion holes near the four corners, but since this cell (4) is conductive, the bolts should not cause electrical conduction with other cells, etc. In order to achieve this, the hole surface of the bolt insertion hole is coated with a suitable insulating resin material.

The inlet side of the electrochemical detector configured as described above was connected to a liquid chromatograph, and phosphate buffer was passed through the free solution to analyze categorical amines and other biological samples. The results are as follows. In addition, the column has 0DS5μm, φ
Using 4 x 250 m1M, the applied voltage for each channel was CHI: 600 mV, CH2: 200 mV, CH
3: Measured as 600 mV, CH4: 200 mV. As shown in Figure 7, first, in C) (1 (channel composed of cells (3a) and (4a) closest to the inlet side, hereinafter in this order), all five types of electrochemically active substances are present. Next, since CH2 has a reduction potential of these samples, CH2 has a reduction potential of 5.
The peak (paneel mandric acid) that appeared at the top indicating an irreversible electrode reaction has disappeared. Furthermore, C
In H3, oxidation potential is applied again, so oxidation current flows,
In CH4, an oxidation potential was further applied, which indicates that a reduction current flows.

Effects of the Invention As is clear from the above, according to the electrochemical detector of the present invention, it is difficult to perform coulometry measurements with excellent electrolytic efficiency. In addition, various effective uses are possible, such as identifying components based on the oxidation or reduction potential of a sample solution, and identifying reactive substances and irreversible substances.

[Brief explanation of drawings]

Figure 1 is a perspective view of an electrochemical detector according to an embodiment with some parts separated; Figure 2 is a vertical sectional view of its main parts; Figure 3 is an end view on the exit side; Figure 4 is a working electrode cell. FIG. 5 is an enlarged sectional view of the center of the working electrode cell, FIG. 6 is an end view of the counter electrode body, and FIG. 7 is a graph showing measurement results in the first to fourth channels.

Claims (1)

[Scope of Claims] A working electrode cell comprising a porous electrode material loaded into a central hole of a flat insulator, and having an inlet and an outlet to the central hole on both sides of the insulator, and the working electrode. A through flow path along the central axis of the cell having end openings corresponding to the cell inlet and outlet, and a reference electrode support hole that communicates directly with this flow path are formed, and at least a portion in contact with the through flow path is conductive. a plurality of reference electrode-counter electrode cells each made of a material and having a terminal attachment hole for connecting this part to the outside as a counter electrode, the working electrode cell and the reference electrode-counter electrode cell being connected to the center hole. A single detection channel is constructed by alternately stacking layers such that the inlet/outlet of the cell and the end face opening of the through channel communicate with each other, and a working electrode cell located on the upstream side and a reference electrode adjacent on the downstream side.
1. A series multi-channel flow-through type coulometric electrochemical detector, characterized in that a counter electrode cell is connected to a measurement circuit as a set of detectors.