JPH03162662A - Electrochemical flow cell - Google Patents

Abstract

PURPOSE:To prevent the mixing of an internal liquid and a soln. to be detected and to maintain a nearly specified potential difference between liquids by using a material which allows the permeation of only the specific ions or exchanges the same in the liquid junction part between the internal liquid of a reference electrode and the soln. to be detected. CONSTITUTION:The electrochemical flow cell is constituted of the reference electrode 1, a counter electrode 2 consisting of platinum, a working electrode 3 consisting of platinum, and a cell body 4 having a bisected structure. An AgCl film is formed on the surface of a silver rod 5 of the electrode 1 and is fixed to a reference electrode body 6. The material, such as cation exchange resin NaF ion of a 'Teflon(R)' system, which allows the permeation of only the ions in the soln. or exchanges the same, is used for the liquid junction part 7 with the soln. to be detected. Such material allows the permeation of only the ions in the soln. and hardly allows the permeation of the solvent itself. The outflow of the internal liquid 8 of the reference electrode and the intrusion of the soln. to be detected into the internal liquid 8 are, therefore, substantially prevented even when the soln. to be detected flows. The potential of the reference electrode 1 remains stable even while the soln. to be detected is static or flows. The measurement with high accuracy is thus executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The electrochemical cell of the present invention can be used in the medical and pharmaceutical fields, for example, for quantifying catecholamines. It can be used in a wide range of applications, such as in the food field for quantifying ascorbic acid and other substances, as well as in various analyzes and quantitative methods using electrochemical measurement methods.

[Summary of the Invention] In electrochemical measurements, the group 4! serves as a standard for potential. In many cases, an electrode is required, and the reference electrode used at that time generally has a structure in which a reference solution having a certain composition is contained therein. The electrochemical flow cell of the present invention uses a material that transmits or exchanges only specific ions at the liquid junction between the internal solution of the reference electrode and the test solution. [Prior Art] Groups l1! used in conventional electrochemical flow cells.
The electrode used had the following structure for the liquid junction between the internal liquid and the test solution. A. Open type liquid junction: The liquid junction has fine holes through which the internal liquid and the test solution come into contact.

B. Sleeve type liquid junction: Internal liquid and test liquid are in contact with each other through a laminated glass.

C. Liquid junction made of porous material: Materials that are permeable to solutions, such as porous glass, porous ivy, and cotton, are used for the liquid junction.

D. Gel-based liquid junction: A gel such as agar is used to bring the inner layer into contact with the test solution.

Furthermore, as a simple measurement method, a bipolar electrochemical flow cell using only a counter electrode and a working electrode without using a reference electrode is also used.

[Problems to be Solved by the Invention] The reference electrodes used in conventional electrochemical flow cells have the following problems.

A. Open type liquid junction: When the test/8-junction is left still, the liquid junction potential is stable, but when used in a flow cell where the test solution is flowing, pressure is applied. This causes problems such as the sample/eight precepts passing through the holes and mixing with the internal solution, or conversely, the internal liquid flowing out into the sample solution due to the pressure difference.

B. Sleeve type junction: If foreign matter gets mixed into the surface of the laminated glass, it is difficult to remove it. Also,
There is a point where the electrochemical flow cell becomes larger than it is structurally possible to miniaturize it.

C. Liquid junction made of porous material: Outflow of internal liquid is as described in A. above.
Although the amount is smaller than that of the open liquid junction, as the pressure difference increases, the amount cannot be ignored. Further, there are problems in that the pores are easily contaminated and must be cleaned using ultrasonic cleaning.

D. There is almost no outflow of the liquid inside the liquid junction part 2 due to the gel, but if a pressure difference occurs, the gel itself may deform or flow. Furthermore, when used for a long period of time, there is a possibility that the gel may be deteriorated or contaminated, and it is very time-consuming to replace the contaminated gel.

In addition, in the conventional reference electrode, the test object? 8 When the liquid is flowing, a potential difference occurs due to the movement of the melt between the electrode internal liquid and the test solution due to pressure, which causes a difference between the liquid junction potential difference in a stationary state. There was a point.

[LI! 1,000 steps to solve the problem] The electrochemical flow cell of the present invention is based on 1! The liquid junction of the electrode uses a material such as ion exchange resin that allows only specific ions to pass through or be exchanged. Such substances are dangerous &
Only the ions inside pass through, but the solvent itself passes through very little, if at all. Are you being examined for this reason?
8? Even under conditions where a pressure difference occurs, such as when the liquid is flowing, there is little or no leakage of the internal liquid or contamination of the test solution into the internal liquid. Further, the liquid junction potential difference is approximately constant whether the test solution is in a stationary state or in a flowing state.

[Action 1 The liquid junction of the reference electrode used in electrochemical measurements must generally satisfy the following conditions.

1. In order to minimize the contamination of the test solution by the electrode internal solution and the solution used for the salt bridge, and conversely the contamination of the electrode internal solution by the test solution 6, the movement of the solution between the liquid junctions must be as small as possible. However, if these are too small, the impedance becomes large and the nighttime potential difference becomes unstable.

2. In order to obtain a stable and reproducible liquid junction potential difference, what is the solution? (The moving speed of l must be constant.

Test} When measuring with a stationary solution, the above conditions can be met even with a conventional reference electrode, but with a flow cell that performs measurements with a flowing sample solution, conventional With reference electrodes, it is difficult to satisfy the above conditions. In the electrochemical flow cell of the present invention, a material such as an ion exchange resin that permeates or exchanges only specific ions is used in the liquid liquid portion of the reference electrode. Such substances have little or no permeability to the solvent itself. Therefore, the internal liquid of the electrode and the test solution rarely or never mix directly, so that the above-mentioned problem of contamination does not occur. In addition, the ion permeation or exchange reaction between the test solution or electrode internal solution and the ion permeation or exchange reaction is an equilibrium reaction caused by the difference in ion concentration, so it should be noted that when the solution is stationary and when it is flowing, The movement speed of ions hardly changes due to the difference in pressure at . For this reason,
Whether the solution is flowing or stationary, the liquid junction potential difference between the front and back surfaces of the ion-permeable or exchange material remains approximately constant. When measuring solutions where the ion concentration in the flowing test solution changes drastically, the ion migration or exchange equilibrium moves, which may change the liquid junction potential difference, but in many electrochemical measurements, Since a certain amount of inorganic salts are often added as a supporting electrolyte, measurements can be performed without problems if a substance that selectively permeates or exchanges these inorganic ions is used in the liquid chamber. can.

[Example] Hereinafter, an example of the electrochemical flow cell of the present invention will be described based on the drawings.

Figure 1 is a schematic diagram of the electrochemical flow cell of the present invention. This electrochemical flow cell consists of a reference electrode 1 and a platinum counter electrode 2. It consists of a platinum working electrode 3 and a cell body 4 that is divided into upper and lower halves. Of these, the reference electrode l
FIG. 2 shows the structure of the device in detail. The silver opening 7 and 5 were electrolyzed in IM HCI, and the surface was coated with Ag.
The prepared Cl film was treated with Epoquine resin to form a base 4
It is fixed to the electrode body 6. Further, a lead wire 10 is connected to the wire rod 5 for establishing conduction with the outside. Nafion (registered trademark of DuPont), a Teflon-based cation exchange resin, is used in the cold liquid test section 7.
The reference electrode body 6 is bonded to the reference electrode body 6 using epoxy resin. Inside the electrode? Il 8 has saturated KC1 water? 8 liquids are used. In order to replenish and replace this electrode internal liquid 8,
The reference electrode pod 6 is provided with an electrode internal insertion opening 9. The reference electrode used in this example is ^g/^g
The reaction of equation 1 is used with the cl electrode. Ag + CI- →AgCl + (!- First equation) In this case, the electrode potential E (Ag/Agc+) is expressed as in the second equation using active 13cl- of chloride ions.

RT E (Ag/8gc+) 1 E' (Ag/A
gCl) - - In a clF ... Second formula Here, E' (Ag/AgCI) is +M of silver monochloride
quasi-electrode potential, 222.34 mV at 25°C
It is. Here, the solubility of silver chloride is expressed by the third equation.

KAgC]=aAg+ ・aCI− − Third equation Substituting this relationship into the second equation yields the fourth equation.

RT E (Ag/AgCl) = E” (Ag/AgC
l) - - 1nKAgclF RT + - In a Ag+... Fourth Formula F From the second formula and the fourth formula, it can be seen that this electrode reversibly responds to Ag+CI-.

Using the electrochemical flow cell of the present invention, 0 at pH 6.0
．． Changes in potential between the platinum working electrode 3 and the base*fl electrode 1 were measured when 2M NatHPO40.1M citric acid Hanofa was kept stationary and when it was allowed to flow. Since the potential of the platinum electrode with respect to the solution in a solution with a constant pH does not change, this is the potential of the reference electrode 3 for the test solution when the test solution is stationary and when it is flowing. is being measured.

The measurement was performed using a pump at a flow rate of 5 ml/min, and after 5 minutes had passed from the start of the measurement, the pump was turned on and
After 5 minutes had elapsed, the pump was turned off, and the potential was measured using a portometer for a total of 15 minutes until 5 minutes had elapsed. The results are shown in FIG.

FIG. 3(a) shows the case when the electrochemical flow cell of the present invention is used, and FIG. 3(b) shows the case when the conventional electrochemical flow cell is used. As can be seen from the figure, when the electrochemical flow cell of the present invention is used, the pump is ON. OFF
The difference in potential at L is extremely small, indicating that the potential is stable.

[Effects of the Invention] In the electrochemical flow cell of the present invention, the group 4! The potential of the electrodes was stable, which enabled highly accurate measurements. Furthermore, since there is little or no mixing between the base electrode internal solution and the test solution, it has become possible to minimize contamination of the test solution.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the electrochemical flow cell of the present invention. Figure 2 is a diagram showing the structure of the reference electrode section of the electrochemical flow cell of the present invention. FIG. 3 is a diagram showing potential stability when using the electrochemical flow cell of the present invention and a conventional electrochemical flow cell. 1 ・Reference electrode 7 ・lei. vi part and above

Claims (1)

[Claims] In an electrochemical flow cell having a structure in which a reference electrode has a reference solution inside, and at least one working electrode and a counter electrode, and has a structure that allows a test solution to pass through, the solution inside the reference electrode and An electrochemical flow cell that uses a substance that permeates or exchanges only specific ions at the liquid junction of the test solution.